Process for improving the quality of high-chromium high-nickel nitrogen-containing stainless steel electrode billets and electroslag ingots

Abstract

This invention relates to a process for improving the quality of high-chromium, high-nickel, nitrogen-containing stainless steel electrode billets and electroslag ingots. The process includes selecting a casting mold, annealing the electrode billet, grinding the electrode billet, and annealing the electroslag ingot. By constraining the usage specifications of the casting mold, the surface quality of the electrode billet is improved, preventing billet cracking or shrinkage cavities at the billet ends. Grinding the entire electrode billet removes surface oxide scale to prevent electroslag entrapment and improves billet cleanliness. Grinding the entire electroslag ingot eliminates surface defects, providing a good surface quality for subsequent forging deformation. After demolding, the temperature of the electrode billet and electroslag ingot is controlled to ensure consistent temperature control from the surface to the core, reducing thermal stress. This reduces the structural stress of the electrode billet and electroslag ingot, decreasing the risk of cracking. The produced high-chromium, high-nickel, nitrogen-containing stainless steel electrode billets and electroslag ingots exhibit good quality control, with no cracking or scrapping occurring.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology for metallic materials, and specifically relates to a process for improving the quality of high-chromium, high-nickel, nitrogen-containing stainless steel electrode blanks and electroslag ingots. Background Technology

[0002] High-chromium, high-nickel, nitrogen-containing stainless steel is a high-performance martensitic heat-resistant stainless steel with excellent comprehensive mechanical properties, good corrosion resistance, and oxidation resistance, making it widely applicable. However, in actual production, due to its high alloy content (approximately 15% Cr, 5% Ni, 0.8% Mo, controlled 0.040%–0.075% N, and small amounts of other auxiliary alloying elements), the austenitic stability of this material is high, with a transformation completion temperature below 80℃. Because the casting or electroslag remelting times differ between the upper and lower parts of the ingot after casting or electroslag remelting, a significant surface temperature difference (approximately 300℃) exists between the upper and lower parts of the ingot. Therefore, the overall ingot microstructure is difficult to transform uniformly, easily generating a large amount of retained austenite, resulting in poor microstructural stability. In subsequent production or storage, the residual austenite is prone to further transformation, leading to excessive structural stress and cracking. This makes production operation control difficult. Manufacturers generally use high-temperature annealing and slow cooling processes, but these methods are not effective in solving the problems of uneven structural transformation and high residual austenite levels causing product cracking, which affects product quality. Therefore, a process to improve the quality of ingots is needed. This process involves selecting the appropriate ingot mold, grinding the electrode blank surface, annealing, electroslag ingot annealing, and further grinding the electroslag ingot to ensure the quality of the electrode blank and electroslag ingot and avoid cracking and scrapping. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a process for improving the quality of high-chromium, high-nickel, nitrogen-containing stainless steel electrode blanks and electroslag ingots, which has better quality control and avoids cracking and scrapping.

[0004] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: Step 1) Selection of casting mold: Select a casting mold with good inner wall quality and preheat it. When using the casting mold, the temperature should be controlled between 30℃ and 120℃. Step 2) Electrode blank annealing: After casting and demolding, place the electrode blank in the air cooling zone for air cooling until the surface temperature of the electrode blank reaches 200℃~500℃. Then, put it into a heating furnace with a furnace temperature of 380℃~450℃ for heat preservation for 2h~10h. After heat preservation, heat up to 600℃~660℃ at a heating rate of ≤60℃ / h. The heat preservation time is calculated as 4h*(effective diameter of electrode blank mm / 100mm). After heat preservation, furnace cool to below 200℃ at a rate of ≤30℃ / h and then air cool to room temperature. Step 3) Grinding the electrode blank: Use a hand-push grinder to grind the entire electrode blank. After grinding, the surface of the electrode blank is free of oxide scale and cracks. Then, it is transferred to electroslag remelting to produce electroslag ingots. Step 4) Electroslag ingot annealing: After electroslag annealing, place the ingot in an air-cooling zone for air cooling until the surface temperature of the ingot reaches 200℃~500℃. Then, place it in a heating furnace with a furnace temperature of 380℃~450℃ for heat preservation for 2h~10h. After heat preservation, raise the temperature to 600℃~660℃ at a heating rate of ≤60℃ / h. The heat preservation time is calculated as 4h*(effective diameter of electroslag ingot mm / 100mm). After heat preservation, furnace cool to below 200℃ at a rate of ≤30℃ / h and then remove from the furnace for air cooling to room temperature. Step 5) Grinding the electroslag ingot: Use a hand-push grinder to grind the entire electroslag ingot. After grinding, the surface of the electroslag ingot is free of oxide scale and cracks, which provides quality assurance for subsequent forging deformation.

