Machine-cleaning-free low-cost cold-rolled ultra-deep-drawn automobile and steel manufacturing method

Abstract

The invention discloses machine-cleaning-free low-cost cold-rolled ultra-deep-drawing automobile steel and a manufacturing method thereof. Ti-containing ultra-low carbon steel components are adopted, after steelmaking RH vacuum treatment is finished, the standing time is 25-35 min, continuous casting bale protective casting is conducted, and an IF steel covering agent is adopted; when the large ladle is replaced, the tundish molten steel amount is 35-45 t, a tundish retaining wall is used, the tundish is recarburized, and the increased nitrogen is smaller than or equal to 5 ppm; and a stopper mechanism is calibrated, a machine with the inclination angle of 6-10 degrees is selected to be used on an automobile plate, the argon flow of a stopper is controlled to be 4.5 + / -0.5 L / min, the argon flow of an upper nozzle is controlled to be 7 + / -1 L / min, ultra-low carbon casting powder is added to the liquid level of a crystallizer, and the fluctuation of the liquid level of the crystallizer is controlled to be within + / -3 mm. The steel has low cost and good mechanical property and surface appearance, and the requirements of automobile steel are met; and through process control of steelmaking, hot rolling and cold rolling, implementation in large-scale production is easy, and additional investment of equipment technical improvement cost is not needed.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a low-cost cold-rolled ultra-deep-drawing automobile steel without machine cleaning and a manufacturing method thereof. Background Art

[0002] With the rapid development of modern automobile technology, my country has become the world's largest automobile producer and consumer, and the demand for cold-rolled automobile plates at home and abroad is increasing. Under the background of overcapacity in steel production and continued low steel prices, the metallurgical industry has begun to enter a period of low profits, and the downstream automobile and home appliance industries are also highly competitive. Under the sluggish market conditions, product competitiveness is weak, and energy conservation and consumption reduction have become one of the important ways for many steel mills to reduce production costs and improve market competitiveness.

[0003] Mechanical cleaning is an effective process to improve surface quality. Inclusions and bubbles are easy to exist at 1-4mm on the surface of continuous casting billets. Through mechanical cleaning process, surface inclusions and bubbles of continuous casting billets can be removed. For example, high-requirement automobile outer panels can be removed through mechanical cleaning process. However, the process cost is relatively high. After mechanical cleaning process, the cost of one ton of steel increases by about 150 yuan.

[0004] Therefore, if the machine-free cleaning process can be adopted for production, and the inclusions and slag in the steelmaking process can be effectively controlled, the slag inclusion defective parts can be timely and accurately discovered and controlled during the downstream cold rolling, and repair and removal can be carried out to avoid the outflow of defects. At the same time, low-temperature annealing can be used in the hot-dip galvanizing process, which will greatly reduce the cost of cold-rolled ultra-deep drawing automotive steel. Summary of the invention

[0005] In view of the above technical problems to be solved, the present invention provides a low-cost cold-rolled ultra-deep-drawn automobile steel without machine cleaning and a manufacturing method. The steel plate has low cost and good mechanical properties and surface morphology, meeting the needs of automobile steel.

[0006] To achieve the above-mentioned purpose, the present invention provides a method for manufacturing ultra-deep-drawing automobile steel with low cost and without machine cleaning, which adopts ultra-low carbon steel containing Ti, including molten iron desulfurization, converter smelting, RH vacuum treatment, continuous casting, hot rolling, pickling, cold rolling and hot-dip galvanizing; after the RH vacuum treatment of steelmaking, the calming time is 25 to 35 minutes, the continuous casting ladle is protected and cast, and an IF steel covering agent is used; when changing the ladle, the amount of molten steel in the middle ladle is 35 to 45 tons, a middle ladle retaining wall is used, and the carbon and nitrogen addition in the middle ladle are ≤5ppm; the stopper rod mechanism is calibrated, and a machine with an inclination angle of 6 to 10 degrees is selected for use on automobile plates, the argon flow rate of the stopper rod is controlled at 4.5±0.5L / min, the argon flow rate of the upper water inlet is controlled at 7±1L / min, ultra-low carbon protective slag is added to the liquid level of the crystallizer, and the fluctuation of the liquid level of the crystallizer is controlled within ±3mm.

