A production method of ferritic stainless steel strip for high-grade mirror polishing

Abstract

The present invention relates to the field of metallurgy and stainless steel production, and is a method for producing high-grade mirror-polished ferritic stainless steel strips, comprising the following steps: Step 1: grinding the ingot; Step 2: adjusting the guide pressure on the coiling side; Step 3: hot-wire descaling with a scale breaker and pickling; Step 4: eight groups of spray pipes, each two spraying in opposite directions, repeatedly flushing in a forward and reverse manner, and adjusting the angle between the spray pipes and the strip surface to 60-70 degrees; Step 5: controlling the concentration of the bright line degreasing liquid at 6-8% and the temperature at 85-90°C. The present invention has the following beneficial effects: the high-grade mirror-polished ferritic stainless steel strips developed and produced by the above method have excellent surface quality. There are no defects such as bright spots and dotted lines after polishing, the surface roughness value Ra after polishing is less than 0.04 microns, and the surface gloss at 20° is greater than 800GU, with a product hit rate of over 85%.

Description

Technical Field

[0001] The invention relates to the fields of metallurgy and stainless steel production, and in particular to a method for producing a ferritic stainless steel strip for high-grade mirror polishing. Background Art

[0002] Ferritic stainless steel, with its excellent performance and elegant appearance, is widely used in railways, urban rail transit, automobiles, petrochemicals, electric power, shipping, containers, water conservancy, bridges, decoration, medical treatment, food, household appliances and kitchenware, aerospace, and other fields. Ferritic stainless steels, such as SUS430, which are suitable for high-end mirror polishing, are used in high-end applications such as automotive decorative strips.

[0003] Because it requires high steel purity, no bright spots, dotted lines and other defects after polishing, high gloss after polishing, and no surface defects such as shading and fogging, the current production hit rate is less than 50%.

[0004] According to the requirements of high-grade mirror-polished ferritic stainless steel on the surface quality of strip steel, the present invention improves the quality of each process of steelmaking, hot rolling and cold rolling, thereby producing strip steel that meets the requirements. Summary of the Invention

[0005] The purpose of the present invention is to solve the above problems and provide a method for producing a high-grade mirror-polished ferritic stainless steel strip.

[0006] The object of the present invention is achieved as follows: A method for producing a ferritic stainless steel strip for high-grade mirror polishing, comprising the following steps: Step 1: grinding the ingot: first use a grinding wheel to grind the edges, then grind the entire surface, and finally use a grinding wheel to finely grind the entire surface; Step 2: adjusting the coiling side guide pressure: the 1# coiling side guide pressure is adjusted to 70-75% of the preset pressure of 7-10KN, and the 2# and 3# coiling side guide pressures are adjusted to 60-70% of the preset pressure; rough descaling uses ultra-high pressure descaling, and the descaling pressure is 35-38MPA; Step 3: hot wire descaling uses a scale breaker + pickling, and the pickling process is adjusted to: H2SO4 concentration 320 ±20g / l, H2SO4 temperature 85±5℃, mixed acid HNO3 concentration 230±20g / l, HF concentration 15±3g / l, mixed acid temperature 45±5℃; scale breaker descaling process: strip thickness 2.5-3.0mm, elongation 2.5-3.0%, thickness 3.5-5.0mm, elongation 1.0-2.0%; step four: 8 groups of spray pipes, each two groups spray in opposite directions, one forward and one backward repeatedly, adjust the angle between the spray pipe and the strip surface to 60-70 degrees; step five: the concentration of the bright line degreasing liquid is controlled at 6-8%, and the temperature is controlled between 85-90℃.

[0007] In step 1, the total grinding rate of the first two passes is 1.5-3.0%, and the grinding rate of the last pass is controlled between 0.5-1.0%.

[0008] The beneficial effects of the present invention are as follows: the high-grade mirror-polished ferritic stainless steel strip developed and produced by the above method has excellent surface quality. It is free of bright spots, dotted lines, and other defects after polishing. The surface roughness Ra after polishing is less than 0.04 microns, and the surface glossiness at 20° is greater than 800 GU. The product hit rate reaches over 85%. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be further described below in conjunction with the accompanying drawings.

[0010] Figure 1 This is a diagram showing the positional relationship between the injection pipe and the strip steel of the present invention.

[0011] Figure 2 This is a diagram showing the position relationship between the original injection pipe and the strip steel.

[0012] Among them: 1. The angle between the nozzle and the strip is 60-70°, 2. The angle between the nozzle and the strip is 80°, and the direction of the arrow is the running direction of the strip. Implementation Method

[0013] 1. Ingot grinding: First, use a 20# grinding wheel for edge grinding, then full surface grinding, and finally a 30# grinding wheel for full surface finishing. The total grinding rate for the first two passes is greater than 2%, and the grinding rate for the final pass is controlled between 0.5-1.0%. This ensures an even grinding of the ingot surface and no grinding marks or color differences after rolling. Subsurface slag is also ground away.

