KR890002614B1 - Process for manufacturing of high tension wire rod for pc steel wire - Google Patents

Abstract

The high tension wire rod is manufactured by (i) heating a billet comprising (in wt.%) 0.72-0.98% C, 0.12-0.35% Si, 0.77-0.82% Mn, not more than 0.023% P, not more than 0.01% S, 0.10-0.30% Cr, 0.005-0.02% Ni, not more than 0.024% Al, balance Fe and unavoidable impurities to 1,150-1,200 deg.C; (ii) hot rolling; (iii) rapid-cooling to 800±10 deg.C; (iv) coiling; (v) cooling to room temperature at a rate of 5- 10 deg.C/sec. without heat treatment.

Description

Manufacturing method of high tensile wire for PC steel wire

1 is a schematic plan view of a control cooling system used in the present invention.

2 is an electron micrograph of the present invention and comparative steel.

The present invention relates to a method for manufacturing high tensile wire for Pb patenting omitted PC having excellent strength and ductility.

In general, high-carbon large-size wire rods, which are used as PC steel wires and large diameter wire ropes, are heated and hot rolled, then wound and cooled at room temperature. The product produced through is poor in fresh processing due to the coarsening of the tissue, so it is hardened in a Pb bath with excellent heat retention, and forms fine pearlite tissue to form a material with high cold freshness and strength. Has been manufactured. However, although the strength and ductility produced by lead bath treatment increase, low productivity, pollution due to lead gas generated from lead bath, and increase of equipment cost for installation of lead bath have emerged as problems. in-line heat treatment methods have been developed.

This in-line heat treatment method delays the transformation time when the austenite is transformed into pearlite and ferrite to produce a material in which a fine pearlite structure with excellent freshness and ductility is formed, and the cooling rate is increased. Increasing or adding alloying elements moves the continuous cooling transformation curve to the left to induce rapid transformation, minimizing the perlite layer spacing and improving quality, but the quality level is lower than that produced by lead bath treatment. It is showing. Therefore, in the present invention to omit the lead bath treatment to obtain a fine pearlite structure excellent in drawing processability and ductility having the same quality as the product of the lead bath treatment, C: 0.72-0.98%, the upper limit was 0.35wt%. Manganese is required to guarantee the strength of the product by improving hardenability, and the lower limit is 0.77wt% because it is an element necessary to secure the strength and ductility by miniaturizing the pearlite layer spacing when transforming from austenite to pearlite and fumlite. As the amount of manganese increased, the upper limit was set to 0.82 wt% because the continuous cooling transformation curve was shifted to the right to easily generate bainite and martensite, which adversely affect freshness. Phosphorus is regulated to less than 0.023wt% because the addition amount decreases ductility and segregation has a bad effect on fresh workability. Therefore, it was regulated to 0.01wt% or less.

In addition, chromium is dissolved in austenite phase during hot rolling to suppress pearlite precipitation during transformation, thereby minimizing the lamella spacing of precipitated pearlite, increasing strength and ductility, and chromium carbide precipitated in pearlite ferrite to control grain boundaries, thereby improving mechanical properties. The lower limit is 0.10wt%, so when chromium is added more than 0.3%, Si: 0.12-0.35%, Mn: 0.77-0.82%, P: 0.023% or less, S: 0.01% or less, Cr: 0.10 -0.30%, Ni: 0.005-0.02%, Total Al: 0.024% or less and the rest of the billet containing iron and fines were heated and hot-rolled to a temperature of 1150 ℃ -1200 ℃, and then rolled Cooling and winding up to 800 ± 10 ℃ directly by using temperature, injecting air in forced air cooling zone, and cooling the temperature of 5-10 ℃ / sec. Let the strength and Type heat treatment is omitted to increase the sex PC relates to a method for producing a high-strength wire rod gangseonyong. Hereinafter, the present invention will be described in detail.

In the description of the chemical composition range, when carbon is more than 0.98 wt%, cementite cementite precipitates at the grain boundary and degrades freshness and ductility, so the upper limit is 0.98% and the appropriate strength of the material used for PC steel wire is determined. The lower limit was 0.72 wt% in order to ensure. Silicon has a lower limit of 0.12wt% in order to secure the strength of the product after material and fresh processing.Since the amount of silicon increases, the ductility of the final product decreases and there are many non-metallic inclusions, which adversely affects the workability. The upper limit was set to 0.30% because bainite and martensite were formed to deteriorate the freshness and ductility.

In addition, Al is an element added to give a deoxidation effect, and when total Al is added in an amount of 0.024% or more, it forms a large number of oxide-based inclusions, which is a cause of cracking and disconnection during hot rolling and new process. Should be limited to at least 0.024%.

