KR100256334B1 - High strength wire rod manufacturing method with excellent freshness - Google Patents

Abstract

PURPOSE: A method for manufacturing a high strength wire rod having superior drawability of rod is provided to manufacture a wire rod representing a high strength of 220 kg/mm2 or more and satisfactory ductility without intermediate heat treatment by properly controlling alloy constituents of steel and a cooling rate of the hot rolled wire rod. CONSTITUTION: The method comprises the processes of hot rolling a steel comprising 0.65 to 0.85 wt.% of C, 0.1 to 0.5 wt.% of Mn, 0.1 to 0.5 wt.% of Si, a balance of Fe and other inevitable impurities, and one or more elements selected from the group consisting of 0.1 to 1.0 wt.% of Ni, 0.1 to 1.0 wt.% of Cu and 0.2 wt.% or less of Cr; manufacturing the cooled steel into a wire rod by cooling the hot rolled steel in a cooling rate of 18 to 25 deg.C/sec; and wire drawing the wire rod to a drawing ratio of 2.5 or more.

Description

High strength wire rod manufacturing method with excellent freshness

1 is a graph showing the change in strength of freshness with addition of Si.

2 is a graph showing the mechanical properties of the deformation amount 2.55 of the invention and the comparative material satisfying the scope of the present invention.

3 is a graph showing the occurrence of delamination at 2.55 strain of the invention and the comparative material satisfying the scope of the present invention.

The present invention relates to a manufacturing method of the freshness used for the wire rope, bead wire and spring, more specifically a method for producing a wire rod excellent in ductility and tensile strength of 220kg / mm ² or more without intermediate heat treatment (patenting) It is about.

Intermediate heat treatment in the production of such fresh wire is performed to control the strength and microstructure of the material, or to control the deformed tissue formed after a certain amount of drawing to allow the wrinkling to the final diameter of the final product. It is almost an essential process in manufacturing.

Therefore, if the ductility of the material is excellent, it is possible to draw directly to the final product line in the state of the material by omitting the intermediate heat treatment as described above. As such, when the material is excellent in ductility and directly drawn to the final product line without intermediate heat treatment, the amount of freshness is increased, thereby improving the strength of the freshness.

However, due to the hardening of the material, the ductility of the material is significantly reduced, and there is a high possibility of occurrence of a salt defect such as delamination when it is fresh, and there is a big disadvantage that there is a possibility of disconnection in a later process. It is likely to occur as the strength or freshness of the material increases. In particular, the increase in fresh dose is much more significant than the increase in material strength.

Therefore, to increase the strength of the freshness it can be seen that it is more effective to improve the strength of the material than the method of increasing the fresh dose. However, the increase in strength of the material fundamentally lowers the ductility of the material itself, so it is impossible to draw directly from the material to the target final product line without intermediate heat treatment.

Therefore, the improvement of the strength of the material alone does not solve the problem of disconnection due to the delamination mentioned above, nor is it possible to omit the intermediate heat treatment.

The most effective method of securing the freshness currently known is to control the microstructure of the material with fine pearlite. Fine pearlite is possible by lowering the transformation temperature during the transformation from austenite to pearlite, and the method of lowering the transformation temperature is a cooling control method for rapid cooling after rolling and a method for lowering the pearlite transformation temperature of the material by the addition of alloying elements. There is this. However, the method of improving the cooling capacity of the cooling facility requires facility investment such as facility investment, so it is not a means of economic product production.

The alloying elements added for the purpose of improving the freshness by the addition of the alloying elements are Cr, Mn, V and the like. However, when the alloying elements are added in a large amount, the hardenability of the material is increased, and thus the low temperature structure of bainite or martensite is formed even at the existing cooling rate, thereby lowering the freshness. In relation to the amount of addition to be determined.

Based on the principle of the addition of the alloying element and the control of the cooling rate, the representative of the conventionally proposed method for producing a high strength wire rod having excellent ductility is Japanese Patent Laid-Open No. 63-4039, Hyeong 4-346619 , US Pat. No. 4,254,526 and US Pat. No. 5,156,692.

The Japanese Laid-Open Patent Publication No. 63-4039 discloses a steel drawing and painting process including C: 0.7-0.95, Si: 0.2-0.5, Mn: 0.4-0.7, V: 0.05-0.2 and Ni: 0.05-0.5%. Repeating this method is characterized by securing the ductility when manufacturing the ultrafine wire at about 0.3mm.

The Japanese Laid-Open Patent Publication No. 4-346619 is a weight%, after patenting a carbon steel containing C: 0.6-1.1%, Si: 0.1-2.0% and Mn: 0.1-2.0%, the fresh processing is 60% or more After carrying out, it is maintained in the range of 50 seconds to 3600 seconds in the range of 50-200 ℃ to recover the degradation of the ductility due to strain aging at the time of manufacturing a good steel wire, because it does not increase the ductility of the steel wire in the near future There is a problem in increasing freshness without heat treatment.

