JP7655658B2 - 400MPa-class corrosion-resistant rebar and its production method - Google Patents

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to a Chinese patent application with application number 202110051522.4, filed on January 15, 2021, and titled "400 MPa-class corrosion-resistant rebar and its production method," the entire contents of which are incorporated herein by reference.

The present invention belongs to the field of metallurgy technology and relates to a 400 MPa-class corrosion-resistant rebar and a method for producing the same.

Reinforced concrete structures are the most widely used structural form in infrastructure construction, and although the theoretical service life of reinforced concrete structures is long, in actual construction, there are many cases of premature failure of reinforced concrete, which not only increases maintenance costs but also leads to a huge waste of energy and resources. Research has shown that coastal reinforced concrete structures are subject to poor environments such as environments rich in chloride ions and sulfates, and high temperature and humidity, and therefore suffer widespread serious corrosion damage just 10 to 15 years after construction, far from reaching the theoretical service life designed.

The concrete in reinforced concrete structures belongs to a strong alkaline environment, in which the surface of the rebar is passivated to produce a stable metal oxide passive film. In the actual use of reinforced concrete structures, the dissolution and repair of the passive film are theoretically in a balanced state, so that the potential at each position on the surface of the rebar is almost the same, ensuring that the rebar is not easily corroded or has a very low corrosion rate. However, when the passive film on the surface of the rebar is damaged by external erosive substances, for example, in a marine environment, when the active chloride ions on the passive film on the surface of the rebar reach a certain concentration, the dissolution and repair of the passive film will lose balance, and the dissolution of the passive film will accelerate to form a corrosion pit, resulting in the rebar skeleton being exposed to the erosive medium, and ultimately leading to the failure of the reinforced concrete structure.

Currently, corrosion inhibitors, surface protective layers, cathodic protection, rebar painting, and other methods have a certain effect on extending the service life of reinforced concrete structures, but improving the corrosion resistance of the steel bars themselves, which are the core of reinforced concrete structures, is the key to solving the corrosion damage problem of reinforced concrete structures.

In addition to corrosion resistance, the mechanical performance, welding performance, production and manufacturing costs of rebars are also important aspects that affect the actual production and application of rebars. For example, stainless steel rebars are a common type of rebar with excellent corrosion resistance. By adding a large amount of alloying elements such as Cr, Ni, Mo, etc., the corrosion resistance can be greatly improved compared to ordinary carbon steel rebars, and the corrosion resistance is very good. However, since a large amount of alloying elements is added to stainless steel rebars, the welding performance is very low, and in actual construction, the welding construction cost of stainless steel rebars is very high, and there is a risk that the reinforced concrete structure will be unstable due to poor welding. In addition, since a large amount of alloying elements is added to stainless steel rebars, their raw material costs and production costs are several times higher than those of ordinary rebars, resulting in high costs and insufficient wide application, and not meeting the social demand for energy saving and consumption reduction. In addition, there is still debate as to whether macrocell corrosion will occur when stainless steel rebars and ordinary rebars are lapped and spliced.

Therefore, how to simultaneously guarantee corrosion resistance, mechanical performance, welding performance, and cost is an important issue in research into corrosion-resistant rebars that has significant social and economic impact.

The present invention aims to provide a 400 MPa-class corrosion-resistant rebar that has excellent corrosion resistance, overall mechanical performance, and welding performance, can be manufactured at low material and process costs, and is suitable for wide use in marine construction, in order to solve the technical problems that existed in the prior art.

In order to achieve the above object of the invention, one embodiment has a chemical composition, in mass percent, of Cr: 9.5-10.4%, Mo: 1.0-1.2%, Mn: 0.3-0.6%, Ni: 0.01-1.00%, Cu: 0.01-0.5%, C≦0.014%, N≦0.004%, Nb: 0.01-0.05%, Si: 0.2-0.6%, S≦ We provide a 400 MPa-class corrosion-resistant rebar containing 0.004%, O≦0.003%, As≦0.01%, P: 0.01-0.03%, Cr+Mo+0.5Mn+0.35Ni+0.25Cu at 11.1-12.2%, C+N+0.3Si+Mn+1.8Nb at 0.4-0.8%, and the balance being Fe and unavoidable impurities.

Preferably, the chemical composition of the reinforcing bar further includes, in mass percent, one or more of V: 0.1-0.15%, Ti: 0.01-0.05%, Al: 0.01-0.03%, and B: 0.0005-0.0020%.

Furthermore, the microstructure of the reinforcing bar is ferrite and bainite, with the proportion of ferrite being 28% to 40%.

Furthermore, the rebar has A, B, C, and D inclusions of ≦1.0 grade according to the GB/T10561 standard.

Furthermore, the rebar has a yield strength of ≥ 420 MPa, a tensile strength of ≥ 540 MPa, an elongation at break of ≥ 18%, and a total elongation at maximum force of ≥ 7.5%.

Preferably, the nominal diameter of the reinforcing bar is between 6 and 32 mm.

Preferably, if the nominal diameter of the reinforcing bar is between 6 and 10 mm, the reinforcing bar is a coiled reinforcing bar, and if the nominal diameter of the reinforcing bar is between 12 and 32 mm, the reinforcing bar is a rod-shaped reinforcing bar.

Furthermore, in an ambient immersion corrosion test, the corrosion rate of the reinforcing steel due to the average weight loss is 0.05 to 0.1 g/( ^m2 ·h), and in a salt spray corrosion test, the corrosion rate of the reinforcing steel due to the average weight loss is 0.01 to 0.04 g/( ^m2 ·h);
In a simulated concrete pore water having a chloride ion concentration of ≧3 mol/L, the self-corrosion potential of the reinforcing bar is −0.1 to −0.15 V and the polarization resistance is 2500 to 3000 kΩ/cm ² ;
The self-corrosion current density is ≦0.13 μA/cm ² .

Preferably, the reinforcing bar can be produced using either process path 1 or process path 2;
The process path 1 includes a hot metal pre-desulfurization process, a converter smelting process, an AOD furnace refining process, an LF furnace refining process, a square billet continuous casting process, a hot continuous rolling process, and a temperature controlled cooling process, which are performed in this order.
The process path 2 includes a hot metal pre-desulfurization process, a converter smelting process, an LF furnace refining process, an RH furnace refining process, a square billet continuous casting process, a hot continuous rolling process, and a temperature controlled cooling process, which are performed in this order.

Preferably, in process route 1, the tapping temperature in the converter smelting process is 1600 to 1660°C, and in the AOD furnace refining process, a high carbon ferrochromium alloy and a molybdenum iron alloy are added to the molten steel to perform initial alloying of the molten steel, and after reduction and slag removal, a manganese alloy is added, the tapping ladle is purged with argon for 5 minutes or more before tapping, 20 kg of aluminum ingot is added to the molten steel during tapping, the tapping temperature is 1630 to 1670°C, and the tapping C content is ≦0.01%, and in the LF furnace refining process After the molten steel reaches the ladle of the LF furnace, the slag is adjusted by adding 13-15 kg of lime and 4.0-6.5 kg of fluorite per ton of molten steel, the white slag holding time is ≧8 min, the soft stirring time is 8-15 min, the tapping temperature is 1600-1620°C, and during the square billet continuous casting process, carbon-free mold flux or ultra-low carbon mold flux is used, the continuous casting temperature is 1520-1560°C, and the casting speed during continuous casting is 1.2-1.6 m/min.

Preferably, in the process path 2, during the converter smelting step, a trace carbon ferrochrome alloy is added to the molten steel during tapping to perform initial alloying of the molten steel, and the tapping temperature is 1700-1750°C; during the LF furnace refining step, argon is bottom-blown into the ladle of the LF furnace at a flow rate of 80-160 L/min throughout the entire process, and the tapping temperature is 1560-1600°C; and during the RH furnace refining step, oxygen blowing into the RH furnace is started after the RH furnace is evacuated for 3 min, and the total amount of oxygen blown is 500-700 Nm ³ , then adding a trace carbon ferrochrome alloy to the molten steel to alloy the molten steel, and when the vacuum level is less than 2 mbar, performing fresh water circulation treatment for 5 minutes or more, the tapping temperature is 1560-1600°C, and the tapping C content is ≦0.015%, and during the square billet continuous casting process, carbon-free mold flux or ultra-low carbon mold flux is used, the continuous casting temperature is 1520-1560°C, and the casting speed during continuous casting is 2.2-2.6 m/min.

Preferably, in both process path 1 and process path 2,
In the hot continuous rolling process, the continuous cast billet is heated in a heating furnace, the heating temperature is 1100 to 1200°C, the furnace time is 60 to 120 min, and then rolled into a rod-shaped threaded rebar having a diameter of 12 to 32 mm, the rolling start temperature is 1000 to 1100°C, and the finish rolling temperature is 850 to 950°C.
In the temperature-controlled cooling step, the rolled rod-shaped threaded reinforcing bar is naturally cooled on a cooling bed, and the temperature when it is transported to the cooling bed is 860 to 920°C.

Preferably, in both process route 1 and process route 2, during the hot continuous rolling process, the continuously cast billet is heated in a heating furnace, the heating temperature is 1080-1130°C, the furnace time is 60-120 min, and then rolled into a coil-shaped threaded rebar with a diameter of 6-10 mm, the rolling start temperature is 980-1030°C, the finish rolling temperature is 850-950°C, and the laying temperature is 830-920°C.

