JPH0248605B2 - KOKYODO * KOENSEIKOSENNOSEIZOHO - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing high strength and high ductility steel wire. (Prior Art) In recent years, there has been an increasing demand for higher strength in hard steel wires such as steel wires for ropes, steel wires for reinforcing tires, steel wires for reinforcing optical fiber cables, and steel wires for long bridges. Although intensive research has been carried out on increasing the strength of hard steel wires, the lack of established technology to prevent the deterioration of ductility that occurs with increased strength is a constraint. It has not yet reached the point where high strength has been achieved. For example, the torsional property, which is an important measure of ductility, is
Journal'' vol. 16, No. 4 (1983), page 50, the improvement can be achieved by subjecting the steel wire after drawing to blueing treatment at high temperature. High temperature treatment leads to a decrease in strength and
Since it is impossible to avoid deterioration of ductility due to surface oxidation in thin wires such as steel wires for reinforcing tires, there is a limit to the application of this method. On the other hand, this method does not involve heat treatment,
Attempts have also been made to improve the ductility of the drawn steel wire by subjecting the drawn steel wire to skin pass drawing. However, as stated in ``Effect of die schedule on mechanical properties and residual stress of steel wire'' in the material submitted to the 20th Wire Drawing Technology Subcommittee of the Nihon University Society for Plasticity Processing, published on November 16, 1984. Such measures hardly improve ductility. Thus, at present, no sufficient method has been found to improve the ductility of steel wire. (Problems to be Solved by the Invention) The object of the present invention is to provide a method for manufacturing a steel wire with excellent ductility that eliminates these drawbacks. (Means for Solving the Problems) As a result of researching various methods for improving the ductility of steel wire, the present inventors found that the steel wire has a specific composition and the difference in hardness between the center and the surface is controlled to 100 or less on the Vickers hardness scale. 0.2-10% by roller rolling process on steel wire
It has been found that the ductility of steel wire can be significantly improved by applying a strain of . That is, the present invention has the following characteristics in weight%: C 0.4-1.0% Si 2.0% or less Mn 0.2-2.0% P 0.02% or less S 0.02% or less N 0.01% or less Cr 0.05-3.0%, Mo 0.01-
1.0%, W0.01~1.0%, Cu0.05~3.0%, Ni0.1~
Contains one or more of 5.0% and Co0.1-5%, and furthermore, if necessary, Al0.001-0.1%,
Ti0.001~0.1%, Nb0.001~0.1%, V0.001~0.1
%, B0.0003~0.05%, and Mg0.001~0.1% 1
A steel wire containing one or more kinds of steel, the balance being iron and unavoidable impurities, and having a difference in hardness between the center and the surface of 100 or less in terms of Vickers hardness, is subjected to roller rolling to give a strain of 0.2 to 10%. This is a manufacturing method for high-strength, high-ductility steel wire. The present invention will be explained in detail below. (Function) First, the reason for limiting the steel wire composition will be described. If C is less than 0.4%, the required strength cannot be obtained, and if it exceeds 1.0%, the ductility deteriorates significantly, so the content is limited to 0.4 to 1.0%. Si is added mainly to take advantage of its solid solution hardening effect, but if the amount added exceeds 2%, the ductility decreases significantly, so the upper limit was set at 2.0%. Mn is added to ensure hardenability and fix S, but if it is less than 0.2%, S will not be fixed sufficiently, and if it is added more than 2%, the hardenability will no longer increase. Limited to ~2.0%. The smaller the amount of P and S, the better in order to improve ductility. If each exceeds 0.02%, it will have a significant negative effect on ductility, so it was limited to 0.02% or less. N is 0.01
If it exceeds 0.01%, it has a negative effect on ductility, so it was limited to 0.01% or less. The above is the basic composition system of the steel wire targeted by the present invention, but in addition, (A) Cr0.05 to 3.0%,
Mo0.01~1%, W0.01~1%, Cu0.05~3%,
One or more of Ni0.1-5%, Co0.1-5%,
Or (B) Al0.001~0.1%, Ti0.001~0.1%,
Nb0.001~0.1%, V0.001~0.1%, B0.0003~0.05
%, one or more types of Mg0.001~0.1%,
It can contain one or both of (A) and (B). First, Cr, Mo, W, Cu, Ni, and Co are added for the purpose of increasing strength and corrosion resistance.
Cr less than 0.05%, Mo less than 0.01%, W less than 0.01%,
If Cu is less than 0.05%, Ni is less than 0.1%, and Co is less than 0.1%, their effects on strengthening and corrosion resistance will not be recognized, so Cr0.05%, Mo0.01%, W0.01%,
The lower limits were set to 0.05% Cu, 0.1% Ni, and 0.1% Co. On the other hand, Cr3% or more, Mo1% or more, W1% or more, Cu3%
At over 5% Ni, and over 5% Co, the effects of these elements on strengthening and corrosion resistance become saturated, while the effect of reducing ductility becomes significant.
The upper limits were Mo1%, W1%, Cu3%, Ni5% and Co5%. Further, from the viewpoint of ductility, it is desirable to suppress the total amount of these elements to 7% or less. Next, Al, Ti, Nb, V, B and Mg are N and S
It is added for the purpose of fixing and improving ductility, but Al less than 0.001%, Ti less than 0.001%,
Nb less than 0.001%, V less than 0.001%, B less than 0.003%,
and Mg less than 0.001%, N and S cannot be fixed, so Al0.001%, Nb0.001%,
The lower limits were V0.001%, B0.003% and Mg0.001%. On the other hand, Al over 0.1%, Ti over 0.1%, Nb over 0.1%,
When V exceeds 0.1%, B exceeds 0.05%, and Mg exceeds 0.1%, the N and S fixing effects of these elements become saturated, while the ductility deterioration effect due to nitrides and sulfides of these elements becomes significant. , Al0.1%, Ti0.1%, Nb0.1%,
