A method for solving the defect of black stripe on the edge of cold-rolled stainless steel plate

Abstract

The present application belongs to the field of steel production, and the black stripe defect is a typical quality defect of a cold-rolled or hot-rolled ferritic stainless steel sheet with Cr < 14% after pickling, which is derived from the surface of a continuous casting billet and has a direct correspondence with the continuous casting strength and the performance of a protective slag. A method for solving the black stripe defect at the edge of a stainless steel cold-rolled sheet completely solves the black stripe defect of a low-chromium ferritic stainless steel sheet through a newly designed continuous casting cooling process and protective slag parameters.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of steel production, and particularly relates to a method for solving the black stripe defect of the edge of a cold-rolled stainless steel plate. BACKGROUND

[0002] The black stripe defect of the edge of a cold-rolled or hot-rolled stainless steel plate exists continuously or discontinuously within a range of 200 mm from the edge of the plate after pickling, and the defect generally occurs on a ferritic stainless steel with a Cr content <14.00%, and is difficult to eliminate by cold rolling and pickling, and has a great influence on the appearance quality of the product. Through analysis of the C content of the defect, it is found that the C in the continuous casting mold powder penetrates into the shell of the continuous casting billet, and cannot be removed during the rolling and pickling process, and is left on the surface of the plate, and forms an obvious color difference with other parts, and appears black under natural light.

[0003] The general solution is to reduce the C content of the mold powder as much as possible to reduce the carbonization of the mold powder to the shell of the billet, but this will bring the problems of rapid melting of the mold powder, and serious problems of billet slagging or severe mold slagging in the mold. Related documents report that the defect is caused by the liquid level fluctuation of the mold, but the improvement effect is not obvious through the implementation of measures such as controlling the liquid level fluctuation. And the defect disappears after the surface of the continuous casting billet is ground, so it is determined that the defect comes from the surface of the billet.

[0004] The present application solves the black stripe defect of the edge of the cold-rolled plate by developing a method for solving the black stripe defect of the edge of the cold-rolled stainless steel plate, and realizes the red rolling of the continuous casting billet without grinding under the condition that the continuous casting billet is not ground, and improves the production efficiency and cost while improving the product quality. SUMMARY

[0005] The present application is aimed at the above problems, and provides a method for solving the black stripe defect of the edge of a cold-rolled stainless steel plate.

[0006] The object of the present application is achieved in that a method for solving the black stripe defect of the edge of a cold-rolled stainless steel sheet comprises the following aspects: (1) design of a protective slag: basicity (CaO / SiO2): 0.7-0.9, melting point: 1100±50℃, C-Total: <2.5%, viscosity: 0.15-0.35 dPa.S; (2) qualified molten steel produced through a preceding refining process, with the end-point temperature of the refining process controlled to be 1560-1600℃, and the superheat of the molten steel in the tundish of continuous casting controlled to be 20-60℃; (3) the insertion depth of a submerged entry nozzle of continuous casting controlled to be 120-140mm; (4) the cooling water flow rate of the crystallizer copper plate set to be 2800-3000L / min per square meter of copper plate before the start of continuous casting; (5) the automatic liquid level control system of the crystallizer of continuous casting normally put into use, with the liquid level fluctuation controlled to be <±5mm; (6) the designed protective slag rapidly added to the crystallizer after the molten steel liquid level of the crystallizer submerges the side hole of the submerged entry nozzle after the start of continuous casting; (7) the protective slag stably and uniformly added after the casting speed of continuous casting is increased to the normal casting speed of 0.80-1.30m / min, to ensure that the slag surface is not red; (8) the thickness of the liquid slag of the protective slag controlled to be in the range of 15mm±2mm through the fine adjustment of the casting speed.

[0007] (3) the inclination angle of the side hole of the submerged entry nozzle is 10°-15° upward.

[0008] The present application has the beneficial effects that the present application improves the stability of continuous casting operation, completely solves the black stripe defect of the edge of a cold-rolled stainless steel sheet, and improves the width control precision of the continuous casting billet, to improve the satisfaction of downstream hot rolling, cold rolling and end users. DETAILED DESCRIPTION

[0009] The black stripe defect of the edge of a cold-rolled stainless steel sheet is a typical defect of the edge of a low-chromium-content stainless steel sheet, which seriously affects the quality image of the product. The main reason for the formation of the defect is that the not completely melted protective slag is rolled into the billet shell between the crystallizer copper plate and the not completely combusted C in the billet shell is not removed in pickling of the cold-rolled sheet, to form a defect with obvious color difference from the matrix, which appears black under natural light. The optimization and improvement effect of the C content of the protective slag and the continuous casting flow field is not obvious. The relevant literature reports that the defect is caused by high C content of the protective slag, but the test effect is not obvious by reducing the C content of the protective slag. The present application achieves good effect by improving the cooling of the crystallizer and the indexes of the protective slag. The present application effectively solves the defect by improving the heat transfer of the protective slag and the cooling intensity of the crystallizer.