The total Al means Al existing in an oxide state such as Souble Al and Al ₂ O ₃ present in the AlN state.

Ni is a component that gives strength improvement effect. If it is added below 0.005%, the strength imparting effect is insignificant. If it is added more than 0.02%, Ni has strength effect. The content is preferably 0.005% -0.02%.

Next, a method of manufacturing a material in the present invention will be described.

The billet is heated to a temperature of 1150-1200 ℃, rolled using a continuous rolling mill, and rapidly cooled to a temperature of 800 ± 10 ℃ within 0.6-1.0 seconds by water spraying to suppress the austenite grain growth of the rolled material. Do it. In addition, after winding the product rapidly cooled in the form of a coil (coil) to produce a product by cooling to a room temperature in the range of 5-10 ℃ / sec cooling rate on a continuously moving conveyor (conveyor).

In the present invention, the reason for the rapid cooling temperature having the most important meaning in the manufacturing process and the setting range of the cooling rate after agitation are as follows. It is cooled to a temperature above 810 ℃, and the upper limit temperature is increased to 810 ℃ because austenite grains are partially uneven in the cross section of the rolled material, and the grains are turned on, thereby producing badite and maltensite which deteriorate fresh processing and ductility. When cooling to a temperature of 790 ℃ or less, the austenite crystal grains are small, hardenability is reduced to obtain a strength suitable for the intended use, the cooling temperature of the lower limit was set to 790 ℃.

On the other hand, the reason for setting the cooling rate range is that when the cooling rate is 5 ° C / sec or less, the diffusion of carbon occurs to some extent when the transformation from austenite to pearlite causes the pearlite layer spacing to be widened, leading to poor strength and ductility, which is not suitable for use. The cooling rate of the lower limit was set at 5 ℃ / sec, and when the cooling rate to room temperature is more than 10 ℃ / sec, the continuous cooling curve is shifted to the left to form bainite and maltensite, which are low-temperature transformations that deteriorate fresh processing and ductility. Therefore, the upper limit cooling rate was set to 10 ° C / sec.

Next, the effects of the present invention will be described in detail with reference to Examples.

Example 1

The comparative steel and the inventive steel were prepared with a wire of 8 mm diameter in the composition shown in Table 1 below.

At this time, the finishing rolling speed was 37 m / sec, and wound at 800 ° C. in order to suppress the growth of the austenite grains due to the heat of rolling. Immediately afterwards, inline heat treatment was performed using the Stelmor facility shown in FIG. . At this time, the cooling rate of the steel was 8 ° C / sec.

TABLE 1

(Unit: wt%)

Table 2 shows the mechanical properties of the product produced by the in-line heat treatment and the results of the optical microscope and electron microscope structure analysis.

Where A, B, C and D have respective compositions shown in Table 1 and are inline heat treated, and A ', B,', C 'and D' have respective compositions of A, B, C and D and 550 The bath was treated for 3 minutes in a lead bath kept at ℃.

TABLE 2

As is apparent from Table 2, the steels B, C, and D of the present invention produced by in-line heat treatment have the same strength and sectional reduction ratio as those of the comparative steel (A'B'C'D ') produced by lead bath treatment. The increase in tensile strength and cross-sectional reduction rate is due to the effect of chromium addition, which delays the transformation time when transforming from austenite to pearlite and ferrite, thereby inhibiting pearlite precipitation. It is due to the miniaturization of the gap.

Table 3 shows the change in tensile strength, which is the measurement of the presence of disconnection and the degree of work hardening during the characterization process of the inventive steel. The experiment was performed using a continuous drawing machine equipped with tungsten carbide (WC) and the drawing speed was 40m / min. Cold drawn with 20.3% exemption. As can be seen from Table 3, the steel of the present invention was processed without disconnection up to 60% of the freshness, which is the manufacturing process of a typical product, and the tensile strength of the product was 10.9-16.5㎏ / 2 mm2 was increased and the work hardening rate was 5.0-6.3 kg / mm2, showing good results.

Table 1

Claims (1)

Weight%, C: 0.72-0.98%, Si: 0.12-0.35%, Mn: 0.77-0.82%, P: 0.023% or less, S: 0.01% or less, Cr: 0.10-0.30%, Ni: 0.005-0.02%, Total Al: 0.024% or less and the remainder of the billet containing iron and fines are heated and rolled to a temperature of 800 ± 10 ℃ after rolling and rolling to a normal temperature of 1150 ℃ -1200 ℃, and then the cooling rate is 5-10 ℃ / Method for producing a high-strength wire for heat treatment omitted PC steel wire, characterized in that cooling to room temperature in sec.

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