KR890002613B1 - Process for manufacturing of high tension wire rod - Google Patents

Abstract

The method for producing high tension wire rod involves (i) heating a billet comprising (in wt.%) 0.08-0.82% C, 0.02-0.23% Si, 0.77-0.82% Mn, not more than 0.023% P, not more than 0.01% S, 0.02-0.1% V, balance Fe and unavoidable impurities to 1,150-1,200 deg.C, (ii) retaining for 1-1.5 hours, (iii) high speed rolling at the rate of 35-40 m/sec, (iv) rapid cooling to 800±10 deg.C by water-injection, (v) coiling and cooling to room temperature at the rate of 10-15 deg.C.

Description

Manufacturing method of vanadium-added high tension wire of vacancy composition by controlled cooling

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

The present invention relates to the production of high strength, high ductility vanadium (V) -added high tensile strength wire rods excellent in cold workability. General steel wire composed of vacancy composition (0.80 / 0.82% carbon) has been used in the material of steel wire for PC, spring, and large diameter wire rope. Wire rods have been required for high strength and high ductility, as well as excellent cold workability, as well as the weight reduction of structures and the reduction of cement consumption for reinforcing concrete such as bridges, telegraph poles and concrete piles.

Therefore, wire rods intended for this purpose are usually quenched in Pb baths maintained at 450-500 ° C. prior to processing to form fine pearlite structures and finely dispersed hard cementite Cementite) and soft ferrite have been cold worked and combined in a fibrous form to obtain high strength.

However, in 1965, with the emergence of controlled cooling facilities, we have tried to reduce the cost of secondary processing and manufacture wire rods with the same mechanical property level by omitting the lead bath treatment before cold working, but the strength of the control cooling wire is always higher than that of the lead bath treatment wire. There have been eleven problems.

Therefore, in order to solve this problem of the controlled cooling wire rod, a small amount of vanadium is added to the general hard steel wire of vacancy composition to precipitate and disperse fine vanadium carbide (VC) in pearlitic ferrite during cooling to disperse and strengthen it. In the case of pearlite transformation, a method of manufacturing vanadium-added high-strength wire rod which is controlled by a cooling method for minimizing the pearlite interlamellar spacing by increasing the supercooling with the A ₁ transformation temperature. do.

The configuration of the present invention is as follows.

According to the present invention, carbon: 0.80-0.82%, silicon: 0.20-0.23%, manganese: 0.77-0.82%, phosphorus: 0.023% or less, sulfur: 0.01% or less, vanadium: 0.02-0.1%, and the rest is iron and After heating the billet containing impurity elements to 1150-1200 ℃ and rolling it at high speed, the rolled product with rolling heat generated at this time is sprayed with water in the range of 800 ± 10 ℃, rapidly cooled and wound up to room temperature. Cooling at a cooling rate of -15 ℃ / Sec.

Hereinafter, the present invention will be described in detail.

First, the component range of the present invention will be described.

In the description of the present invention, the composition ratio means weight%.

Carbon decreases cold workability by grain boundary precipitation of Proeutectoid Cementite but improves elasticity, so the upper limit is 0.82% and the lower limit is 0.80% to secure the appropriate strength of the steel.

Silicon needed to increase strength and lowered ductility, but the upper limit was 0.23% as a reinforcing means by substitutional employment, and the lower limit was 0.20% considering the degree of cold work hardening.

Since manganese not only improves the strength and ductility by making the pearlite layer spacing fine, but also improves the hardenability, the lower limit is 0.77% and the upper limit is easily generated because bainite and martensite, which worsen cold workability, are easily generated. Was 0.82% or less. Phosphorus is regulated to less than 0.023% because it lowers toughness and affects cold working. Sulfur was lowered to 0.01% because it lowered toughness and formed an emulsion, affecting cold workability. Vanadium increases the supercooling according to the control cooling pulse Lai tikhwe precipitated dispersion strengthening effect, and austenite (Austenite) and pearlite redistribution on the cementite by diffusion along the interface or the A ₁ transformation temperature rise in the light during the pearlite lamellar For this purpose, the lower limit was set to 0.02% and the upper limit was set to 0.1% to prevent the occurrence of low temperature transformation.

Next, a rolling and cooling method of the present invention will be described.

In general, when rolling at high temperature, recrystallization occurs depending on the conditions such as rolling temperature, speed, and deformation amount.

The present invention utilizes this phenomenon to refine the austenite grains and to increase the transformed nucleation number and speed during cooling so as to easily generate fine pearlite. The billet is heated to more than 1150 ℃ and maintained for 1 hour-1 hour and 30 minutes until the inside and outside temperature of the billet is uniform, and then high-speed rolling is carried out at this time, the rolling speed is 35m / sec-40m / sec is preferred and a rolling speed of 90 m / sec is possible.

