KR19990055107A - Step cooling method of high carbon wire to suppress martensite generation - Google Patents

Abstract

The present invention contains C: 0.4-0.9%, Si: 0.01-1.0%, Mn: 0.1-1.0%, P: 0.03% or less, S: 0.03% or less, Al: 0.01-1.0% by weight, and the balance Fe And high-carbon steels composed of impurities, which are inevitably contained, to be heated to at least 1000 ° C, followed by hot wire rolling. After rolling, cooling is performed at a speed of 15-25 ° C / sec at 900-550 ° C and 5 at 550-300 ° C. The cooling step of -10 ℃ / sec to improve the workability and minimize the martensite generation in the center of the high-carbon wire step cooling method for suppressing the martensite generation, martensite is an inferior wire structure It can prevent the thickening of cementite in pearlite tissue during wire rod cooling without occurrence, and it can solve the problem of disconnection when drawing by martensite and thick cementite in pearlite tissue and narrow the lamellar spacing in pearlite tissue. It is effective to secure a proper tensile strength for steel wire.

Description

Step cooling method of high carbon wire to suppress martensite generation

The present invention relates to a step cooling method of a high carbon wire rod for suppressing the generation of martensite, more specifically, by controlling the cooling rate according to the cooling temperature effectively prevents the generation of martensite regardless of the amount of segregation of the center of the wire rod for rolling It relates to a step cooling method that can be done.

In general, high carbon wire is a wire rod that is processed into a wire rope, hard wire, etc., the most important item in the quality of the wire is to ensure the structure of the wire uniformly.

1 is a process chart showing a hot rolling process of a high carbon wire, and FIG. 2 is a process chart showing a drawing and heat treatment process of a high carbon wire.

In the hot rolling process of high carbon wire rods, the wire rods are heated in a heating furnace at 1000-1250 ° C. before hot rolling to increase the temperature of the wire rods. Then, the wire rods are hot rolled and wound in a winding machine to cool the wire rods. Cooling then begins immediately while passing through the winder.

After hot rolling, the cooled high carbon wire goes through a drawing and heat treatment process. The drawing and drawing process of the wire is the most important process in the manufacturing process.

In the drawing and heat treatment process of high carbon wire, hot rolled and cooled wire is drawn and heat treated and fresh again.

Conventionally, step cooling is also used to cool the wire rod after hot rolling.

In the conventional step cooling method, eight coolers are installed at a lower portion of the wire rod passing through the winding machine to cool the wire rod passing through the upper stage by blowing cold air.

Conventionally, when cooling a wire in a coil state when manufacturing a high carbon wire, it is required to secure a fine pearlite structure in order to secure a maximum tensile strength of the product state after drawing, so that cold cooling is applied as much as possible.

In general, when the winding temperature, that is, the cooling start temperature is 800-900 ℃ to 900-550 ℃ to cool at a cooling rate of 18 ℃ / sec, and at 550-300 ℃ to cool at a cooling rate of 15 ℃ / sec.

As in the conventional method, when cold cooling is applied, the impurity element content of the central segregation zone is higher than that of the matrix, resulting in segregation and transformation delay, and residual austenite is transformed at low temperature so that martensite, which is an inferior tissue, is martensite. )

When martensite, which is a hard tissue, is generated in the cooling process, disconnection occurs frequently in the drawing process.

The present invention for solving the above problems is to provide a cooling method that can prevent the generation of martensite regardless of the amount of segregation of the center of the wire rod for wire uniformity by controlling the cooling conditions performed after hot rolling. It aims to do it.

1 is a process chart showing a hot rolling process of a high carbon wire rod,

2 is a process chart showing the drawing and heat treatment process of high carbon wire;

3 is a graph showing the constant temperature transformation curve for each cross-sectional position of the wire rod,

Figure 4a is a wire rod texture picture of the invention steel hot rolled,

Figure 4b is a photograph of the wire structure of the hot rolled comparative steel.

The present invention for achieving the above object by weight% C: 0.4-0.9%, Si: 0.01-1.0%, Mn: 0.1-1.0%, P: 0.03% or less, S: 0.03% or less, Al: 0.01- High carbon steel containing 1.0% and the balance of Fe and other unavoidable impurities are heated to 1000 ℃ or higher, followed by hot wire rolling, and after rolling, the speed is 15-25 ℃ / sec at 900-550 ℃. It is a step cooling method of high carbon wire rod for suppressing martensite generation, which is characterized by improving the workability and minimizing martensite generation by cooling at 550-300 ℃ and cooling at a rate of 5-10 ℃ / sec. .

Hereinafter, the present invention will be described in detail.

In the present invention, the coiling temperature, which is the starting point of cooling when the wire is cooled after hot rolling, is maintained in the range of 800-900 ° C., and the temperature of the pearlite transformation temperature range of 900-550 ° C. is 15-25 ° C./sec. Cooling and cooling rate below 10 ℃ / sec is applied to 550-300 ℃ after the pearlite transformation temperature zone for the following reasons.

When the cooling start temperature of the wire is set to a high temperature of more than 900 ℃, there is a fear of grain boundary cementite, and when starting cooling at a low temperature of less than 800 ℃, martensite structure occurs due to excessive transformation driving force have.

Therefore, it is preferable to maintain the cooling start temperature of the wire rod in the range of 800-900 ° C. as much as possible to prevent the generation of grain boundary cementite and to prevent the occurrence of martensite structure.

