Method for solving surface cracks of super austenitic stainless steel plate

Abstract

The invention belongs to the field of steelmaking, and relates to a super austenitic stainless steel casting blank surface spraying material and a matched casting blank coping and spraying process. The spraying material has the characteristic of high-temperature oxidation resistance, and can be completely and firmly attached to the surface of a casting blank after being uniformly sprayed on the surface of the casting blank which is finely ground and has a certain surface temperature. The casting blank sprayed by the spraying material is heated by a heating furnace and is subjected to hot rolling, so that the problems of high surface temperature and poor thermoplasticity of the casting blank during heating and crack defects on the surface of a plate after hot rolling are solved, and the rolling rejection rate of the super austenitic stainless steel is reduced.

Description

Technical Field

[0001] The present invention relates to the field of steelmaking, and particularly to a method for solving surface cracks of super austenitic stainless steel plates. Background Art

[0002] When the pitting corrosion resistance equivalent (PREN = [Cr] + 3.3[Mo] + 16[N]) of chromium-nickel austenitic stainless steel is ≥ 40%, it can be called super austenitic stainless steel. The most prominent feature of the performance of super austenitic stainless steel is that in a harsh corrosion environment, the pitting corrosion resistance and crevice corrosion resistance of this type of steel are excellent, not only far superior to all the original austenitic stainless steels, but also comparable to some well-known nickel-based corrosion-resistant alloys. Due to the high chromium and molybdenum content in super austenitic stainless steel, the difficulties in the production of this type of steel in metallurgical plants and its use by users are: the poor hot plasticity of the steel, the mastery of hot working processes, and during hot working, heat treatment and welding, brittle phases such as χ (σ) are prone to precipitate, resulting in surface crack defects on super austenitic stainless steel plates, generating rolling rejects, and affecting the manufacturing cost.

[0003] Due to the high chromium and molybdenum content in super austenitic stainless steel, the difficulties in the production of this type of steel in metallurgical plants and its use by users are: the poor hot plasticity of the steel, the mastery of hot working processes, and during hot working, heat treatment and welding, brittle phases such as χ (σ) are prone to precipitate, resulting in surface crack defects on super austenitic stainless steel plates, generating rolling rejects, and affecting the manufacturing cost.

[0004] The present invention provides a surface spraying material for super austenitic stainless steel billets and a supporting billet grinding and spraying process. This spraying material has the characteristic of high-temperature oxidation resistance. When it is evenly sprayed on the surface of a billet that has been finely ground and has a certain surface temperature, the spraying material can adhere to the billet surface completely and firmly.

[0005] The billet sprayed with the spraying material, after being heated in a heating furnace and hot-rolled, solves the problems of high surface temperature of the billet during heating, poor hot plasticity, and surface crack defects on the plate after hot rolling, and reduces the rolling reject rate of super austenitic stainless steel. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for solving surface cracks of super austenitic stainless steel plates in view of the above problems.

[0007] The object of the present invention is achieved as follows: A method for solving the surface cracks of super austenitic stainless steel plates, comprising the following steps: Step 1: Prepare coating powder: Grind and proportion bauxite, quartz sand, and chromite powder. The composition of the coating powder after proportioning is: chromium oxide: 12 - 16%, silicon oxide: 4 - 8%, aluminum oxide: 75 - 84%, others ≤ 1%; Step 2: Prepare surface spraying material: Mix and stir the coating powder, water glass, and water according to a weight ratio of 1:1.5:1.5, and load it into a spray gun after stirring; Step 3: Grind the billet: After cutting the super austenitic stainless steel billet, let the surface temperature of the billet cool naturally to 450 - 500 °C, and use a grinding machine and a hot grinding wheel to grind the billet. The surface roughness of the billet after grinding reaches below 80 μm; Step 4: Spray: When the surface temperature of the billet is 250 - 300 °C, use an alumina spray gun to spray the upper and lower surfaces of the billet, and the spraying thickness is 0.3 - 0.5 mm; Step 5: Perform subsequent rolling on the billet after spraying.