Preferably, both process paths 1 and 2 include an in-line pickling process and a packaging process that are performed in sequence after the temperature-controlled cooling process, and in the in-line pickling process, the rebar is passed through a pickling tank, a passivation tank, and a drying device in that order, and the gas outlets of the pickling tank are distributed around the center line of the pickling tank.

Furthermore, when two of the reinforcing bars are joined as a welded sample by electroslag pressure welding, the fracture point in a tensile test of the resulting welded sample is formed in the base material of the two reinforcing bars.

Compared to the prior art, the beneficial effects of the present invention include:

(1) Under the premise of ultra-low carbon design, the contents and relative relationships of Cr, Mo, Mn, Ni, and Cu are reasonably designed, and the contents and relative relationships of C, N, Si, Mn, and Nb are reasonably designed, so that the rebar contains a reasonable proportion of ferrite and bainite dual-phase microstructure, and the overall performance of the rebar is excellent. Specifically, the mechanical properties of the rebar are: yield strength ≧420MPa, tensile strength ≧540MPa, elongation at break ≧18%, and total elongation at maximum force ≧7.5%. Regarding corrosion resistance, in ambient immersion corrosion tests and salt spray corrosion tests, the corrosion resistance is improved by 45 times or more compared to normal HRB 400, and in electrochemical corrosion tests, the self-corrosion potential exceeds 0.4 V in noble width compared to normal HRB 400, the polarization resistance is much higher than normal HRB 400, and the self-corrosion current density is equivalent to 1/65 or less of normal HRB 400. Regarding welding performance, it is easy to weld, the weld point structure is strong and difficult to break, and the break point in the tensile test of the welded sample is formed in the rebar base material.

(2) According to the above chemical composition design plan, it is possible to achieve excellent corrosion resistance, comprehensive mechanical performance and welding performance, while at the same time, the cost of alloying elements is low, energy saving and consumption is reduced, and it can be manufactured through multiple process routes, reducing the cost of the production process, and is suitable for actual production and processing, with greater social significance and economic benefits.

The present invention aims to provide a method for producing 400 MPa-class corrosion-resistant rebars that have excellent corrosion resistance, overall mechanical performance, and welding performance, have low material and process costs, and are suitable for widespread use in marine construction, in order to solve the technical problems that existed in the prior art.

In order to achieve the above object of the invention, one embodiment comprises:
(1) A method for smelting molten steel by sequentially performing a hot metal pre-desulfurization process, a converter smelting process, an AOD furnace refining process, and an LF furnace refining process, or a method for smelting molten steel by sequentially performing a hot metal pre-desulfurization process, a converter smelting process, an LF furnace refining process, and an RH furnace refining process, and continuously casting the obtained molten steel into a steel billet, and a chemical composition of the steel billet is, in mass percent, Cr: 9.5 to 10.4%, Mo: 1.0 to 1.2%, Mn: 0.3 to 0.6%, Ni: 0.01 to 1.00%, Cu: 0.01 to 0.05%, and Cu: 0.02 to 0.05%. 0.01-0.5%, C≦0.014%, N≦0.004%, Nb: 0.01-0.05%, Si: 0.2-0.6%, S≦0.004%, O≦0.003%, As≦0.01%, P: 0.01-0.03%, and Cr+Mo+0.5Mn+0.35Ni+0.25Cu is 11.1-12.2%, C+N+0.3Si+Mn+1.8Nb is 0.4-0.8%, and the balance is Fe and unavoidable impurities;
(2) The steel billet obtained in step 1 (which means the steelmaking step; the same applies below) is heated in a heating furnace, the heating temperature is 1100-1200°C, the residence time is 60-120 min, and then rolled into a rod-shaped threaded rebar with a diameter of 12-32 mm, the rolling start temperature is 1000-1100°C, the finish rolling temperature is 850-950°C, and then the rolled rod-shaped threaded rebar is naturally cooled on a cooling bed, and the temperature when it is transported to the cooling bed is 860-920°C;
Alternatively, the present invention provides a method for producing a 400 MPa-class corrosion-resistant rebar, comprising: heating the steel billet obtained in step 1 in a heating furnace at a heating temperature of 1080 to 1130°C and a residence time of 60 to 120 min; subsequently rolling the billet into a coil-shaped threaded rebar having a diameter of 6 to 10 mm; a rolling start temperature of 980 to 1030°C, a finish rolling temperature of 850 to 950°C, and a laying temperature of 830 to 920°C; and subsequently cooling the rolled coil-shaped threaded rebar by a delayed Stelmor cooling method, with all fans below the roller conveyor turned off.

Preferably, in step 1, the chemical composition of the steel billet further includes, in mass percent, one or more of V: 0.1-0.15%, Ti: 0.01-0.05%, Al: 0.01-0.03%, and B: 0.0005-0.0020%.

Preferably, in step 1, when molten steel is smelted by sequentially using a hot metal pre-desulfurization process, a converter smelting process, an AOD furnace refining process, and an LF furnace refining process, the tapping temperature in the converter smelting process is 1600 to 1660°C, and in the AOD furnace refining process, a high carbon ferrochromium alloy and a molybdenum iron alloy are added to the molten steel to perform initial alloying of the molten steel, and after reduction and slag removal, a manganese alloy is added, the tapping ladle is purged with argon for 5 minutes or more before tapping, 20 kg of an aluminum ingot is added to the molten steel during tapping, the tapping temperature is 1630 to 1670°C, and the tapping temperature is 1630 to 1670°C. the content of is ≦0.01%, in the LF furnace refining process, after the molten steel reaches the ladle of the LF furnace, the slag is adjusted by adding 13-15 kg of lime and 4.0-6.5 kg of fluorite per ton of molten steel, the white slag holding time is ≧8 min, the soft stirring time is 8-15 min, the tapping temperature is 1600-1620°C, in the square billet continuous casting process, carbon-free mold flux or ultra-low carbon mold flux is used, the continuous casting temperature is 1520-1560°C, and the casting speed during continuous casting is 1.2-1.6 m/min,
In the case where molten steel is smelted by sequentially using a hot metal preliminary desulfurization process, a converter smelting process, an LF furnace refining process, and an RH furnace refining process, in the converter smelting process, a trace carbon ferrochrome alloy is added to the molten steel during tapping to perform initial alloying of the molten steel, and the tapping temperature is 1700 to 1750°C; in the LF furnace refining process, argon is bottom-blown into the ladle of the LF furnace at a flow rate of 80 to 160 L/min throughout the entire process, and the tapping temperature is 1560 to 1600°C; and in the RH furnace refining process, the RH furnace is evacuated for 3 min, and then oxygen blowing into the RH furnace is started, and the total amount of oxygen blown is 500 to 700 Nm ³ , then adding a trace carbon ferrochrome alloy to the molten steel to alloy the molten steel, and performing fresh water circulation treatment for 5 minutes or more when the vacuum degree is less than 2 mbar, the tapping temperature is 1560-1600°C, and the tapping C content is ≦0.015%, and during the square billet continuous casting process, carbon-free mold flux or ultra-low carbon mold flux is used, the continuous casting temperature is 1520-1560°C, and the casting speed during continuous casting is 2.2-2.6 m/min.

Preferably, the method of production comprises:
(3) The method further includes an in-line pickling step in which the reinforcing bars obtained in step 2 (which means a controlled rolling and controlled cooling step; the same applies below) are sequentially passed through a pickling tank, a passivation tank and a drying device to perform in-line pickling, the gas outlets of the pickling tank are distributed around the center line of the pickling tank, and the reinforcing bars are packaged after leaving the drying device.

Furthermore, when two reinforcing bars manufactured by the above production method are joined as a welded sample by electroslag pressure welding, a breaking point in a tensile test of the obtained welded sample is formed in the base material of the two reinforcing bars.

Furthermore, the microstructure of the rebar produced using the above production method is ferrite and bainite, with the proportion of ferrite being 28% to 40%.

Furthermore, the rebars manufactured using the above production method have A, B, C, and D inclusions of grade ≦1.0 according to the GB/T10561 standard.

Furthermore, the rebar produced by the above production method has a yield strength of ≥ 420 MPa, a tensile strength of ≥ 540 MPa, an elongation at break of ≥ 18%, and a total elongation at maximum force of ≥ 7.5%.

Furthermore, the reinforcing bar manufactured by the above-mentioned production method has a corrosion rate of 0.05 to 0.1 g/( ^m2 ·h) based on the average weight loss of the reinforcing bar in an ambient immersion corrosion test, and a corrosion rate of 0.01 to 0.04 g/(m2· ^h ) based on the average weight loss of the reinforcing bar in a salt spray corrosion test.
h)
In a simulated concrete pore water having a chloride ion concentration of ≧3 mol/L, the self-corrosion potential of the reinforcing bar is −0.1 to −0.15 V and the polarization resistance is 2500 to 3000 kΩ/cm ² ;
The self-corrosion current density is ≦0.13 μA/cm ² .

