JPS607004B2 - Directly patented wire manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Regarding the manufacturing method 1 of the Naohiko patented wire rod of the present invention, in particular, by specifying the chemical composition and hot rolling conditions of the steel material, the wire rod has excellent wire drawability with a uniform fine pearlite structure. This made it possible to obtain directly patented high carbon steel wire rods.

High carbon steel wire used by cold drawing is conventionally hot rolled material, which is cooled to room temperature, then reheated and subjected to lead patenting or air patenting, followed by cold drawing processing. However, in recent years, due to the demand for energy conservation and cost reduction, as well as pollution problems (particularly the generation of hazardous waste due to the removal of lead attached to wires after lead patenting treatment), "Directly patented wire rods" have been developed with the aim of effectively utilizing the heat contained in hot-rolled materials and omitting the lead patenting process, and have now become the mainstream of steel wire rods.

This direct patented wire rod is a wire rod after hot rolling.
By adjusting cooling with an appropriate cooling medium, it can be used as is.
It has workability that can withstand wire drawing processing. Note that the patenting treatment herein refers to a heat treatment in which a steel wire, which is generally in the austenitizing temperature range, is transformed into a steel having a uniform fine pearlite structure through continuous cooling transformation or isothermal transformation using an appropriate coolant. With the development of this direct patenting wire rod that utilizes rolling heat, it has become possible to omit the first of the multiple patenting treatments that were required in the secondary processing steps after hot rolling. However, with the aim of completely eliminating the reheating patenting process,
``Direct product drawing,'' in which directly heat-treated wire is drawn to the desired final wire diameter and then turned into a product, is also being put into practical use. By the way, in parallel with the above-mentioned technology, constant progress is being made in the wire drawing technology itself, with the aim of further improving the wire drawing efficiency, such as increasing the drawing speed or reducing the area per pass. Efforts are being made to increase the wire drawing ratio and reach a predetermined area reduction ratio with as few passes as possible.

In this case, if the ductility of the wire strip is insufficient, wire breakage will occur during the wire drawing process, so in order to deal with this problem, it is necessary to stably manufacture and supply wire rods with excellent ductility. It is hoped that this will be possible. However, the development of the directly patented material was aimed at improving the strength level and strength variation, and aimed at obtaining a material comparable to reheated lead patented material, with the aim of reducing the area reduction rate per pass. It was not possible to meet the demands for improvement and faster wire drawing. In order to solve the above problems, the present inventors focused on high carbon steel wire rods containing nitride-forming elements, and investigated the behavior of metallurgical factors that are thought to control the ductility of the wire rods by simply rolling. As a result of a detailed study of the austevite grain size (y grain size) and nitride precipitation behavior, etc. at each stage of the direct patenting material manufacturing process, including not only the adjustment cooling stage at the end, but also the component design, rolling process, and billet heating stage, we found that: In bran material to which N is added as a nitride-forming element, the set temperature for billet heating is an important factor in improving the ductility of L directly patented wire rods, and the heating temperature is within the range usually adopted (approximately 110,000 We have found that it is extremely effective to set the temperature at a lower temperature than the above). The present invention was completed based on the above findings. ．． That is, the present invention provides a high carbon steel billet containing C, Si, Mn and, if necessary, Cr in certain amounts, and about 0.02 to 0.1% of AI as a nitride-forming element. After heating to a temperature of 1050q○, hot rolling was performed to obtain a steel wire rod in which approximately three or more plates of aluminum nitride (AIN) were precipitated. In the meantime, the present invention provides a method for directly producing a patented wire rod in which the steel wire rod is controlled and cooled to give a uniform fine pearlite structure.
This makes it possible to perform cold wire drawing, and ensures sufficient ductility to withstand high-speed wire drawing in cold wire drawing and an increase in surface loss per pass.

In addition, conventional measures to improve the ductility of fine pearlitic steel include adding nitride-forming elements (AI, Ti, Nb, etc.) and regulating the billet rolling temperature.
A method for manufacturing steel wire has been proposed in which nitrogen in steel is fixed as nitride and the nitride is also used to refine the austenite grains (Japanese Patent Laid-Open No. 49-123923).
(Japanese Patent Publication No. 47-51684, etc.), these are all aimed at reheated patented materials, and are not intended to directly improve the ductility of patented materials as in the present invention.

Furthermore, in conventional methods, the aim is generally to reduce the amount of undissolved nitrides during billet heating, or to completely solidify them, and for this purpose, the heating temperature is set at a high temperature of about 1100 q0 or more.

