A method for producing a high-ni steel sheet with reduced surface scratches

Abstract

This invention discloses a method for producing high-Ni steel sheets with reduced surface scratches. The Ni content of the steel sheet is 3.3%–10.0% by weight. The production process is as follows: converter + refining + vacuum treatment + continuous casting + billet heating + rolling + quenching + tempering + finishing + warehousing and shipping. The steel sheet is rolled at a high final rolling temperature of 870–900℃. After rolling, the steel sheet is ACC water-cooled with a water-to-water ratio controlled at 1.4–1.5, resulting in a slightly convex shape with a convexity of 2–3 mm / m. Before heat treatment, the four corners of the steel sheet are cut into rounded arcs and polished smooth with a radius of 10–30 mm. After tempering, the steel sheet is water-cooled with a water volume of 3000–5000 m³. 3 / h, water-cooled to room temperature. The high-Ni steel plate produced by the above process has good surface quality, with a scratch rate of no more than 10% and unplanned scratches accounting for no more than 1%.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a method for producing high-Ni steel thin plates that reduces surface scratches. Background Technology

[0002] High-nickel alloy steel plates (such as 5Ni steel and 9Ni steel) are widely used in the manufacturing of high-end equipment such as liquefied natural gas (LNG) storage tanks and cryogenic pressure vessels due to their excellent low-temperature toughness, high strength, and good corrosion resistance. These critical equipment have extremely stringent requirements for the surface quality of materials, because even tiny scratches, indentations, and other defects on the surface can become stress concentration points, inducing crack propagation under low-temperature service conditions, seriously threatening the structural integrity and safety of the equipment.

[0003] In the current manufacturing process of high-nickel steel plates, especially in key processes such as rolling, cutting, and finishing, surface scratches are easily generated. During rolling, steel adhering to the surface of the rolls or minor peeling, as well as foreign objects on the conveyor rollers, can all form periodic or randomly distributed longitudinal and transverse scratches on the surface when in contact with the high-temperature slab. In the cutting stage, whether it is flame cutting or plasma cutting, the molten slag splashed onto the steel plate surface, if not cleaned properly, can easily cause serious scratches on the steel plate surface during subsequent handling and transportation. In the finishing process, including straightening, stacking, and hoisting, due to the hard contact between the steel plate and the equipment or the steel plate itself, the lack of effective surface protection measures can also introduce scratches that are difficult to repair.

[0004] While existing technologies generally employ some conventional protective measures, such as strengthening the inspection and cleaning of rolls and roller conveyors and optimizing lifting tools, these methods are mostly decentralized and passive, lacking a systematic and proactive protection plan that runs through the entire production process. The protective effect is unstable and cannot fundamentally eliminate the problem of scratches on the surface of high-value high-nickel steel plates, resulting in a decrease in product qualification rate, an increase in secondary processing costs, and even affecting its application in high-end fields due to substandard surface quality.

[0005] Therefore, there is an urgent need for a systematic and effective method that covers the entire process from rolling to finishing to minimize scratches on the surface of high-nickel steel plates, so as to meet the stringent requirements of the high-end market for material surface quality, enhance product competitiveness, and ensure the safety and reliability of downstream equipment. Summary of the Invention

[0006] The present invention aims to provide a method for producing high-Ni steel sheets with reduced surface scratches, resulting in high-Ni steel sheets with good surface quality, a scratch rate of no more than 10%, and unplanned scratches of no more than 1%.

[0007] The technical solution adopted in this invention is: A method for producing high-Ni steel sheet with reduced surface scratches, wherein the Ni content of the high-Ni steel sheet is 3.3% to 10.0% by weight, and the production process is as follows: converter + refining + vacuum treatment + continuous casting + billet heating + rolling + quenching + tempering + finishing + warehousing. The surface scratch rate of the produced high-Ni steel sheet shall not exceed 10%, and the unplanned scratches shall not exceed 1%. Key process steps include: 1) The steel plate is rolled at a high final rolling temperature of 870-900℃.

[0008] 2) After rolling, the steel plate is cooled by ACC water, and the water ratio between the upper and lower layers is controlled at 1.4 to 1.5. The steel plate is slightly convex upward with a convexity of 2 to 3 mm / m.

[0009] 3) When cutting the steel plate before heat treatment, the four corners of the steel plate are cut into arcs and polished smooth, with an arc radius of 10-30mm.

[0010] 4) After tempering, the steel plate is water-cooled with a water volume of 3000-5000 m³. 3 / h, water-cooled to room temperature.

[0011] The beneficial effects of this invention are as follows: The steel plate is rolled using a high final rolling temperature process, which significantly improves the flatness of the rolled steel plate and avoids wavy defects caused by excessively low rolling temperatures, thus preventing increased contact between the lower surface of the steel plate and the roller conveyor, which could lead to scratches. The steel plate is then subjected to ACC water cooling after rolling. Reducing the amount of water used during the cooling process allows the steel plate to form an upward convex shape, further reducing contact between the lower surface of the steel plate and the roller conveyor, preventing scratches. Simultaneously, the deformation caused by water cooling after rolling will be straightened during subsequent heat treatment, eliminating the need for additional cold straightening. When the steel plate is slit before heat treatment, the corners are rounded and polished smooth, preventing sharp corners from scratching the underlying steel plate during transport. Water cooling after tempering increases the surface hardness of the steel plate, preventing excessively deep scratches and avoiding unplanned breakage. Detailed Implementation

[0012] The present invention will now be described in further detail with reference to specific embodiments. Example 1

[0013] The production method for high-Ni steel sheet, with a Ni content of 3.3% by weight and a sheet thickness of 9mm, involves the following process: converter + refining + vacuum treatment + continuous casting + billet heating + rolling + quenching + tempering + finishing + warehousing. Key process steps include: 1) The steel plate is rolled at a high final rolling temperature of 900℃.