Compared to the prior art, the beneficial effects of the present invention include:

(1) Based on the design premise of ultra-low carbon, the contents and relative relationships of Cr, Mo, Mn, Ni, and Cu are rationally designed, and the contents and relative relationships of C, N, Si, Mn, and Nb are rationally designed, so that the rebar contains a dual-phase microstructure of ferrite and bainite in a reasonable ratio, and the overall performance of the rebar is excellent. Specifically, the mechanical performance of the rebar is as follows: yield strength ≧420 MPa, tensile strength ≧540 MPa, elongation at break ≧18%, and total elongation at maximum force ≧7.5%. Regarding corrosion resistance, in ambient immersion corrosion tests and salt spray corrosion tests, the corrosion resistance is 45 times higher than that of normal HRB400, and in electrochemical corrosion tests, the self-corrosion potential exceeds 0.4 V in noble width compared to normal HRB400, the polarization resistance is much higher than that of normal HRB400, and the self-corrosion current density is 1/65 or less than that of normal HRB400. Regarding welding performance, it is easy to weld, the weld point structure is strong and difficult to break, and the break point in the tensile test of the welded sample is formed in the rebar base material.

(2) According to the above chemical composition design plan, it is possible to achieve excellent corrosion resistance, comprehensive mechanical performance and welding performance, while at the same time, the cost of alloying elements is low, energy saving and consumption is reduced, and it can be manufactured through multiple process routes, reducing the cost of the production process, and is suitable for actual production and processing, with greater social significance and economic benefits.

(3) Furthermore, based on the above chemical composition design proposal, by combining process control in controlled rolling and controlled cooling, the structure, mechanical properties, corrosion resistance, and welding performance of the rebar can be further optimized to further improve the overall performance of the rebar; the process operations in the hot continuous rolling process are simple and easy to control, and the smooth progress of the work situation in actual production can be ensured.

The technical solutions of the present invention are further illustrated below by specific embodiments, but the scope of the claimed invention is not limited by the description in the specification.
First Embodiment

This embodiment provides a corrosion-resistant rebar, particularly a hot-rolled deformed rebar, whose chemical composition, in mass percent, is as follows: Cr: 9.5-10.4%, Mo: 1.0-1.2%, Mn: 0.3-0.6%, Ni: 0.01-1.00%, Cu: 0.01-0.50%, C≦0.014%, N≦0.004%, Nb: 0.01-0.05%, Si: 0.2-0.6%, S≦0.004%, O≦0.003%, As≦0.01%, P: 0.01-0.03%, and the balance is Fe and unavoidable impurities.

The mass percentages of Cr, Mo, Mn, Ni and Cu in the chemical composition of the reinforcing bar further satisfy 11.1%≦Cr+Mo+0.5Mn+0.35Ni+0.25Cu≦12.2%, and the mass percentages of C, N, Si, Mn and Nb further satisfy 0.4%≦C+N+0.3Si+Mn+1.8Nb≦0.8%.

Here, the role of each chemical component in the reinforcing bar is explained below.

Cr is an important corrosion-resistant element, which can form an oxide passivation film on the surface of the reinforcing bar to effectively prevent the oxidation of the reinforcing bar and improve the corrosion resistance of the reinforcing bar skeleton. Especially when coexisting with elements such as Mo and Ni, the reinforcing bar can obtain better corrosion resistance and avoid the occurrence of pitting corrosion. In addition, the Cr element can also improve the hardenability of the reinforcing bar. In the chemical composition design of the present invention, the Cr content is controlled to 9.5-10.4%.

Mo is an important corrosion-resistant element. Whether in a reducing acid environment or a strongly oxidizing salt solution environment, the addition of Mo can passivate the surface of the rebar, and can also prevent pitting corrosion of the rebar in a chloride solution, thus improving the overall corrosion resistance of the rebar in various environments. In addition, the effect of Mo in suppressing pearlite transformation is very significant, and at the same time, when combined with Cr, a carbide-forming element, it can promote the formation of bainite. In addition, Mo can promote the refinement of crystal grains and improve the hardenability and heat resistance of the rebar, but if the Mo content is too high, the oxidation resistance of the rebar will deteriorate. In the chemical composition design of the present invention, the Mo content is controlled to 1.0-1.2%.

Mn is a solid solution strengthening element that can increase the strength of the rough wire and, in combination with the harmful element S, can reduce the hot brittleness of the rebar. Mn is also important as a deoxidizer, desulfurizer, and austenite former. However, if the Mn content is too high, the plasticity, impact toughness, and welding performance of the rebar will all decrease. In the chemical composition design of the present invention, the Mn content is controlled to 0.3 to 0.6%.

Ni is an important corrosion-resistant element, which gives reinforcing bars high corrosion resistance in acidic and alkaline environments, as well as high rust prevention and heat resistance at high temperatures. Ni is also an austenite-forming element, and can improve corrosion resistance by giving the steel material a uniform austenitic structure. In the chemical composition design of the present invention, the Ni content is controlled to 0.01-1.00%.

Cu is an important corrosion-resistant element that contributes to improving the corrosion resistance of rebars, but if the Cu content is too high, the plasticity of the steel material decreases and hot rolling cracks may occur. In the chemical composition design of the present invention, the Cu content is controlled to 0.01 to 0.50%.

C is an austenite-forming element, and by controlling the carbon content to be below the solubility limit of ferrite, it is possible to improve the uniformity of the steel microstructure and component distribution, reduce the potential difference between each region inside the rebar, and lower the corrosion rate. In the chemical composition design of the present invention, the C content is controlled to 0.014% or less.

N is an austenite-forming element, and a high N content reduces the plasticity of the reinforcing bar and is also disadvantageous in controlling the ratio of ferrite and bainite in the reinforcing bar structure. In the chemical component design of the present invention, the N content is controlled to 0.004% or less.

Nb is an element that strengthens micro-alloys and can play a role in precipitation strengthening and grain refinement strengthening during the rolling process (for example, the hot continuous rolling process described below). However, if the Nb content is too high, the plasticity of the rebar decreases and the cost increases. In the chemical composition design of the present invention, the Nb content is controlled to 0.01-0.05%.

Si is a solid solution strengthening element. It dissolves in ferrite, inhibits the diffusion of C in austenite, delays the ferrite and pearlite transformation, and can increase the yield strength and tensile strength of rebars. However, if the Si content is too high, the plasticity of the steel material decreases and the welding performance of the rebar deteriorates. In the chemical composition design of the present invention, the Si content is controlled to 0.2-0.6%.

P can increase the strength and corrosion resistance of reinforcing bars, but it is prone to segregation in steel, and if the P content is too high, the mechanical performance at low temperatures decreases. In the chemical composition design of the present invention, the P content is controlled to 0.01 to 0.03%.

Cr+Mo+0.5Mn+0.35Ni+0.25Cu is very important for the comprehensive control of the corrosion resistance, plasticity and cost of rebar. On the one hand, it makes the oxide film on the surface of the rebar have sufficient density, improves the corrosion resistance and repair ability of the rebar body, and ensures the corrosion resistance of the rebar oxide film and the rebar body. On the other hand, it avoids the low proportion of ferrite in the rebar structure, and is favorable for the control of the microstructure and its proportion of the rebar, thereby improving the plasticity of the rebar and increasing the breaking elongation rate and the total elongation rate at maximum force. In yet another aspect, it reduces the addition of valuable alloy elements, reduces costs, and promotes the generalization, design and use of construction. In the chemical component design of the present invention, Cr+Mo+0.5Mn+0.35Ni+0.25Cu meets 11.1-12.2%.

C+N+0.3Si+Mn+1.8Nb is very important for the comprehensive control of the mechanical performance of rebar, such as strength and plasticity. On the one hand, it ensures that the alloying elements can fully exert the effects of solid solution strengthening, precipitation strengthening, microstructural strengthening, etc., and enhances the strength of the rebar. On the other hand, it avoids a low proportion of ferrite in the rebar microstructure and a high proportion of bainite in the rebar microstructure, that is, it optimizes the respective proportions of ferrite and bainite in the rebar microstructure, enhances the plasticity of the rebar, and increases the elongation at break and the total elongation at maximum force. In the chemical component design of the present invention, C+N+0.3Si+Mn+1.8Nb meets 0.4-0.8%.

In general, compared with the prior art, the design of the chemical components of the present invention has the following advantages: (1) Under the premise of ultra-low carbon design, the content and related relationships of Cr, Mo, Mn, Ni, and Cu are reasonably designed, and the content and related relationships of C, N, Si, Mn, and Nb are reasonably designed, so that the microstructure of the rebar is ferrite and bainite, of which the proportion of ferrite is 28%-40% and the proportion of bainite is 60%-72%. In addition, the rebar has excellent corrosion resistance, comprehensive mechanical performance, and welding performance, and has excellent overall comprehensive performance, which is suitable for the use needs of marine engineering. (2) According to the above chemical component design plan, it can achieve excellent corrosion resistance, comprehensive mechanical performance, and welding performance, while the cost of alloy elements is low, energy saving and reduced consumption are achieved, and it can be manufactured through multiple process routes, reducing the cost of the production process, and is suitable for actual production and processing, and has higher social significance and economic effect.

As described above, the microstructure of the reinforcing bar is ferrite and bainite, with the proportion of ferrite being 28% to 40% and the proportion of bainite being 60% to 72%. Thus, the influence of the microstructure of the reinforcing bar and the proportion of ferrite and bainite is specifically reflected in the following two aspects. One is the influence on mechanical performance, and by controlling the proportion of ferrite and bainite in this embodiment, appropriate yield strength and good elongation, including the elongation at break and the total elongation at maximum force, can be guaranteed, ensuring good overall mechanical performance. The other is the influence on corrosion resistance, and by ensuring a certain proportion of bainite structure, the corrosion resistance of the reinforcing bar can be increased.

