WO2022131591A1 - Steel wire with improved drawability, and manufacturing method therefor - Google Patents

Abstract

A steel wire with improved drawability, and a manufacturing method therefor are disclosed. A steel wire according to the present invention comprises, by wt%, 0.52-0.69% of C, 0.3-0.8% of Mn, 0.1-0.5% of Si, and the balance of Fe and inevitable impurities, wherein the carbon content of cementite in pearlite is 7 at.% or more, and the following formula (1) is satsified. (1) [TS]+exp(ε)*10 < 1,500 (In formula (1), [TS] means the tensile strength (MPa) of a wire before drawing, and ε means draw strain.)

Description

Steel wire with improved drawability and manufacturing method therefor

The present invention relates to a steel wire having improved wire drawing property and a method for manufacturing the same, and more particularly, to a steel wire having improved torsional properties and wire drawing property without delamination, and a method for manufacturing the same.

In general, several methods can be used to obtain a high strength steel wire.

First, a method of increasing the strength of the material itself may be used. That is, as one of the methods for obtaining a high-strength steel wire, a method of increasing the strength of the material itself by adding a large amount of a reinforcing element to increase the strength of the steel may be used. A representative example of such a strengthening element is carbon. When the carbon content increases, the fraction of cementite, which is a hard phase, increases inside the wire rod, and the lamellar spacing of the pearlite structure becomes dense, thereby improving the strength of the material. In addition to carbon, a technique for adding various alloying elements has been proposed.

Alternatively, the strength can be improved by increasing the draw strain of the steel wire. At this time, as the wire-drawing strain of the material is closely related to the ductility of the material, the material itself does not break during wire-drawing and the easier it is processed, the more advantageous it is to improve strength.

If a large amount of alloying elements are simply added to improve the strength of the wire rod, problems such as wire breakage may occur due to poor ductility of the wire rod in the subsequent steel wire manufacturing process after the wire rod rolling. Therefore, the most economical method of increasing the strength of a steel wire is to reduce the amount of alloying elements and increase the wire-drawing strain.

However, in general, delamination occurs when the wire strain rate increases, and if delamination occurs during a twist test of a wire, it is regarded as defective, and the maximum draw strain rate at which delamination does not occur is defined as a fresh system.

The occurrence of delamination is related to the decomposition of cementite. When the delamination of cementite occurs due to an increase in the wire-drawing strain, carbon of the cementite is discharged to the ferrite, which rapidly reduces the plastic deformation ability of the ferrite and causes cracks. This acts as a major obstacle to increasing the strength of the steel wire.

Therefore, a high-strength steel wire capable of suppressing the occurrence of delamination while increasing the wire-drawing strain is required.

An object of the present invention is to provide a steel wire with improved wire-drawing properties and a method for manufacturing the same by controlling the strength of the wire rod and slowing the decomposition rate of cementite.

The steel wire with improved wire drawing ability according to an embodiment of the present invention contains, by weight, C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, the remaining Fe and unavoidable impurities, and in pearlite The cementite carbon content is 7at.% or more, and the following formula (1) is satisfied.

(1) TS+exp(ε)*10 < 1500

(In Equation (1), [TS] is the tensile strength of the wire before drawing (MPa), and ε means the strain rate of wire drawing)

The tensile strength of the wire rod may be 700 to 1,000 MPa.

The number of twists of the steel wire may be 30 or more.

In the steel wire, delamination may not occur at a wire-drawing strain of 4.02 or less.

A method of manufacturing a steel wire for a spring having improved fatigue life and toughness according to an embodiment of the present invention includes C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, the remaining Fe and unavoidable impurities. hot rolling the billet to obtain a wire rod; cooling the hot-rolled wire rod at a cooling rate of 3 to 20° C./s; and obtaining a steel wire by wire-drawing the cooled wire rod to satisfy Equation (1) below.

(1) [TS]+exp(ε)*10 < 1500

(In Equation (1), [TS] is the tensile strength of the wire before drawing (MPa), and ε means the strain rate of wire drawing)

During wire-drawing, delamination may not occur at a wire-drawing strain of 4.02 or less.

In the steel wire according to an embodiment of the present invention, by controlling the strength of the wire rod and slowing the decomposition rate of cementite, it is possible to suppress delamination and increase torsional characteristics and freshness even during wire-drawing with a high wire-drawing strain.

Specifically, in the steel wire according to the embodiment of the present invention, the number of twists can be secured to 27 or more even at a drawing strain of 4.02, and delamination does not occur during wire drawing, so that the freshness can be increased, and ultimately, having ultra-high strength Steel wire can be provided.

The steel wire with improved wire drawing ability according to an embodiment of the present invention contains, by weight, C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, the remaining Fe and unavoidable impurities, and in pearlite The cementite carbon content is 7at.% or more, and the following formula (1) is satisfied.

(1) TS+exp(ε)*10 < 1500

(In Equation (1), [TS] is the tensile strength of the wire rod before drawing (MPa), and ε means the strain rate).

