JPH11302784A - High strength steel wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve strength and wire drawing property and to prevent deterioration in cutting resistance even when the wire has flaws during transportation by specifying the compsn. comprising C, Si, Mn, P, S and Fe and the metal structure, and further specifying the hardness of the wire surface layer and difference of hardness from that of the base body. SOLUTION: This steel wire consists of, by weight, 0.25 to 1.20% C; 0.01 to 2.0% Si; 0.2 to 1.1% Mn; <=0.02% P; <=0.01% S; and if necessary, further one or more kinds of 0.005 to 0.05% Nb; 0.005 to 0.035% Ti; 50.10 % Al: 0.005 to 0.060% V; 0.05 to 1.0% Cu; 0.05 to 1.0% Ni, 0.05 to 0.5% Cr; 0.05 to 0.35 Mo; 0.0005 to 0.005% Ca; 0.0005 to 0.007% Mg; 0.0005 to 0.005% REM; 0.0005 to 0.005% B; and the balance Fe and inevitable impurities. The structure of the steel essentially consists of pearlite. The hardest structure of the surface layer, and the difference in hardness from that of the base body are controlled to <=600 Hv and <=300 Hv, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength steel wire having excellent drawability, which is used for a wire rope, a PC steel, a spring, a steel cord, etc. by a heat treatment method immediately before drawing.

[0002]

2. Description of the Related Art High-strength steel wire is subjected to various types of patenting as intermediate heat treatment during wire drawing, that is, direct patenting using rolling heat, lead patenting, or air patenting, followed by cold working such as wire drawing. After that, it is provided for the production of high-strength steel wires such as wire ropes, PC steel wires, springs, steel cords, and the like through a bluing process or a quenching and tempering process.

As disclosed in Japanese Patent Publication No. 47-51684, for example, as means for improving wire drawing workability, it is necessary to refine carbides or nitrides to refine austenite grains during patenting. Widely used.

However, even a material provided with such a means for improving wire drawing workability has no effect on flaws caused by handling during transport, and even if flaws occur during transport, breakage resistance to breakage occurs. There is a demand for a wire rod that does not deteriorate the properties.

[0005] As a method of reducing flaws during transportation, it is common practice to strictly pack and transport a wire coil. When packing a wire coil, it is very costly, and as a countermeasure, for example, in JP-A-5-201420, packing is automated.

[0006]

The problem with the prior art described above is that even if the drawability is improved by improving the material quality,
The handling may cause scratches during handling, and a hardened structure such as abraded martensite may be formed on the steel surface, resulting in a decrease in the breaking resistance to wire drawing of the material.

[0007] The present invention provides a high-strength steel wire that does not reduce the disconnection resistance even if a flaw occurs during transportation.

[0008]

For a wire rope, a PC steel wire, a spring, a steel cord, etc., a secondary processing maker secures material properties such as predetermined wire diameter and strength. For this reason, it is necessary to transport from the steelworks to the secondary processing maker, and more or less handling flaws occur during transport.

At this time, very hard martensite is formed on the surface layer of the steel. Even when a steel material excellent in wire drawing workability is used, martensite is generated due to the handling flaw, and the number of breaks increases. For this reason, even if surface martensite is generated,
A steel material that has excellent wire breakage resistance and does not deteriorate wire drawing workability is required.

The present inventors investigated handling flaws generated during transportation, investigated the effect of the hardened portion structure, particularly martensite, on the drawability, and clarified the following. The drawability is reduced due to the formation of surface martensite. The softening of the martensite structure in the surface layer is effective for improving the drawability.

At the time of drawing a die, martensite on the surface layer is broken perpendicular to the drawing direction due to its hardness, and a part of the martensite falls off as the drawing proceeds. The thickness of the martensite hardly decreases and sinks into the center of the base material of the pearlite-based structure.
A notch-sensitive crack is generated at the interface between the end portion of the martensite and the base material, and the disconnection resistance is reduced.

That is, the initial crack of martensite itself can be reduced by reducing the hardness of the surface martensite. In addition, the indentation of martensite into the base material, which promotes the generation of cracks with high notch sensitivity at the interface between the end of the martensite and the base material, is achieved by reducing the difference in strength between the base material and martensite by tempering. Can be suppressed.

Therefore, the present invention is as follows. weight%
C: 0.25 to 1.20% Si: 0.01 to 2.0% Mn: 0.2 to 1.1% P: 0.02% or less S: 0.01% or less, the balance being iron and unavoidable impurities The structure is mainly pearlite. The hardness of the hardest structure of the surface layer is 600Hv or less, and the hardness difference between the base material and the hardest structure is 3
High strength steel wire with excellent disconnection resistance of less than 00Hv.

Further, Nb: 0.005 to 0.05% Ti: 0.005 to 0.035% Al: 0.10% or less V: 0.005 to 0.060% Cu: 0.05 to 1.0% Ni: 0.05 to 1.0% Cr: 0.05 to 0.5 % Mo: 0.05 to 0.35% Ca: 0.0005 to 0.005% Mg: 0.0005 to 0.007% REM: 0.0005 to 0.005% B: 0.0005 to 0.005% High strength steel wire with excellent properties.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the chemical composition of high-strength steel wires having excellent drawability in the present invention will be described.

C: C is a basic element that controls the strength and ductility of steel, and generally, the higher the C, the higher the strength.
In order to ensure strength and hardenability, the content is set to 0.25% or more. However, when C exceeds 1.2%, proeutectoid cementite is formed and the drawability is reduced, so the upper limit is set to 1.2%.

