JP3221943B2 - Low-alloy steel wire rod for high-strength ultrafine wire with good drawability and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-alloy steel wire rod for high-strength ultrafine wires having good drawability and a method for producing the same. Conventionally, when a low-alloy steel wire is applied to an ultrafine wire, it is necessary to first off-line lead-pattern the hot-rolled wire. However, by using the present invention, wire drawing can be performed without first performing off-line lead patenting, so that the cost of a high-strength ultrafine wire can be reduced.

[0002]

2. Description of the Related Art Several production methods have been proposed to omit the first off-line lead patenting of a hot-rolled low alloy steel wire rod, but all of them relate to a large diameter wire having a final product diameter of 1 mm or more. There is no proposal for a high-strength ultrafine wire of 0.50 mm or less, which is the object of the present invention.

For example, in Japanese Patent Application Laid-Open No. 50-92216, by adding Mn or Mn or Cr, the tensile strength can be reduced to 1128 MPa (115 kgf / mm) even if the cooling speed after hot wire rolling is slow.
² ) It discloses a manufacturing method that can be performed as described above. This is a method for adjusting and cooling a hot-rolled wire rod for a PC steel wire, and is a manufacturing method capable of increasing the ultimate strength of a PC steel wire without performing first lead patenting off-line. In the case of an extra fine wire, the drawing limit (drawing limit = 1n (d _o / d _n ) ² , d _o :
This method cannot be used because it is necessary to increase the hot-rolled wire diameter (d _n : drawing diameter at which the reduction is reduced to 30%) to 2.5 or more and to omit the first off-line lead patenting. This is because, in the case of PC steel wire, the required drawing limit is as small as about 1. In Japanese Patent Application Laid-Open No. 3-79719, the heating temperature and the finish rolling temperature of a wire for a Si-Cr spring are set to 1000 ° C. or less,
After forced cooling to 0-750 ° C, 600 ° C at 1-10 ° C / s
It is disclosed to cool down. Low alloy steel wire for high-strength ultra-fine wire because temperature control from heating temperature to hot wire rolling temperature is required, and since the target is a spring with a large diameter wire, the required logarithmic distortion is small. Not applicable to Therefore, development of a low-alloy steel wire rod for high-strength ultrafine wires having excellent drawability and a method for producing the same have been desired.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances. The present invention controls the microstructure of a hot-rolled wire and draws the wire without conducting lead patenting offline. An object of the present invention is to provide a low-alloy steel wire rod for high-strength ultrafine wires having a processing limit of 2.5 and a method for producing the same. If the drawing limit is 2.5 or more, it is equivalent to a conventional carbon steel wire, and industrial application of a low alloy steel wire to an ultrafine wire is promoted.

[0005]

That is, the gist of the present invention is as follows. (1) C: 0.80 to 1.10%, Si: 0.10 to
1.00%, Mn: 0.10 to 0.60%, Cr: 0.
For high-strength ultrafine wires with good drawability, characterized in that the steel consisting of 10 to 0.60%, balance iron and unavoidable impurities has a perfect pearlite structure with lamella spacing of 0.08 to 0.12 μm. Low alloy steel wire rod.