This specification does not describe all elements of the embodiments, and general content in the technical field to which the present invention pertains or content that overlaps among the embodiments is omitted.

Also, when a part "includes" a component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

The singular expression includes the plural expression unless the context clearly dictates otherwise.

Hereinafter, the present invention will be described in detail.

The steel wire with improved drawability according to an embodiment of the present invention includes, by weight, C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, the remaining Fe and unavoidable impurities, and wire drawing The cementite carbon content in the post pearlite is 7 at.% or more, and the following formula (1) is satisfied.

(1) [TS]+exp(ε)*10 < 1500

In Equation (1), [TS] is the tensile strength (MPa) of the wire rod before wire drawing, and ε means the wire-drawing strain.

Hereinafter, the reason for numerical limitation of the alloying element content in an embodiment of the present invention will be described. Hereinafter, unless otherwise specified, the unit is % by weight.

The content of C is 0.52 to 0.69%.

C is an element added to improve the strength of the steel wire. When the C content is less than 0.52%, the effect of improving the strength is not sufficient, and when the C content exceeds 0.69%, the strength of the steel can be secured but the ductility is reduced. It is preferable to control with

The content of Mn is 0.3 to 0.8%.

Mn is an effective element for increasing hardenability. When the content of Mn is less than 0.3%, the above-described effects cannot be sufficiently obtained, and when the content of Mn exceeds 0.8%, central segregation may occur, and there is a very high possibility of causing a low-temperature structure. Therefore, in the present invention, the content of Mn It is preferable to control it to 0.3 to 0.8%.

The content of Si is 0.1 to 0.5%.

Si is an effective element to improve the cleanliness of the wire rod and to strengthen the steel by being dissolved in ferrite, which is a matrix structure. When the content of Si is less than 0.1%, the above-mentioned effect cannot be obtained, and when the content of Si exceeds 0.5%, it can become a crack propagation path when the amount of wire drawing is large. The content is preferably controlled to 0.1 to 0.5%.

In addition to the above composition, the remainder is Fe, and other impurities are included inevitably in the manufacturing process. The present invention does not exclude the addition of other alloying elements other than the above-mentioned alloy composition.

In the steel wire with improved drawability according to an embodiment of the present invention, the cementite carbon content in pearlite after drawing may be 7 at.% or more.

In the steel wire before wire drawing, the carbon content of cementite (Fe ₃ C) in pearlite is 25 at.%, and through the wire drawing process, the carbon content of cementite in pearlite is lower than 25 at.%. If the carbon content in cementite is less than 7at.%, delamination may occur, so the carbon content in cementite is limited to 7at.% or more.

The steel wire with improved wire drawing workability according to an embodiment of the present invention satisfies the following formula (1).

(1) [TS]+exp(ε)*10 < 1500

In Equation (1), [TS] is the tensile strength (MPa) of the wire rod before wire drawing, and ε means the wire-drawing strain.

The draw strain ε is expressed as 2ln(di/df). Here, di means the initial diameter of the steel wire before drawing, and df means the diameter of the steel wire after drawing.

According to the present invention, by controlling the tensile strength and wire strain rate of the wire rod so that the value of Equation (1) is less than 1,500, it is possible to slow down the cementite decomposition rate and suppress the occurrence of delamination. In general, when excessive drawing strain is applied in the wire drawing process, carbon present in cementite is discharged to ferrite, which sharply reduces the plastic deformation capacity of ferrite, causing cracks and increasing the possibility of delamination. If it is reduced to satisfy 1), the cementite decomposition rate can be slowed down even at a high wire-drawing strain, and thus delamination can be suppressed.

Specifically, a case in which the wire drawing strain rate is 3.0 or more when performing wire drawing is usually regarded as excessive deformation. A steel wire having high strength can be provided. The ultra-high strength steel wire with increased freshness of the present invention can be applied to products such as tire cord, saw wire, wire rope, piano wire, and bridge steel wire.

The tensile strength of the wire rod according to the present invention may be in the range of 700 to 1,000 MPa.

Next, a method for manufacturing a steel wire having improved wire drawing workability according to an embodiment of the present invention will be described.

The method for manufacturing a steel wire with improved wire drawing property according to an embodiment of the present invention, by weight, C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, remaining Fe and unavoidable impurities. Hot rolling the billet to obtain a wire rod; cooling the hot-rolled wire rod at a cooling rate of 3 to 20° C./s; and wire-drawing the cooled wire rod so as to satisfy Equation (1) below to obtain a steel wire.

(1) [TS]+exp(ε)*10 < 1500

In Equation (1), [TS] is the tensile strength (MPa) of the wire rod before wire drawing, and ε means the wire-drawing strain.

The steel wire with improved wire drawability according to the present invention is obtained by hot-rolling a billet containing the alloy composition described above to obtain a wire rod, then cooling the hot-rolled wire rod, and the cooled wire rod is wire-drawn to satisfy Equation (1). can

At this time, the billet may be heated to a temperature range of 900 to 1100 °C and then hot-rolled in a temperature range of 800 °C to 1200 °C.