The Japanese Laid-Open Patent Publication No. 4-254526 is a weight%, after the hot rolling of the steel containing C: 0.9-1.3%, Si: 0.1-2.0%, and Cr: 0.1-1.3%, the cornerstone semethite is generated After quenching the temperature range, it is cooled at a cooling rate of 8 ° C./sec or less to the temperature at which the pearlite transformation ends, or it is kept at a constant temperature after quenching to the pearlite transformation temperature to suppress the formation of cementite cementite to increase the freshness of the ductility. This is how you do it. However, this method is not applicable because the cementite cementite is not formed in the amount of carbon below 0.9%, and in addition, it is difficult to control the cooling rate by dividing the cooling rate into two stages during cooling after rolling.

The U.S. Patent No. 5,156,692 is a method of increasing the freshness by controlling the pearlite block size to 5㎛ or less by applying a strain during the heat-painting heat treatment during the ductility of the steel containing 0.7-0.9% of carbon. In this method, it is possible to secure the freshness according to the miniaturization of pearlite blocks, but it is practically difficult to deform during heat treatment.

The above methods focus on the heat treatment conditions and the ductility in thin wires when the intermediate heat treatment is performed during the drawing process in order to manufacture the ultrafine wire products using various chemical composition systems. No method is proposed.

Thus, the present inventors, unlike the above methods, by omitting the intermediate heat treatment, the amount of freshness is increased so that not only the strength of the freshness is excellent, but also the ductility is excellent, the research and experiment, and based on the results suggest the present invention It is an object of the present invention to provide a method for manufacturing a wire rod exhibiting high strength and good ductility of 220 kg / mm ² or more without appropriately controlling the cooling rate of the alloy component system of the steel and the hot rolled wire rod.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention is a method of manufacturing a wire rod, in weight percent, C: 0.65-0.85%, Mn: 0.1-0.5%, Si: 0.1-0.5%, the rest: Fe and other unavoidable impurities as a base component, Manufactured from wire rods by hot rolling the steel formed by adding at least one selected from Ni: 0.1-1.0%, Cu: 0.1-1.0% and Cr: 0.2% and cooling it to a cooling rate range of 18-25 ° C / sec. After that, the present invention relates to a high-strength wire rod manufacturing method having excellent stretchability, which includes drawing a wire at a draw amount of 2.5 or more.

Hereinafter, the present invention will be described in more detail.

In order to achieve the above object, in the present invention, first, it is preferable to form the steel as described above, and the reason thereof is as follows.

C is the most effective element to increase the strength, but when a large amount is added, the cementite sementite precipitates and the ductility of the line decreases as the amount of carbon increases even if the cementite cementite is not precipitated. Therefore, in order to increase the freshness without heat treatment, it should be managed below 0.85%. In addition, when the alloying element is added, the vacancy transformation to pearlite occurs at a relatively low carbon content compared to general carbon steel, so even at low carbon content, it is possible to secure a vacancy structure having a cornerstone ferrite content of 1% or less, but when the carbon content is further reduced, Since the increase in freshness decreases and the strength decreases, the lower limit thereof is preferably limited to 0.65%.

Since Si is an element necessary for deoxidation of steel, if the content is too small, the deoxidation effect is not sufficient, so it should be added at least 0.1%. In addition, Si plays a role of increasing the strength of wire rod by solid solution strengthening of ferrite in pearlite. When the freshness is reduced to 2.5 or more, it is difficult to increase the strength of the wire due to the addition of Si (Fig. 1) .Si is also an element that does not meet the object of the present invention because it promotes decarburization of billets in a heating furnace during wire rod manufacture. It is preferable to limit the upper limit to 0.5% in consideration of the deoxidation effect.

Mn is not only deoxidation effect in the production of the steel, but also sulfur in the material to form a manganese emulsified (MnS) to prevent red brittleness by sulfur, 0.1% or more should be added. In addition, Mn is a very effective element for minimizing strength increase and pearlite interlayer spacing, but when added excessively, Mn is more likely to cause segregation and lowers the critical cooling rate at which martensite occurs. In addition, it is preferable to limit the upper limit of Mn to 0.5% since the fresh system is significantly lowered than other elements.

Cr lowers the pearlite transformation temperature, which is a very effective element for minimizing the interlayer spacing and increasing the strength of the pearlite. However, when a large amount is added, a low temperature structure such as martensite is likely to occur when the cooling rate is high. Since it is high, it is preferable to limit the upper limit to 0.2% in this invention by making into the upper limit the quantity which a low temperature structure does not generate | occur | produce at the cooling rate of 18-25 degreeC / sec.

Ni has little effect on the transformation temperature of pearlite, so it has little effect on the change of steel strength and pearlite interlayer spacing, but it is very effective in improving the ductility of steel. In order to achieve the ductile effect of the steel as described above, the addition amount should be 0.1% or more, and the addition of 1% or more cancels the effect of cost reduction by omission of heat treatment, so the upper limit is preferably limited to 1%.

Cu is added for the purpose of improving the mechanical peelability of the material scale, but the experimental results of the present inventors showed the effect of improving the ductility almost similar to Ni as well as the above-described addition purpose. Therefore, the lower limit is set to 0.1%, and if too much is added, there is a high possibility of surface grooves during continuous casting.

