KR19980052456A - Method for manufacturing cold-rolled wire rod with excellent spheroidizing heat treatment - Google Patents

Abstract

The present invention relates to a method for producing a cold-rolled wire rod having excellent spherical heat treatment properties of hot rolled 5.5 to 42 mm Ψ dimensions used as a material for cold-rolling or cutting products after drawing and heat treatment.

The manufacturing method of the cold-rolling wire rod excellent in the spheroidizing heat treatment property of this invention is C: 0.25-0.60%, Si: 0.10-0.35%, Mn: 0.30-2.0%, P: 0.030% or less, S: A steel consisting of 0.030% or less, Cr: 1.5% or less, Mo: 0.5% or less, Cu: 0.10% or less, Al: 0.005 to 0.070%, balance Fe, and other unavoidably contained impurities, is 1100 in a heating furnace before wire rolling. Heating to ～ 1300 ℃, maintaining the surface temperature of the material during the wire rolling to 950 ℃ or higher, coarsening the austenite particles to ASTM No.8 or lower, and selecting the wire-rolled steel at the cooling start temperature of 880-1000 ℃. During cooling, cooling is performed at a cooling rate of 10-25 ℃ / second in the temperature range of 630-1000 ℃ and at a rate of 5-15 ℃ / second in the temperature range of 630-500 ℃ to control the ferrite fraction of the cooled wire to 12% or less. After spheroidizing heat treatment, the spheroidization rate is over 88% and the spheroidized cementite particles are uniformly distributed. And as a base.

Description

Method for producing cold-rolled wire rod with excellent spheroidizing heat treatment property.

The present invention relates to a method for producing a cold rolled wire rod having excellent spheroidizing heat treatment property of hot rolled 5.5 to 42 mm Ψ dimension used as a material for making a cold press or a cut product after the drawing and heat treatment process.

The hot rolling manufacturing process of the wire rod is manufactured through a process of heating the wire rod and the wire rod rolling process, and then cooling the wire rod in the winding machine to cool the wire rod, as shown in FIG. 1. Various methods are known in the related art, and are generally manufactured by cold rolling a hot rolled steel including C: 0.025-0.050%, Si: 0.010-0.035%, and Mn: 0.30-2.0%.

However, in general, hot-rolled silicon-kilted steels (C: 0.025-0.050%, Si: 0.010-0.035%, Mn: 0.30-2.0%) produced in 5.5 to 42 mm Ψ dimensions have lowered toughness and spheroidized heat treatment. In the case of the conventional method of manufacturing the wire rod of silicon-kilted steel, such as poor properties, in order to ensure hardening heat treatment property when cooling the wire in the coil state after hot rolling, that is, it is required to secure the coarse structure as much as possible. In the case of slow cooling in the steel, ferrite nucleation and growth are facilitated in the process of cooling the wire coil after hot rolling, so that the ferrite fraction (occupancy ratio) increases, making it difficult to secure a uniform nodular structure during nodular heat treatment.

Accordingly, the present invention is suitable for hot rolling cold rolling with excellent spheroidizing heat treatment property by appropriately controlling the metal structure of the steel in the process of selecting an appropriate steel chemical composition in the steelmaking process of the steel and hot rolling and cooling the billet with wire. The purpose is to provide a method for manufacturing the wire rod.

1 is a view schematically showing a conventional wire rod hot rolling manufacturing process,

2 is a view showing a manufacturing process of a cold-rolled wire rod according to the present invention,

3 (a) and (b) are micrographs of the hot rolled wire structure, (a) is the invention steel, (b) is a photograph of the comparative steel,

4 (a) and (b) are photographs showing the microscopic structure of the wire rod after spheroidization heat treatment, (a) is the invention steel, and (b) is a photograph of the comparative steel.

In order to achieve the above object, in the present invention, in weight%, C: 0.25 to 0.60%, Si: 0.10 to 0.35%, Mn: 0.30 to 2.0%, P: 0.030% or less, S: 0.030% or less, Cr: 1.5 Steel consisting of% or less, Mo: 0.5% or less, Cu: 0.10% or less, Al: 0.005 to 0.070%, balance Fe and other unavoidable impurities are heated to 1100 to 1300 ° C. in a heating furnace before wire rod rolling, Maintain the material surface temperature above 950 ℃ during wire rod rolling to make the austenitic particles as coarse as possible under ASTM No.8, and select the cold rolled steel as the cooling start temperature 880-1000 ℃ to cool 630-1000 ℃ In the region, cooling is carried out at a cooling rate of 10-25 ° C./sec and cooling at a rate of 5-15 ° C./sec in a temperature range of 630-500 ° C. to control the ferrite fraction of the cooled wire to 12% or less. % Or more and spheroidized heat treatment, characterized in that the spheroidized cementite particles are uniformly distributed Provided is a method for producing a cold-rolling wire rod having excellent properties.

