KR20010048739A - Method for continuous casting bearing steel - Google Patents

Abstract

PURPOSE: A method for continuous casting a bearing steel is provided to reduce center segregation by synthetically interpreting influences on the center segregation by each key technologies in the continuous casting and controlling the conditions thereof. CONSTITUTION: The method comprises the steps of controlling a degree of overheating in a tundish (3) of molten steel comprising 0.95 to 1.02 wt.% of C, 0.25 to 0.45 wt.% of Mn, 0.15 to 0.25 wt.% of Si, 0.045 wt.% or less of P, 0.010 to 0.040 wt.% of sol-Al and 1.35 to 1.55 wt.% of Cr to 12 to 15 deg.C; casting the molten steel at a casting speed of 0.60 to 0.63 m/min by injecting the molten steel into a mold (7); solidifying the strip by cooling a strip transferred after passing through the mold to a water-liter steel-ton of 0.11 to 0.17 l/kg in a second cooling zone (8); and light reduction rolling the solidified strip to a thickness reduction of 6 to 7mm, wherein S-EMS (standard-electric magnetic stirring) is controlled at a frequency of 10 Hz and current density of 301 to 400 A, and F-EMS (final-electric magnetic stirring) is controlled at a frequency of 15 Hz and current density of 401 to 500 A in the second cooling zone (8).

Description

Continuous casting method of bearing steel {Method for continuous casting bearing steel}

The present invention relates to a method for manufacturing a bearing steel requiring high wear resistance and high fatigue characteristics in a high speed rotational motion, and more particularly, to a method for continuously casting a bearing steel made of a coarse material without the occurrence of central segregation.

Recently, due to the rapid development of the automotive industry and the mechanical industry, a bearing steel having excellent wear resistance and fatigue resistance is required in a high-speed rotational movement, and high carbon and high chromium steel have been developed and used. Coarse materials are used for such bearing steel materials, but are disadvantageous in terms of productivity. Therefore, although efforts have been made to use performance materials instead of crude materials, continuous casting techniques have not yet been established.

Table 1 below shows the chemical composition of the bearing steel.

Chemical composition (weight) C Si Mn P S Sol.Al Cr N 0.956-1.02 0.15-1.02 0.25-0.45 ≤0.04 ≤0.07 0.010-0.04 1.35-1.55 ≤60ppm

Bearing steel is a representative steel of silicon + aluminum composite deoxidation steel. It is produced as semi-finished products through converter → cob steel → rolled steel sheet → wire rod. This semi-finished product is processed into bearing steel by wire processing company.

The present inventors produced by applying the continuous continuous casting conditions (Table 2 below) to produce the cast steel by continuously casting the bearing steel, as a result of the center segregation in the playing room state as shown in Fig. 8 (a, b) Got.

Superheat Casting speed 2nd cooling pattern Electronic Stirring Device Under light pressure Strand final 20 ℃ 0.65 m / min 0.27ℓ / kg 10 Hz-300 A 15 Hz-400 A 4mm

Of course, it is possible to solve this problem by controlling the subsequent process conditions for the slab in which the central segregation is formed, but it is not a fundamental solution.

The present invention provides a continuous casting method of bearing steel which can reduce the central segregation by comprehensively analyzing the influence of each element technology on the central segregation in continuous casting and controlling these conditions.

1 is a schematic diagram of a continuous casting facility

2 to 7 are graphs showing the casting structure and the central segregation rate according to the casting conditions in the continuous casting process

8 is an internal quality picture of the cast steel

8 (a) (b) is a tissue photograph of a conventional material

Figure 8 (c) is a tissue photograph of the invention material

* Description of the symbols for the main parts of the drawings *

1 .... ladle 3 .... tundish

5 .... Immersion nozzle 7 .... Mold

8 .... 2nd cooling stand 9 ....

Bearing steel continuous casting method of the present invention for achieving the above object, by weight, C: 0.95 to 1.02, Mn: 0.25 to 0.45, Si: 0.15 to 0.25, P: 0.045 or less, sol-Al: 0.010 to 0.040, Managing the superheat degree in the tundish of 12 to 15 DEG C for molten steel including Cr: 1.35 to 1.55;

Injecting the molten steel into a mold and casting at a speed of 0.60 to 0.63 m / min;

Cooling and solidifying the cast steel being passed through the mold to a non-aqueous quantity of 0.11 to 0.17 l / kg in a secondary cooling stand;

It is configured to include; step of reducing the thickness of the thickness of the solidified slab to 6-7mm.

Hereinafter, the present invention will be described in detail.

In the present invention, the continuous casting of the bearing steel to produce a casting material has the technical significance, the target steel is a kind of bearing steel by weight of C: 0.95 to 1.02, Mn: 0.25 to 0.45, Si: 0.15 to 0.25, P: 0.045 or less, sol-Al: 0.010-0.040, Cr: 1.35-1.55, and the steel is comprised.

In the present invention, in the continuous casting equipment shown in the example shown in Figure 1, the casting material such as superheat degree, casting speed, non-quantity in the secondary cooling zone, light pressure load, etc. are strictly controlled to obtain the casting material without center segregation. To manufacture. In the present invention, such casting conditions are also focused on reducing the internal segregation in the cast steel to reduce the center segregation by increasing the equiaxed crystallinity, it is focused.