However, according to detailed observations by the present inventors, with regard to the precipitation behavior of nitrides during the manufacturing process of direct patenting materials, nitrides once dissolved in the austenitic material are difficult to control during the rolling process and subsequent winding process. It has been shown that almost no redeposition occurs during the cooling process. When we look back at the Jikou method based on these facts, we find that approximately 950 qo after rolling.
In the conventional method, which applied reheating patenting before and after,
Because a large amount of nitride precipitates during reheating, it was found that under the billet heating temperature conditions of the conventional method, it was not possible to expect a sufficient addition effect of nitride-forming elements to improve the ductility of directly patented materials. Ru. That is, under the heating conditions of the conventional method, almost no nitrides such as AI and V remain, and the effects of these additive elements are not utilized in any way to improve the ductility of the direct patenting material. As described above, it can be said that the mechanism of improving the ductility of high carbon steel wire in the method of the present invention is essentially different from that in the conventional method.
The steel used in the present invention contains the following constituent elements.
C is required to be about 0.6% or more in order to increase the strength of the steel wire.

However, many? Too much pro-eutectoid cementite is harmful to health.
Since it precipitates at grain boundaries, it is desirable that the upper limit be about 1.0%. Si is useful for improving the strength of steel wires, but if added in excess, it will reduce the ductility of the ferrite itself, so approximately 2
．． It is added in a range of 0% or less.

Mn is effective in improving the hardenability of steel, and is also an essential component element for increasing strength by making the pearlite lamellar spacing more dense, and for this purpose it is added in an amount of about 0.3% or more. .

In particular, it is desirable to increase the amount added to increase the strength of large meridian wire rods. However, if the amount is too large, it will cause a significant delay in pearlite transformation, making it impossible to complete the transformation within the time required for rolling and patenting processes. Therefore, it is desirable to set the upper limit to about 1.4%. AI is added to refine the austenite grains (grain size) and fix N in the steel.

In order to refine the Y grains, as will be described later, it is necessary to precipitate approximately 3 or more grains during billet heating, and it is particularly preferable to precipitate approximately 5 grains or more. For this reason, it is necessary to add approximately 0.02% or more of AI. From the perspective of nitrogen fixation, “A
The larger the amount of I added, the more advantageous it is, but if it is too large, AIN will precipitate excessively on the austenite grain boundaries, and AI20
Since the amount of 3 produced also increases and impairs ductility, the upper limit is preferably set to about 0.1%. N is an essential element for combining with the above-mentioned peaks to form AIN, but the amount normally contained in high carbon steel wire rods (about several tens of willows) is sufficient.

However, this does not prevent it from being added up to about 10 cm if necessary. In addition to the above elements, the following elements can be added.

Like Mn, Cr has the effect of improving hardenability and improving strength by making the spacing between pearlite lamellas finer.

However, like Mn, excessive addition causes retardation of pearlite transformation, so it should be added in an amount of about 1.5% or less.
Other impurities such as P and S may be present within the range normally allowed for this type of steel.

Next, billet heating, rolling conditions, etc. will be explained.
The billet heating temperature during rolling of high carbon steel wire rods has conventionally been generally set at about 1100 qo or higher, but in the present invention it is set at about 800 to 1050 qo.

By heating the billet to a low temperature of about 105,000 °C or less, nitrogen, which is harmful to ductility, can be fixed as undissolved nitrides, and the dissolved nitrides remain after the final rolling until pearlite transformation begins. This can prevent the growth of y-grains that occur during the process, and can help refine the structure.
For such nitrogen fixation, it is desirable to keep the heating temperature as low as possible within a range that does not interfere with the rolling operation, and in the present invention, it is set to about 800 pm or higher. At temperatures below 800°C, although N is fixed as MN, the deformation resistance during rolling increases, the rolling load on the machine increases, and surface roughness occurs.

In order to prevent the growth of Y-grains, it is effective to leave approximately 3 mm or more of NN remaining when heating the billet.

In particular, about 5 plates or more are desirable. For this purpose, it is desirable that the billet heating temperature be about 1000q○ or less. The size of the y grains during billet heating by adjusting the billet heating temperature as described above has a strong influence on the y grain size after final rolling. Obtainable.

This ensures superior ductility compared to conventional directly patented materials. After the billet is heated as described above,
Subjected to hot rolling.

In hot rolling, the mountains N remaining during billet heating are removed.
In order to prevent solid solution and disappearance due to temperature rise during rolling,
It is desirable to adjust the steel wire temperature so that it does not exceed the billet heating temperature (approximately 1050:00).
In order to make the grain refinement and pearlite structure more effective and further increase the ductility of the obtained steel wire, rolling from the intermediate stand to the finishing stand or at the finishing stand is performed at a temperature of about 90,000 or less. It is also effective to employ so-called "low temperature rolling".