[0005] Compared with the prior art, the process of this invention has the following advantages: 1. By constraining the usage specifications of the casting mold, the surface quality of the electrode blank is improved, avoiding cracking or shrinkage cavities at the blank ends. 2. Grind the entire electrode blank to remove the surface oxide scale and prevent it from being entangled during electroslag removal, thereby improving the cleanliness of the ingot blank; 3. Polish the entire surface of the electroslag ingot to eliminate surface defects and provide good surface quality for subsequent forging and deformation. 4. After demolding, the surface temperature of the electrode blank and electroslag ingot is controlled to ensure the consistency of temperature control from the surface of the electrode blank and electroslag ingot to the core, thereby reducing thermal stress. 5. By using software to simulate the microstructure transformation process, approximately <5% of residual austenite is retained, thereby reducing the microstructure stress of the electrode billet and electroslag ingot and reducing the risk of cracking.

[0006] The high-chromium, high-nickel, nitrogen-containing stainless steel electrode blanks and electroslag ingots produced according to the present invention have good quality control, with no cracking or scrapping occurring, thus meeting production needs. Detailed Implementation

[0007] Example 1: Specifications: Φ400mm electrode blank and Φ600mm electroslag ingot; Chemical composition: C=0.03%, Si=0.29%, Mn=0.33%, Cr=15.29%, Ni=4.52%, S=0.001%, P=0.012%, Mo=0.81%, V=0.08%, Al=0.006%, N=0.055%, with the remainder being Fe; Manufacturing method is as follows: Step 1) Selection of casting mold: Select a casting mold with good inner wall quality and preheat it. When using the casting mold, the temperature should be controlled at 78℃. Step 2) Electrode blank annealing: After casting and demolding, place the electrode blank in the air cooling zone for air cooling until the surface temperature of the electrode blank reaches 350℃~500℃. Then, put it into a heating furnace with a furnace temperature of 400℃ for holding for 5 hours. After holding, raise the temperature to 650℃ at a rate of 60℃ / h and hold for 16 hours. After holding, furnace cool to 198℃ at a rate of 25℃ / h and then remove from the furnace for air cooling to room temperature. Step 3) Grinding the electrode blank: Use a hand-push grinder to grind the entire electrode blank. After grinding, there is no oxide scale or cracks on the surface of the electrode blank. Then, it is transferred to the electroslag process. Step 4) Electroslag ingot annealing: After electroslag annealing, place the ingot in an air cooling zone for air cooling until the surface temperature of the electroslag ingot reaches 350℃~500℃. Then, place it in a heating furnace at a furnace temperature of 400℃ for holding for 5 hours. After holding, raise the temperature to 650℃ at a rate of 50℃ / h and hold for 24 hours. After holding, furnace cool to 195℃ at a rate of 25℃ / h and then remove from the furnace for air cooling to room temperature. Step 5) Grinding the electroslag ingot: Use a hand-push grinder to grind the entire electroslag ingot. After grinding, the surface of the electroslag ingot is free of oxide scale and cracks, which provides quality assurance for subsequent forging deformation.

[0008] The test results after production according to the above heat treatment process are shown in Table 1: Table 1 Test Results Quality requirements Cracking is not allowed. Actual testing The quality is acceptable and no cracking has occurred. After production using the process of the present invention for high-chromium, high-nickel, nitrogen-containing stainless steel electrode blanks and electroslag ingots, the electrode blanks and electroslag ingots are of qualified quality and no cracking occurs.