[0007] Furthermore, the pickling is performed at the tail of the pickling mill, and the position of the inclusion defect is confirmed by a meter inspection instrument, and then repaired and removed to prevent the inclusion and slag defects from flowing out.

[0008] Furthermore, in the hot-dip galvanizing process, the annealing temperature is 820-840° C., and the strip speed is controlled at 100-130 m / min.

[0009] Furthermore, the sedation time is 25 to 30 minutes.

[0010] Furthermore, when changing to a large ladle, the amount of molten steel in the middle ladle is 35-40t.

[0011] Furthermore, the stopper rod argon gas flow rate is controlled at 4.5-5.0 L / min.

[0012] Furthermore, the argon flow rate at the upper water inlet is controlled at 6-7 L / min.

[0013] Furthermore, the strip speed is controlled at 100-120 m / min.

[0014] Also provided is a machine-free, low-cost, cold-rolled, ultra-deep-drawn automobile steel, which is prepared by the above-mentioned manufacturing method.

[0015] Furthermore, the thickness of the steel is 0.50-1.0 mm.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: the automotive steel of the present invention has low cost and good mechanical properties and surface morphology, meeting the demand for automotive steel; the present invention is easy to implement in large-scale production through process control of steelmaking, hot rolling and cold rolling, and does not require additional investment in equipment technical transformation costs, and is suitable for the field of automotive outer panel steel products. DETAILED DESCRIPTION

[0017] The present invention is further described with reference to the following specific examples.

[0018] Example 1

[0019] Conventional ultra-low carbon steel containing Ti is used. The specific implementation process starts with desulfurization of molten iron. After converter smelting, the molten steel is vacuum treated. After the steelmaking vacuum is completed, the calming time is 35 minutes. The continuous casting ladle is protected and cast. IF steel covering agent is used. When changing the ladle, the amount of molten steel in the middle ladle is 40t. The middle ladle retaining wall is used. The carbon and nitrogen increase in the middle ladle are ≤5ppm. The stopper mechanism is calibrated. A machine with an inclination angle of 9 degrees is selected for use on automobile plates. The argon flow rate of the stopper is controlled at 4.4L / min, and the argon flow rate of the upper water inlet is controlled at 7.2L / min. Ultra-low carbon protective slag is added to the liquid level of the crystallizer. The fluctuation of the liquid level of the crystallizer is controlled within ±3mm, and the casting billet does not require machine cleaning. After conventional hot rolling and acid rolling processes, at the tail of the acid rolling unit, the position of the inclusion defect is confirmed by the surface inspection instrument, and then repaired and removed to avoid the outflow of inclusions and slag defects. In the hot-dip galvanizing process, a low-temperature annealing process is used, and the annealing temperature is 830°C. At the same time, the strip speed is matched according to the strip thickness, and the strip speed is controlled at 120m / min. The grain size is 7.5, the yield strength is 145MPa, the tensile strength is 280MPa, the elongation is 45%, the R average value is 2.2, and the N90 value is 0.23, which meets the requirements of high surface (surface sorting degree 1000) of automobile outer panels. Compared with the normal machine cleaning process, the cost per ton of steel is reduced by 170 yuan.

[0020] Example 2

[0021] Conventional ultra-low carbon steel containing Ti is used. The specific implementation process starts with the desulfurization of molten iron. After converter smelting, the molten steel is vacuum treated. After the steelmaking vacuum is completed, the calming time is 30 minutes. The continuous casting ladle is protected and cast. IF steel covering agent is used. When changing the ladle, the amount of molten steel in the middle ladle is 38t. The middle ladle retaining wall is used. The carbon and nitrogen increase in the middle ladle are ≤5ppm. The stopper mechanism is calibrated. The machine with an inclination angle of 8 degrees is selected for use on automobile plates. The argon flow rate of the stopper is controlled at 4.6L / min, and the argon flow rate of the upper water inlet is controlled at 6.2L / min. Ultra-low carbon protective slag is added to the liquid level of the crystallizer. The fluctuation of the liquid level of the crystallizer is controlled within ±3mm, and the casting billet does not need machine cleaning. After conventional hot rolling and acid rolling processes, at the tail of the acid rolling unit, the position of the inclusion defect is confirmed by the surface inspection instrument, and then repaired and removed to avoid the outflow of inclusions and slag defects. In the hot-dip galvanizing process, a low-temperature annealing process is used, and the annealing temperature is 820°C. At the same time, the strip speed is matched according to the strip thickness, and the strip speed is controlled at 100m / min. The grain size is 7.5, the yield strength is 155MPa, the tensile strength is 300MPa, the elongation is 46%, the R average value is 2.2, and the N90 value is 0.23, which meets the requirements of high surface (surface sorting degree 1000) of the automobile outer panel. Compared with the normal machine cleaning process, the cost per ton of steel is reduced by 170 yuan.