[0014] 2. High-quality mirror-polished steel sheets are prone to bright spots and dotted lines. Analysis shows this is primarily due to small sparks and particles falling onto the strip surface during the hot rolling process, caused by scraping between the coiler guide and the strip edge. Therefore, the coiler guide pressure was adjusted: the pressure on the #1 coiler guide was adjusted to 70-75% of the preset pressure, and the pressure on the #2 and #3 coiler guides was adjusted to 60-70% of the preset pressure. Furthermore, ultra-high pressure descaling was used for rough descaling, with the descaling pressure increased from 25-28 MPa to 35-38 MPa.

[0015] 3. To eliminate the granular dark lines on the surface of high-grade mirror panels, the hot wire descaling process was improved from a scale breaker + shot blasting machine + pickling to a scale breaker + pickling process. The removal of the shot blasting process is mainly to prevent the steel shot from leaving uneven pits on the strip surface during the blasting process. The pits remain on the strip surface after rolling and form dark lines. To maintain the descaling effect, the pickling process was adjusted to: H2SO4 concentration 320±20g / l, H2SO4 temperature 85±5℃, mixed acid HNO3 concentration 230±20g / l, HF concentration 15±3g / l, and mixed acid temperature 45±5℃. The descaling in the second point is the descaling of hot-rolled ingots, and the descaling in the third point is the descaling of ingots after they are rolled into hot-rolled strips. The descaling is mainly done by two methods: descaling by a scale breaker and pickling. The descaling process of the scale breaker is for strips with a thickness of 2.5-3.0mm and an elongation of 2.5-3.0%, and a thickness of 3.5-5.0mm and an elongation of 1.0-2.0%.

[0016] 4. To prevent the strip surface from becoming foggy and glossy after annealing due to residual carbon and dirt marks caused by incomplete cleaning of the rolling oil, the spray angle of the bright line degreasing box's nozzles was improved to enhance surface cleaning effectiveness. Before the improvement, all nozzles aligned their spray direction with the strip's travel direction and were at an angle of 80° to the strip surface. The relative velocity between the spraying water and the steel plate was the difference between the water velocity and the plate's travel speed, resulting in a relatively weak impact on the steel plate and poor cleaning effectiveness. After the improvement, each of the eight groups of nozzles sprays in opposite directions. This repeated forward and reverse cleaning, like rubbing the strip with your hands, enhances surface cleaning and degreasing. Furthermore, the nozzle angle was adjusted to 60-70 degrees relative to the strip surface to increase horizontal spray force and facilitate degreasing removal.

[0017] 5. The concentration of bright line degreasing liquid is controlled at 6-8%, and the temperature is controlled between 85-90℃, which has the best cleaning effect on the strip surface.

[0018] Ferritic stainless steel, with its excellent performance and exquisite appearance, is widely used in railways, urban rail transit, automobiles, petrochemicals, electric power, ships, containers, water conservancy projects, bridges, decoration, medical treatment, food processing, household appliances and kitchenware, aerospace, and other fields. Ferritic stainless steels suitable for high-end mirror polishing, such as SUS430, are used in high-end applications such as logos and automotive trim. However, due to the high purity requirements of the steel, the absence of post-polishing defects such as bright spots and dotted lines, and the high gloss after polishing, without shading, fogging, and other surface defects, the current production success rate is less than 50%.

[0019] According to the surface quality requirements of ferritic stainless steel for high-grade mirror polishing, through quality improvements in steelmaking, hot rolling and cold rolling processes, its surface quality is excellent: there are no bright spots, dotted lines and other defects after polishing, the surface roughness value Ra after polishing is less than 0.04 microns, and the 20° surface gloss is greater than 800GU, and the product hit rate is over 85%. Example 1

[0020] Steel type: SUS430, raw material thickness: 3.0mm, finished product thickness: 0.5mm.

[0021] ⑴ Ingot grinding: Grind three times, the first time is side grinding, the second time is full grinding, grinding wheel 20#, the total grinding rate is 2.6%, the third time is full grinding, grinding wheel 30#, the grinding rate is 0.8%.

[0022] (2) The rough descaling pressure of hot rolling is 36Mpa, and the guide pressure on the coiling inlet side is: the guide pressure on the coiling side of 1# is 72% of the preset pressure, and the guide pressure on the coiling side of 2# and 3# is 65% of the preset pressure.

[0023] ⑶ The hot wire descaling process is a scale breaker + pickling, and the pickling process is: H2SO4 concentration 330g / l, H2SO4 temperature 86℃, mixed acid HNO3 concentration 220g / l, HF concentration 13g / l, and mixed acid temperature 45℃.