In the present invention, the molten steel of the ladle 1 is injected into the tundish 3 in the continuous casting facility of Figure 1 and introduced into the mold (7) through the immersion nozzle (5), in this case, the tundish ( The superheat degree of 3) shall be 12-15 degreeC. Since the superheat degree is determined by the following Equation 1, the present invention manages the temperature of the molten steel in the tundish so that the superheat degree is maintained in consideration of the theoretical solidification temperature.

[Relationship 1]

Superheat = temperature of molten steel in tundish-theoretical solidification temperature of molten steel

If the superheat is less than 12 ℃, the temperature of the molten steel can be lowered to block the immersion nozzle. If the temperature is greater than 15 ℃, the equiaxed crystal is too low to increase the center segregation. This degree of superheat is much lower than the normal level, according to the study of the present invention, if the superheat degree is large, the columnar apical tissue develops well, the equiaxed ligament becomes thin and the solute thickening steel flows over the center, and the center segregation is likely to be generated.

When the molten steel in the tundish is injected into the mold and casting, it is desirable to set the casting speed to 0.60 to 0.63 m / min, which is lower than the conventional (about 0.65 m / min) casting speed. When the casting speed is fast, the solute-enriched molten steel flows over the center due to convection, so it is easy to generate central segregation because it passes through the equipment quickly in an unsolidified state. Therefore, in the present invention, the casting speed is lowered to 0.60 to 0.63 m / min. If the casting speed is less than 0.60 m / min, the casting time is too long, and the end temperature of the casting is too low, so that the immersion nozzle may be blocked, and the casting speed is 0.63. This is because the central segregation rate increases when it exceeds m / min.

In addition, although the slab conveyed through a mold is cooled by the secondary cooling stand 8, the specific water quantity at this time shall be 0.11-0.17 L / kg. This is the minimum amount required for the cooling of the cast steel is 0.11ℓ / kg or more, and the larger the non-abundance, the lower the equiaxed crystal and the greater the amount of coagulation shrinkage, which is disadvantageous to the reduction of central segregation, so it is 0.17ℓ / kg or less.

The slag solidified while passing through the secondary cooling zone (9) is pressure-reduced, the segregation grain diameter decreases as the amount of reduction decreases, and the flow rate of the residual molten steel due to solidification shrinkage is reduced to suppress the center segregation. Therefore, in the present invention, the thickness reduction rate of the cast steel in the process under light pressure is increased to 6 to 7 mm compared to the normal level. This is because when the thickness reduction amount is 6mm or more, there is less internal cracking and the equiaxed crystallinity is higher, which is advantageous for reducing the center segregation, and when the thickness reduction rate exceeds 7mm, internal cracking occurs.

Meanwhile, S-EMS (Strand-Electric Magnetic Stiring), which is an electronic stirrer, is installed directly below the mold in the secondary cooling zone of the continuous casting facility, and is usually installed at a position about 3.18m away from the hot water surface of the mold. In addition, F-EMS (Final-Electric Magnetic Stiring) is installed under the S-EMS, and is usually installed about 7.18m away from the hot water surface of the mold. In the present invention, the frequency and current density of the S-EMS and F-EMS are controlled to 301 to 400 A at 10 Hz and 401 to 500 A at 15 Hz, respectively, in order to reduce the center segregation more completely.

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

EXAMPLE

The molten steel which consists of C: 0.95-1.02, Mn: 0.25-0.45, Si: 0.15-0.25, P: 0.045 or less, sol-Al: 0.010-0.040, Cr: 1.35-1.55 by weight is equipped with the apparatus of FIG. In the continuous casting at, the segregation rate of the central segregation was investigated by varying the superheat, casting speed, specific quantity, and pressure drop.

As can be seen from Figures 2 to 7, when the casting conditions of the present invention is satisfied, there is little occurrence of internal cracks and many equiaxed crystals, so it can be seen that the amount of central segregation is low.

On the other hand, as shown in Figure 8 (c), in the case of continuous casting according to the present invention it can be seen that the internal quality level of the cast steel is very good.

As described above, according to the present invention, since the bearing steel can be produced as a cast material without the center segregation, it is possible to replace all the coarse materials in the past, which has a useful effect of dramatically improving productivity.

Claims (2)

By weight, the molten steel which contains C: 0.95-1.02, Mn: 0.25-0.45, Si: 0.15-0.25, P: 0.045 or less, sol-Al: 0.010-0.040, Cr: 1.35-1.55 by tundish Managing the superheat degree at 12 to 15 ° C; Injecting the molten steel into a mold and casting at a speed of 0.60 to 0.63 m / min; Cooling and solidifying the cast steel being passed through the mold to a non-aqueous quantity of 0.11 to 0.17 l / kg in a secondary cooling stand; Continuously casting the solidified cast steel to reduce the thickness of the thickness to 6-7mm; continuous casting method of a bearing steel comprising a. The method of claim 1, wherein in the secondary cooling zone, S-EMS is 301 to 400A at a frequency of 10Hz, F-EMS is 401 to 500A at a frequency of 15Hz.