(2) C: 0.80 to 1.10%, Si:
0.10 to 1.00%, Mn: 0.10 to 0.60%,
Cr: 0.10 to 0.60%, the balance consisting of steel consisting of iron and inevitable impurities is 0.4 to 4.0 ° C./s after hot rolling.
A method for producing a low-alloy steel wire rod for a high-strength ultrafine wire having a good wire drawing property, characterized by cooling at a low temperature. The present inventors have found through long-term research that there is a correspondence between the lamella spacing of the pearlite structure and the drawing limit, and that an optimum lamella spacing exists. If this phenomenon is utilized, a low-alloy steel wire rod for high-strength ultrafine wires with good drawing workability can be economically manufactured. FIG. 1 shows the relationship between the lamella spacing and the drawing limit. Changes in tensile strength and drawing when the 5.5 mm wire was drawn were measured, and the logarithmic strain at which the drawing was reduced to 30% was taken as the drawing limit. When the drawing is 30% or less, breakage occurs during high-speed drawing due to insufficient ductility of the steel wire.
From FIG. 1, it can be seen that if the lamella spacing is 0.08 to 0.12 μm, the drawing limit becomes 2.5 or more. In the case of carbon steel, wire drawing is often performed industrially from about 5.5 mm to 1.6 mm (drawing limit of 2.5). Therefore, the drawing limit of 2.5 is one index of a wire having good drawing properties. When the lamella spacing is coarse, the thickness of cementite, which is a pearlite constituent factor, becomes large and the workability deteriorates, so that the drawing limit is lowered. In addition, it is presumed that the transformation start temperature must be lowered in order to reduce the lamella spacing, so that the pearlite structure is disturbed and the drawing limit is lowered. FIG. 2 shows the relationship between the cooling speed and the lamella spacing. The cooling rate was an average cooling rate between 850 and 650 ° C. If the cooling speed is 0.4 to 4.0 ° C / s, the lamella
The interval becomes 0.08 to 0.12 μm. In the case of a Si-Cr-based low alloy steel wire, drawability is improved by reducing the cooling speed as compared with carbon steel. Cold speed 0.4 ~
C is from 0.80 to 1.10 even at 4.0 ° C./s
%, The appearance of proeutectoid cementite can be prevented.

The present invention has a wire diameter of 0.5 mm or less and a tensile strength of 3 mm or less.
It is intended for high-strength ultrafine wires of 200 MPa or more. Therefore, if C is 0.80% or less, the content cannot be increased to 3200 MPa or more even when Si and Cr are added. Therefore, the content is set to 0.80% or more. Further, when C is 1.10% or more, the appearance of proeutectoid cementite cannot be suppressed when the lamella spacing is set to 0.08 to 0.12 μm. Next, if the content of Si is 0.10% or less, very small surface flaws occur on the surface of the ultrafine wire due to insufficient deoxidation. Therefore, the content of Si is set to 0.10% or more. When the Si content is 1.00% or more, the hardening action of ferrite becomes large, and even if the lamella spacing is controlled, the wire drawing limit of 2.5 or more becomes impossible. Therefore, the Si content is set to 1.00% or less. If Mn is 0.10% or less, hot brittleness due to S cannot be prevented, so Mn is set to 0.10% or more.
If the content is 0.60% or more, a pearlite structure disturbed in the center segregation part at the time of final patenting is generated, and the ductility of the ultrafine wire is deteriorated. Therefore, it is set to 0.60% or less. Cr was set to 0.10% or more which is necessary for increasing the strength of the ultrafine wire. However, when the content is 0.60% or more, considering that undissolved carbide is likely to be generated at the time of final patenting and that the ultimate strength of the product is saturated, 0.60% which is most effective for increasing the strength is considered.
0% or less.

Hereinafter, the present invention will be described with reference to examples.

[0009]

EXAMPLE 5.5 Low-alloy steel wire rod shown in Table 1 was melted in vacuum and 5.5 was melted.
mm hot-rolled wire. At this time, the cooling speed after hot rolling was changed. Using this 5.5 mm wire, drawability and characteristics of a 0.20 mm extra fine wire of the final product were examined. Those which cannot be drawn directly from a 5.5 mm wire to 1.4 mm were subjected to intermediate lead patenting at 3.2 mm. In addition, all are 1.4mm
After the final lead patenting was performed, ultrafine wire drawing was performed.

[0010]

[Table 1]

In Table 1, CR is the cooling speed (° C./s), PS
Is the lamella spacing (μm), TS is the tensile strength (MPa) of the hot-rolled wire, P is the complete pearlite structure in the structure of the wire, C + P is the pearlite structure containing proeutectoid cementite,
PS is the lamella spacing of the wire rod (μm), DL is the drawing limit (mm is the wire diameter at the drawing limit, and logarithmic strain is 1 n (d _O / d _n ) ^{2, the} drawing limit). As the characteristics of the 0.20 mm steel wire, tensile strength and twisting characteristics were examined. The quality of the twisting process was judged by the presence or absence of disconnection when a two-stranded wire was trial-produced at a twisting speed of 18000 rpm.