However, when the rolling speed is 35m / sec or less, the production yield drops, the heat unit rises, the rolling motor load is severe due to the temperature drop, the cooling speed is difficult to control, and when the rolling speed is more than 90m / sec, the rolling motor load is severe and there is a risk of work. Cooling speed adjustment becomes difficult.

Thus, austenitic grain growth of the rolled material is suppressed and forced rapid cooling by water injection is carried out to 800 ± 10 ° C. within 1.0 second. At this time, if the coiling temperature is higher than 810 ° C, the carbon atom diffusion distance is increased due to the austenite grain growth, resulting in uneven development of the pearlite layer, which increases the strength of the material but deteriorates the ductility.

In addition, below 790 ° C, the carbon atom diffusion distance is shortened, but the martensitic bainite, which is a low temperature transformation, can be easily produced, which acts as a cause of disconnection during cold working.

On the other hand, by winding the cold-rolled rolled product in the form of a coil to continuously control the air flow on the conveyor (Conveyor) by cooling the cooling rate to room temperature at 10-15C / sec.

At this time, the cooling rate is a factor directly affecting the final quality, and the coarse pearlite or grain boundary ferrite is formed when the temperature is less than 10 ° C./sec. Thus, the lower limit cooling rate is 10 ° C./sec. In addition, the diffusion rate of carbon atoms is slower than 15 ° C./sec, resulting in insufficient development of the pearlite layer and the appearance of cementite particles dispersed in the substrate or martensite in the segregation of carbon. The upper limit cooling rate was set to 15 ° C / sec in order to deteriorate processing and ductility.

Hereinafter, embodiments of the present invention will be described.

Example 1

The billet having the composition shown in Table 1 was rolled and controlled cooled using an apparatus as shown in FIG. 1 to prepare a wire rod of 8.0 mm.

At this time, the heating condition of billet was 1200 ℃ × 1.5hr and final rolling speed was 37m / sec. Also, to suppress austenite grain growth by rolling heat, winding temperature was adjusted to 800 ℃ to adjust the water spray and then cooling rate. The air blowing amount of air was adjusted to 12 ° C./sec.

1 is a plan schematic view of a device suitable for carrying out the present invention, where 1 is a heating furnace, 2 is a horizontal ball rolling stand (25), 3 is a water cooling zone, 4 is a winder, and 5 is a conveyor.

TABLE 1

TABLE 2

As shown in Table 2, the present invention materials 1, 2 and 3 showed a higher tensile strength of 4.6-7.5 kg / mm 2 and a good sectional reduction rate of 46.5% or more as compared with the comparative material A. It can be seen that the synergistic factor is due to the decrease in the coarse pearlite spacing due to the addition of vanadium and the decrease in the coarse pearlite content. Particularly, the comparative strength B of 0.19% vanadium-added steel increased the tensile strength but the cross-sectional reduction rate was 38.6% This is due to the occurrence of martensite, a low temperature transformation state.

Example 2

In order to investigate the cold workability, four steps of continuous cold fresh and cold workability were performed with a drawing speed of 40 m / min and an average reduction of 20.3% for the specimens of Example 1 using a drawing machine fixed with Tungsten Scan Carbide (WC Dies). And the degree of work hardening was measured and shown in Tables 3 and 4, respectively.

TABLE 3

TABLE 4

* Tensile Strength Difference = Tensile Strength (5.08mmø) -Tensile Strength (8.0mmø)

As shown in Table 3 and Table 4, the present invention materials 1, 2, 3 showed cold workability of 60% or more, which is equivalent to that of the comparative material, and the tensile strength increased 8.7-11.9 kg / mm 2.

The work hardening at this time was 4.7 kg / mm 2 or less, showing good results. However, the low cold workability of 48% was observed for comparative material B, which contains 0.19% vanadium high tensile wire containing local martensite, causing stress due to stress concentration around light martensite and pearlite during cold working and commercialization. It was impossible.

As described above, according to the present invention, by adding a small amount of vanadium and cooling by a controlled cooling method, the fine vanadium carbide is precipitated and dispersed and dispersed in pearlitic ferrite during cooling, and the supercooling with A ₁ transformation temperature during pearlite transformation. It is possible to manufacture high tensile wire with excellent saddle strength and cold workability by increasing the layer spacing by increasing.

Claims (1)

By weight, carbon: 0.08-0.82%, silicon: 0.02-0.23%, manganese: 0.77-0.82%, phosphorus: 0.023% or less, sulfur: 0.01% or less, vanadium: 0.02-0.1% and the rest are iron and impurities It is heated to 1150-1200 ℃ and maintained for 1 hour-1 hour 30 minutes, and then it is rapidly rolled at a rolling speed of 35m / sec-40m / sec and rapidly cooled by water spraying to a range of 800 ± 10 ℃. The method for producing vanadium-added high tensile strength wire of vacancy document by controlled cooling, characterized in that the cooling is carried out at a cooling rate of 10-15 ° C / sec to room temperature.

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