[0022] Example 3

[0023] Conventional ultra-low carbon steel containing Ti is used. The specific implementation process starts with desulfurization of molten iron. After converter smelting, the molten steel is vacuum treated. After the steelmaking vacuum is completed, the calming time is 28 minutes. The continuous casting ladle is protected and cast. IF steel covering agent is used. When changing the ladle, the amount of molten steel in the middle ladle is 39 tons. The middle ladle retaining wall is used. The carbon and nitrogen increase in the middle ladle are ≤5ppm. The stopper mechanism is calibrated. A machine with an inclination angle of 7 degrees is selected for use on automobile plates. The argon flow rate of the stopper is controlled at 4.7L / min, and the argon flow rate of the upper water inlet is controlled at 6.5L / min. Ultra-low carbon protective slag is added to the liquid level of the crystallizer. The fluctuation of the liquid level of the crystallizer is controlled within ±3mm, and the casting billet does not require machine cleaning. After conventional hot rolling and acid rolling processes, at the tail of the acid rolling unit, the position of the inclusion defect is confirmed by the surface inspection instrument, and then repaired and removed to avoid the outflow of inclusions and slag defects. In the hot-dip galvanizing process, a low-temperature annealing process is used, and the annealing temperature is 840°C. At the same time, the strip speed is matched according to the strip thickness, and the strip speed is controlled at 130m / min. The grain size is 7.5, the yield strength is 158MPa, the tensile strength is 302MPa, the elongation is 47%, the R average value is 2.3, and the N90 value is 0.22, which meets the requirements of high surface (surface sorting degree 1000) of the automobile outer panel. Compared with the normal machine cleaning process, the cost per ton of steel is reduced by 170 yuan.

[0024] Example 4

[0025] Conventional ultra-low carbon steel containing Ti is used. The specific implementation process starts with desulfurization of molten iron. After converter smelting, the molten steel is vacuum treated. After the steelmaking vacuum is completed, the calming time is 29 minutes. The continuous casting ladle is protected and cast. IF steel covering agent is used. When changing the ladle, the amount of molten steel in the middle ladle is 37t. The middle ladle retaining wall is used. The carbon and nitrogen increase in the middle ladle are ≤5ppm. The stopper mechanism is calibrated. A machine with an inclination angle of 6 degrees is selected for use on automobile plates. The argon flow rate of the stopper is controlled at 5.0L / min, and the argon flow rate of the upper water inlet is controlled at 6.6L / min. Ultra-low carbon protective slag is added to the liquid level of the crystallizer. The fluctuation of the liquid level of the crystallizer is controlled within ±3mm, and the casting billet does not require machine cleaning. After conventional hot rolling and acid rolling processes, at the tail of the acid rolling unit, the position of the inclusion defect is confirmed by the surface inspection instrument, and then repaired and removed to avoid the outflow of inclusions and slag defects. In the hot-dip galvanizing process, a low-temperature annealing process is used, and the annealing temperature is 825°C. At the same time, the strip speed is matched according to the strip thickness, and the strip speed is controlled at 120m / min. The grain size is 7.5, the yield strength is 160MPa, the tensile strength is 310MPa, the elongation is 44%, the R average value is 2.1, and the N90 value is 0.21, which meets the requirements of high surface (surface sorting degree 1000) of automobile outer panels. Compared with the normal machine cleaning process, the cost per ton of steel is reduced by 170 yuan.

