CN102784800A - Control method for bearing steel center porosity defect - Google Patents

Abstract

The invention provides a control method for loose defects in the center of bearing steel. The continuous casting adopts weak cooling system, low superheat and low casting speed, and the tundish adopts low fire and automatic baking, controls the current intensity and frequency of electromagnetic stirring of the crystallizer, and heats Furnace loading temperature < 850°C, soaking section temperature at 1200-1220°C, total heating time ≥ 5h, large-reduction rolling is adopted, and the reduction in the first 2 passes is controlled at 70-80mm; each steel tank is used for stacking finished products Multiple cans are stacked in a row. The invention can realize the continuous casting of bearing steel, without taking slag blocking measures and controlling the oxygen content of tapping during the converter smelting process, and refining without special topping slag modification treatment, which can effectively prevent the problem of water blocking of bearing steel inclusions, greatly Improve the low-magnification quality level of bearing steel, improve the internal quality and performance of bearing steel, and improve the quality pass rate of bearing steel.

Description

A control method for loose defects in the center of bearing steel

technical field

The invention belongs to the field of metallurgical technology of iron and steel, and in particular relates to a control method for preventing center loose defects of bearing steel.

Background technique

The use of bearing steel is mostly under the condition of coexistence of various alternating loads such as tensile stress, shear force and friction force. Therefore, the rolled bearing steel must have high and uniform hardness, that is, the bearing steel used should have strict The uniformity of the microstructure, especially the segregation degree of the macroscopic and microscopic structures of carbon, sulfur, and phosphorus, and the uniformity of the size, spacing, and shape distribution of the precipitated carbide particles, thus putting forward higher requirements for the quality of the low-magnification structure of bearing steel.

Due to the longer distance from the liquidus line to the solid phase of high-carbon chromium bearing steel, low-magnification structural defects are more likely to occur. Especially when the continuous casting production process is used to produce bearing steel, because the continuous casting production process has greater cooling intensity than die casting, and the interface temperature gradient is large, it is easy to cause the enrichment of dendrites, resulting in periodic and intermittent cracks in the center of the slab. Shrinkage cavity and central segregation, accompanied by central porosity and fine pores, directly affect the internal quality and performance of bearing steel, reduce the quality pass rate of bearing steel, and cause unqualified accidents. In order to prevent the looseness of the center of the bearing steel, the current measures are to control the number of continuous casting, improve the slag blocking effect, control the oxygen content of the steel, and carry out a series of technological means such as refining and top slag modification, which not only increases the production process, but also increases the the difficulty of control.

Contents of the invention

The purpose of the present invention is to provide a method that can effectively prevent loose defects in the center of the bearing steel, improve the quality of the low-magnification structure of the bearing steel, and increase the qualified rate of the quality of the bearing steel.

For this reason, the solution that the present invention takes is:

A control method for loose defects in the center of bearing steel, characterized in that:

(1) Continuous casting process control:

The secondary cooling water of continuous casting adopts a weak cooling system, and the specific water volume is controlled at 15m ³ /ton of steel. The compressed air and water distribution in each area are as follows:

area Cooling water distribution ratio (%) Gas supply (m ³ /h) Mold foot roll 26 100 Support guide upper part 23.5 100 Lower part of the support guide 16 100 arc section 21.5 200 Arc two section 13 100

Low superheat and low casting speed are adopted, the superheat is controlled at 10-20°C, and the casting speed is controlled at 0.53-0.57m/min;

(2), tundish baking system:

The tundish is baked on a low fire for 3-5 hours and then automatically baked for 2-2.5 hours, with the highest baking temperature reaching 1450-1460°C;

(3) Electromagnetic stirring control:

The electromagnetic stirring adopts the crystallizer electromagnetic stirring, the current intensity is 500-550A, and the frequency is 1.5Hz;

(4), continuous rolling heating system control:

Use hot charging, close the burner in the preheating section before hot charging, the furnace charging temperature is <850°C, and the temperature in the soaking section is 1200-1220°C; the total heating time of the heating furnace is ≥10h, and the total time of the soaking section and the heating section is ≥ 5h;

(5), rolling system control:

A 950mm rolling mill is used, and the reduction in the first two passes is controlled at 70-80mm;

(6), stacking slow cooling:

The cooling bed is used for slow cooling at high temperature. The stacking height of the finished products should be higher than the upper edge of the steel trough. The hot steel slabs poured last time are stored around the steel trough. Multiple cans are stacked continuously in each steel trough until the steel trough is full, and then slowly cooled to room temperature.

The beneficial effects of the present invention are:

1. The present invention can realize continuous casting of bearing steel.

2. The present invention does not need to take slag blocking measures and control the oxygen content of tapping during the converter smelting process, and does not need special top slag modification treatment for secondary refining.

3. The present invention can effectively prevent the problem of bearing steel inclusions blocking the water outlet, and can ensure the stability of production.

4. The present invention can greatly improve the low-magnification quality level of bearing steel, improve the internal quality and service performance of bearing steel, improve the quality pass rate of bearing steel, and increase the low-magnification quality level of bearing steel from 1.5 to 0.5. The qualified rate of quality increased from 91.5% to 99%.

Detailed ways

Taking GCr15 bearing steel as an example below, the present invention will be further described. The size of the billet is 280×380mm, and the size of the rolled steel plate is 120×120mm.