In addition, the wire temperature immediately after exiting the water cooling zone attached to the finishing mill row (immediately after the water cooling zone exit or water cooling zone cooling), that is,
As the rolling finishing temperature increases, the grains become coarser and the ductility decreases.

However, the amount of free N (N that has not become MN) depends on the heating temperature and is almost independent of the rolling end temperature (water belt outlet temperature). 950°C is sufficient. If the finishing temperature is set too low, a difference in structure between the inside and outside will occur, which is undesirable. On the other hand, if the temperature is set too high, scale increases and the yield decreases, or mechanical properties deteriorate due to coarse grains. There are no special restrictions on the method of cooling the steel wire rod after rolling, but
Needless to say, appropriate controlled cooling should be carried out to provide a fine pearlite structure.

Figure 1 shows the y of a steel wire rod that is heated and hot rolled after heating a billet of a material equivalent to SWRS82B containing about 0.036% AI, and wound up into a loop after final rolling until the start of transformation. It is a graph showing the influence of billet heating temperature on particle size. In the figure, curve 1 is billet heating temperature:
1000oo, 2 is 110000, 3 is 1200q
In each case o. From the figure, when the heating temperature is 1100 qo or more, the grains become coarse due to grain growth, whereas when the heating temperature is 1050 qo or less by the method of the present invention, the y immediately after winding
It can be seen that the grains are fine and grain growth hardly occurs, giving a preferable fine grain structure. Next, the method of the present invention and the properties of the obtained steel wire will be specifically explained with reference to Examples.

In addition, in Tables 1 and 3, the finishing rolling temperature is the water cooling zone outlet temperature after finishing rolling. Example 1 Using two types of steel shown in Table 1 as test materials, a patented material was directly produced using Stelmorline (blast cooling method), and 75% wire drawing was performed.

Table 2 shows the rolling conditions and properties of the obtained wire rod. Table 1: Chemical composition of sample materials (wt%) Table 2: Rolling conditions and wire properties *1: Wire diameter: 7th side, *2: Wire diameter: 11th.

As shown in Table 2, the low-temperature billet heated materials (Nos. 2, 3, 5 and 6) produced by the method of the present invention can be used both in the rod (directly patented material) and after wire drawing (75% wire drawn material). also has better ductility than that of conventional high-temperature heating materials.Also, test No. 2 and No. 3, N
o. 5 and no. As is clear from the comparison of No. 6, it is also recognized that the effect of improving ductility can be obtained by low-temperature rolling. As described above, according to the method of the present invention, the ductility of the directly patented wire village can be significantly increased, and the wire drawing efficiency can be greatly improved.

Furthermore, the low heating temperature of the billet has the effect of preventing decarburization and reducing the amount of scale adhesion during billet heating, and also contributes to improving the surface quality of the obtained steel wire rod. Note that the method of the present invention can be applied to nitride-forming elements other than AI (
For example, it is possible to directly manufacture patented wire rods using steel to which Nb, Ti, Zr, V, etc. are added to the same extent as AI, and increase its ductility, but if too much Nb, Ti, Zr, V, etc.
Excessive nitrides precipitate and impair ductility. Example
2 As shown in Table 3, straight twill patenting materials were manufactured in the same manner as in Example 1 using two types of spring steels as test materials.

The rolling conditions and the results obtained are shown in Table 4. Table 3
Chemical composition of the sample material (wt%) Table 4 Rolling conditions and wire rod characteristics *3: Wire diameter: 8 wire, *4: Wire rod rule: 9 Yanagi As shown in Table 4, the method of the present invention heating material (No. 9
"10, 12) are conventional high temperature heating materials (No. 7, 8)
, 11).

When steel C and D are treated by conventional high-temperature heating (1100 pm), bainite appears immediately after rolling, even after sufficient water cooling.On the other hand, with the low-temperature heating of the present invention, VN and AIN are Of course, since VC (V4C3) is also rolled while remaining melted, it not only improves ductility by fixing C and N, but also reduces hardenability by reducing hardness V, etc., and the tensile strength of the rolled material increases. The carbonitride of Nb is stable even at higher temperatures than V, so it is effective in preventing the coarsening of grains after rolling and preventing overcooling.

[Brief explanation of drawings]

FIG. 1 is a graph showing the influence of billet heating temperature on y particle size change after wire loop winding. Figure 1

Claims (1)

[Claims] 1 C0.6-1.0%, Si2.0% or less, Mn0.
A billet of high carbon steel containing 3 to 1.4% Al and 0.02 to 0.1% Al is heated to a temperature of 800 to 1050°C, then hot rolled, and after the final hot finish rolling, it is rolled up. A method for producing a direct patented wire rod with excellent ductility, characterized by controlling and cooling the steel wire rod to form a uniform fine pearlite structure.