[0009] Example 2: Φ400mm electrode blank and Φ600mm electroslag ingot; chemical composition: C=0.027%, Si=0.29%, Mn=0.33%, Cr=15.29%, Ni=4.51%, S=0.001%, P=0.011%, Mo=0.81%, V=0.08%, Al=0.007%, N=0.056%, with the remainder being Fe; its manufacturing method is as follows: Step 1) Selection of casting mold: Select a casting mold with good inner wall quality and preheat it. When using the casting mold, the temperature should be controlled at 88℃. Step 2) Electrode blank annealing: After casting and demolding, place the electrode blank in the air cooling zone for air cooling until the surface temperature of the electrode blank reaches 350℃~500℃. Then, put it into a heating furnace with a furnace temperature of 400℃ for holding for 5 hours. After holding, raise the temperature to 650℃ at a rate of 60℃ / h and hold for 16 hours. After holding, furnace cool to 197℃ at a rate of 25℃ / h and then remove from the furnace for air cooling to room temperature. Step 3) Grinding the electrode blank: Use a hand-push grinder to grind the entire electrode blank. After grinding, there should be no oxide scale or cracks on the surface of the electrode blank. Then, proceed with electroslag remelting. Step 4) Electroslag ingot annealing: After electroslag annealing, place the ingot in an air cooling zone for air cooling until the surface temperature of the electroslag ingot reaches 350℃~500℃. Then, place it in a heating furnace at a furnace temperature of 400℃ for holding for 5 hours. After holding, raise the temperature to 650℃ at a rate of 50℃ / h and hold for 24 hours. After holding, furnace cool to 198℃ at a rate of 25℃ / h and then remove from the furnace for air cooling to room temperature. Step 5) Grinding the electroslag ingot: Use a hand-push grinder to grind the entire electroslag ingot. After grinding, the surface of the electroslag ingot is free of oxide scale and cracks, which provides quality assurance for subsequent forging deformation.

[0010] The test results after production according to the above heat treatment process are shown in Table 2: Table 2 Test Results Quality requirements Cracking is not allowed. Actual testing The quality is acceptable and no cracking has occurred. After production using the process of the present invention for high-chromium, high-nickel, nitrogen-containing stainless steel electrode blanks and electroslag ingots, the electrode blanks and electroslag ingots are of qualified quality and no cracking occurs.

Claims

1. A process for improving the quality of high-chromium, high-nickel, nitrogen-containing stainless steel electrode billets and electroslag ingots, characterized in that: The specific process is carried out according to the following steps: Step 1) Selection of casting mold: Select a casting mold with good inner wall quality and preheat it. When using the casting mold, the temperature should be controlled between 30℃ and 120℃. Step 2) Electrode blank annealing: After casting and demolding, place the electrode blank in the air cooling zone for air cooling until the surface temperature of the electrode blank reaches 200℃~500℃. Then, put it into a heating furnace with a furnace temperature of 380℃~450℃ for heat preservation for 2h~10h. After heat preservation, heat up to 600℃~660℃ at a heating rate of ≤60℃ / h. The heat preservation time is calculated as 4h*(effective diameter of electrode blank mm / 100mm). After heat preservation, furnace cool to below 200℃ at a rate of ≤30℃ / h and then air cool to room temperature. Step 3) Grinding the electrode blank: Use a hand-push grinder to grind the entire electrode blank. After grinding, the surface of the electrode blank is free of oxide scale and cracks. Then, it is transferred to electroslag remelting to produce electroslag ingots. Step 4) Electroslag ingot annealing: After electroslag annealing, place the ingot in an air-cooling zone for air cooling until the surface temperature reaches 200℃~500℃. Then, place it in a heating furnace at a furnace temperature of 380℃~450℃ for holding for 2h~10h. After holding, raise the temperature to 600℃~660℃ at a rate of ≤60℃ / h. The holding time is calculated as 4h*(effective diameter of electroslag ingot mm / 100mm). After holding, furnace cool to below 200℃ at a rate of ≤30℃ / h, then remove from the furnace and air-cool to room temperature. Step 5) Grinding the electroslag ingot: Use a hand-push grinder to grind the entire electroslag ingot. After grinding, the surface of the electroslag ingot is free of oxide scale and cracks, which provides quality assurance for subsequent forging deformation.

2. The process for improving the quality of high-chromium, high-nickel, nitrogen-containing stainless steel electrode billets and electroslag ingots according to claim 1, characterized in that: The high-chromium, high-nickel, nitrogen-containing stainless steel electrode blanks and electroslag ingots comprise the following components by mass percentage: C≤0.06%, Si≤0.70%, Mn≤1.50%, Cr=15.00%~17.00%, Ni=4.00%~6.00%, S≤0.015%, P≤0.020%, Mo=0.80%~1.50%, V≤0.19%, Al≤0.050%, N=0.02%~0.08%, with the remainder being Fe.