JPH11199977A - Wire rod excellent in wire drawability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wire rod excellent in wire drawablity, particularly in rod drawability in wire drawability subsequent to to hot working. SOLUTION: By regulating the pearlitic nodule size of a rolling stock to <=18 μm, a wire rod excellent in wire drawability can be obtd. For obtaining the wire rod having high strength, the componental compsn. is preferably composed of, by mass, 0.50 to 0.80% C, 0.15 to 2.50% Si, 0.20 to 1.0% Mn, and the balance Fe with inevitable impurities, and moreover, it is recommended that <=2.0% (0% is not included) Cr and/or <=0.20% (0% is not included) V is incorporated therein. Furthermore, for obtaining excellent rod drawability, the central segregation degree of the wire drawing rolling stock is preferably regulated to <=0.10, and the lamellar interval in the pearlitic structure of the rolling stock is preferably regulated to <=1000 Å.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire rod excellent in wire drawing workability, and more particularly to a wire rod used for a spring, a wire rope, a high-strength bolt and the like which require a predetermined strength. The present invention relates to a wire having excellent drawability.

[0002]

2. Description of the Related Art Generally, a wire rod requiring a predetermined strength, such as a spring, is subjected to controlled cooling after working to a wire diameter of 5.0 to 25 mmφ by hot rolling. The wire that has been controlled and cooled is processed into a smaller wire diameter by repeatedly drawing and heat-treating by cold drawing, and after being formed into a predetermined product shape, quenched and tempered to be a final product. Therefore, in manufacturing the final product, the higher the wire drawing property of the hot-rolled wire is, the more easily the manufacturing cost can be reduced.

As a technique for improving the drawability of a high-strength steel wire, Japanese Patent Publication No. 7-11060 discloses a high-strength steel wire in which the width of the Mn segregation zone is limited. Since it is premised that lead patenting treatment is performed beforehand, there has been a demand for development of a wire rod having high wire drawing workability, that is, excellent in drawability, without performing patenting treatment.

Japanese Patent Laid-Open Publication No. Hei 8-295931 discloses a method for improving the raw pulling property.
Although a method of converting a main structure to bainite using a strain diagram is disclosed, improvement of the bioproducibility was insufficient.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and is a wire rod excellent in wire drawing workability, particularly excellent in drawability in wire drawing after hot working. It is intended to provide.

[0006]

The wire rod of the present invention which has solved the above-mentioned problems has a gist that the pearlite nodule size of the rolled material is 18 μm or less.

To obtain a high-strength wire, the component composition is C:
0.50 to 0.80%, Si: 0.15 to 2.50%,
It is desirable to contain Mn: 0.20 to 1.0%, with the balance being Fe and inevitable impurities, and further Cr: 2.0% or less (excluding 0%) and / or V: 0.20% or less. (Not including 0%) is recommended.

In order to obtain excellent drawability, the center segregation degree of the drawn wire is desirably 1.10 or less, and the lamella spacing of the pearlite structure of the rolled material is 1000 °.
It is preferable to set the following.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION For the purpose of solving the above-mentioned problems, the present inventors have studied on the influence of pearlite nodules on the shrimpability. As a result, it has been found that when the pearlite nodule becomes large, the area of the nodule interface becomes small and the ductility of the rolled material is reduced, so that the wire drawing workability is deteriorated. FIG. 1 is a graph showing the relationship between the pearlite nodule size of a high-strength steel wire and the critical wire-drawing reduction rate during raw drawing. It can be seen that when the pearlite nodule size is 18 μm or less, the line drawing limit area reduction rate is 85% or more, exhibiting extremely excellent raw-drawing properties.

[0010] The drawability is affected by the center segregation of the rolled material and the lamella spacing of the pearlite structure of the rolled material. When the degree of center segregation of the rolled material is 1.1 or less, the degree of microscopic embrittlement due to segregation is reduced, and the occurrence of internal cracks generated during drawing is suppressed, so that wire drawing workability is improved. It is recommended that the center segregation degree of the rolled material be 1.1 or less. Further, if the lamella spacing of the pearlite structure of the rolled material is too large, the toughness of the rolled material is reduced, and internal cracks are easily generated during wire drawing. . Hereinafter, the reason for setting the chemical component range of the present invention will be described.

C is an element effective for increasing the strength, and is desirably contained at least 0.5% in order to exhibit sufficient strength as a spring or the like. However, if the content is too large, the toughness is reduced. Therefore, the upper limit is preferably set to 0.8%.

Si is an element necessary for deoxidizing steel, and is desirably contained in an amount of 0.15% or more in order to effectively exhibit a deoxidizing effect. However, if added excessively, the ductility deteriorates, so the upper limit is preferably set to 2.0%.

Mn, like Si, is a deoxidizing element, and is preferably added in an amount of 0.20% or more in order to improve the hardenability of steel and secure strength and toughness as a spring or the like. However, if the amount of Mn is too large, a segregated portion of Mn is formed, and a supercooled structure such as martensite or bainite is generated to deteriorate wire drawing workability. Therefore, the upper limit is preferably 1.0%. .