Specifically, in terms of mechanical performance, the rebar is a rebar of 400 MPa class or higher, with a yield strength of ≥ 420 MPa, a tensile strength of ≥ 540 MPa, an elongation at break of ≥ 18%, and a total elongation at maximum force of ≥ 7.5%.

The inclusions in the rebar are also very well controlled. Specifically, the A, B, C, and D inclusions in the rebar are all ≦1.0 grade according to the GB/T10561 standard. This increases the toughness of the rebar under low-temperature conditions, which is advantageous in ensuring the mechanical performance of the rebar.

Furthermore, in terms of corrosion resistance, in ambient immersion corrosion tests and salt spray corrosion tests of the reinforcing bars, the corrosion resistance is improved by 45 times or more compared to normal HRB400. Specifically, in ambient immersion corrosion tests, the corrosion rate based on the average weight loss of the reinforcing bars is 0.05 to 0.1 g/( ^m2 .
h), and in a salt spray corrosion test, the corrosion rate of the reinforcing steel due to the average weight loss is 0.01 to 0.04 g/( ^m2 ·h);
In a simulated concrete pore water having a chloride ion concentration of ≧3 mol/L, the self-corrosion potential of the reinforcing bar is −0.1 to −0.15 V and the polarization resistance is 2500 to 3000 kΩ/cm ² ;
The self-corrosion current density is ≦0.13 μA/cm ² .

The specific method of the ambient immersion corrosion test used here is as follows: The treated sample is placed in an ambient immersion test box, and the test is conducted in accordance with the YB/T4367 corrosion test method for rebar in a chloride ion environment, with the solution being 2.0±0.05 (wt%) NaCl, the pH being 6.5-7.2, the solution temperature being 45°C±2°C, and the drying temperature being 70°C±10°C, and the corrosion rate is obtained by the average weight loss over 168 hours through continuous testing.

The specific method of the salt spray corrosion test used is as follows: The treated sample is placed in a salt spray test box, and the test is performed in accordance with GB/T10125 Corrosion test in artificial atmosphere - Salt spray corrosion test, the solution is 2.0±0.05 (wt%) NaCl, the pH is 6.5-7.2, the solution temperature is 35°C±2°C, and the corrosion rate is obtained by the average weight loss in 168 hours by continuous testing.

In an electrochemical corrosion test, under the corrosion test conditions of simulated concrete pore water with a chloride ion concentration of ≧3 mol/L, the self-corrosion potential of the rebar is −0.1 to −0.15 V, which is 0.4 V more noble than that of normal HRB400. The polarization resistance of the rebar is 2500 to 3000 kΩ/ ^cm2 , which is much higher than that of normal HRB400. The self-corrosion current density of the rebar is ≦0.13 μA/ ^cm2 , which is 1/65 or less of that of normal HRB400.

The specific method of the electrochemical corrosion test used here is as follows. The electrochemical test was performed in accordance with GB/T24196-2009 "Corrosion of Metals and Alloys/Electrochemical Test Methods/Guideline for the Implementation of Electrostatic Potential Polarization and Potentiodynamic Polarization Measurements," using a three-electrode system, with a saturated calomel electrode as the reference electrode, a Pt sheet as the auxiliary electrode, and simulated concrete pore water with a chloride ion concentration of ≧3 mol/L as the test solution. The scanning range of the polarization curve test was -300 to 600 mV relative to the sample's self-corrosion potential, and the scanning speed was 1 mV/s. The scanning frequency range of the electrochemical impedance test was 10 ^-2 to 10 ⁵ Hz, and the AC excitation signal amplitude was ±
It is 5mV.

From the above, it can be seen that the reinforcing bars have excellent corrosion resistance, and when corrosion performance tests were conducted in a simulated seawater solution, all of the indicators were far superior to those of ordinary screw steel of the same grade.

Regarding weldability, the rebar is easy to weld, and when two of the rebars are joined as a welded sample by electroslag pressure welding, the weld structure is strong and not easily broken, and the break point in a tensile test of the welded sample is formed in the rebar base material, not at the weld point.

Preferably, in this embodiment, the nominal diameter of the rebar is 6 to 32 mm.

Here, when the nominal diameter of the reinforcing bar is 6-10mm, the reinforcing bar is a coil reinforcing bar, and when the nominal diameter of the reinforcing bar is 12-32mm, the reinforcing bar is a rod reinforcing bar, thus satisfying the requirements for reinforcing bars in marine construction, and also improving the overall mechanical performance and corrosion resistance of the reinforcing bar structure by designing the diameter.
Second Embodiment

This embodiment provides a corrosion-resistant rebar, specifically a hot-rolled deformed rebar suitable for marine construction. The main difference from the first embodiment is that the performance of the rebar is further improved by adding one or more of V: 0.1-0.15%, Ti: 0.01-0.05%, Al: 0.01-0.03%, and B: 0.0005-0.0020% to the chemical composition.

Specifically, in this embodiment, the chemical composition of the reinforcing bar includes, in mass percent, any one or more of the following four: Cr: 9.5-10.4%, Mo: 1.0-1.2%, Mn: 0.3-0.6%, Ni: 0.01-1.00%, Cu: 0.01-0.50%, C≦0.014%, N≦0.004%, Nb: 0.01-0.05%, Si: 0.2-0.6%, S≦0.004%, O≦0.003%, As≦0.01%, P: 0.01-0.03%, and V: 0.1-0.15%, Ti: 0.01-0.05%, Al: 0.01-0.03%, B: 0.0005-0.0020%, with the remainder being Fe and unavoidable impurities.

Furthermore, as in the first embodiment, the mass percentages of Cr, Mo, Mn, Ni, and Cu in the chemical composition of the reinforcing bar further satisfy 11.1%≦Cr+Mo+0.5Mn+0.35Ni+0.25Cu≦12.2%, and the mass percentages of C, N, Si, Mn, and Nb further satisfy 0.4%≦C+N+0.3Si+Mn+1.8Nb≦0.8%.

Here, the roles of elements such as Cr, Mo, Mn, Ni, Cu, C, N, Nb, Si, and P in the reinforcing bar, and the design effects of Cr+Mo+0.5Mn+0.35Ni+0.25Cu and C+N+0.3Si+Mn+1.8Nb are the same as in the first embodiment, and detailed explanations will be omitted. Below, the roles of the optional elements V, Ti, Al, and B in this embodiment will be explained.

V is an element that strengthens micro-alloys, and can precipitate V(C,N) compounds during the rolling process (for example, the hot continuous rolling process described below). It has a certain precipitation strengthening effect, as well as inhibiting the growth of austenite and ferrite crystal grains and strengthening the crystal grains by refining them. However, if the V content is too high, the plasticity of the reinforcing bar decreases and the cost increases. In the chemical composition design of the present invention, the V content is controlled to 0.1-0.15%.

Ti has a greater affinity with C element than Cr, and therefore can effectively prevent intergranular corrosion by avoiding the precipitation of chromium carbide and the occurrence of chromium deficiency at grain boundaries. In addition, adding an appropriate amount of Ti can form fine TiOx and TiN that are diffused and distributed in the steel sheet. However, if the Ti content is too high, the viscosity of the molten steel increases, which is disadvantageous for smelting the molten steel, and the size of the TiOx formed becomes coarse, deteriorating the toughness of the steel sheet. In the chemical composition design of the present invention, the Ti content is controlled to 0.01-0.05%.

Al is a commonly used deoxidizer that can increase the electrode potential of the rebar body, improving corrosion resistance, and inhibiting the growth of austenite grains to increase the strength of the rebar. However, if the Al content is too high, the amount of oxides in the steel will increase, which may impair the weldability of the rebar. In the chemical composition design of the present invention, the Al content is controlled to 0.01-0.03%.

B is a strengthening element that plays a significant role in improving rebar strength, but if the B content is too high, it is detrimental to improving intergranular corrosion resistance. In the chemical composition design of the present invention, the B content is controlled to 0.0005-0.0020%.

In this embodiment, by selectively adding any one or more of V, Ti, Al and B, the performance of the reinforcing bar can be further improved over that of the first embodiment, and the reinforcing bar has better corrosion resistance, mechanical strength, plasticity and welding performance, making construction easier and having a longer theoretical service life when used in marine construction.
Third Embodiment

This embodiment provides a method for producing corrosion-resistant rebar, which can be used for both the production and manufacturing of the corrosion-resistant rebar of the first embodiment and the production and manufacturing of the corrosion-resistant rebar of the second embodiment.

In this embodiment, the process path of the production method includes a hot metal pre-desulfurization process, a converter smelting process, an AOD furnace refining process, an LF furnace refining process, a square billet continuous casting process, a hot continuous rolling process, a temperature controlled cooling process, and a packaging process, which are performed in this order. The production method will be described in detail below in the order of the steps.

(1) Steelmaking Step In this step, molten steel is smelted using a hot metal pre-desulfurization step, a converter smelting step, an AOD furnace refining step, and an LF furnace refining step in this order, and the obtained molten steel is continuously cast into a steel billet in the square billet continuous casting step.