Example 1:

1. Continuous casting process control:

The secondary cooling water of continuous casting adopts a weak cooling system, and the specific water volume is controlled at 15m ³ /ton of steel. The compressed air volume and water volume distribution in each area are as follows:

area Cooling water distribution ratio (%) Gas supply (m ³ /h) Mold foot roll 26 100 Support guide upper part 23.5 100 Lower part of the support guide 16 100 arc section 21.5 200 Arc two section 13 100

Low superheat and low casting speed are adopted, considering that low superheat and low casting speed are prone to flocculation accidents, which is not conducive to continuous casting of multiple furnaces, so the superheat is controlled at 12°C and the casting speed is controlled at 0.54m/min.

2. Tundish baking system:

The tundish is baked on a low fire for 5 hours and then automatically baked for 2 hours, with a maximum temperature of 1450°C.

3. Electromagnetic stirring control:

The electromagnetic stirring adopts the crystallizer electromagnetic stirring, the current intensity is 550A, and the frequency is 1.5Hz.

4. Continuous rolling heating system control:

In order to improve the internal structure of the bearing steel, hot charging is adopted. Before hot charging, the burners in the preheating section are turned off, the furnace charging temperature is 840°C, and the temperature in the soaking section is controlled at 1210°C; the total time of soaking section and heating section is 8h, and the heating The total time of furnace heating is 11h.

5. Rolling system control:

Using a 950mm rolling mill, in order to obtain an instantaneous larger compression ratio, the reduction in the first pass is 78mm, and the reduction in the second pass is 74mm.

6. Slow cooling of stacking:

The cooling bed is used to cool slowly under the rush temperature. The finished products are stacked higher than the upper edge of the steel trough, and the hot steel slabs poured last time are stored around the steel trough. Each steel trough is stacked continuously until the steel trough is full and slowly cooled to room temperature. .

Example 2:

1. Continuous casting process control:

The secondary cooling water of continuous casting adopts a weak cooling system, and the specific water volume is controlled at 15m ³ /ton of steel. The compressed air and water distribution in each area are as follows:

area Cooling water distribution ratio (%) Gas supply (m ³ /h) Mold foot roll 26 100 Support guide upper part 23.5 100 Lower part of the support guide 16 100 arc section 21.5 200 Arc two section 13 100

Low superheat and low casting speed are adopted, considering that low superheat and low casting speed are prone to flocculation accidents, which is not conducive to continuous casting of multiple furnaces, so the superheat is controlled at 18°C and the casting speed is controlled at 0.56m/min.

2. Tundish baking system:

The tundish is baked on a low fire for 3.5 hours and then automatically baked for 2.5 hours, with a maximum temperature of 1460°C.

3. Electromagnetic stirring control:

The electromagnetic stirring adopts the crystallizer electromagnetic stirring, the current intensity is 500A, and the frequency is 1.5Hz.

4. Continuous rolling heating system control:

In order to improve the internal structure of the bearing steel, hot charging is adopted. Before hot charging, the burners in the preheating section are closed, the furnace charging temperature is 830°C, and the temperature in the soaking section is controlled at 1220°C; the total time of soaking section and heating section is 7h, 1 #The total heating time of the heating furnace is 12h.

5. Rolling system control:

Using a 950mm rolling mill, in order to obtain an instantaneously larger compression ratio, the reduction in the first pass is 80mm, and the reduction in the second pass is 75mm.

6. Slow cooling of stacking:

The cooling bed is used to cool slowly under the rush temperature. The finished products are stacked higher than the upper edge of the steel trough, and the hot steel slabs poured last time are stored around the steel trough. Each steel trough is stacked continuously until the steel trough is full and slowly cooled to room temperature. .

Claims (1)

1. bearing steel center porosity defect Control method is characterized in that:

(1), continuous casting process control:

Cold system a little less than the continuous casting secondary cooling water adopts, the specific water is controlled at 15m ³/ ton steel, each regional compressed air, water yield quantity allotted are:

The zone Cooling water allocation proportion (%) Air demand (m ³/h） Crystallizer foot roll 26 100 A top is led in support 23.5 100 A bottom is led in support 16 100 One section of arc 21.5 200 Two sections of arcs 13 100

Adopt low overheat and low pulling rate, the degree of superheat is controlled at 10-20 ℃, and pulling rate is controlled at 0.53-0.57m/min;

(2), tundish baking system:

Tundish toasts 2-2.5h after adopting little fire baking 3-5h automatically, and the baking maximum temperature reaches 1450-1460 ℃;

(3), electromagnetic agitation control:

Electromagnetic agitation adopts crystallizer electromagnetic agitation, current strength 500-550A, frequency 1.5Hz;

(4), tandem rolling heating cycle control:

Adopt hot charging, before the hot charging preheating section burner is closed, charging temperature＜850 ℃, the soaking zone temperature is at 1200-1220 ℃; Heating furnace heating total time >=10h, wherein soaking zone and bringing-up section total time >=5h;

(5), rolling pattern control:

Adopt the 950mm milling train, preceding 2 reductions in pass are controlled at 70-80mm;

(6), stacking slow cooling:

Warm cold bed slow cooling is down robbed in employing, and finished product is stacked and highly wanted high lander upper edge, deposits one around the steel tank and waters inferior hot steel billet, and each steel tank multiple tank is stacked continuously, piles with until steel tank, and slow cooling is to room temperature.