Since the C content of steel types A and B is 0.8% or less, the drawing limit is 2.5 or more, but the tensile strength of a 0.20 mm steel wire is reduced to 3200 MPa or less. Since the steel type C has a high C content of 1.12%, the drawing limit is 2.5 or less. In addition, ultrafine wire drawing from 1.4 mm to 0.20 mm could not be performed. Since the steel type D has a high Si content of 1.09%, the lamella spacing is 0.09 μm, but the drawing limit is 2.5 or less due to solid solution hardening by Si.

[0013] For the steel type E, the drawing limit was 2.5 or more, but Mn was as high as 0.70%, so that it could not be drawn to 0.20 mm in the final ultrafine drawing. Steel type F contains 0.63 Cr
%, The drawing limit was 2.5 or less. Further, it was not possible to draw down to 0.20 mm at the time of the final extra fine wire drawing.
Steel type G has a wire drawing limit of 2.5 or more, but has a Cr content of 0.2.
Since it is as low as 05%, the tensile strength of 0.20 mm steel wire is 320
It became 0MPa or less.

Although the chemical composition of the steel types H and I is within the range of the steel of the present invention, the lamella spacing is 0.08 to 0 since the cooling rate is not in the range of 0.4 to 4.0 ° C./s. .12 μm, and the drawing limit was 2.5 or less. However, 3.
Intermediate lead patenting was performed at 2 mm and wire drawing was performed to 1.4 mm, and final lead patenting at 1.4 mm was performed to ultrafine wire drawing to 0.20 mm. The tensile strength of the 0.20 mm steel wire was 3200 MPa or more, and the twistability was good.

The steel types J and K are the steels of the present invention. In any case, wire drawing can be performed from 5.5 mm to 1.4 mm or less, and the drawing limit is 2.5 or more. Direct drawing from 5.5mm wire to 1.4mm, 0.2mm after final lead patenting
Extra fine wire drawing was performed to 0 mm. 4000 at 0.20mm
A tensile strength of MPa or more was obtained. As described above, according to the present invention, a low alloy steel wire having good drawability and capable of achieving a high strength of 3200 MPa or more can be obtained.

[0016]

After the hot wire is rolled, the lamella spacing is adjusted at a cooling rate of 0.4 to 4.0 ° C./s to make the lamella spacing 0.08 to 0.12 μm.
By controlling to a perfect pearlite structure of m, a drawing limit of 2.5 or more is possible without performing first lead patenting off-line. Thereby, the low alloy steel wire can obtain the same drawability as the carbon steel wire, and the cost of the low alloy steel wire for high-strength ultrafine wires can be reduced. The low-alloy steel wire, like the carbon steel wire, has a large cost reduction effect by being able to draw a hot-rolled wire off-line without first lead patenting, so that the present invention has great industrial significance.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a lamella spacing of a pearlite structure and a drawing limit.

FIG. 2 is a diagram showing a relationship between a cooling speed after hot wire rolling and lamella spacing.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 8/06 C21D 9/52

Claims (2)

(57) [Claims] 1. C: 0.80-1.10%, Si: 0.
10-1.00%, Mn: 0.10-0.60%, C
r: steel having 0.10 to 0.60%, balance consisting of iron and unavoidable impurities, having a perfect pearlite structure having a lamella spacing of 0.08 to 0.12 μm, and a good high drawability. Low alloy steel wire for high strength ultrafine wires. 2. C: 0.80 to 1.10%, Si: 0.
10-1.00%, Mn: 0.10-0.60%, C
r: 0.10 to 0.60%, the steel comprising the balance iron and unavoidable impurities is hot-rolled and then cooled at 0.4 to 4.0 ° C./s. A method for producing a good low-strength steel wire for high-strength ultrafine wires.