[0010] The present application solves the problem of C penetration into the continuous casting shell in the protective slag by optimizing the melting rate, viscosity and other indicators of the protective slag. The process has the characteristics of good stability, strong process fault tolerance, and is not affected by the fluctuations of the mold level control, the steel overheating degree, the seasonal cooling water temperature, the operation and other fluctuations.

[0011] The method improves the thickness of the casting shell by enhancing the heat transfer between the continuous casting and the protective slag, and reduces the risk of the liquid surface fluctuation involving the incompletely melted protective slag by increasing the mold liquid slag thickness.

[0012] The key points of the method control are: enhancing the continuous casting and cooling strength to improve the thickness of the casting shell and the strength of the shell after leaving the mold to reduce the liquid surface fluctuation caused by the roller extrusion; and realizing the liquid slag thickness greater than the amplitude of the mold liquid surface fluctuation by increasing the melting rate of the protective slag.

[0013] The design ideas mainly include the following aspects: improving the cooling water flow rate of the continuous casting mold and the heat transfer performance of the protective slag to improve the continuous casting and cooling effect, and improve the strength of the shell leaving the mold; optimizing the melting rate of the protective slag to stabilize the thickness of the liquid protective slag in the mold, realize uniform coverage of the liquid slag, and make the C in the protective slag unable to penetrate into the continuous casting shell; and optimizing the viscosity of the liquid protective slag to ensure uniform penetration of the liquid slag into the gap between the shell and the copper plate of the mold, realize uniform cooling of the shell, and solve the cracks caused by the continuous casting and cooling.

[0014] The key control parameters of the implementation of the present application include the following points: 1. The design of the protective slag is as follows.

[0015]

[0016] 2. Continuous casting mold cooling water: the cooling water flow rate of each square meter of copper plate of the mold copper plate is 2800-3000 L / min in the range of 0.80-1.30 m / min.

[0017] The key control parameters of the implementation of the scheme include the following points: 1. The qualified molten steel produced by the front refining process, control the refining endpoint temperature, ensure the superheat of the continuous casting tundish molten steel in 20-60℃. 2. The immersion nozzle insertion depth is controlled in 120-140mm, and the inclination angle of the immersion nozzle side hole is 10°-15° upward. 3. Before continuous casting, the crystallizer cooling water is set to the flow rate of >2800L / min per square meter of copper plate (wide and narrow surface are set according to this flow rate). 4. The continuous casting crystallizer automatic liquid level control system is normally put into use, and the liquid level fluctuation is <±5mm. 5. After the continuous casting, when the crystallizer molten steel liquid level submerges the side hole of the immersion nozzle, the designed protective slag is quickly added to the crystallizer. 6. When the continuous casting speed is increased to the normal casting speed, the protective slag is stably and uniformly added, and the slag surface is ensured not to be red. 7. The thickness of the protective slag liquid slag is controlled in the range of 15mm±2mm through speed control.

[0018] Case one (410 stainless steel)

[0019] 1. The front refining process adjusts the temperature of the molten steel with good purity and composition meeting the composition requirements in table 2 to 1550-1670℃, and then transfers to the continuous casting process.

[0020] 2. The continuous casting sets the first cooling water flow rate to 2800-3000L / min per square meter of copper plate, and the second cooling water is set according to the specific water quantity of 1.3-1.6L / kg.

[0021] 3. The continuous casting opens the baked tundish (refractory material temperature >1000℃) to the casting position, and opens the argon for purging. After purging for >5min, the long nozzle is sleeved to the ladle lower nozzle through the continuous casting ladle manipulator (the sealing ring is added between the long nozzle bowl and the ladle lower nozzle), and then the ladle slide is opened through the hydraulic system to make the molten steel pour into the continuous casting tundish.

[0022] 4. When the molten steel liquid level in the tundish submerges the lower edge of the long nozzle, the tundish covering agent is started to be added, and the amount of the covering agent is ensured to uniformly cover the surface of the molten steel.

