JPS58144451A - Steel wire material-rod steel excellent in cold processability - Google Patents

Abstract

PURPOSE:To provide a steel wire material.rod steel excellent in cold processability and having a perlite main structure, wherein the min. hardness part in a cross are is offset from the center thereof to a certain degree and hardness distribution is made eccentric. CONSTITUTION:After a steel wire material.rod steel is heated to an A3 deformation point by a direct heat treatment method or a reheating treatment method, mist cooling or jet mist cooling is carried out by supplying a cooling medium only from one direction to obtain the steel wire material.rod steel wherein the min. hardness part in the cross area thereof is parted by 0.2d or more (wherein d is the diameter of the steel wire material.rod steel) from the center thereof and hardness distribution is made eccentric and the main structure thereof is perlite. The obtained steel wire material.rod steel is excellent in cold processability and generates no cutting or internal crack by usual wire drawing processing, withdrawing processing or extrusion processing as well as receives almost no influence in the tensile strenght thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides steel wire rods and rods with excellent cold workability that do not cause wire breakage during wire drawing (C cuppy fracture) or internal cracks (chevron cracks) during extrusion or drawing. lol
41 related.

Hard steel wire and piano wire are subjected to wire drawing as a pearlite (+ ferrite) structure by direct patenting or reheating patenting (lead patenting, etc.) using rolling heat, but in this wire drawing process, There is a phenomenon called cuppy fracture where the wire breaks from the center. In such wires, which are given strength through work hardening due to cold working, not only do wire breakage impede the ability to increase the strength, but
Wire drawing work is significantly hindered. In addition, when carbon steel and low alloy steel for mechanical structures used in various machine parts are subjected to extrusion or drawing as a ferrite/pearlite structure, internal cracks called chevron cracks may occur. .

In order to solve the above-mentioned problem during cold working, the inventors of the present invention conducted extensive research and found that the lowest hardness part in the cross section is W6 wire.
It has been discovered that wire rod steel bars with pearlite as their main structure are less likely to break during wire drawing and to develop internal cracks during extrusion/drawing operations if they are separated from the center of the steel bar by a predetermined distance or more and the hardness distribution is eccentric. , we have completed the present invention.

That is, the object of the present invention is to provide a steel wire bar having pearlite as its main structure, in which the lowest hardness part in the cross section is 0.2 d or more from the center of the wire bar (where d is the diameter of the wire bar). The object of the present invention is to provide a steel wire rod having excellent cold workability and having an eccentric hardness distribution.

- Examining the mechanism of cuppy fracture and internal crack generation in the series, we find that in both cases, cracks occur from the center of the wire rod/steel bar. From a plastic mechanics point of view, this is due to the fact that the maximum tensile stress acts at the axial center of the wire rod/steel bar during cold working, and from a metallographic point of view,
The center of ordinary wire rods and steel bars cools more slowly than the surface layer, resulting in a structure consisting mainly of relatively coarse pearlite.As a result, ductility decreases and the material defects described above are more likely to occur. Conceivable.

Therefore, in the present invention, by separating the lowest hardness part in the cross section of the steel wire rod/bar by a predetermined distance from the center and making it eccentric, the maximum stress acting part and the lowest hardness part during cold working are smoothed, and the above-mentioned wire breakage and internal It reduces the occurrence of crank to 1 defense.

In order to manufacture steel wire rods and steel bars with eccentric hardness distribution, it is necessary to use direct heat treatment or reheating heat treatment methods to supply refrigerant uniformly from the surface of the material or steel bars, but only in one direction. need to be supplied.

When such heat treatment is carried out by a direct heat treatment method, it is possible to use the wI wire direct heat treatment apparatus according to Japanese Patent Application No. 54-38049 owned by the present applicant.

Specific examples of the refrigerant include water (including hot water), mist, blast air, etc., and mist cooling or blast mist cooling is preferable.

The steel wire rod obtained by such a cooling method becomes a steel whose main structure is pearlite. If the carbon content of the steel is less than the eutectoid composition, the steel will have a ferrite-pearlite structure consisting mainly of pearlite. In addition, as such steel wire rod, C
093 to 0.9% hard steel wire piano wire is exemplified.