[0008] In Step 1, the particle size of the coating powder ≤ 0.1 mm.

[0009] The beneficial effect of the present invention is: After the implementation of the invention, the billet sprayed with the sprayed material, after being heated in a heating furnace and hot-rolled, solves the problems of high surface temperature of the billet during heating, poor hot plasticity, and crack defects on the surface of the plate after hot rolling, and reduces the rejection rate of super austenitic stainless steel rolling. Detailed implementation mode

[0010] The present invention relates to a super austenitic stainless steel billet with a steel grade of 904L, whose cross-sectional dimensions are thickness × width: 200 mm × (1000 - 2100 mm), and its steel grade composition is C ≤ 0.02%, Si ≤ 1%, Mn ≤ 2%, P ≤ 0.04%, S ≤ 0.03%, 19% ≤ Cr ≤ 23%, 23% ≤ Ni ≤ 28%, 1% ≤ Cu ≤ 2%, 4% ≤ Mo ≤ 5%, N ≤ 0.1%, and the rest is Fe and inevitable impurities.

[0011] The steps of the embodiment are as follows: The present invention relates to a spraying material for the surface of a super austenitic stainless steel slab and a supporting slab grinding and spraying process. This spraying material has the characteristic of high-temperature oxidation resistance. When it is evenly sprayed on the surface of a slab that has been finely ground and has a certain surface temperature, the spraying material can adhere to the slab surface completely and firmly. The specific process is as follows: 1. Grind and proportion bauxite, quartz sand, and chromite powder. The composition of the coating powder after proportioning is: chromium oxide: 12-16%, silicon oxide: 4-8%, aluminum oxide: 75-84%, others ≤1%. 2. Mix and stir the coating powder, water glass, and water according to a weight ratio of 1:1.5:1.5, and load the mixture into a spray gun after stirring. 3. After the super austenitic stainless steel slab is cut, the surface temperature of the slab naturally cools to 450-500°C. Use a fully automatic slab hot grinding machine and grind it with a 20# hot grinding wheel. After grinding, the surface roughness of the slab reaches below 80μm. When the surface temperature of the slab is 250-300°C, use a special spraying device to spray the upper and lower surfaces of the slab, with a spraying thickness of 0.3-0.5mm, and then perform rolling after spraying. Example 1

[0012] In this example, the steel grade of the super austenitic stainless steel slab is 904L, with a cross-sectional size of thickness × width: 200mm × 1250mm. The chemical composition of the steel grade is C: 0.012%, Si: 0.4%, Mn: 1.1%, P: 0.031%, S: 0.002%, Cr: 19.2%, Ni: 24.1%, Cu: 1.2%, Mo: 4.2%, N: 0.04%, and the rest are Fe and unavoidable impurities. The steps of the embodiment are as follows: (1) Grind and proportion bauxite, quartz sand, and chromite powder. The composition of the coating powder after proportioning is: chromium oxide: 12.5%, silicon oxide: 4.1%, aluminum oxide: 83.0%, others: 0.4%.

[0013] (2) Mix and stir the coating powder, water glass, and water according to a weight ratio of 1:1.5:1.5, and load the mixture into a spray gun after stirring.

[0014] (3) After the 904L super austenitic stainless steel slab is cut, the surface temperature of the slab naturally cools to 468°C. Use a fully automatic slab hot grinding machine and grind it with a 20# hot grinding wheel. After grinding, the surface roughness of the slab is 61μm. When the surface temperature of the slab is 263°C, use a special spraying device to spray the upper and lower surfaces of the slab, with a spraying thickness of 0.34mm, and then perform rolling after spraying.

[0015] After the slab is rolled, the surface crack defects of the sheet are solved, and the rolling rejection rate is 0%.

