Solution to forming cracking of high chromium ferritic stainless steel 820 plate

Abstract

The application discloses a solution to the forming cracking of high-chromium ferrite stainless steel 820 plate type, which comprises the following steps: adjusting the forming roll gap to 1.3-1.6 times of the thickness of the plate to compensate for the elastic recovery of the material; adopting water-based emulsion lubrication (water-oil ratio 95:5-90:10, containing 0.1%-0.5% thiophosphate) or pasting a 50-80-micron polymer protective film for protection; and controlling the forming line speed to be less than or equal to 30 m / min. Through the synergistic regulation of the forming parameters and the protection process, the application solves the cracking problem of the high-chromium ferrite stainless steel caused by work hardening, friction stress and strain concentration. The method can reduce the cracking rate from 30% to less than 1%, optimizes the surface roughness Ra value to 0.3-0.5 microns, and improves the production line comprehensive efficiency by 15%, and is suitable for the industrialized production of 820 corrugated plates for building roofs.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel forming technology, and in particular relates to a solution for cracking during the forming of high-chromium ferritic stainless steel 820 plates. Background Technology

[0002] High-chromium ferritic stainless steel (typical grades include, but are not limited to, SUS443 and SUS445J2) is widely used in harsh outdoor environments such as building roofs and curtain wall systems due to its excellent corrosion resistance, high-temperature oxidation resistance, and cost advantage (compared to austenitic stainless steel 304 and 316). The typical processing technology for its roof panels involves multi-pass continuous roll forming to the target sheet shape. The commonly used sheet shape is YX50-410-820 (referred to as the 820 sheet shape), which has high structural strength and excellent waterproofing and aesthetics.

[0003] However, high-chromium ferritic stainless steel has defects such as low room temperature plasticity and obvious work hardening tendency due to its high chromium content of 20~30wt%. During continuous roll forming, stress concentration is likely to occur at the point of maximum bending deformation of the sheet. Especially in the processing of sheet with a thickness of ≥0.5mm, the crack incidence rate can reach 30%, which seriously restricts the yield and engineering reliability.

[0004] Therefore, there is an urgent need to develop an efficient and low-cost composite process to solve the problem of cracking during the forming of high-chromium ferritic stainless steel 820 plates by synergistically controlling forming parameters and protective measures, while taking into account both production efficiency and surface quality. Summary of the Invention

[0005] To at least partially solve the technical problems existing in the prior art, the present invention provides a solution to the forming cracking of high-chromium ferritic stainless steel 820 plates.

[0006] The present invention provides a solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates, wherein the high-chromium ferritic stainless steel has a chromium content of 20-30 wt%, and the method includes the following steps: Forming roller gap control: Adjust the forming roller gap to 1.3 to 1.6 times the thickness of the sheet material to be processed; Lubrication protection or film protection: Applying lubricant to the sheet and forming rollers during the forming process for lubrication protection or applying a polymer protective film to the surface of the sheet for protection; Forming: Control the forming system to a forming line speed of ≤30m / min, and perform continuous roll forming of 820 plate shape.

[0007] Furthermore, in the above-described solution to the forming cracking of high-chromium ferritic stainless steel 820 plates, in the forming roller gap control step, for high-chromium ferritic stainless steel plates with a thickness of 0.5mm~1.0mm, the forming roller gap is adjusted to 1.4~1.6 times the plate thickness; for high-chromium ferritic stainless steel plates with a thickness >1.0mm, the forming roller gap is adjusted to 1.3~1.5 times the plate thickness.

[0008] Furthermore, in the above-described solution to the forming cracking of high-chromium ferritic stainless steel 820 plates, in the lubrication or protective film application step, the lubricant is a water-based emulsion, and the mass ratio of water to oil in the water-based emulsion is 95:5~90:10, wherein the oil can be at least one of mineral oil, synthetic ester or vegetable oil.

[0009] Furthermore, in the above-mentioned solution to the forming cracking of high-chromium ferritic stainless steel 820 plates, the water-based emulsion also includes an extreme pressure additive of 0.1% to 0.5% by mass, wherein the extreme pressure additive is a thiophosphate ester.