When cooling at a cooling rate faster than 25 ℃ / sec in the temperature range of 900 to 550 ℃ before the transformation in the cooling rate there is a problem that the martensite hard tissue, which cannot be drawn in the post-process to the base structure.

On the other hand, when the wire is cooled at a cooling rate of less than 5 ° C./sec in the temperature range of 550-300 ° C. after transformation, the thickness of cementite in the pearlite structure becomes excessively thick, which impairs the freshness and causes disconnection.

Therefore, cooling at a cooling rate of 15-25 ° C / sec at 900-550 ° C and a cooling rate of 5-10 ° C / sec at 550-300 ° C results in excessive martensite generation and excessive cementite thickness in the pearlite structure. It is preferable because the problem of thickening can be solved.

In addition, by quenching at the cooling rate of 15-25 ℃ / sec to the pearlite transformation temperature range of steel, the gap between lamellae in the pearlite structure is narrowed to secure the tensile strength suitable for hard steel wire, and 5-10 ℃ / after the pearlite transformation temperature region. The slow cooling of sec is performed to induce untransformed austenite in the center to perlite.

Figure 3 shows a comparison of the constant temperature transformation curve for each cross-sectional position of the wire rod when the cooling by the conventional cooling method and the cooling method of the present invention.

In the case of cooling by the conventional cooling method, the martensite structure is generated by cooling at almost the same cooling rate during the entire cooling process, and in particular, the martensite structure is generated by the strong cooling in the central segregation part.

On the other hand, in the cooling method of the present invention, the occurrence of martensite is suppressed by quenching in the early stage, and the martensite structure is suppressed in the central segregation portion by slow cooling in the step of cooling the central segregation portion, thereby generating a large amount of pearlite structure in the center portion. It was.

Therefore, it can be seen that the cooling method of the present invention is more effective in suppressing the generation of martensite than the conventional cooling method.

The present invention will be described in more detail with reference to the following Examples.

(Example)

Steel having a composition as shown in Table 1 was prepared as steel pieces having a cross-sectional dimension of 160 mm × 160 mm.

division C Si Mn P S Cr Ni Cu Al Comparative steel 0.71 0.23 0.78 0.020 0.018 0.10 0.04 0.10 0.025 Inventive Steel 1 0.71 0.25 0.80 0.018 0.014 0.08 0.07 0.11 0.015 Inventive Steel 2 0.70 0.23 0.77 0.019 0.016 0.05 0.06 0.13 0.010 Inventive Steel 3 0.72 0.27 0.79 0.021 0.015 0.12 0.06 0.11 0.005

After preparing the comparative steel and the invention steel 1 to the invention steel 3 having the composition shown in Table 1, the steel was heated under the conditions as shown in Table 2, and then subjected to wire rolling and cooled.

division Heating temperature (℃) Air cooling start temperature (℃) Cooling speed before transformation (℃ / sec) Cooling rate after transformation (℃ / sec) Comparative steel 1050 830 18 16 Inventive Steel 1 1050 830 21 5 Inventive Steel 2 1100 830 18 5 Inventive Steel 3 1150 830 18 4

After the wire was rolled under the conditions as shown in Table 2, the structure and mechanical properties of the comparative steel and the inventive steel were measured, and the results are shown in Table 3 below.

division Martensite generation area ratio (%) Tensile Strength (kg / mm ² ) Perlite generation area ratio (%) Comparative steel 5 114 10 Inventive Steel 1 0 117 5 Inventive Steel 2 0 115 8 Inventive Steel 3 0 114 10

As can be seen from the results of Table 3, martensite was not generated as 0% in the case of the inventive steels 1 to 3, while the ratio of martensite generation area, which is an inferior tissue, was 5%.

The tensile strength of the tensile strength In Comparative Steel Tensile strength 114kg / mm ² being the inventive steels 1 to 3 compared with the invention steel as 114-117kg / mm ^2, a tensile strength of higher than the invention, the same as Comparative Steel Tensile strength of steel or It was.

In the case of the pearlite generation area ratio, the comparative steel was 10%, whereas the invention steel 1 was 5% and the invention steel 2 was 8%, but the invention steel 3 was the same as 10%.

Figures 4a and 4b shows a picture of the wire structure of the hot rolled comparative steel and the inventive steel.

In the case of the inventive steel, the martensite, which is a hard tissue, does not occur, but the structure is uniform, but in the case of the comparative steel, martensite is generated in 5% of the area, and thus the tissue is not uniform.

The high carbon wire produced by cooling according to the method of the present invention does not generate martensite, which is an insulated wire structure, and prevents the thickness of cementite in the pearlite structure from being thickened by the wire martensite and pearlite. It was able to solve the problem of disconnection when drawing.

In addition, there is an effect of narrowing the lamellar spacing in the pearlite structure to secure an appropriate tensile strength for light steel wire.

Claims (1)

% By weight C: 0.4-0.9%, Si: 0.01-1.0%, Mn: 0.1-1.0%, P: 0.03% or less, S: 0.03% or less, Al: 0.01-1.0%, balance Fe and other unavoidable After heating the high carbon steel composed of impurity contained above 1000 ℃ and performing hot wire rolling, it is cooled after rolling and cooled at a speed of 15-25 ℃ / sec at 900-550 ℃ and 5- at 550-300 ℃. Step cooling method of high carbon wire rod for suppressing martensite generation, characterized by improving the fresh workability and minimizing martensite generation by cooling at a rate of 10 ℃ / sec.