[0016] Another example of a steel grade is a super austenitic stainless steel slab of 904L, with a cross-sectional dimension of thickness × width: 200 mm × 1525 mm. Its steel grade composition is C: 0.015%, Si: 0.5%, Mn: 1.2%, P: 0.038%, S: 0.001%, Cr: 19.3%, Ni: 25.0%, Cu: 1.3%, Mo: 4.4%, N: 0.05%, and the rest is Fe and inevitable impurities. The steps of the example are as follows: (1) Grind and proportion bauxite, quartz sand, and chromite powder. The composition of the coated powder after proportioning is: chromium oxide: 14.7%, silicon oxide: 6.0%, aluminum oxide: 79.1%, and others: 0.2%.

[0017] (2) Mix and stir the coated powder, water glass, and water according to a weight ratio of 1:1.5:1.5, and load it into a spray gun after stirring.

[0018] (3) After cutting the 904L super austenitic stainless steel slab, the surface temperature of the slab naturally cools to 462 °C. Use a fully automatic slab hot grinding machine and grind it with a 20# hot grinding wheel. After grinding, the surface roughness of the slab is 69 μm. When the surface temperature of the slab is 282 °C, use a special spraying device to spray the upper and lower surfaces of the slab, with a spraying thickness of 0.42 mm, and then perform rolling after spraying.

[0019] After rolling the slab, the surface crack defects of the sheet are solved, and the rolling rejection rate is 0%. Example 2

[0020] The steel grade of this example is a super austenitic stainless steel slab of 904L, with a cross-sectional dimension of thickness × width: 200 mm × 1650 mm. Its steel grade composition is C: 0.011%, Si: 0.3%, Mn: 1.3%, P: 0.026%, S: 0.001%, Cr: 20.3%, Ni: 25.6%, Cu: 1.1%, Mo: 4.1%, N: 0.04%, and the rest is Fe and inevitable impurities. The steps of the example are as follows: (1) Grind and proportion bauxite, quartz sand, and chromite powder. The composition of the coated powder after proportioning is: chromium oxide: 14.5%, silicon oxide: 5.2%, aluminum oxide: 79.9%, and others: 0.4%.

[0021] (2) Mix and stir the coated powder, water glass, and water according to a weight ratio of 1:1.5:1.5, and load it into a spray gun after stirring.

[0022] (3)After the 904L super austenitic stainless steel slab is cut, the surface temperature of the slab is naturally cooled to 477 °C, and it is ground using a fully automatic slab hot grinding machine with a 20# hot grinding wheel. After grinding, the surface roughness of the slab is 73 μm. When the surface temperature of the slab is 271 °C, the upper and lower surfaces of the slab are sprayed using a special spraying device, with a spraying thickness of 0.35 mm, and then rolling is carried out.

[0023] After the slab is rolled, the surface crack defects of the sheet are solved, and the rolling rejection rate is 0%.

[0024] The above are only specific embodiments of the present invention, but the structural features within the scope of protection of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the field of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for solving surface cracks of super austenitic stainless steel sheet, characterized by: The following steps are involved: Step 1: Prepare coating powder: Grind and mix bauxite, quartz sand and chromium ore powder. The coating powder composition after mixing is: chromium oxide: 12-16%, silicon oxide: 4-8%, aluminum oxide: 75-84%, and other ingredients ≤ 1%; Step 2: Prepare the surface spray material: mix the coating powder, water glass and water in a weight ratio of 1:1.5:1.5, and then load into the spray gun after stirring; Step 3: Ingot grinding: After the super austenitic stainless steel ingot is cut, the surface temperature of the ingot is naturally cooled to 450-500°C, and the ingot is ground using a grinding machine and a hot grinding wheel. After grinding, the surface roughness of the ingot is less than 80μm; Step 4: Spraying: When the surface temperature of the ingot is 250-300°C, use an alumina spray gun to spray the upper and lower surfaces of the ingot with a spray thickness of 0.3-0.5mm; Step 5: The sprayed ingot is subsequently rolled.

2. The method for solving surface cracks of super austenitic stainless steel sheet according to claim 1, characterized in that: The particle size of the coating powder in step 1 is ≤0.1 mm.