The upper limits were V0.1%, B0.05% and Mg0.1%. Note that it is desirable for ductility to suppress the total amount of these elements to 0.2% or less. Next, a very important feature of the present invention is that the difference in hardness between the center and the surface of the steel wire targeted by the present invention is limited to 100 or less in terms of Vickers hardness, and this is essential in the manufacturing process of the present invention. This is because cracks will occur if the hardness difference exceeds 100 during the roller rolling process described below. In this case, the hardness difference is 60
The following is particularly desirable. In addition, as a means to suppress the hardness difference between the center and the surface of the steel wire to 100 or less, preferably 60 or less, for example, low-temperature casting in the continuous casting process, electromagnetic stirring, or It is effective to soak the pieces at high temperatures. In this case, the strength of the steel wire is not particularly limited, but the tensile strength
Particularly remarkable effects can be obtained when the method of the present invention is applied to steel wires of 130 Kgf/mm ² or more. Next, the greatest feature of the present invention is that the steel wire as described above is subjected to roller rolling to give a strain of 0.2 to 10%. FIG. 1 schematically shows this roller rolling process, in which a is a front view and b is a side view, in which a steel wire 2 is passed between a group of rolls in which a plurality of rolls 1 are driven and rotated. , thereby giving a strain to the surface of the steel wire 2. As a means for controlling the amount of strain, for example, adjusting the amount of reduction by the roll 1 can be mentioned. In this case, the means for applying strain is limited to roller rolling because other processing methods such as skin pass wire drawing hardly improve the ductility even if the same strain is applied. Next, we will explain in detail the reason why the strain applied by roller rolling was limited to 0.2 to 10%. The ductility of a steel wire is usually determined by the elongation in a tensile test, the reduction of area, the number of rotations until breakage in a twist test (twist value), the form of breakage at that time, or a bending test. Among these ductility evaluation criteria, the one that deteriorates most significantly as the strength of the steel wire increases is the fracture mode in the torsion test. Figure 2 schematically shows the fracture form in the torsion test, where a shows a normal fracture situation, but as the strength increases, cracking as shown in Figure b shows. The frequency of abnormal ruptures increases. This is due to the fact that cracks 3 occur in the longitudinal direction on the surface of the steel wire 2 during a twisting test conducted by gripping the steel wire 2 with a gripping jig 4, as schematically shown in FIG. Therefore, the occurrence of abnormal fracture can be considered to mean deterioration of the ductility of the steel wire in the circumferential direction. The fact that the ductility of steel wire in the circumferential direction is most likely to deteriorate as the strength increases is actually during bending of steel wire.
This can also be understood from the fact that vertical cracks may occur in the longitudinal direction even though bending breaks do not occur, and that longitudinal cracks may also occur when twisted wires are processed, even though twist breaks do not occur. . In this way, it can be said that the fracture mode in the torsion test is the most important ductility evaluation criterion for steel wire. The present inventors found that applying roller rolling to the surface of the steel wire is extremely effective in suppressing the occurrence of abnormal fractures in this twisting test, and investigated the appropriate range of the amount of processing strain. The results revealed that almost no improvement effect was observed when the processing strain was less than 0.2%. On the other hand, it has become clear that when the processing strain exceeds 10%, minute cracks occur on the surface, and the ductility of the steel wire in the circumferential direction actually deteriorates.
For this reason, the amount of strain caused by roller rolling is
It was limited to a range of 0.2-10%. This roller rolling process may be performed at any stage of the process after wire drawing until the steel wire is used as a product, but if it is performed after bluing or plating, it may be performed again at a temperature of 250°C or less. It is preferable to perform a bluing treatment in view of stress relaxation properties and the like. The manufacturing method of the present invention is also effective in improving the fatigue properties, corrosion fatigue properties, delayed fracture properties, stress corrosion cracking properties, and setting properties of steel wires. The present invention is also effective in improving the durability and fatigue properties of products made using steel wire, such as ropes, steel wire-reinforced tires, and steel wire-reinforced plastics. Next, the effects of the present invention will be explained in more detail with reference to Examples. (Example) Composition, wire diameter, strength, difference in Bitkers hardness between the center and surface of the steel wires used in the example, amount of strain applied by roller rolling, and twisting test, fatigue test, and salt salt test for these steel wires Table 1 shows the results of underwater corrosion fatigue tests, delayed fracture tests, stress corrosion cracking tests, and fatigue tests, as well as the results of fatigue tests on products manufactured using these steel wires. No. in the same table.