Hereinafter, the present invention will be described in detail with reference to the preferred embodiments.

Figure 2 is a schematic drawing of the cold-rolled wire rod, heat treatment process is shown, after the low temperature annealing after manufacturing the wire rod, followed by pickling and drawing process, spherical annealing and pickling again, skin pad (Skin Pass) It is made through the process of manufacturing through wheat.

First, in the present invention, the reason for limitations such as the component range of the added element, the heating temperature and rolling temperature of the steel, and the numerical limitation in the cooling conditions will be described below.

During the hot rolling process, by controlling the billet heating temperature to 1100 ~ 1300 ℃ in the furnace, the austenitic particles of the heated steel were coarsened to minimize the effect of particle refinement of the cooling structure during final wire cooling.

In addition, the temperature of the material to be rolled during the wire rod is maintained at 950 ℃ or more to minimize the recrystallization of the steel billet (Billet) and coarse austenite particles during the rolling to minimize the effect of refining the cooling structure particles of the wire rod during cooling of the wire rod.

The cooling start temperature (winding temperature) during wire rod cooling after rolling is maintained in the range of 880 ℃ ~ 1000 ℃, and the temperature range (630 ℃ ~ 1000 ℃) before perlite transformation during wire rod cooling is cooled at 15 ~ 25 ℃ / sec. In the temperature range (630 to 550 ° C.) of the pearlite, the transformation temperature zone of the steel was cooled at a cooling rate of 5 to 15 ° C./sec.

The wire cooling start temperature is maintained in the range of 880 to 1000 캜 to facilitate the growth of austenite particles at high temperatures. This serves to minimize the nucleation sites of ferrite during wire rod cooling by coarsening austenite particles.

In addition, in the temperature range where the ferrite is at or above the temperature range (630 to 1000 ° C.), that is, the temperature range where the ferrite grows, it is quenched at a cooling rate of 15 to 25 ° C./sec. A cooling rate of 5 to 15 ° C./sec is applied to secure a fine pearlite structure that is easily spheroidized. According to this method, it is possible to ultimately minimize the ferrite fraction and maximize the perlite fraction to enable a uniform spherical structure, that is, a uniform distribution of the spherical particles, thereby obtaining an excellent spheroidized heat treatment structure.

The reason for setting the cooling rate will be described below.

The reason for setting the cooling rate is that the bainite or martensite hard structure, which cannot be drawn in the post-process, occurs when cooling to more than 25 ℃ / sec in the temperature range before transformation, and when the wire is cooled to 5 ℃ / sec or less in the transformation temperature range, The thickness of cementite in the tissue becomes excessively thick, which leads to prolongation of spheroidization treatment time and coarsening of the spheroidizing particles, thereby deteriorating the spheroidization heat treatment property (tissue). This is because fresh processing becomes impossible.

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

(Example)

Inventive steel and comparative steel having a composition as shown in Table 1 below were made into 160 mm × 160 mm steel sections with cross-sectional dimensions, and then wires were rolled after heating the steel under the conditions shown in Table 2. Table 3 shows the structure and mechanical properties of the inventive steel and the comparative steel in the state that the wire rod is completed, Figure 3 (a), (b) and 4 (a), (b) shows the microscopic structure of the invention steel and the comparative steel It is a photograph. As can be seen from this, according to the invention steel, it can be seen that the ferrite fraction is low, and the spheroidization heat treatment property is improved, and the mechanical properties are also improved.

Table 1 (%)

TABLE 2

TABLE 3

Therefore, as described above, according to the method for producing a cold-rolled wire rod having excellent spheroidizing heat treatment property of the present invention, the toughness (cold-pressure composition) is improved, and a wire rod having improved spheroidizing heat treatment property is obtained, thereby improving the product quality. Useful effects can be obtained.

Claims (1)

By weight%, C: 0.25 to 0.60%, Si: 0.10 to 0.35%, Mn: 0.30 to 2.0%, P: 0.030% or less, S: 0.030% or less, Cr: 1.5% or less, Mo: 0.5% or less, Cu : 0.10% or less, Al: 0.005 to 0.070%, remainder Fe and other unavoidable impurity steels are heated to 1100 to 1300 ° C in a heating furnace before wire rolling, and the material surface temperature during wire rolling is 950 ° C or more. Austenitic particles are coarsened to ASTM No. 8 or less as much as possible, and the wire-rolled steel is selected at a cooling start temperature of 880-1000 ° C., and a cooling rate of 10-25 ° C./sec in the 630-1000 ° C. temperature range during cooling is maintained. The ferrite fraction of the cooled wire rod is controlled to 12% or less by cooling at a rate of 5-15 ℃ / sec in the temperature range of 630-500 ℃, and the spheroidization rate is 88% or more after spheroidization heat treatment, and the spheroidized cementite particles are uniformly A method for producing a cold-rolled wire rod having excellent spheroidization heat treatment properties, characterized in that it is distributed.