When the production method is used to manufacture the corrosion-resistant rebar of the first embodiment, it can be understood that the chemical composition of the steel billet obtained in this step is consistent with the chemical composition of the rebar of the first embodiment, that is, the chemical composition of the obtained steel billet is, in mass percent, Cr: 9.5-10.4%, Mo: 1.0-1.2%, Mn: 0.3-0.6%, Ni: 0.01-1.00%, Cu: 0.01-0.50%, The alloy contains C≦0.014%, N≦0.004%, Nb: 0.01-0.05%, Si: 0.2-0.6%, S≦0.004%, O≦0.003%, As≦0.01%, P: 0.01-0.03%, and contains 11.1-12.2% of Cr+Mo+0.5Mn+0.35Ni+0.25Cu, 0.4-0.8% of C+N+0.3Si+Mn+1.8Nb, and the balance being Fe and unavoidable impurities. Similarly, when the production method is used to manufacture the corrosion-resistant rebar of the second embodiment, the chemical composition of the steel billet obtained in this step is consistent with that of the rebar of the second embodiment, that is, the chemical composition of the steel billet obtained is, in mass percent, Cr: 9.5-10.4%, Mo: 1.0-1.2%, Mn: 0.3-0.6%, Ni: 0.01-1.00%, Cu: 0.01-0.50%, C≦0.014%, N≦0.004%, Nb: 0.01-0.05%, Si: 0.2-0.6%. %, S≦0.004%, O≦0.003%, As≦0.01%, P: 0.01-0.03%, and contains one or more of the following four elements: V: 0.1-0.15%, Ti: 0.01-0.05%, Al: 0.01-0.03%, B: 0.0005-0.0020%, and Cr+Mo+0.5Mn+0.35Ni+0.25Cu is 11.1-12.2%, C+N+0.3Si+Mn+1.8Nb is 0.4-0.8%, and the balance is Fe and unavoidable impurities.

Furthermore, the tapping temperature of the converter smelting process is 1600-1660°C, which ensures the effectiveness of decarbonization and dephosphorization, and is advantageous for the subsequent alloying.

In the AOD furnace refining process, after comprehensive consideration, low-cost high-carbon ferrochrome alloy and molybdenum iron alloy are added to the molten steel to perform initial alloying of the molten steel, and after reduction, the slag is removed to reduce the content of impurity elements such as P. Thereafter, manganese alloy is added to complete the initial alloying at the same time as deoxidization. Before tapping, the ladle for tapping is purged with argon for 5 minutes or more, and the molten steel is cooled to 200°C.
To reduce secondary oxidation, 20 kg of aluminum ingot is added to the molten steel during tapping, the tapping temperature is 1630-1670°C, and the tapping C content is ≦0.01%, so as to ensure the decarbonization effect of the molten steel and the production tact time.

During the LF furnace refining process, after the molten steel reaches the ladle of the LF furnace, the slag is adjusted by adding 13-15 kg of lime and 4.0-6.5 kg of fluorite per ton of molten steel, the white slag holding time is ≥ 8 min, the soft stirring time is 8-15 min, and the tapping temperature is 1600-1620°C, and the deoxidation and desulfurization of the molten steel is completed in stages.

During the square billet continuous casting process, the molten steel tapped from the LF furnace refining process is continuously cast into a billet, where carbon-free mold flux or ultra-low carbon mold flux is used to prevent carbon buildup in the molten steel, and the temperature of continuous casting is 1520-1560°C, and the casting speed during continuous casting is 1.2-1.6 m/min to ensure continuous casting.

(2) Controlled rolling and controlled cooling In this step, the steel billet obtained in step 1 is rolled into a rebar with a nominal diameter of 6 to 32 mm by a hot continuous rolling process, and then a temperature controlled cooling process is carried out. The specific process plan of this step varies depending on the nominal diameter of the rebar.

Specifically, in the case of a rebar with a nominal diameter of 12 to 32 mm, in this step, during the hot continuous rolling process, the steel billet obtained in step 1 is heated in a heating furnace, the heating temperature is 1100 to 1200°C, and the furnace time is 60 to 120 min, so that the alloying elements are sufficiently redissolved to be advantageous for the exertion of their strengthening effect. Then, it is rolled into a rod-shaped threaded rebar with a diameter of 12 to 32 mm, the rolling start temperature is 1000 to 1100°C, and the finish rolling temperature is 850 to 950°C, so that the austenite grains are maintained at a constant size. Then, during the temperature controlled cooling process, the rolled rod-shaped threaded rebar is naturally cooled on a cooling bed, and the temperature when it is transported to the cooling bed is 860 to 920°C, ensuring the size and ratio control of the subsequent ferrite and pearlite.

In the case of rebars with a nominal diameter of 6 to 10 mm, in this step, during the hot continuous rolling process, the steel billet obtained in step 1 is heated in a heating furnace, the heating temperature is 1080 to 1130°C to favor sufficient re-dissolution of alloy elements, and the furnace time is 60 to 120 min. Then, it is rolled into a coil-shaped threaded rebar with a diameter of 6 to 10 mm, and the rolling start temperature is 980 to 1030°C, the finish rolling temperature is 850 to 950°C, and the laying temperature is 830 to 920°C to maintain the austenite grains at a constant size. Then, during the temperature-controlled cooling process, the rolled coil-shaped threaded rebar is cooled by a delayed Stelmor method, all the fans below the roller conveyor are turned off, and the ferrite and pearlite transformations are completed on the roller conveyor.

(3) Packaging The rebar cooled in step 2 is packed for transportation and use in construction.

As a result, the advantageous effects of the production method of this embodiment compared to the conventional technology are as follows:

(1) The chemical composition is designed on the premise of ultra-low carbon design, and the contents and relative relationships of Cr, Mo, Mn, Ni, and Cu are reasonably designed, and the contents and relative relationships of C, N, Si, Mn, and Nb are reasonably designed, so that the microstructure of the manufactured rebar is ferrite and bainite, of which the proportion of ferrite is 28%-40%, and the proportion of bainite is 60%-72%. In addition, the rebar has excellent corrosion resistance, comprehensive mechanical performance and welding performance, and has excellent overall performance, which is suitable for the use needs of marine engineering.

(2) According to the above chemical composition design plan, the process route is reasonable, especially the process control in controlled rolling and controlled cooling is reasonable, the overall performance of the obtained rebar is further optimized, there is no cracking defect during rolling, and the cost of alloying elements is low, energy saving and reducing consumption, the cost of the production process is reduced, it is suitable for actual production and processing, the process operation is simple and easy to control, and the smooth progress of the working situation in actual production is guaranteed, which has higher social significance and economic benefits.
Fourth Embodiment

This embodiment provides a method for producing corrosion-resistant rebar, which can be used for both the production and manufacturing of the corrosion-resistant rebar of the first embodiment and the production and manufacturing of the corrosion-resistant rebar of the second embodiment.

In this embodiment, the process path of the production method includes a hot metal pre-desulfurization process, a converter smelting process, a LF furnace refining process, a RH furnace refining process, a square billet continuous casting process, a hot continuous rolling process, a temperature controlled cooling process, and a packaging process, which are performed in this order. In other words, the difference between this embodiment and the third embodiment is only the hot metal pre-desulfurization process, the converter smelting process, the LF furnace refining process, the RH furnace refining process, and the square billet continuous casting process, i.e., only the steelmaking step. Below, the production method of this embodiment will be described in detail with respect to only the steelmaking step.

(1) Steelmaking Step In this step, molten steel is smelted using a hot metal pre-desulfurization step, a converter smelting step, an LF furnace refining step, and an RH furnace refining step in this order, and the obtained molten steel is continuously cast into a steel billet in the square billet continuous casting step.

When the production method is used to manufacture the corrosion-resistant rebar of the first embodiment, it can be understood that the chemical composition of the steel billet obtained in this step is consistent with the chemical composition of the rebar of the first embodiment, that is, the chemical composition of the obtained steel billet is, in mass percent, Cr: 9.5-10.4%, Mo: 1.0-1.2%, Mn: 0.3-0.6%, Ni: 0.01-1.00%, Cu: 0.01-0.50%, The alloy contains C≦0.014%, N≦0.004%, Nb: 0.01-0.05%, Si: 0.2-0.6%, S≦0.004%, O≦0.003%, As≦0.01%, P: 0.01-0.03%, and contains 11.1-12.2% of Cr+Mo+0.5Mn+0.35Ni+0.25Cu, 0.4-0.8% of C+N+0.3Si+Mn+1.8Nb, and the balance being Fe and unavoidable impurities. Similarly, when the production method is used to manufacture the corrosion-resistant rebar of the second embodiment, the chemical composition of the steel billet obtained in this step is consistent with that of the rebar of the second embodiment, that is, the chemical composition of the steel billet obtained is, in mass percent, Cr: 9.5-10.4%, Mo: 1.0-1.2%, Mn: 0.3-0.6%, Ni: 0.01-1.00%, Cu: 0.01-0.50%, C≦0.014%, N≦0.004%, Nb: 0.01-0.05%, Si: 0.2-0.6%. %, S≦0.004%, O≦0.003%, As≦0.01%, P: 0.01-0.03%, and contains one or more of the following four elements: V: 0.1-0.15%, Ti: 0.01-0.05%, Al: 0.01-0.03%, B: 0.0005-0.0020%, and Cr+Mo+0.5Mn+0.35Ni+0.25Cu is 11.1-12.2%, C+N+0.3Si+Mn+1.8Nb is 0.4-0.8%, and the balance is Fe and unavoidable impurities.