[0023] 5. When the amount of the molten steel in the tundish reaches 80% of the maximum capacity of the tundish, the temperature of the molten steel in the tundish is measured, and when the temperature meets the range of 1520-1540℃, the stopper of the tundish is opened to start pouring the molten steel in the tundish into the continuous casting crystallizer through the immersion nozzle (whole / part), and the protective slag in table 3 is immediately added when the liquid level height in the crystallizer submerges the side hole of the immersion nozzle, and the casting is started, until the speed reaches the normal casting speed of 1.1-1.3m / min.

[0024] 6. The casting blank is cut according to the planned required specification, the head and tail skins of continuous casting are normally ground, and the other casting blanks are all directly transferred to the next process for rolling.

[0025]

[0026] Case two (409L)

[0027] 1. The front refining process transfers the molten steel with good purity and composition meeting the requirements in Table 4 to the continuous casting process after adjusting the temperature to 1590-1600℃.

[0028] 2. The continuous casting sets the first cold water flow to 2800-3000 L / min per square meter of copper plate, and sets the second cold water according to a water ratio of 1.3-1.6 L / kg.

[0029] 3. The continuous casting opens the reheated tundish (refractory temperature >1000℃) to the casting position and opens the argon for purging, after purging for more than 5 minutes, the long nozzle is sleeved to the ladle lower nozzle through the continuous casting ladle manipulator (a sealing ring is added between the long nozzle bowl and the ladle lower nozzle), and then the ladle slide plate is opened through the hydraulic system to make the molten steel pour into the continuous casting tundish.

[0030] 4. When the molten steel liquid level in the tundish submerges the lower edge of the long nozzle, start adding tundish covering agent, and the amount of covering agent added ensures that the covering agent can uniformly cover the surface of the molten steel.

[0031] 5. When the amount of molten steel in the tundish reaches 80% of the maximum capacity of the tundish, measure the temperature of the molten steel in the tundish, and when the temperature meets the range of 1540-1570℃, open the stopper of the tundish to start pouring the molten steel in the tundish into the continuous casting mold through the submerged nozzle (whole / part), immediately add the protective slag in Table 5 when the liquid level in the mold submerges the side hole of the submerged nozzle, and start pouring until the casting speed reaches the normal pouring speed of 0.90-1.20 m / min.

[0032] 6. The casting blank is cut according to the planned required specification, the head and tail skins of continuous casting are normally ground, and the other casting blanks are all directly transferred to the next process for rolling.

[0033]

[0034] The above only describes specific embodiments of the present application, but the structural features of the scope of protection of the present application are not limited thereto, any changes or modifications made by those skilled in the art within the scope of the present application are covered by the patent scope of the present application.

Claims

1. A method for solving the edge black stripe defect of a cold-rolled stainless steel sheet, characterized by: The following aspects are included: (1) Design of the protective slag: basicity (CaO / SiO2): 0.7-0.9, melting point: 1100±50℃, C-Total: <2.5%, viscosity: 0.15-0.35 dPa.S; (2) The qualified molten steel produced through the preceding refining process is controlled to have a refining end point temperature of 1560-1600℃, and to ensure that the molten steel in the tundish has a superheat of 20-60℃; (3) The submerged entry nozzle of the continuous casting is controlled to have an insertion depth of 120-140mm; (4) The cooling water of the mold is set to have a flow rate of 2800-3000 L / min per square meter of copper plate before the start of continuous casting; (5) The automatic liquid level control system of the continuous casting mold is normally put into use, and the liquid level fluctuation is <±5mm; (6) The designed protective slag is added to the mold after the molten steel liquid level of the mold submerges the side hole of the submerged entry nozzle after the start of continuous casting; (7) The protective slag is stably and uniformly added after the casting speed is increased to the normal casting speed of 0.80-1.30 m / min, to ensure that the slag surface is not red; (8) The liquid slag thickness of the protective slag is controlled to be in the range of 15mm±2mm through fine adjustment of the casting speed; (3) The inclination angle of the side hole of the submerged entry nozzle is 10°-15° upward; The cooling effect of the continuous casting mold is improved, and the strength of the billet shell out of the mold is improved by increasing the flow rate of the cooling water of the continuous casting mold and the heat transfer performance of the protective slag; the thickness of the liquid protective slag in the mold is stabilized, the uniform coverage of the liquid slag is realized, and the C in the protective slag cannot penetrate into the billet shell by optimizing the melting rate of the protective slag; the uniform cooling of the billet shell is realized by optimizing the viscosity of the liquid protective slag to ensure that the liquid slag uniformly penetrates into the gap between the billet shell and the copper plate of the mold, and the cracks of the cast billet caused by the strong cooling of the continuous casting and cooling are solved.

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