Examples of the bar steel include carbon steel for mechanical structures containing CO11 to 0.6%, or low alloy steel containing alloying elements such as Ni, Cr1Mo, and B (5% or less).

The steel wire rod according to the present invention has poor cold workability, and has a 11j+
.

Normal wire drawing and drawing. Due to the extrusion process, wire breakage or internal cracks will not occur. therefore,
Cold working efficiency can be improved. Note that the tensile strength itself is hardly affected by the hardness distribution in the cross section of the wire.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example (1) Wire rod (12 mmφ) of common test steel shown in Table 1 was 90
After heating for 0°CXS minutes, the wire is cooled from one direction using a suitable combination of front wind and mist to obtain a cross-sectional hardness distribution as shown in FIG. Note that the isohardness lines are shown in Hv units. The lowest hardness part is 2.5 to 4 meters (0
, 2 to 0.33d, where d is the wire diameter).

Example 1 When using the same wire as in the example except for applying heat treatment evenly from the periphery of the wire using the conventional lead patenting method, the cross section of the wire with the lowest hardness part located almost in the center as shown in Figure 2. Obtain hardness distribution.

Table 1 Chemical composition of test steel W [% Test Example 1 Wire rods with various hardness distributions obtained in the examples and comparative samples were subjected to a tensile test, and the results shown in Figure 3 were obtained. Ta.

As is clear from this, the tensile strength was almost constant regardless of the eccentricity of the hardness distribution, but the reduction of area (ductility) increased with the eccentricity of 0.2d as the boundary, and the It can be seen that it is preferable that the position of the lowest hardness portion be separated from the center by 0.2 d or more.

Test Example 2 Wire rods having various hardness distributions obtained in Examples and Comparative Examples were cold drawn under the following wire drawing conditions, and the limit processing rate until cuppy fracture occurred was examined. 4th result
As shown in the figure.

Wire drawing processing conditions Die angle: 20 1-pass area reduction rate: 15% Wire drawing speed: 20 m/min As is clear from this, the limit processing rate varies depending on the steel type, and cuppy fracture occurs and separation occurs as the amount of C decreases. However, it can be seen that the limit machining rate improves from eccentricity of 0.2 or more in all steel types.

Note that even after wire drawing, the hardness distribution state (minimum hardness eccentricity I) in the cross section of the wire does not change significantly (see a comparison between FIG. 1A and FIG. 5).

As is clear from the following explanation, the wire rod according to the present invention has the lowest hardness part eccentrically offset by 0.2 d or more from the center, so it is more narrow than the conventional one while maintaining tensile strength. It is possible to provide a steel wire bar which has effects such as improved ductility and an increase in the cuppy rupture rate, and which does not cause wire breakage or internal cracks during cold working.

[Brief explanation of the drawing]

Figure 1 shows the cross-sectional hardness of the steel wire rod and steel bar according to the present invention.
Fig. 2 is a schematic diagram showing the cross-sectional hardness distribution of conventional steel wire rods and bars, Fig. 3 is a graph showing the tensile test results, Fig. 4 is a graph showing the cuppy rupture limit test results, Figure 5 shows the steel wire shown in 1iffi (a) being wire drawn (
FIG. 2 is a schematic diagram showing the cross-sectional hardness distribution after 60% wire drawing (12φ-9.3φ). Note that the hardness distribution is expressed by Hv isohardness lines. Patent Applicant Kobe Steel Co., Ltd., 1 person, 1 person, 1 person, 1 person, 1 person, 1 person, 1 person, 1 person, 1 person, 1 (a)
Figure 5 Figure 1 (b) Figure 1 (c) C condyle 267- Figure 2 (a) Figure 2 (b) 4R Figure 2 (C) C Fukuoka

Claims (1)

[Claims] Steel wire rods and steel bars whose main structure is pearlite, and the lowest hardness in the cross section is 0.0 mm from the center of the steel wire rod or steel bar.
Steel wire rods and steel bars with excellent cold workability, which are separated by 2d or more (where d is the diameter of the steel wire rod or steel bar) and have an eccentric hardness distribution.