Furthermore, in the converter smelting process, a trace amount of carbon ferrochrome alloy is added to the molten steel during tapping to perform initial alloying of the molten steel, and the C content in the molten steel is controlled as much as possible in terms of alloy addition to increase efficiency, and the tapping temperature is 1700-1750°C, thereby ensuring the dephosphorization effect and preparing for the subsequent smelting.

During the LF furnace refining process, argon is blown into the LF furnace ladle at a bottom flow rate of 80 to 160 L/min throughout the entire process, and the tapping temperature is 1560 to 1600°C, which ensures that the alloy in the ladle is melted and homogenized, and is advantageous for controlling the production takt time.

In the RH furnace refining process, the RH furnace is evacuated for 3 minutes, and then oxygen injection into the RH furnace is started, with a total amount of oxygen injection of 500-700 ^Nm3 . Then, a trace carbon ferrochrome alloy is added to the molten steel to alloy the molten steel. As the Cr alloying is completed in stages, the carbon increase in the molten steel decreases. When the vacuum level becomes less than 2 mbar, fresh water circulation is performed for 5 minutes or more. The tapping temperature is 1560-1600°C, and the tapping C content is ≦0.015%, ensuring the decarbonization effect.

During the square billet continuous casting process, the molten steel tapped from the LF furnace refining process is continuously cast into a billet, and carbon-free mold flux or ultra-low carbon mold flux is used to prevent the increase in carbon in the molten steel. The temperature of the continuous casting is 1520-1560°C, and the casting speed during the continuous casting is 2.2-2.6 m/min, which is advantageous for continuous casting.

As mentioned above, the controlled rolling and controlled cooling step in step 2 and the packaging process in step 3 are both similar to those in the third embodiment, so detailed explanations will be omitted.

As a result, the advantageous effects of the production method of this embodiment compared to the conventional technology are as follows:

(1) The chemical composition is designed based on the premise of ultra-low carbon design, and the respective contents and related relationships of Cr, Mo, Mn, Ni, and Cu are rationally designed, and the respective contents and related relationships of C, N, Si, Mn, and Nb are rationally designed. As a result, the microstructure of the manufactured rebar is ferrite and bainite, of which the proportion of ferrite is 28%-40% and the proportion of bainite is 60%-72%. In addition, the rebar has excellent corrosion resistance, comprehensive mechanical performance, and welding performance, and has excellent overall performance, which is suitable for the use needs of marine engineering.

(2) According to the above chemical composition design plan, the process route is reasonable, especially the process control in controlled rolling and controlled cooling is reasonable, the overall performance of the obtained rebar is further optimized, there is no cracking defect during rolling, and the cost of alloying elements is low, energy saving and reducing consumption, the cost of the production process is reduced, it is suitable for actual production and processing, the process operation is simple and easy to control, and the smooth progress of the working situation in actual production is guaranteed, which has higher social significance and economic benefits.
Fifth Embodiment

This embodiment provides a method for producing corrosion-resistant rebar, the process path of which includes a hot metal pre-desulfurization process, a converter smelting process, a LF furnace refining process, a RH furnace refining process, a square billet continuous casting process, a hot continuous rolling process, a temperature-controlled cooling process, an in-line pickling process, and a packaging process, which are performed in sequence.

In this embodiment, the hot metal pre-desulfurization process to the temperature-controlled cooling process may be carried out in the third embodiment or in the fourth embodiment. In other words, this embodiment is based on the third or fourth embodiment, and an in-line pickling process is added before the packaging process. In the following, only the in-line pickling process will be described, and other detailed descriptions will be omitted.

Specifically, in the in-line pickling process, that is, after the temperature-controlled cooling process and before the packaging process, the rebar is passed through a pickling tank, a passivation tank, and a drying device in that order to achieve in-line pickling of the rebar. Here, in order to enhance the effect of pickling, the gas outlets of the pickling tank are distributed around the center line of the pickling tank.

The present invention will be further described below by providing Examples 1 to 16 of the present invention. It is understood that the following are only some of the preferred examples of the present invention and do not represent all embodiments of the present invention, and other examples based on the above embodiments do not deviate from the technical gist of the present invention.

First, in Examples 1 to 16 and Comparative Examples 1 to 4, reinforcing bars are provided, and the chemical components of the reinforcing bars are as shown in Table 1. Among them, Example 12 is implemented in the first embodiment described in the present invention, the other examples are implemented in the second embodiment described in the present invention, and Comparative Examples 1 to 4 do not meet any of the embodiments of the present invention.

The production methods of Examples 1 to 8 employ a process path that includes a hot metal pre-desulfurization process, a converter smelting process, an AOD furnace refining process, an LF furnace refining process, a square billet continuous casting process, a hot continuous rolling process, a temperature-controlled cooling process, and an in-line pickling process, which are carried out in this order. Each process is described below.

(1) In the molten iron pre-desulfurization process, the molten iron is pre-desulfurized.

(2) In the converter smelting process, the tapping temperature is 1600 to 1660°C.

(3) In the AOD furnace refining process, high carbon ferrochromium alloy and molybdenum iron alloy are added to the molten steel to perform initial alloying of the molten steel, and after reduction and slag removal, manganese alloy is added. Before tapping, the tapping ladle is purged with argon for 5 minutes or more. 20 kg of aluminum ingot is added to the molten steel during tapping. The tapping temperature is 1630-1670°C, and the tapping C content is ≦0.010%.
It is.

(4) In the LF furnace refining process, after the molten steel reaches the ladle of the LF furnace, the slag is adjusted by adding 13 to 15 kg of lime and 4.0 to 6.5 kg of fluorite per ton of molten steel, the white slag holding time is ≧8 min, the soft stirring time is 8 to 15 min, and the tapping temperature is 1600 to 1620°C.

(5) In the square billet continuous casting process, the molten steel tapped from the LF furnace refining process is continuously cast into a billet, in which carbon-free mold flux or ultra-low carbon mold flux is used, the temperature of the continuous casting is 1520-1560°C, and the casting speed during the continuous casting is 1.2-1.6 m/min.

(6) In the hot continuous rolling process, in Examples 1 to 4, the billet is heated in a heating furnace, the heating temperature is 1100 to 1200°C, the furnace time is 60 to 120 min, and then rolled into a rod-shaped threaded rebar with a diameter of 12 to 32 mm, the rolling start temperature is 1000 to 1100°C, and the finish rolling temperature is 850 to 950°C. In Examples 5 to 8, the billet is heated in a heating furnace, the heating temperature is 1080 to 1130°C, the furnace time is 60 to 120 min, and then rolled into a coil-shaped threaded rebar with a diameter of 6 to 10 mm, the rolling start temperature is 980 to 1030°C, the finish rolling temperature is 850 to 950°C, and the laying temperature is 830 to 920°C.

(7) In the temperature-controlled cooling process, in Examples 1 to 4, the rolled rod-shaped threaded rebar is naturally cooled on a cooling bed, and the temperature when it is transported to the cooling bed is 860 to 920°C. In Examples 5 to 8, the rolled coil-shaped threaded rebar is cooled using a delayed Stelmor method, and all fans below the roller conveyor are turned off.

(8) In the in-line pickling process, the rebar is passed through a pickling tank, a passivation tank, and a drying device in order to achieve in-line pickling of the rebar, where the gas outlets of the pickling tank are distributed around the center line of the pickling tank, and then the rebar is packaged.

The production method of Examples 9 to 16 employs a process path that includes a hot metal pre-desulfurization process, a converter smelting process, a LF furnace refining process, a RH furnace refining process, a square billet continuous casting process, a hot continuous rolling process, a temperature-controlled cooling process, and an in-line pickling process, which are carried out in this order. Each process is described below.

(1) In the hot metal pre-desulfurization process, the hot metal is pre-desulfurized, and after desulfurization, the S content is ≦0.001% and the slag removal rate is ≧95%.

(2) In the converter smelting process, a trace carbon ferrochromium alloy is added to the molten steel during tapping to initially alloy the molten steel, and the tapping temperature is 1700-1750°C.

(3) In the LF furnace refining process, argon is blown into the LF furnace ladle at a bottom flow rate of 80 to 160 L/min throughout the entire process, and the tapping temperature is 1560 to 1600°C.

(4) In the RH furnace refining process, after the RH furnace is evacuated for 3 min, oxygen injection into the RH furnace is started, and the total amount of oxygen injection is 500-700 ^Nm3 . Then, the molten steel is alloyed by adding a trace carbon ferrochromium alloy to the molten steel. When the vacuum level is less than 2 mbar, the fresh water circulation treatment is performed for 5 min or more. The tapping temperature is 1560-1600 ° C, and the tapping C content is ≦ 0.015%.

(5) In the square billet continuous casting process, the molten steel tapped in the LF furnace refining process is continuously cast into a billet, in which a carbon-free mold flux or an ultra-low carbon mold flux is used, the continuous casting temperature is 1520-1560°C, and the casting speed during continuous casting is 2.2-2.6 m/min.