Examples 1, 4, 8, 10, and 12 are examples of the present invention, and the others are comparative examples. In addition, the criteria or means for various tests in the same table are as follows. First, the abnormal rupture rate in the twisting test indicates the rate at which abnormal ruptures shown in FIG. 1b occur in the twisting test. Settling rate indicates the residual shear strain after applying torsional stress of 60% of the tensile strength to the steel wire and leaving it for 96 hours. Delayed failure time is 80Kgf/mm ² in 0.1N hydrochloric acid solution
It shows the time until rupture when a tensile stress of . The stress corrosion cracking time indicates the time until rupture when a tensile stress of 70 Kgf/mm ² is applied in a 0.5% acetic acid + 5% saline solution. Rope fatigue limit ratio is JIS1
In the bending fatigue limit of the No. rope, the fatigue limit of the rope manufactured with the steel wire of the comparative example is set as 1, and the fatigue limit of the rope manufactured with the steel wire of the invention example is shown in comparison. Corrosion fatigue life indicates the number of rotations until the steel wire breaks under a load of 20 kgf/mm ² in a rotating bending fatigue test in 3% saline solution. Fatigue limit indicates the fatigue limit stress in a rotating bending fatigue test of steel wire. The breakage rate of cords in tires indicates the breakage rate of cords in tires after traveling 100,000 km with a load of 500 kg. The fatigue limit ratio of plastic plate is 1mm thick reinforced with 100 steel wires per ^1mm2
The fatigue limit in bending fatigue of a plastic plate with a width of 10 mm is compared with the fatigue limit of a plastic plate reinforced with steel wire as a comparative example as 1. Next, in Table 1, test numbers 1 to 3 are all results for steel wires having the same composition with a wire diameter of 7.4 mm, a tensile strength of 168 Kgf/mm ² , and a hardness difference of 46 between the center and surface. No. 1 shows the effect of adding 1.0% roller rolling, and the abnormal fracture occurrence rate in the twisting test is 0. In contrast, those that were not subjected to roller rolling processing,
No. 2, the one with a strain of 0.03%, and No. 3 have abnormal fracture occurrence rates of 65% and 55%, respectively. It turns out to be extremely effective. Furthermore, the fatigue resistance and delayed fracture characteristics have also been significantly improved. Next, No. 4 to 7 all have a wire diameter of 3.2 mm and tensile strength.
The results are for galvanized steel wires with the same composition of 212 Kgf/mm ² and a hardness difference of 75 between the center and surface.
Of these, No. 4 shows the results when 0.6% strain was applied by roller rolling and further aging treatment was performed at 220℃ for 30 seconds, and the abnormal rupture rate in the twisting test was 5. %, thus it can be seen that the ductility is significantly improved. This steel wire also showed excellent stress corrosion cracking properties. Furthermore, ropes made from this steel wire had excellent fatigue properties. On the other hand, No. 5, which was not subjected to roller rolling,
In No. 6, which was subjected to roller rolling processing up to 12%, fine cracks were generated under the surface and the ductility decreased.
In addition, in steel wire No. 7, which had a hardness difference of 132 between the center and the surface, cracks occurred in the center of the steel wire during roller rolling, resulting in a decrease in ductility. Also, No. 8 and 9 both have a wire diameter of 0.8 mm and weigh 270 kg.
f/mm ² , tensile strength with a hardness difference of 70 between the center and the surface, and relates to steel wires with the same composition.
8 shows the results when roller rolling with a strain of 3.2% was applied. Similarly, the abnormal rupture rate in the twisting test was 0, indicating that the improvement in ductility was significant. It also has excellent corrosion fatigue properties. On the other hand, in No. 9, which was not subjected to roller rolling, the abnormal fracture rate in the twisting test reached 90%. Next, No. 10 and 11 both have a wire diameter of 0.22 mm, and are 356
This relates to a steel wire with a tensile strength of Kgf/mm ² and a hardness difference of 27 between the center and surface. Of these, No. 10 was subjected to 0.8% roller rolling and further aged at 150℃ for 1 hour. However, the abnormal rupture rate in the twisting test was 0, the ductility was significantly improved, and the fatigue properties of the steel wire were also improved. On the other hand, in No. 11, which was not subjected to roller rolling, the abnormal fracture rate in the twisting test was extremely high at 85%. This steel wire also has excellent fatigue properties. It is also found that tires reinforced with cords made from steel wires subjected to this roller rolling process have excellent fatigue properties. Furthermore, Nos. 12 and 13 both relate to ultra-fine wires with a wire diameter of 0.08 mm, a tensile strength of 393 Kgf/mm ² , and a hardness difference of 40 between the center and the surface. Of these, No. 12 is 2% The abnormal fracture rate in the twist test is 5% when roller rolling is applied, and the abnormal fracture rate of No. 13 without roller rolling is 100%.
%, the improvement in ductility is remarkable. Plastic plates reinforced with steel wires that have been subjected to this roller rolling process also exhibit excellent fatigue properties. Finally, Nos. 14, 15, 16, 17, and 18 have compositions, hardness differences, and roller rolling strains that are outside the scope of the present invention, so the abnormal rupture rate in the torsion test is extremely high, and they lack ductility. That is clear. (Effects of the Invention) As is clear from the above examples, according to the present invention, it is possible to provide a high strength and high ductility steel wire by a simple means, and the industrial effects are extremely significant.