[0026] Example 5

[0027] Conventional ultra-low carbon steel containing Ti is used. The specific implementation process starts with desulfurization of molten iron. After converter smelting, the molten steel is vacuum treated. After the steelmaking vacuum is completed, the calming time is 27 minutes. The continuous casting ladle is protected and cast. IF steel covering agent is used. When changing the ladle, the amount of molten steel in the middle ladle is 36 tons. The middle ladle retaining wall is used. The carbon and nitrogen increase in the middle ladle are ≤5ppm. The stopper mechanism is calibrated. A machine with an inclination angle of 5 degrees is selected for use on automobile plates. The argon flow rate of the stopper is controlled at 40L / min, and the argon flow rate of the upper water inlet is controlled at 7.3L / min. Ultra-low carbon protective slag is added to the liquid level of the crystallizer. The fluctuation of the liquid level of the crystallizer is controlled within ±3mm, and the casting billet does not require machine cleaning. After conventional hot rolling and acid rolling processes, at the tail of the acid rolling unit, the position of the inclusion defect is confirmed by the surface inspection instrument, and then repaired and removed to avoid the outflow of inclusions and slag defects. In the hot-dip galvanizing process, a low-temperature annealing process is used, and the annealing temperature is 835°C. At the same time, the strip speed is matched according to the strip thickness, and the strip speed is controlled at 115m / min. The grain size is 7.5, the yield strength is 148MPa, the tensile strength is 282MPa, the elongation is 45%, the R average value is 2.3, and the N90 value is 0.22, which meets the requirements of high surface (surface sorting degree 1000) of automobile outer panels. Compared with the normal machine cleaning process, the cost per ton of steel is reduced by 170 yuan.

[0028] Example 6

[0029] Conventional ultra-low carbon steel containing Ti is used. The specific implementation process starts with desulfurization of molten iron. After converter smelting, the molten steel is vacuum treated. After the steelmaking vacuum is completed, the calming time is 32 minutes. The continuous casting ladle is protected and cast. IF steel covering agent is used. When changing the ladle, the amount of molten steel in the middle ladle is 36 tons. The middle ladle retaining wall is used. The carbon and nitrogen increase in the middle ladle are ≤5ppm. The stopper mechanism is calibrated. A machine with an inclination angle of 4 degrees is selected for use on automobile plates. The argon flow rate of the stopper is controlled at 4.5L / min, and the argon flow rate of the upper water inlet is controlled at 8L / min. Ultra-low carbon protective slag is added to the liquid level of the crystallizer. The fluctuation of the liquid level of the crystallizer is controlled within ±3mm, and the casting billet does not require machine cleaning. After conventional hot rolling and acid rolling processes, at the tail of the acid rolling unit, the position of the inclusion defect is confirmed by the surface inspection instrument, and then repaired and removed to avoid the outflow of inclusions and slag defects. In the hot-dip galvanizing process, a low-temperature annealing process is used, and the annealing temperature is 836°C. At the same time, the strip speed is matched according to the strip thickness, and the strip speed is controlled at 118m / min. The grain size is 7.5, the yield strength is 148MPa, the tensile strength is 282MPa, the elongation is 46%, the R average value is 2.3, and the N90 value is 0.22, which meets the requirements of high surface (surface sorting degree 1000) automotive outer panels. Compared with the normal machine cleaning process, the cost per ton of steel is reduced by 170 yuan.

[0030] Comparative Example 1

[0031] Conventional Ti-containing ultra-low carbon steel composition is used. Normal steelmaking, casting machine cleaning treatment, hot-dip galvanizing process, annealing temperature is 850℃, and strip speed is controlled at 100m / min. The steel plate grain size is 7.5, yield strength is 143MPa, tensile strength is 280MPa, elongation is 46%, R average value is 2.3, N90 value is 0.22, and the steel plate surface meets the sorting degree requirement of 1000. The cost price per ton of steel is relatively high.

[0032] Comparative Example 2

[0033] Conventional Ti-containing ultra-low carbon steel composition is used. Normal steelmaking, casting machine cleaning treatment, hot-dip galvanizing process, annealing temperature is 830℃, and strip speed is controlled at 130m / min. The steel plate has a grain size of 7.5, a yield strength of 153MPa, a tensile strength of 300MPa, an elongation of 43%, an R average value of 2.3, an N90 value of 0.22, and the surface of the steel plate meets the requirement of sorting degree 1000. The cost per ton of steel is 20 yuan lower than that of comparative example 1, and the reduction is not large.