(6) In the hot continuous rolling process, in Examples 9 to 12, the billet is heated in a heating furnace, the heating temperature is 1100 to 1200°C, the furnace time is 60 to 120 min, and then rolled into a rod-shaped threaded rebar with a diameter of 12 to 32 mm, the rolling start temperature is 1000 to 1100°C, and the finish rolling temperature is 850 to 950°C. In Examples 13 to 16, the billet is heated in a heating furnace, the heating temperature is 1080 to 1130°C, the furnace time is 60 to 120 min, and then rolled into a coil-shaped threaded rebar with a diameter of 6 to 10 mm, the rolling start temperature is 980 to 1030°C, the finish rolling temperature is 850 to 950°C, and the laying temperature is 830 to 920°C.

(7) In the temperature-controlled cooling process, in Examples 9 to 12, the rolled rod-shaped threaded rebar is naturally cooled on a cooling bed, and the temperature when it is transported to the cooling bed is 860 to 920°C. In Examples 13 to 16, the rolled coil-shaped threaded rebar is cooled using a delayed Stelmor method, and all fans below the roller conveyor are turned off.

(8) In the in-line pickling process, the rebar is passed through a pickling tank, a passivation tank, and a drying device in order to achieve in-line pickling of the rebar, where the gas outlets of the pickling tank are distributed around the center line of the pickling tank, and then the rebar is packaged.

The production method used in Comparative Examples 1 to 4 is the conventional process route of converter smelting, square billet continuous casting, hot continuous rolling, and cooling on a cooling bed, among which, during the hot continuous rolling process, the heating temperature in the heating furnace is 1210 to 1290°C, the rolling start temperature is 1090 to 1170°C, the temperature when transported to the cooling bed is ≧1100°C, and the material is naturally cooled on the cooling bed.

The rebars of Examples 1 to 16 and Comparative Examples 1 to 4 were sampled using the same test method to detect their mechanical performance, and the mechanical performance of each Example and Comparative Example is as shown in Table 2.

As can be seen from Table 2, Examples 1 to 16 are clearly superior to Comparative Examples 1 to 4 in terms of mechanical performance, and meet the requirements for 400 MPa-class earthquake-resistant rebar, with a yield strength of ≧420 MPa, a tensile strength of ≧540 MPa, an elongation at break of ≧18%, and a total elongation at maximum force of ≧7.5%.

The rebars of Examples 1 to 16 and Comparative Examples 1 to 4 were subjected to ambient immersion corrosion tests, salt spray corrosion tests, and electrochemical corrosion tests using the same method, and the test results are shown in Table 3.

The specific method of the ambient immersion corrosion test used is as follows: The treated sample is placed in an ambient immersion test box, and the test is conducted in accordance with the YB/T4367 corrosion test method for rebar in a chloride ion environment, with the solution being 2.0±0.05 (wt%) NaCl, pH 6.5-7.2, solution temperature 45°C±2°C, and drying temperature 70°C±10°C, and the corrosion rate is obtained by the average weight loss over 168 hours through continuous testing.

The specific method of the salt spray corrosion test used is as follows: The treated sample is placed in a salt spray test box, and the test is performed in accordance with GB/T10125 Corrosion test in artificial atmosphere - Salt spray corrosion test, the solution is 2.0±0.05 (wt%) NaCl, the pH is 6.5-7.2, the solution temperature is 35°C±2°C, and the corrosion rate is obtained by the average weight loss in 168 hours by continuous testing.

The specific method of the electrochemical corrosion test used is as follows: The electrochemical test is performed in accordance with GB/T24196-2009 "Corrosion of metals and alloys/Electrochemical test methods/Guideline for carrying out electrostatic potential polarization and potentiodynamic polarization measurements", using a three-electrode system, the reference electrode is a saturated calomel electrode, the auxiliary electrode is a Pt sheet, and the test solution is simulated concrete pore water with a chloride ion concentration of ≧3 mol/L. The scanning range of the polarization curve test is -300 to 600 mV with respect to the sample self-corrosion potential, and the scanning speed is 1 mV/s. The scanning frequency range of the electrochemical impedance test is 10 ^-2 to 10 ⁵ Hz, and the AC excitation signal amplitude is ±5 mV.

As can be seen from Table 3, Examples 1 to 16 are significantly superior in terms of corrosion resistance to Comparative Examples 1 to 4. In the ambient immersion corrosion test, the corrosion rate due to the average weight loss of the reinforcing bar was 0.05 to 0.1 g/( ^m2 ·h), and in the salt spray corrosion test, the corrosion rate due to the average weight loss of the reinforcing bar was 0.01 to 0.04 g/( ^m2 ·h). The corrosion resistance was comparable to that of ordinary HRB400.
The self-corrosion potential of the rebar is -0.1 to -0.15 V in simulated concrete pore water with a chloride ion concentration of ≧3 mol/L, which is 0.4 V more noble than that of normal HRB400. The polarization resistance of the rebar is 2500 to 3000 kΩ/ ^cm2 , which is much higher than that of normal HRB400. The self-corrosion current density of the rebar is ≦0.13 μA/ ^cm2 , which is 1/6 that of normal HRB400.
Equivalent to 5 or less.

The reinforcing bars of Examples 1 to 16 were sampled for inclusion detection and microstructure detection. As a result, the A-type, B-type, C-type, and D-type inclusions in the GB/T10561 standard were all ≦1.0 grade, and the microstructure was ferrite and bainite, with the proportion of ferrite being 28% to 40% and the proportion of bainite being 60% to 72%.

Furthermore, the rebars of Examples 1 to 16 were sampled and subjected to welding tests using electroslag pressure welding. Tensile tests were then performed on the welded samples in accordance with the room temperature test method standard for Part 1 of the tensile test for metallic materials in GBT228.1-2010. As a result, it was found that the fracture point in the tensile test of the welded samples was formed in the rebar base material, not at the position of the weld point, and the weld performance of the resulting rebar was excellent.

Claims (18)

