KR100340498B1 - A Method for Manufracturing a High Carbon Hard Steel Wire Rode Having Superior Anti-rust on its Surface - Google Patents

Abstract

PURPOSE: A manufacture method of a high carbon hard steel wire rod having superior anti-rust on its surface is provided to prevent exfoliation of secondary scale, thus prevent high carbon hard steel wire rod from rust. CONSTITUTION: The method for manufacturing a high carbon hard steel wire rod having superior anti-rust on its surface includes the steps of continuous casting a billet comprising C 0.60 to 0.90 wt.%, Si 0.10 to 0.40 wt.%, Mn 0.30 to 0.80 wt.%, sol Al 0.005 to 0.060 wt.%, a balance of Fe and incidental impurities; reheating the billet followed by wire rod rolling; and starting quenching process of the hot rolled wire rod from the temperature range of 750 to 800°C at a cooling rate of 10 to 15°C/sec.

Description

A method for manufracturing a high carbon hard steel wire rod having superior anti-rust on its surface

The present invention relates to a method for manufacturing a high carbon steel wire rod, and more particularly, to suppress the scale scattering of the high carbon steel wire rod to reduce rust caused by reoxidation of the surface generated during wire transfer or loading. It relates to a manufacturing method.

In general, high carbon steel wire rods are reheated to 1000-1300 ° C by heating or rolling the billet manufactured by casting or slab rolling, and then rolled by a roll in a hot state, cooled by water spray, and then heated to 700-880 ° C by a coil winder. The wound coil is moved by a conveyor and is manufactured through a wire rod manufacturing process where it is quenched through a forced cooling stand that is operated by an air blower. The manufactured wire is made to secure the strength and texture required for each application. do.

Usually, the primary oxidation scale of the wire rod surface generated during reheating or wire rolling during wire rod manufacturing process is mostly removed during the wire rod rolling process, but the secondary scales that are coiled in the cooling zone where the air blower is operated are sensible heat in the cooling zone. It is scattered by the environmental pollution, as well as the disadvantages of wear of the rolling equipment and the workability of the workers is reduced. Above all, the site where the scale is dropped after the secondary scale is scattered may cause rusting of the wire surface by reoxidation during transport or loading of the wire. When rust occurs due to the reoxidation of the wire surface, mechanical scale peeling or mechanical peeling is performed to remove rusted scale at the final demand, but mechanical scale peeling is almost impossible to remove the scale. In addition, scale peeling by pickling treatment may also cause environmental pollution as well as an increase in manufacturing cost. In addition, the surface of the wire rod due to the rust generation is poor in the degree of roughness, there is a problem in the drawing processing of fine wire. Therefore, when manufacturing wire rods for thin wire, the rust generated on the wire rod surface should be easily removed from the final demand, and fundamentally, it is necessary to prevent rust generation on the wire rod surface.

Therefore, the present invention prevents the secondary scale from scattering on the surface of the wire rod by appropriately controlling the steel components and cooling conditions in the manufacture of high carbon hard wire rods with high secondary scale scattering, while maintaining surface mechanical properties similar to those of conventional wire rods. It is an object of the present invention to provide a method for manufacturing a high carbon hard steel wire which is extremely reduced.

1 is a graph showing the correlation between the thickness of the wire surface and the degree of occurrence thereof

2 is a schematic diagram for explaining a method for measuring the degree of scattering of a wire rod surface scale.

The present invention for achieving the above object in the manufacturing method of high carbon hard steel wire, in weight%, C: 0.60-0.90%, Si: 0.10-0.40%, Mn: 0.30-0.80%, Soluble Al: 0.005-0.060%, And continuously cast the steel pieces composed of the balance Fe and other unavoidable impurities, and then reheat the steel pieces to roll the wire rods, and then start cooling the rolled wire at a temperature range of 750-800 ° C. to quench them at a rate of 10-15 ° C. per second. The present invention relates to a method for producing a high carbon light steel wire rod is reduced surface rust generation.

Hereinafter, the present invention will be described in detail.

First, the subject steel grade in accordance with the present invention is a high carbon wire having a tensile strength in the range of about 90-120 Kg / mm 2. Preferred examples include steel grades including carbon: 0.60-0.90%, Si: 0.10-0.40%, Mn: 0.30-0.80%, and soluble Al: 0.005-0.006%.

When the carbon component in the steel is less than 0.6%, the Si component is less than 0.10%, or the Mn component is less than 0.3%, it is difficult to obtain the strength required by the present invention, and the carbon component is more than 0.9% or the Si component is more than 0.4% When the Mn component is more than 0.8%, an abnormal structure that is not suitable for the present invention occurs when applied at a cooling start temperature, which is a key component of the present invention, which will be described later. Thus, it is difficult to obtain suitable mechanical properties as a wire rod. In addition, the soluble Al component is an element that controls the size of the final structure according to the temperature change before and after the transformation of the steel, and when added below the lower limit, there is a fear of martensite transformation of residual austenite by increasing the austenite size. Non-metallic inclusions are present in the steel to impair freshness.