【table】

【table】

[Table] ○ marks are examples of the present invention

[Brief explanation of drawings]

Figures 1 a and b are schematic diagrams showing the roller rolling processing means, where a is a front view, b is a side view, and Figures 2 a and b.
3 is a schematic diagram of the fracture form of the torsion test material, a is a normal fracture, b is an abnormal fracture, and FIG. 3 is a schematic diagram of a crack that occurs on the surface of the steel wire during the torsion test. 1...Roll, 2...Steel wire, 3...Crack, 4...
...Gripping jig.

Claims (1)

[Claims] 1 Weight%: C 0.4-1.0% Si 2.0% or less Mn 0.2-2.0% P 0.02% or less S 0.02% or less N 0.01% or less The balance consists of iron and inevitable impurities, and the difference in hardness between the center and surface A method for producing a high-strength, high-ductility steel wire, which is characterized by applying a strain of 0.2 to 10% to a steel wire having a Bitkers hardness of 100 or less by roller rolling. 2 Weight% C 0.4-1.0% Si 2.0% or less Mn 0.2-2.0% P 0.02% or less S 0.02% or less N 0.01% or less Cr0.05-3.0%, Mo0.01-1.0%, W0.01-1.0
%, Cu0.05~3.0%, Ni0.1~5.0% and Co0.1~5
%, the balance is iron and unavoidable impurities, and the difference in hardness between the center and the surface is less than 100 in terms of Vickers hardness.The steel wire is rolled to a strain of 0.2 to 10% by roller rolling. A method for manufacturing a high strength and high ductility steel wire characterized by giving. 3 Weight%: C 0.4-1.0% Si 2.0% or less Mn 0.2-2.0% P 0.02% or less S 0.02% or less N 0.01% or less Al 0.001-0.1%, Ti 0.001-0.1%, Nb 0.001-
0.1%, V0.001~0.1%, B0.0003~0.05%, and
Contains one or more types of Mg0.001~0.1%, the balance is iron and unavoidable impurities, and the difference in hardness between the center and the surface is 100 or less in terms of Bitkers hardness. A method for producing high-strength, high-ductility steel wire characterized by applying 10% strain. 4 Weight%: C 0.4-1.0% Si 2.0% or less Mn 0.2-2.0% P 0.02% or less S 0.02% or less N 0.01% or less Cr0.05-3.0%, Mo0.01-1.0%, W0.01-1.0
%, Cu0.05~3.0%, Ni0.1~5.0% and Co0.1~5
%, Al0.001~0.1%, Ti0.001~0.1%, Nb0.001~
0.1%, V0.001~0.1%, B0.0003~0.05%, and
Contains one or more types of Mg0.001~0.1%, the balance is iron and unavoidable impurities, and the difference in hardness between the center and the surface is 100 or less in terms of Bitkers hardness. A method for producing high-strength, high-ductility steel wire characterized by applying 10% strain.