[0010] Furthermore, in the above-mentioned solution to the cracking of high-chromium ferritic stainless steel 820 plate during forming, the lubricant is applied by spraying at a pressure of 0.2~0.5MPa and a flow rate of 10~20L / min. In the forming unit, a spraying point is set every 4~6 forming rollers.

[0011] Furthermore, in the above-mentioned solution to the forming cracking of high-chromium ferritic stainless steel 820 plates, in the lubrication or protective film application step, the material of the polymer protective film is polyvinyl chloride, polyethylene or polypropylene, the thickness is 50~80μm, and the tensile strength of the polymer protective film is ≥20MPa and the elongation is ≥200%.

[0012] Furthermore, in the above-mentioned solution to the cracking problem in the forming of high-chromium ferritic stainless steel 820 plates, when applying the polymer protective film, the stress of the pressure roller used is 8~10kN, and the film application speed is synchronized with the forming line speed.

[0013] The solution to the cracking problem in the forming of high-chromium ferritic stainless steel 820 plates uses a high-chromium ferritic stainless steel 820 plate forming equipment system, including forming unit, gap adjustment mechanism, lubrication spraying device or film application device. The gap adjustment mechanism is used to adjust the gap between the forming rollers to 1.3 to 1.6 times the thickness of the sheet material to be processed; The lubrication spraying device includes a liquid storage tank, a pressure pump, and spray nozzles. The spray nozzles are spaced apart between the forming rollers of the forming unit, and the spraying pressure of the spray nozzles is adjustable in the range of 0.2~0.5MPa. The film application device includes an unwinding machine, a tension controller, and a pressure roller, wherein the stress of the pressure roller is adjustable in the range of 8~10kN.

[0014] Furthermore, the solution to the cracking problem during the forming of high-chromium ferritic stainless steel 820 sheets is applied in the industrial production of high-chromium ferritic stainless steel 820 corrugated sheets for building roofing.

[0015] The solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates of the present invention has the following advantages and beneficial effects: This invention significantly reduces the crack incidence rate to below 1%, significantly improves the yield, effectively improves surface quality, and optimizes the surface roughness Ra value of the surface in contact with the forming roller to 0.3-0.5μm; it also reduces downtime for mold repair due to cracks and effectively improves production efficiency. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for further understanding of the embodiments of the present invention and constitute a part of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram showing the locations where the 820 plate is prone to cracking. Figure 2 A schematic diagram showing the distribution of lubrication spraying or film application equipment; Figure 3 The figures show a comparison of the surface roughness of the roller mark contact surface, where a represents the surface roughness of the roller mark contact surface in the prior art, and b represents the surface roughness of the roller mark contact surface in the solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0018] The present invention provides a solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates, wherein the high-chromium ferritic stainless steel has a chromium content of 20-30 wt%, and the method includes the following steps: Forming roller gap control: Adjust the forming roller gap to 1.3 to 1.6 times the thickness of the sheet material to be processed to compensate for the elastic recovery caused by the work hardening of high chromium ferritic stainless steel, and reduce local deformation stress and crack initiation; For high-chromium ferritic stainless steel sheets with a thickness of 0.5mm to 1.0mm, the forming roller gap is adjusted to 1.4 to 1.6 times the sheet thickness; for high-chromium ferritic stainless steel sheets with a thickness greater than 1.0mm, the forming roller gap is adjusted to 1.3 to 1.5 times the sheet thickness. The gap adjustment is achieved manually, and a feeler gauge with an accuracy of ±0.01 mm is used for measurement to ensure that the consistency deviation of the roller gap in each pass is ≤0.02 mm. Lubrication protection or film protection: When applying a lubricant to the sheet and forming rollers for lubrication protection during the forming process, the lubricant is a water-based emulsion with a water-to-oil mass ratio of 95:5 to 90:10. The oil can be at least one of mineral oil, synthetic ester, or vegetable oil, and an extreme pressure additive of 0.1% to 0.5% by mass is added. The extreme pressure additive is a thiophosphate ester to enhance lubrication performance. The lubricant is applied by spraying at a pressure of 0.2-0.5 MPa and a flow rate of 10-20 L / min. In the forming unit, a spraying point is set every 4-6 forming rollers. When a polymer protective film is applied to the surface of the sheet during the molding process, the polymer protective film is made of polyvinyl chloride, polyethylene or polypropylene, with a thickness of 50~80μm, and the tensile strength of the polymer protective film is ≥20MPa and the elongation is ≥200%. When applying the polymer protective film, the stress of the pressure roller is 8~10kN, and the film application speed is synchronized with the molding line speed. Forming: Control the forming system's forming line speed to ≤30m / min, and perform continuous roll forming of 820 plate shape to extend the deformation coordination time of the plate, reduce dynamic stress impact, and avoid crack propagation caused by excessive strain rate.