On the other hand, the high carbon steel having the above composition is continuously cast into steel pieces, and then reheated to form a wire rod, and the rolled wire is subjected to a cooling stand for air cooling. The present invention is characterized by preventing the surface rust of the final wire rod while remaining in the secondary scale formed in the cooling zone at an appropriate level. To this end, the inventors looked at the degree of scattering of the secondary scale. That is, the inventors of the present invention, the scattering of the secondary scale is related to the crack of the scale itself, wherein the distribution of the secondary scale cracks indicating the degree of scattering of the secondary scale has a crack occurrence distribution according to the secondary scale thickness. As a result of the difference, the second scale thickness distribution of high carbon steel was investigated by finding the second scale thickness distribution section with the lowest crack occurrence to derive the optimum cooling condition for the formation of the second scale with the proper thickness. First, as shown in FIG. 1, in the section where the secondary scale is thin, the thermal expansion coefficient due to scale generation is small, so that the occurrence of cracks is small in the scale, but as the thickness gradually increases, the thermal expansion coefficient according to the secondary scale thickness is increased. It can be seen that the secondary scale cracks are increased and the secondary scale is scattered by the sensible heat in the cooling zone. However, when the secondary scale becomes larger than the critical thickness, the toughness of the secondary scale itself due to thermal expansion becomes small, and the crack is reduced.

Therefore, it can be seen that the minimum thickness of the crack on the secondary scale is preferably kept below about 5㎛. Here, in comparison with the conventional wire rod, conventionally, the rolled wire rod was started to be cooled at a temperature range of about 830-850 ° C., where the thickness of the secondary scale generated in the conventional high carbon wire rod was about 8-12 μm. .

As a result, based on FIG. 1, in the case of the conventional high carbon wire rod, the secondary scale of the wire rod surface may be estimated to be about 75% or more, resulting in very severe scattering.

However, in the present invention, in order to maintain the thickness of the secondary scale of the rolled wire rod in the manufacture of high carbon steel to about 5 μm or less, the rolled wire rod is lowered to about 750-800 ° C. to start cooling to obtain the appropriate secondary scale thickness. In addition, the cooling rate was limited to 10-15 ° C./sec to greatly suppress the scattering of the secondary scale and to obtain a pearlite structure suitable for the wire rod. At this time, the reason for not using the method of reducing the crack of the secondary scale by inducing the thickness of the secondary scale in the present invention as shown in FIG. 1 is to eventually increase the cooling start temperature, which is a control factor of the secondary scale thickness. If the wire rod stays in the cementite transformation region for a long time due to the characteristics of the high carbon steel, grain boundary cementite, which is a fatal structure of the fresh wire, is generated, which is undesirable.

In the present invention, the cooling start temperature is 750 ~ 800 ℃, the reason is that the cooling start temperature should be less than 800 ℃ to obtain the target secondary thickness thickness, but less than 750 ℃ low temperature tissue is generated fresh it's difficult.

In addition, the reason why the cooling rate is limited to 10-15 ° C./sec is because cementite is generated when the cooling rate is out of the lower limit, and it is difficult to obtain a target strength, and martensite is generated when it is out of the upper limit.

When such cooling conditions are applied, the secondary scale scattering during the manufacture of high carbon wires is maintained at least 20%, so that rust generation on the surface of the final wire can be maintained at less than about 10%. There is an advantage that it is effective for the drawing processing of thin wire without the scale peeling process.

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

Example

The steel composition ranges in weight percent, including: C: 0.60-0.90%, Si: 0.10-0.40%, Mn: 0.30-0.80%, and soluble Al: 0.005-0.060% in the converter, and continuously By casting the casting speed to 1.5-2.0m / min through a casting machine to manufacture a rectangular steel piece with a cross section of 160mm, reheat it to about 1000-1300 ℃, and then wound up after rolling the wire to a diameter of 5.5-12.0mm to start cooling By varying the temperature and cooling rate as shown in Table 1, the scattering degree of the secondary scale was measured, and the thickness of the secondary scale and the degree of cracking were compared. At this time, the measurement method of the secondary scale, as shown in Fig. 2, immediately after manufacturing the wire rod 1 is cut by a predetermined length, the amount of the secondary scale (2) remaining in the unit surface area, and the scattered surface (3) The ratio was investigated. In addition, the mechanical characteristics and textures were similar to those of conventional materials, and the quality characteristics shown in Table 1 were obtained through the tensile test and the microscopic structure test, respectively, to see if they had the processing characteristics.

division Cooling start temperature (℃) Cooling rate (℃ / sec) Tensile Strength (kg / ㎡) Tissue Scale scattering amount per unit surface area (%) Rust generation rate per unit surface area (%) Conventional material A 850 15 95-115 Pearlite 75 35 Conventional material B 830 15 95-115 Pearlite 70 25 Invention 1 750 10 94-110 Pearlite 10 2 Invention 2 750 15 98-120 Pearlite 8 4 Invention 3 800 10 96-100 Pearlite 2 0 Conventional material C 810 17 97-105 Martensite 6 3

As shown in Table 1, as a result of the present invention for reducing the scattering of the secondary scale, in the case of the wire rod manufacturing result invention material (1-3), the demand quality characteristics similar to the conventional material (AC), It was possible to manufacture high-carbon hard wire rods with excellent surface quality characteristics by preventing large scale scattering and effectively plasticizing surface rust.

As described above, the present invention can significantly reduce the surface rust generation of the high carbon light steel wire with high secondary scale scattering by appropriately controlling the steel component and cooling conditions of the high carbon wire rod, thereby peeling off the surface scale of the wire rod. The drawing processability is improved even without treatment, and thus, it is very useful for the drawing processing of thin wires.

Claims (2)

In the manufacturing method of high carbon light steel wire, In weight percent, continuously cast steel pieces composed of C: 0.60-0.90%, Si: 0.10-0.40%, Mn: 0.30-0.80%, soluble Al: 0.005-0.060%, and balance Fe and other unavoidable impurities, After reheating the steel strip and rolling the wire, the rolled wire is started to cool in a temperature range of 750-800 ° C. and rapidly cooled at a speed of 10-15 ° C. to produce rust-reduced high carbon steel wire. . The method of claim 1, wherein the surface rust generation of the quenched wire is maintained at less than 10%.

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