Si: Si must be added as a deoxidizing element in an amount of 0.01% or more. In addition, steel is solid-solution strengthened. However, when added in an excessive amount, descaling becomes worse, and the wire drawing workability is reduced, so the upper limit value is set to 2.0%.

Mn: Mn needs to be added as a deoxidizing element in an amount of 0.2% or more. In addition, there is an effect that hardenability is improved and uniform pearlite is generated in the cross section of the wire. But Mn
Is an element that tends to segregate, so that under normal patenting conditions, if it exceeds 1.1%, large martensite will be formed on the Mn segregation peak in the central segregation part, which significantly impairs wire drawing workability, so the upper limit was set to 1.1%. .

P, S: P and S must be kept as low as possible because they segregate at crystal grain boundaries and deteriorate the properties of steel. The upper limit of P is set to 0.02% or less, and the upper limit of S is set to 0.01% or less.

The above are essential elements, but the following elements are added as necessary. Nb, Ti: One or more of Nb, Ti, and Al are added to form carbides or nitrides to improve the ductility of the wire. The lower limit of Nb is 0.005% and the lower limit of Ti is 0.005%
It is. However, the effect saturates when Nb exceeds 0.05% and Ti exceeds 0.035%. Therefore, the upper limits of Nb are 0.05% and Ti are 0.035%.

Al: Al is a deoxidizing element and is added to fix N in steel and to make fine-grained austenite. If it exceeds 0.1%, the effect will be saturated, so the upper limit is 0.1%.

Cu, Ni, Cr, Mo, V: Cu, Ni, Cr and M
o is 0.05 to 1.0 for Cu because of the strong strengthening effect of steel
%, 0.05-1.0% for Ni, 0.05-0.5 for Cr
%, 0.05 to 0.35% for Mo, and 0.005 to 0.
One or more kinds are added within the range of 060%.

Ca, Mg, REM: Ca, Mg, and REM are added in an amount of 0.0005% or more because steel forms fine oxides in the steel and makes austenite fine. However, 0.005% in Ca, M
Addition of more than 0.007% in g and more than 0.005% in REM results in coarsening of the oxide and lowers the drawability. 0.0005 to 0.00 for Ca
5%, 0.0005-0.007% for Mg, 0.0 for REM
One or more kinds are added within the range of 005 to 0.005%.

B: B is an element that improves the hardenability by adding a small amount, and the lower limit is 0.0005%. 0.005
%, BN precipitates and the effect of improving hardenability cannot be obtained. The addition range of B was set to 0.0005 to 0.005%.

It is important in the present invention that the hardness of the hardened structure is 600 Hv or less, and the difference between the hardness of the base material and the hardened structure is 3 hours.
00Hv or less. In order to suppress cracks in the initial stage of the wire drawing process due to martensite in the surface layer, the hardness of the hardened structure needs to be 600 Hv or less.

In order to suppress the indentation of martensite into the base material, which promotes the generation of cracks with high notch sensitivity at the interface between the end of the martensite, which is the hardened structure, and the base material, the base material and the hardened state The difference in the hardness of the tissue needs to be 300Hv or less.

Although the method of softening the hardened structure is not mentioned in the present invention, heat treatment by tempering is desirable. Tempering may be any of furnace heating, induction heating, and electric heating, and is not particularly limited.

[0028]

EXAMPLE A billet having a cross section of 122 mm square, which was subjected to continuous casting of the chemical components shown in Table 1 and then subjected to decomposition and rolling, was heated at 1100 ° C., and then heated to 5.5 to 13 mm.
Was rolled. Laser was applied to artificially generate martensite on the surface layer of the wire, and rapid heating and rapid cooling were performed. The tempering conditions were as shown in Table 2, and then the wire was drawn. The drawing conditions were set at a reduction in area of 15 to 25%, and the drawing limit was determined. Steels A to H are the newly developed steels, and have good wire drawing workability for a predetermined strength, and even if there is a hardened structure, the disconnection resistance does not decrease.

[0029] Steels I to K had poor disconnection resistance because the chemical composition of the steel was not appropriate. Steel I has a large C content and has a high hardness of the hardened structure, and therefore has poor wire drawability. Steel J had a large amount of Mn, and steel K had a large amount of Si. Steel LM
No good material properties can be obtained because the hardness of the material is not appropriate. Steel L had the hardest structure and hardened wire drawability. Steel M is an example of disconnection due to a high hardness difference between the base material and the hardened structure.

[0030]

According to the present invention, a high-strength steel wire excellent in disconnection resistance can be obtained, which is industrially very effective.

[0031]

[Table 1]

[0032]

[Table 2]

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Yasunobu Miyazaki 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division

Claims (2)

[Claims] 1. Structure containing, by weight%, C: 0.25 to 1.20% Si: 0.01 to 2.0% Mn: 0.2 to 1.1% P: 0.02% or less S: 0.01% or less, with the balance being iron and inevitable impurities Is mainly a pearlite wire, the hardness of the hardest structure of the surface layer is 600Hv or less, and the hardness difference between the base material and the hardest structure is 3
High strength steel wire with excellent disconnection resistance of less than 00Hv. 2. The chemical composition of the wire is as follows: Nb: 0.005 to 0.05% Ti: 0.005 to 0.035% Al: 0.10% or less V: 0.005 to 0.060% Cu: 0.05 to 1.0% Ni: 0.05 to 1.0% Cr: 0.05 0.5 to 0.5% Mo: 0.05 to 0.35% Ca: 0.0005 to 0.005% Mg: 0.0005 to 0.007% REM: 0.0005 to 0.005% B: 0.0005 to 0.005% 1. High strength steel wire with excellent disconnection resistance.