[0019] Furthermore, the high-chromium ferritic stainless steel 820 plate forming equipment system used in the solution to the forming crack of high-chromium ferritic stainless steel 820 plate includes forming unit, gap adjustment mechanism, lubrication spraying device or film application device. The gap adjustment mechanism is used to adjust the gap between the forming rollers to 1.3 to 1.6 times the thickness of the sheet material to be processed; The lubrication spraying device includes a liquid storage tank, a pressure pump, and spray nozzles. The spray nozzles are spaced apart between the forming rollers of the forming unit, and the spraying pressure of the spray nozzles is adjustable in the range of 0.2~0.5MPa. The film application device includes an unwinding machine, a tension controller, and a pressure roller, wherein the stress of the pressure roller is adjustable in the range of 8~10kN.

[0020] Furthermore, the solution to the cracking problem during the forming of high-chromium ferritic stainless steel 820 sheets is applied in the industrial production of high-chromium ferritic stainless steel 820 corrugated sheets for building roofing.

[0021] Example 1 Using 0.6mm thick SUS443 stainless steel strip as the base material, its chemical composition by weight percentage is C: 0.011%, Cr: 20.65%, Cu: 0.33%, V: 0.15%, Ti: 0.23%. The following steps are used to process the 820 plate type: Forming roller gap control: Based on the plate thickness of 0.6mm, the gap between the 18 forming rollers is adjusted to 0.85~0.90mm (1.42-1.5 times the plate thickness). A feeler gauge with an accuracy of ±0.01mm is used to measure to ensure that the roller gap deviation of each pass is ≤0.02mm. Lubrication and protection: A water-based emulsion lubricant is prepared with a water to mineral oil mass ratio of 92:8, and 0.3wt% of thiophosphate extreme pressure additive is added. The lubricant temperature is controlled at 23℃. Lubrication spraying points are set every 4 rollers in the molding unit, with a spraying pressure of 0.4MPa and a flow rate of 15L / min. Molding: The molding system is controlled to have a molding line speed of 30m / min for continuous roll forming.

[0022] Processing six rolls using this process, each weighing 6-7 tons, revealed the following: the crack incidence rate of the sheet material was 0.9%, and the surface roughness Ra value of the surface in contact with the forming roller was 0.385μm. Example 2 Using 0.6mm thick SUS443 stainless steel strip as the base material, its chemical composition by weight percentage is C: 0.011%, Cr: 20.65%, Cu: 0.33%, V: 0.15%, Ti: 0.23%. The following steps are used to process the 820 plate type: Forming roller gap control: Based on the plate thickness of 0.6mm, the gap between the 18 forming rollers is adjusted to 0.85~0.90mm (1.42-1.5 times the plate thickness). A feeler gauge with an accuracy of ±0.01mm is used to measure to ensure that the roller gap deviation of each pass is ≤0.02mm. Film protection: A 60μm thick polyvinyl chloride protective film with a tensile strength of 22 MPa and an elongation of 210% is selected; a film application device is set at the feeding end of the forming unit, the pressure roller stress is adjusted to 9kN, and the film application speed is synchronized with the forming line speed. Molding: The molding system is controlled to have a molding line speed of 30m / min for continuous roll forming.

[0023] Processing 6 rolls using this process, each roll weighing 6-7 tons, the test results showed that the crack incidence rate of the sheet was 1.0%, and the surface roughness Ra value of the surface in contact with the forming roller was 0.376μm.

[0024] Comparative Example SUS443 stainless steel strips of the same specifications were processed using traditional methods. The forming roller gap was 1.1 times the plate thickness, with no lubrication or protective coating, and the forming line speed was 35 m / min. Testing revealed that the plate cracking rate was 30%, the surface roughness Ra value was 0.818 μm, and the machine repeatedly had to be shut down for mold repairs due to cracks, resulting in low production efficiency.