[0014] 2) After rolling, the steel plate is cooled by ACC water. The ACC water volume is reduced from the conventional water ratio setting, and the water ratio is controlled at 1.4. The steel plate is slightly convex with a convexity of 2mm / m.

[0015] 3) When cutting the steel plate before heat treatment, cut the four corners of the steel plate into arcs and grind them smooth, with an arc radius of 30mm.

[0016] 4) After tempering, the steel plate is water-cooled with a water volume of 5000m³. 3 / h, water-cooled to room temperature. Example 2

[0017] The production method for high-Ni steel sheet, with a Ni content of 10.0% by weight and a sheet thickness of 8mm, involves the following process: converter + refining + vacuum treatment + continuous casting + billet heating + rolling + quenching + tempering + finishing + warehousing. Key process steps include: 1) The steel plate is rolled at a high final rolling temperature of 870℃.

[0018] 2) After rolling, the steel plate is cooled by ACC water. The ACC water volume is reduced from the conventional water ratio setting, and the water ratio is controlled at 1.5. The steel plate is slightly convex with a convexity of 3mm / m.

[0019] 3) When cutting the steel plate before heat treatment, cut the four corners of the steel plate into arcs and grind them smooth, with an arc radius of 10mm.

[0020] 4) After tempering, the steel plate is water-cooled with a water volume of 3000m³. 3 / h, water-cooled to room temperature. Example 3

[0021] The production method for high-Ni steel thin plates, with a Ni content of 5.0% by weight and a plate thickness of 11mm, involves the following process: converter + refining + vacuum treatment + continuous casting + billet heating + rolling + quenching + tempering + finishing + warehousing. Key process steps include: 1) The steel plate is rolled at a high final rolling temperature of 880℃.

[0022] 2) After rolling, the steel plate is cooled by ACC water. The ACC water volume is reduced from the conventional water ratio setting, and the water ratio is controlled at 1.47. The steel plate is slightly convex with a convexity of 2.6 mm / m.

[0023] 3) When cutting the steel plate before heat treatment, cut the four corners of the steel plate into arcs and grind them smooth, with an arc radius of 15mm.

[0024] 4) After tempering, the steel plate is water-cooled with a water volume of 4000m³. 3 / h, water-cooled to room temperature. Example 4

[0025] The production method for high-Ni steel thin plates, with a Ni content of 9.6% by weight and a plate thickness of 9mm, involves the following process: converter + refining + vacuum treatment + continuous casting + billet heating + rolling + quenching + tempering + finishing + warehousing and shipping. Key process steps include: 1) The steel plate is rolled at a high final rolling temperature of 860℃.

[0026] 2) After rolling, the steel plate is cooled by ACC water. The ACC water volume is reduced from the conventional water ratio setting, and the water ratio is controlled at 1.42. The steel plate is slightly convex with a convexity of 2.1 mm / m.

[0027] 3) When cutting the steel plate before heat treatment, cut the four corners of the steel plate into arcs and grind them smooth, with an arc radius of 20mm.

[0028] 4) After tempering, the steel plate is water-cooled with a water volume of 4700m³. 3 / h, water-cooled to room temperature. Example 5

[0029] The production method for high-Ni steel thin plates, with a Ni content of 4.9% by weight and a plate thickness of 10mm, involves the following process: converter + refining + vacuum treatment + continuous casting + billet heating + rolling + quenching + tempering + finishing + warehousing. Key process steps include: 1) The steel plate is rolled at a high final rolling temperature of 890℃.

[0030] 2) After rolling, the steel plate is cooled by ACC water. The ACC water volume is reduced from the conventional water ratio setting, and the water ratio is controlled at 1.49. The steel plate is slightly convex with a convexity of 2.4 mm / m.

[0031] 3) When cutting the steel plate before heat treatment, the four corners of the steel plate are cut into arcs and polished smooth, with an arc radius of 12mm.

[0032] 4) After tempering, the steel plate is water-cooled with a water volume of 3700m³. 3 / h, water-cooled to room temperature.

[0033] The surface quality and mechanical properties of the steel plates in the above embodiments are shown in Table 1.

[0034] Table 1. Test results of surface quality and mechanical properties of steel plates in the examples. .

[0035] The steel plates produced in the above embodiments comply with the standard EN10028-4-2014. The steel plates have good surface quality, with a scratch rate not exceeding 10% and unplanned scratches not exceeding 1%.

Claims

1. A method for producing high-Ni steel sheet with reduced surface scratches, wherein the Ni content of the high-Ni steel sheet is 3.3% to 10.0% by weight, and the production process is as follows: converter + refining + vacuum treatment + continuous casting + billet heating + rolling + quenching + tempering + finishing + warehousing, characterized in that: The surface scratch rate of the produced high-Ni steel sheet shall not exceed 10%, and the unplanned damage caused by scratches shall not exceed 1%. Key process steps include: 1) The steel plate is rolled at a high final rolling temperature of 870-900℃; 2) After rolling, the steel plate is cooled by ACC water, and the water ratio between the top and bottom is controlled at 1.4 to 1.

5. The steel plate is slightly convex upward with a convexity of 2 to 3 mm / m. 3) When cutting the steel plate before heat treatment, the four corners of the steel plate are cut into arcs and polished smooth, with an arc radius of 10-30mm; 4) After tempering, the steel plate is water-cooled with a water volume of 3000-5000 m³. 3 / h, water-cooled to room temperature.