At this time, the cooling of the wire rod may be performed at a cooling rate of 3 to 20 ℃ / s. If the cooling rate is less than 3 ℃ / s, there is a problem that fragmented and coarse pearlite is generated, and when the cooling rate is more than 20 ℃ / s, there is a problem that low-temperature structures such as martensite are generated. Therefore, in the present invention, it is preferable to control the cooling rate of the wire rod to 3 to 20 ℃ / s.

Then, the cooled wire rod can be wire-drawn so as to satisfy Equation (1) described above.

Hereinafter, it will be described in more detail through preferred embodiments of the present invention. However, the following examples are only examples for explaining the present invention in detail, and do not limit the scope of the present invention.

Example

Inventive Example 1 To 3 is a cooling rate of 17 ℃ / s, Inventive Examples 5, 6 and Comparative Example 1 is cooled at a cooling rate of 5 ℃ / s to obtain a wire rod, Inventive Examples 1 to 5 and Comparative Example 1 in Table 1 A steel wire was manufactured by wire drawing according to the conditions of cementite carbon content, wire strength, and wire strain rate shown in Table 1 below. Table 1 below shows the number of twists and the occurrence of delamination of the steel wire thus manufactured.

The number of twists in the steel wire was defined as the number of revolutions until the steel wire was broken during the torsion test applying lateral stress, and the occurrence of delamination was indicated by checking whether a helical breakage defect appeared at the broken wire.

division	Wire rod strength (MPa)	fresh strain rate	Cementite carbon content (at.%)	number of twists (episode)	delamination Occurrence	Equation (1) value
Invention Example 1	856	3.57	12	36	non-occurring	1211
Invention Example 2	844	3.79	11	34	non-occurring	1287
Invention Example 3	848	4.02	9	30	non-occurring	1405
Invention Example 4	948	3.57	10	35	non-occurring	1303
Invention Example 5	950	3.79	9	33	non-occurring	1393
Comparative Example 1	967	4.02	6	24	Occur	1524

As shown in Table 1, it was confirmed that the invention materials 1 to 5 prepared under the cementite carbon content and wire drawing conditions consistent with the present invention not only had an excellent number of twists of 30 times or more, but also did not cause delamination. . Specifically, in Comparative Example 1 in which the cementite carbon content in the pearlite after wire drawing was 6at.% and the value of Equation (1) exceeds 1,500, the number of twists was remarkably low to 24 times, and delamination occurred, but the cementite carbon content In the case of invention materials 1 to 5, which is 9 at.% or more and the formula (1) value is less than 1,500, the number of twists of 30 times or more was shown, and delamination did not occur. When the wire-drawing strain increases, the possibility of occurrence of delamination increases, but when comparing Inventive Example 3 and Comparative Example 1, Inventive Example 3 has the same wire-drawing strain as Comparative Example 1, but by reducing the tensile strength of the wire rod by 119 MPa, the number of twists is reduced by 30 By securing more than once, it was confirmed that delamination was suppressed.

In the above bar, exemplary embodiments of the present invention have been described, but the present invention is not limited thereto, and those of ordinary skill in the art may not depart from the concept and scope of the following claims. It will be appreciated that various modifications and variations are possible.

According to an embodiment of the present invention, it is possible to provide a steel wire having improved wire drawing properties and a method for manufacturing the same by controlling the strength of the wire rod and slowing the decomposition rate of cementite.

Claims (6)

1. By weight, C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, the remaining Fe and unavoidable impurities are included, and the cementite carbon content in the pearlite is 7 at.% or more, and the following formula (1 ) with improved drawing processability that satisfies the

   (1) TS+exp(ε)*10 < 1500

   (In Equation (1), [TS] is the tensile strength of the wire before drawing (MPa), and ε means the strain rate of wire drawing)
2. The method of claim 1,

   The tensile strength of the wire rod before the wire drawing is,

   A steel wire with improved drawability of 700 to 1,000 MPa.
3. The method of claim 1,

   The number of twists of the steel wire is,

   Steel wire with improved drawing processability of 27 or more.
4. The method of claim 1,

   A steel wire with improved wire-drawing properties that does not cause delamination at the wire-drawing strain of 4.02 or less.
5. Obtaining a wire rod by hot rolling a billet containing C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, remaining Fe and unavoidable impurities by weight %;

   cooling the hot-rolled wire rod at a cooling rate of 3 to 20° C./s; and

   A method of manufacturing a steel wire with improved wire-drawing properties, comprising: obtaining a steel wire by wire-drawing the cooled wire rod so as to satisfy the following formula (1).

   (1) [TS]+exp(ε)*10 < 1500

   (In Equation (1), [TS] is the tensile strength of the wire before drawing (MPa), and ε means the strain rate of wire drawing)
6. 6. The method of claim 5,

   A method of manufacturing a steel wire with improved wire drawing property in which delamination does not occur at a wire drawing strain of 4.02 or less during wire drawing.