[0025] Table 1 shows a comparison of the results of the above embodiments and comparative examples: Table 1

[0026] As shown in Table 1, the process method of the present invention can significantly reduce the cracking rate of high-chromium ferritic stainless steel 820 plates, while optimizing the surface quality, and has significant industrial application value.

[0027] In summary, compared with the prior art, the solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates of the present invention has the following advantages and beneficial effects: This invention significantly reduces the crack incidence rate to below 1%, significantly improves the yield, effectively improves surface quality, and optimizes the surface roughness Ra value of the surface in contact with the forming roller to 0.3-0.5μm; it also reduces downtime for mold repair due to cracks and effectively improves production efficiency.

[0028] It should be noted that, unless otherwise expressly specified and limited, the term "connection" or its synonyms should be interpreted broadly in this document. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. Furthermore, expressions such as "first" and "second" are merely used to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Meanwhile, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. In addition, the terms "front," "rear," "left," "right," "upper," and "lower" in this document refer to the placement states shown in the accompanying drawings.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates, characterized in that, The high-chromium ferritic stainless steel has a chromium content of 20-30 wt%, and the method includes the following steps: Forming roller gap control: Adjust the forming roller gap to 1.3 to 1.6 times the thickness of the sheet material to be processed; Lubrication protection or film protection: Applying lubricant to the sheet and forming rollers during the forming process for lubrication protection or applying a polymer protective film to the surface of the sheet for protection; Forming: Control the forming system to a forming line speed of ≤30m / min, and perform continuous roll forming of 820 plate shape.

2. The solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates according to claim 1, characterized in that, In the forming roller gap control step, for high chromium ferritic stainless steel sheets with a thickness of 0.5mm to 1.0mm, the forming roller gap is adjusted to 1.4 to 1.6 times the sheet thickness; for high chromium ferritic stainless steel sheets with a thickness greater than 1.0mm, the forming roller gap is adjusted to 1.3 to 1.5 times the sheet thickness.

3. The solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates according to claim 1, characterized in that, In the lubrication or film protection step, the lubricant is a water-based emulsion, wherein the mass ratio of water to oil in the water-based emulsion is 95:5 to 90:10, wherein the oil can be at least one of mineral oil, synthetic ester or vegetable oil.

4. The solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates according to claim 3, characterized in that, The water-based emulsion also includes 0.1% to 0.5% by mass of an extreme pressure additive, which is a thiophosphate.

5. The solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates according to claim 3, characterized in that, The lubricant is applied by spraying at a pressure of 0.2-0.5 MPa and a flow rate of 10-20 L / min. In the forming unit, a spraying point is set every 4-6 forming rollers.

6. The solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates according to claim 1, characterized in that, In the lubrication or protective film application step, the polymer protective film is made of polyvinyl chloride, polyethylene or polypropylene, with a thickness of 50~80μm, and the tensile strength of the polymer protective film is ≥20MPa and the elongation is ≥200%.

7. The solution to the forming cracking problem of high-chromium ferritic stainless steel 820 plates according to claim 6, characterized in that, When applying the polymer protective film, the stress of the pressure roller is 8~10kN, and the film application speed is synchronized with the forming line speed.

8. A high-chromium ferritic stainless steel 820 plate forming equipment system for implementing the method of any one of claims 1-7, characterized in that, This includes molding units, gap adjustment mechanisms, lubrication spraying devices, or film application devices; The gap adjustment mechanism is used to adjust the gap between the forming rollers to 1.3 to 1.6 times the thickness of the sheet material to be processed; The lubrication spraying device includes a liquid storage tank, a pressure pump, and spray nozzles. The spray nozzles are spaced apart between the forming rollers of the forming unit, and the spraying pressure of the spray nozzles is adjustable in the range of 0.2~0.5MPa. The film application device includes an unwinding machine, a tension controller, and a pressure roller, wherein the stress of the pressure roller is adjustable in the range of 8~10kN.

9. The application of the method described in any one of claims 1-7 in the industrial production of high-chromium ferritic stainless steel 820 corrugated sheets for building roofs.

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