Therefore, the upper limit thereof is limited to 1%, and when the amount is 0.5% or more, it is possible to suppress the occurrence of defects during continuous casting by adding Ni and composite.

In general, when carbon steel is used, heat treatment is performed after drawing in the range of about ε = 2 or less, because the ductility of the material is insufficient, and delamination is more likely to occur in further deformation. However, in the case of the present invention, the material ductility is increased by the addition of alloying elements such as Ni and Cu, so that delamination does not occur even if? = 2.5 or more, so that intermediate heat treatment can be omitted.

In the present invention, after the steel is formed to have the alloying system as described above, it is preferable to manufacture the wire rod by manufacturing it as a billet, hot rolling and cooling to a cooling rate range of 18-25 ℃ / sec, the reason is as follows. .

In the present invention, after cooling the hot rolling of the steel composition as described above, it is preferable to control the cooling rate so that the structure is not formed bainite or martensite, but a pearlite having an interlayer spacing of 0.15 µm or less, the cooling rate is 18 ℃ If it is slower than / sec, there is a problem that the formed pearlite structure is coarse, and the interlayer spacing is increased to 0.15 µm or more, thereby degrading workability.

When the cooling rate is faster than 25 ° C / sec, the structure of the pearlite becomes fine and the interlayer spacing is maintained at 0.15 μm or less. However, some martensite is formed in the structure, which lowers the freshness. It is preferable to limit the range to 25 ° C / sec.

In the present invention, after manufacturing the wire rod by cooling in the cooling rate range as described above, it is drawn to the final wire without intermediate heat treatment, in this case, if the diameter of the wire rod is 5.5-7mm, the freshness ε = 2.5-3.5 Freshness is more preferable in the range.

As described above, if the wire is manufactured using the method of the present invention for adjusting the alloying component and controlling the cooling rate, high strength and high ductility can be produced without intermediate heat treatment, which is an indispensable step in manufacturing the conventional freshness.

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

Example 1

The steel ingot having the chemical composition as shown in Table 1 was prepared by billet by vacuum melting and then hot rolled to prepare a wire rod. The wire rod thus prepared was continuously cooled at a cooling rate of 5 ° C./sec to 250 ° C./sec, and then the presence of martensite was examined through histological examination. As a result, in the case of the comparative materials 13 and 14, the transformation to martensite is partially progressed at a cooling rate of 15 ° C./sec or more, and this steel grade is not barned in the future, and the remaining martensite transformation does not occur, namely, The wire was cut with a 25% cross-sectional reduction rate for the comparative material (1-3) and the inventive material (6-12), and specimens were taken for each pass to check the tensile strength, the cross-sectional reduction rate, and the presence of delamination. Is shown in FIG.

At this time, the amount of wire deformation is calculated by ε = 21n (Do / D), Do means wire diameter of the fresh material, and D means wire diameter after drawing.

FIG. 2 shows the cross sectional reduction rate and tensile strength indicating the ductility of the wire at 2.55 wire strain, and FIG. 3 shows the occurrence of such delamination.

As can be seen in Figures 2 and 3, in the case of the invention materials (6, 11, 12) satisfying the scope of the present invention, the tensile strength is higher than that of the carbon steel of 0.82% C, 0.7% C as the comparative material It can be seen that the excellent ductility and exhibits excellent properties of high strength and high ductility without the occurrence of delamination.

Example 2

Tensile strength and d while changing the deformation amount to 2.82, 3.13 and 3.41 for the steel grades (1, 2, 5, 8, 10, 11, 12) of Table 1 after the drawing process in the same process as in Example 1 The occurrence of lamination was observed and the results are shown in Table 2 below.

As can be seen in Table 2, the present invention (11,12) was able to produce a high-strength wire without the delamination up to 2.82, like the comparative material (5), the invention material (8,10) It can be seen that a high strength ductility of 250 kg / mm ² or more can be secured without delamination at a deformation amount of 3.41.

In addition, in Table 2, when the diameter of the material is 5.5mm, the deformation amount is 2.5mm, the wire diameter is 1.5mm, and the deformation amount is 3.4mm, so the wire diameter is 1.0mm. This means that it is possible to manufacture a good steel wire to secure and maintain a high strength.

As described above, the present invention, by appropriately controlling the alloy component system of the steel, the cooling rate after hot rolling and the amount of deformation during drawing, the wire material having a high strength characteristic of tensile strength of 220kg / mm ² or more and excellent ductility and the generation of delamination It can be produced effectively without heat treatment.

Claims (1)

In the manufacturing method of the wire rod, in terms of weight%, C: 0.65-0.85%, Mn: 0.1-0.5% or less, Si: 0.1-0.5% or less, the rest: Fe and other unavoidable impurities as base components, and Ni Steel produced by adding at least one selected from: 0.1-1.0%, Cu: 0.1-1.0% and Cr: 0.2% or less is hot rolled and cooled to a cooling rate of 18-25 ° C / sec. After, the high-strength wire manufacturing method excellent in the ductility, characterized in that the wire is drawn in a fresh dose of 2.5 or more.