[0034] Comparative Example 3

[0035] Conventional Ti-containing ultra-low carbon steel composition is used. Normal steelmaking, ingot cleaning-free treatment, normal hot rolling and acid rolling processes, in the hot-dip galvanizing process, annealing temperature is 850℃, and the strip speed is controlled at 100m / min. The steel plate has a grain size of 7.5, a yield strength of 143MPa, a tensile strength of 280MPa, an elongation of 46%, an R average of 2.3, and an N90 value of 0.22. The performance meets the requirements, but the surface of the steel plate does not meet the requirements of a sorting degree of 1000.

[0036] It can be seen from the above examples that the hot-dip galvanized sheet obtained by the process of the present invention is low-cost, and the performance and surface quality can meet the user's requirements. The hot-dip galvanized sheet produced by the present invention has a thickness of 0.50-1.0 mm, and its mechanical properties are as follows: yield strength 140-165 MPa, tensile strength 270-330 MPa, elongation ≥ 42%, R average ≥ 1.8, N90 ≥ 0.21, and the steel sheet surface meets the requirement of sorting degree 1000. The cost per ton of steel is 170 yuan / ton lower than the conventional process.

Claims

1. A method for manufacturing ultra-deep-drawing automobile steel without machine cleaning and low cost, using ultra-low carbon steel containing Ti, including hot metal desulfurization, converter smelting, RH vacuum treatment, continuous casting, hot rolling, pickling, cold rolling and hot-dip galvanizing; characterized in that: After the steelmaking RH vacuum treatment is completed, the calming time is 25 to 35 minutes, and the continuous casting ladle is used for protective casting, and IF steel covering agent is used; when changing the ladle, the molten steel volume in the middle ladle is 35 to 45 tons, and the middle ladle retaining wall is used, and the carbon and nitrogen increase in the middle ladle is ≤5ppm; the stopper mechanism is calibrated, and a machine with an inclination angle of 6 to 10 degrees is selected for use on automotive panels, the argon flow rate of the stopper is controlled at 4.5±0.5L / min, and the argon flow rate of the upper water inlet is controlled at 7±1L / min, and ultra-low carbon protective slag is added to the liquid level of the crystallizer, and the crystallizer liquid level fluctuation is controlled within ±3mm.

2. The method for manufacturing low-cost cold-rolled ultra-deep-drawn automobile steel without machine cleaning according to claim 1, characterized in that: The pickling process is performed at the tail of the pickling mill, and the position of the inclusion defect is confirmed by a meter inspection instrument, and then the inclusion defect is repaired and removed.

3. The method for manufacturing low-cost cold-rolled ultra-deep-drawn automobile steel without machine cleaning according to claim 1, characterized in that: In the hot-dip galvanizing process, the annealing temperature is 820-840° C., and the strip speed is controlled at 100-130 m / min.

4. The method for manufacturing low-cost cold-rolled ultra-deep-drawn automobile steel without machine cleaning according to claim 1, characterized in that: The sedation time is 25 to 30 minutes.

5. The method for manufacturing low-cost cold-rolled ultra-deep-drawn automobile steel without machine cleaning according to claim 1, characterized in that: When changing to a large ladle, the amount of molten steel in the middle ladle is 35-40t.

6. The method for manufacturing low-cost cold-rolled ultra-deep-drawn automobile steel without machine cleaning according to claim 1, characterized in that: The stopper rod argon gas flow rate is controlled at 4.5-5.0 L / min.

7. The method for manufacturing low-cost cold-rolled ultra-deep-drawn automobile steel without machine cleaning according to claim 1, characterized in that: The argon gas flow rate at the water inlet is controlled at 6-7 L / min.

8. The method for manufacturing low-cost cold-rolled ultra-deep-drawn automobile steel without machine cleaning according to claim 1, characterized in that: The strip speed is controlled at 100-120 m / min.

9. A low-cost cold-rolled ultra-deep-drawn automobile steel without machine cleaning, characterized in that: The steel is steel produced by the manufacturing method according to claim 1.

10. The steel according to claim 9, characterized in that: The thickness of the steel is 0.50-1.0 mm.