[0024] (4) Bright degreasing uses improved degreasing equipment, that is, the spray pipe is at an angle of 65 degrees to the strip surface, and the spray directions of every two groups of 8 groups of spray pipes are opposite.

[0025] ⑸The concentration of bright line degreasing liquid is 6.5%, and the temperature is controlled at 85℃.

[0026] Effect: Excellent surface quality: no bright spots, dotted lines and other defects after polishing. The surface roughness value after polishing is Ra=0.03 microns, and the surface glossiness at 20° is greater than 1100GU. The product hit rate reaches 88%. Example 2

[0027] Steel type: SUS430, raw material thickness: 2.0mm, finished product thickness: 0.4mm.

[0028] ⑴ Ingot grinding: Grind three times, the first time is side grinding, the second time is full grinding, grinding wheel 20#, the total grinding rate is 2.3%, the third time is full grinding, grinding wheel 30#, the grinding rate is 0.9%.

[0029] (2) The rough descaling pressure of hot rolling is 37 MPa, and the guide pressure on the coiling inlet side is: the guide pressure on the coiling side of 1# is 73% of the preset pressure, and the guide pressure on the coiling side of 2# and 3# is 68% of the preset pressure.

[0030] ⑶ The hot wire descaling process is a scale breaker + pickling, and the pickling process is: H2SO4 concentration 320g / l, H2SO4 temperature 85℃, mixed acid HNO3 concentration 240g / l, HF concentration 16g / l, and mixed acid temperature 47℃.

[0031] (4) Bright degreasing uses improved degreasing equipment, that is, the spray pipe is at an angle of 65 degrees to the strip surface, and the spray directions of every two groups of 8 groups of spray pipes are opposite.

[0032] ⑸The concentration of bright line degreasing liquid is 7%, and the temperature is controlled at 88℃.

[0033] Effect: Excellent surface quality: no bright spots, dotted lines and other defects after polishing. The surface roughness value after polishing is Ra=0.025 microns, and the surface glossiness at 20° is greater than 1050GU. The product hit rate reaches 86%.

[0034] Ferritic stainless steel, with its excellent performance and exquisite appearance, is widely used in railways, urban rail transit, automobiles, petrochemicals, electric power, ships, containers, water conservancy projects, bridges, decoration, medical treatment, food processing, household appliances and kitchenware, aerospace, and other fields. Ferritic stainless steels suitable for high-end mirror polishing, such as SUS430, are used in high-end applications such as logos and automotive trim. However, due to the high purity requirements of the steel, the absence of post-polishing defects such as bright spots and dotted lines, and the high gloss after polishing, without shading, fogging, and other surface defects, the current production success rate is less than 50%.

[0035] According to the surface quality requirements of ferritic stainless steel for high-grade mirror polishing, through quality improvements in steelmaking, hot rolling and cold rolling processes, its surface quality is excellent: there are no bright spots, dotted lines and other defects after polishing, the surface roughness value Ra after polishing is less than 0.04 microns, and the 20° surface gloss is greater than 800GU, and the product hit rate is over 85%.

[0036] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by any technician in this field within the scope of the present invention are included in the patent scope of the present invention.

Claims

1. A method for producing a high-grade mirror-polished ferritic stainless steel strip, characterized in that: The following steps are involved: Step 1: Grinding of the ingot: first use the grinding wheel to grind the edge, then grind the entire surface, and finally use the grinding wheel to fine-tune the entire surface; Step 2: Adjust the guide pressure on the coiling side: adjust the guide pressure on the coiling side of No. 1 to 70-75% of the preset pressure of 7-10KN, and adjust the guide pressure on the coiling sides of No. 2 and No. 3 to 60-70% of the preset pressure; use ultra-high pressure descaling for rough descaling, and the descaling pressure is 35-38MPA; Step 3: Hot wire descaling is performed by a scale breaker + pickling. The pickling process is adjusted to: H2SO4 concentration 320±20g / l, H2SO4 temperature 85±5℃, mixed acid HNO3 concentration 230±20g / l, HF concentration 15±3g / l, mixed acid temperature 45±5℃; the scale breaker descaling process is for strip thickness 2.5-3.0mm, elongation 2.5-3.0%, and thickness 3.5-5.0mm, elongation 1.0-2.0%; Step 4: 8 groups of spray pipes, with each two groups spraying in opposite directions, repeatedly flushing one forward and one backward, and adjust the angle between the spray pipe and the strip surface to 60-70 degrees; Step 5: The concentration of the bright line degreasing liquid is controlled at 6-8%, and the temperature is controlled between 85-90℃.

2. The method for producing a high-grade mirror-polished ferritic stainless steel strip according to claim 1, wherein: In step 1, the total grinding rate of the first two passes is 1.5-3.0%, and the grinding rate of the last pass is controlled between 0.5-1.0%.

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