It is desirable to add Cr because it has the effect of refining the pearlite structure and improving the toughness. However, if added in a large amount, the transition density in the ferrite after the heat treatment is increased and the ductility of the wire after the wire drawing is improved, so the upper limit is preferably set to 2.0%.

V is desirably added because it refines the γ grain size and improves the toughness value. However, if added in an amount of 0.20% or more, carbides are generated and precipitated, and the rolled material is hardened to deteriorate the toughness. Therefore, it is preferable to set the upper limit to 0.20%.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention, and any design changes based on the gist of the preceding and following aspects will be described. Are included within the technical scope of

[0017]

EXAMPLES Example 1 C: 0.59%, Si: 1.37%, Mn: 0.66
%, Cr: 0.69%, and using a balance of Fe and unavoidable impurities to form a 155 mm square billet of 8%.
Heated to 50-1000 ° C, processed to 8mmφ by hot rolling, and cooled at 800-600 ° C to about 2-3 ° C.
The temperature was adjusted and cooled at a rate of / sec to produce a pearlite nodule size wire rod shown in Table 1. The pearlite nodule size is a value obtained by measuring the size (length of the long axis) of five pearlite nodules in a 0.125 mm square in the visual field at a magnification of 400 times the cross section of the wire using an optical microscope and averaging the values. It is. The wire material was dry-drawn at a die angle of 15 degrees, and the area reduction rate at the time of cut-off at the cuppy was defined as the wire-drawing limit area reduction rate. The results are shown in Table 1 and FIG.

[0018]

[Table 1]

No. Nos. 1 to 3 are steels of the present invention, which have a large wire-drawing critical area reduction rate and have excellent drawability. On the other hand, Comparative Steel No. having a pearlite nodule size outside the range of the present invention.
Each of Nos. 4 to 7 has a small wire-drawing limit area reduction rate and is inferior in the grooving property.

Example 2 155 mm having various center segregations with the chemical components shown in Table 2
The square billet was hot-rolled to 8 mmφ, and a wire made of pearlite having various microstructures (nodule size, lamella spacing) shown in Table 2 was produced by controlled cooling.
The heating temperature during hot rolling is the same as that of No. 30 is 1000 ° C
In other cases, the temperature was 900 ° C., and the cooling rate after hot rolling was no. No. 28 was 7.5 ° C./sec. No. 29 was 1.0 ° C./sec. 11-27
And No. The cooling rate of 30 to 31 was 2.5 ° C / sec.

The center segregation of the wire is determined by performing a line analysis by EPMA in a direction crossing the center segregation portion of the wire, measuring the maximum concentrated portion (C ₁ ) of the C concentration, and obtaining C ₁ / C ₀ in FIG. The segregation degree was taken.

Regarding the lamella spacing, the value measured by cross-sectional observation is larger than the actual spacing because the cutting direction of pearlite is not necessarily the vertical direction of the lamella.
Then, the cross section was observed at about 7000 times by SEM, the lamella spacing of 20 pearlite colonies exhibiting the same lamella spacing was measured for one sample, and the order of the lamella spacing was shown in FIG. The sample was arranged as shown, an extrapolated straight line was drawn, and the intersection with the vertical axis was set as the value of the lamella spacing of the sample (the lamella spacing is 750 ° in the example of FIG. 3). The wire material was dry-drawn at a die angle of 15 degrees, and the area reduction rate at the time of cut-off at the cuppy was defined as the wire-drawing limit area reduction rate. The results are shown in Table 2.

[0023]

[Table 2]

No. Nos. 20 to 27 are comparative examples in which the component compositions are out of the range of the present invention, and all have low wire-drawing reduction rates and inferior drawability. No. No. 28 is a comparative example when the lamella spacing is too large. In No. 29, the pearlite nodule size was too large. Numeral 30 is a comparative example in which the degree of center segregation of the wire is too large. On the other hand, the present invention example No. satisfying all the requirements according to the present invention. Nos. 11 to 19 have a large wire-drawing limit area reduction rate and are excellent in the drawability.

[0025]

As described above, according to the present invention, it is possible to provide a wire rod which is excellent in wire drawing workability and particularly excellent in raw drawability in wire drawing work after hot working.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the pearlite nodule size of a high-strength steel wire and the critical wire-drawing reduction rate during raw drawing.

FIG. 2 is an explanatory diagram illustrating a method of calculating a center segregation degree.

FIG. 3 is a graph showing a method for determining a value of a lamella interval.

Claims (6)

[Claims] 1. A wire having excellent drawability, characterized in that the pearlite nodule size of the rolled material is 18 μm or less. 2. In mass%, C: 0.50 to 0.80%, Si: 0.15 to 2.5
2. The wire according to claim 1, containing 0% and Mn: 0.20 to 1.0%, the balance being Fe and unavoidable impurities. 3. The wire according to claim 2, further comprising Cr: 2.0% or less (excluding 0%). 4. The wire according to claim 2, further comprising V: 0.20% or less (excluding 0%). 5. The wire according to claim 1, wherein the center segregation degree of the rolled material is 1.10 or less. 6. The wire according to claim 1, wherein the lamella spacing of the pearlite structure of the rolled material is 1000 ° or less.