Chemical composition in mass percent: Cr: 9.5-10.4%, Mo: 1.0-1.2%, Mn: 0.3-0.6%, Ni: 0.01-1.00%, Cu: 0.01-0.5%, C≦0.014%, N≦0.004%, Nb: 0.01-0.05%, Si: 0.2-0.6%, S≦0.004%, O≦0.00 A 400MPa-class corrosion-resistant rebar containing 3%, As≦0.01%, P: 0.01-0.03%, Cr+Mo+0.5Mn+0.35Ni+0.25Cu at 11.1-12.2%, C+N+0.3Si+Mn+1.8Nb at 0.4-0.8%, and the balance being Fe and unavoidable impurities. The 400 MPa-class corrosion-resistant rebar according to claim 1, characterized in that the chemical components further include, in mass percent, one or more of V: 0.1-0.15%, Ti: 0.01-0.05%, Al: 0.01-0.03%, and B: 0.0005-0.0020%. The 400 MPa-class corrosion-resistant rebar according to claim 1, characterized in that the microstructure is ferrite and bainite, with the proportion of ferrite being 28% to 40%. The 400 MPa-class corrosion-resistant rebar according to claim 1, in which the A, B, C, and D inclusions in the GB/T10561 standard are all ≦1.0 grade. The 400 MPa class corrosion-resistant rebar according to claim 1, characterized in that it has a yield strength of ≥ 420 MPa, a tensile strength of ≥ 540 MPa, an elongation at break of ≥ 18%, and a total elongation at maximum force of ≥ 7.5%. The 400 MPa-class corrosion-resistant rebar according to claim 1, characterized in that the nominal diameter is 6 to 32 mm. The 400 MPa class corrosion-resistant reinforcing bar according to claim 6, characterized in that it is a coil-shaped reinforcing bar having a nominal diameter of 6 to 10 mm, or a rod-shaped reinforcing bar having a nominal diameter of 12 to 32 mm. In an ambient immersion corrosion test, the corrosion rate based on average weight loss is 0.05 to 0.1 g/( ^m2 ·h), and in a salt spray corrosion test, the corrosion rate based on average weight loss is 0.01 to 0.04 g/( ^m2 ·h);
The 400MP according to claim 1, characterized in that in simulated concrete pore water having a chloride ion concentration of ≧3 mol/L, the self-corrosion potential is −0.1 to −0.15 V, the polarization resistance is 2500 to 3000 kΩ/cm ² , and the self-corrosion current density is ≦0.13 μA/cm ^2.
Class A corrosion resistant steel bars. Chemical composition in mass percent: Cr: 9.5-10.4%, Mo: 1.0-1.2%, Mn: 0.3-0.6%, Ni: 0.01-1.00%, Cu: 0.01-0.5%, C≦0.014%, N≦0.004%, Nb: 0.01-0.05%, Si: 0.2-0.6%, S≦0.004%, O≦0.00 3%, As≦0.01%, P: 0.01-0.03%, Cr+Mo+0.5Mn+0.35Ni+0.25Cu is 11.1-12.2%, C+N+0.3Si+Mn+1.8Nb is 0.4-0.8%, and the balance is Fe and unavoidable impurities.
Either process path 1 or process path 2 is used,
The process path 1 includes a hot metal pre-desulfurization process, a converter smelting process, an AOD furnace refining process, an LF furnace refining process, a square billet continuous casting process, a hot continuous rolling process, and a temperature controlled cooling process, which are performed in this order.
The process path 2 is a method for producing a 400 MPa-class corrosion-resistant rebar, which is characterized by including a molten iron pre-desulfurization process, a converter smelting process, a LF furnace refining process, a RH furnace refining process, a square billet continuous casting process, a hot continuous rolling process, and a temperature-controlled cooling process , which are performed in this order . In the process path 1,
The tapping temperature of the converter smelting process is 1600 to 1660°C,
In the AOD furnace refining process, a high carbon ferrochromium alloy and a molybdenum iron alloy are added to the molten steel to perform initial alloying of the molten steel, and after reduction and slag removal, a manganese alloy is added. Before tapping, the tapping ladle is purged with argon for 5 minutes or more. During tapping, 20 kg of aluminum ingot is added to the molten steel. The tapping temperature is 1630-1670°C, and the tapping C content is ≦0.010%.
In the LF furnace refining process, after the molten steel reaches the ladle of the LF furnace, slag is adjusted by adding 13 to 15 kg of lime and 4.0 to 6.5 kg of fluorite per ton of molten steel, the white slag holding time is ≧8 min, the soft stirring time is 8 to 15 min, and the tapping temperature is 1600 to 1620 ° C.,
10. The method for producing a 400 MPa-class corrosion-resistant rebar as claimed in claim 9, characterized in that in the square billet continuous casting process , carbon-free mold flux or ultra-low carbon mold flux is used, the temperature of continuous casting is 1520-1560°C, and the casting speed during continuous casting is 1.2-1.6 m/min. In the process path 2,
In the converter smelting process, a trace carbon ferrochrome alloy is added to the molten steel during tapping to perform initial alloying of the molten steel, and the tapping temperature is 1700 to 1750°C;
During the LF furnace refining process, argon is blown from the bottom into the ladle of the LF furnace at a flow rate of 80 to 160 L/min throughout the process, and the tapping temperature is 1560 to 1600°C;
In the RH furnace refining process, the RH furnace is evacuated for 3 minutes, and then oxygen is blown into the RH furnace, with a total amount of oxygen blown being 500-700 ^Nm3 ; then, a trace carbon ferrochrome alloy is added to the molten steel to alloy the molten steel; when the vacuum level is less than 2 mbar, fresh water is circulated for 5 minutes or more; the tapping temperature is 1560-1600°C; and the tapping C content is ≦0.015%;
10. The method for producing a 400 MPa-class corrosion-resistant rebar as claimed in claim 9, characterized in that in the square billet continuous casting process , carbon-free mold flux or ultra-low carbon mold flux is used, the temperature of continuous casting is 1520-1560°C, and the casting speed during continuous casting is 2.2-2.6 m/min. In both process path 1 and process path 2,
In the hot continuous rolling process, the continuous cast billet is heated in a heating furnace, the heating temperature is 1100 to 1200°C, the furnace time is 60 to 120 min, and then rolled into a rod-shaped threaded rebar having a diameter of 12 to 32 mm, the rolling start temperature is 1000 to 1100°C, and the finish rolling temperature is 850 to 950°C.
The method for producing a 400 MPa-class corrosion-resistant rebar according to claim 9, characterized in that during the temperature-controlled cooling process , the rolled rod-shaped threaded rebar is naturally cooled on a cooling bed, and the temperature when it is transported to the cooling bed is 860 to 920 ° C. In both process path 1 and process path 2,
The method for producing a 400 MPa-class corrosion-resistant rebar according to claim 9, characterized in that, in the hot continuous rolling process, the continuously cast billet is heated in a heating furnace at a heating temperature of 1080-1130°C and a residence time of 60-120 min, and then rolled into a coil-shaped threaded rebar having a diameter of 6-10 mm, the rolling start temperature is 980-1030°C, the finish rolling temperature is 850-950°C, and the laying temperature is 830-920°C. Both process route 1 and process route 2 include an in-line pickling step and a packaging step, which are performed in sequence after the temperature controlled cooling step;
10. The method for producing 400 MPa-class corrosion-resistant rebar according to claim 9, wherein in the in-line pickling process , the rebar is passed through a pickling tank, a passivation tank and a drying device in this order, and the gas outlets of the pickling tank are distributed around the center line of the pickling tank. (1) A method for smelting molten steel by sequentially performing a hot metal pre-desulfurization process, a converter smelting process, an AOD furnace refining process, and an LF furnace refining process, or a method for smelting molten steel by sequentially performing a hot metal pre-desulfurization process, a converter smelting process, an LF furnace refining process, and an RH furnace refining process, and continuously casting the obtained molten steel into a steel billet, and a chemical composition of the steel billet is, in mass percent, Cr: 9.5 to 10.4%, Mo: 1.0 to 1.2%, Mn: 0.3 to 0.6%, Ni: 0.01 to 1.00%, Cu: 0.01 to 0.05%, and Cu: 0.02 to 0.05%. 0.01-0.5%, C≦0.014%, N≦0.004%, Nb: 0.01-0.05%, Si: 0.2-0.6%, S≦0.004%, O≦0.003%, As≦0.01%, P: 0.01-0.03%, and Cr+Mo+0.5Mn+0.35Ni+0.25Cu is 11.1-12.2%, C+N+0.3Si+Mn+1.8Nb is 0.4-0.8%, and the balance is Fe and unavoidable impurities;
(2) The steel billet obtained in the steelmaking step is heated in a heating furnace, the heating temperature is 1100 to 1200°C, and the furnace time is 60 to 120 min. Then, the steel billet is rolled into a rod-shaped threaded rebar having a diameter of 12 to 32 mm, the rolling start temperature is 1000 to 1100°C, and the finish rolling temperature is 850 to 950°C. Then, the rolled rod-shaped threaded rebar is naturally cooled on a cooling bed, and the temperature when it is transported to the cooling bed is 860 to 920°C.
Alternatively, the steel billet obtained in the steel making step is heated in a heating furnace at a heating temperature of 1080 to 1130°C and a residence time of 60 to 120 min, and then rolled into a coil-shaped threaded rebar having a diameter of 6 to 10 mm at a rolling start temperature of 980 to 1030°C, a finish rolling temperature of 850 to 950°C, and a laying temperature of 830 to 920°C. Thereafter, the rolled coil-shaped threaded rebar is cooled by Stelmor cooling, and a controlled rolling/controlled cooling step is included in which all fans below the roller conveyor are turned off. The method for producing a 400 MPa-class corrosion-resistant rebar according to claim 15, characterized in that in the steelmaking step , the chemical components of the steel billet further include, in mass percent , any one or more of V: 0.1-0.15%, Ti: 0.01-0.05%, Al: 0.01-0.03%, and B: 0.0005-0.0020%. In the steelmaking step , when molten steel is smelted by sequentially using a hot metal pre-desulfurization process, a converter smelting process, an AOD furnace refining process, and an LF furnace refining process, the tapping temperature in the converter smelting process is 1600 to 1660°C, and in the AOD furnace refining process, a high carbon ferrochromium alloy and a molybdenum iron alloy are added to the molten steel to perform initial alloying of the molten steel, and after reduction and slag removal, a manganese alloy is added. Before tapping, the tapping ladle is purged with argon for 5 minutes or more. 20 kg of an aluminum ingot is added to the molten steel during tapping. The tapping temperature is 1630 to 1670°C. the content is ≦0.01%, during the LF furnace refining process, after the molten steel reaches the ladle of the LF furnace, 13-15 kg of lime and 4.0-6.5 kg of fluorite are added per ton of molten steel to adjust the slag, the white slag holding time is ≧8 min, the soft stirring time is 8-15 min, the tapping temperature is 1600-1620°C, during the square billet continuous casting process, carbon-free mold flux or ultra-low carbon mold flux is used, the continuous casting temperature is 1520-1560°C, and the casting speed during continuous casting is 1.2-1.6 m/min,
In the case where molten steel is smelted by sequentially using a hot metal preliminary desulfurization process, a converter smelting process, an LF furnace refining process, and an RH furnace refining process, in the converter smelting process, a trace carbon ferrochrome alloy is added to the molten steel during tapping to perform initial alloying of the molten steel, and the tapping temperature is 1700 to 1750°C; in the LF furnace refining process, argon is bottom-blown into the ladle of the LF furnace at a flow rate of 80 to 160 L/min throughout the entire process, and the tapping temperature is 1560 to 1600°C; and in the RH furnace refining process, the RH furnace is evacuated for 3 min, and then oxygen blowing into the RH furnace is started, and the total amount of oxygen blown is 500 to 700 Nm ³ , then adding a trace carbon ferrochrome alloy to the molten steel to alloy the molten steel, and performing fresh water circulation treatment for 5 minutes or more when the vacuum degree is less than 2 mbar, the tapping temperature is 1560-1600°C, the tapping C content is ≦0.015%, and in the square billet continuous casting process, carbon-free mold flux or ultra-low carbon mold flux is used, the continuous casting temperature is 1520-1560° C , and the casting speed during continuous casting is 2.2-2.6 m/min. (3) The method for producing 400 MPa-class corrosion-resistant rebars according to claim 15, further comprising an in-line pickling step of passing the rebar obtained in the controlled rolling and controlled cooling steps through a pickling tank, a passivation tank and a drying device in order to perform in-line pickling, the gas outlets of the pickling tank are distributed around the center line of the pickling tank, and the rebar is packaged after leaving the drying device.