A method for quality control of high-chromium high-nickel nitrogen-containing stainless steel ingot

Abstract

The present application relates to a kind of high-chromium high-nickel nitrogen-containing stainless steel forging billet quality control method, which can not only reduce forging heating fire times and save production cost, but also effectively improve the overall quality of the forging billet, suitable for the forging billet with outer diameter ≤350mm, first manufacturing intermediate billet with certain forging ratio + intermediate billet normalizing + air cooling + hydrogen annealing + forging billet surface temperature control + limited speed heating and step temperature holding + normalizing + temperature control cooling to promote microstructure transformation + high-temperature tempering and isothermal transformation composite process, which not only reduces forging heating fire times, saves production cost, but also effectively improves the overall quality of the forging billet.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology for metallic materials, and specifically relates to a quality control method for high-chromium, high-nickel, nitrogen-containing stainless steel forgings that can not only reduce the number of forging heating cycles and save production costs, but also effectively improve the overall quality of the forging billet. Background Technology

[0002] Currently, high-chromium, high-nickel, nitrogen-containing stainless steel forgings are a type of high-performance martensitic heat-resistant stainless steel. Due to its high alloy content (approximately 15% Cr, 5% Ni, 0.8% Mo, controlled amounts of 0.040%–0.075% N, and small amounts of other auxiliary alloying elements), this material possesses excellent comprehensive mechanical properties, good corrosion resistance, and oxidation resistance, making it widely applicable. However, in actual production, the forging temperature range is narrow, only 950℃ to 1180℃. Below 950℃, brittle σ-phase precipitates, causing surface and edge cracking during forging deformation, leading to scrapping. Therefore, production control is challenging. To avoid cracking due to brittle σ-phase precipitates during deformation, more stringent control measures are needed during the forging process. Repeated reheating in the furnace leads to a longer production cycle in the entire forging process, resulting in coarse grains in the forged billet. In addition, when manufacturers use conventional annealing after general forging, due to the high alloy content and low high-temperature transformation point of this material, the commonly used process can cause untransformed residual austenite and martensite to undergo inversion into austenite during cooling and heating. Therefore, it is easy to produce mixed grain size and excessive transformation stress of residual austenite, resulting in cracking and scrapping. This affects the production progress and market competitiveness of high-chromium, high-nickel, nitrogen-containing stainless steel forging billets. Therefore, in order to improve the overall quality of high-chromium, high-nickel, nitrogen-containing stainless steel forging billets, a new method is needed to improve the quality of forging billets. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a quality control method for high-chromium, high-nickel, nitrogen-containing stainless steel forging billets. This method can eliminate internal stress in the forging billet, reduce hardness, prevent forging billet cracking, avoid microstructure inheritance, promote the overall quality uniformity of the forging billet and refine the grains, thereby improving the overall quality of the forging billet and meeting production needs.

[0004] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: Step 1) High-temperature normalizing of intermediate billets: First, manufacture intermediate billets with a forging ratio of 2.0 to 3.0. After forging, the intermediate billets are placed in a heating furnace at 750℃ to 850℃ to wait for material. After the material is waiting, the temperature is raised to 960℃ to 980℃ at a heating rate of ≤100℃ / h and held for 1h to 15h. After the holding time, the billets are removed from the furnace and air-cooled until the surface temperature of the intermediate billets reaches 90℃ to 180℃. Step 2) Temperature-controlled tempering: After air cooling, the intermediate billet is placed in a heating furnace at 80℃~200℃ and kept at that temperature for 1h~10h. Step 3) Annealing: After holding at the temperature, heat to 600℃~650℃ at a heating rate of ≤100℃ / h, hold for 5h~40h, and after holding, furnace cool to below 200℃ at a cooling rate of ≤30℃, then air cool to room temperature, and then heat forging to form the final required forging billet. Step 4) Pre-cooling after forging: After forging, place the forging billet in the air cooling zone for air cooling until the surface temperature of the forging billet reaches 150℃~200℃. Step 5) High-temperature normalizing: After air cooling, the forging billet is placed in a heating furnace at 200℃~250℃ and held for 1h~10h. After holding, the temperature is increased to 550℃~650℃ at a heating rate of ≤80℃ / h and held for 1h~5h. Then, the temperature is increased to 930℃~960℃ at full power and held for 1h~15h. After holding, the billet is removed from the furnace and air-cooled until the surface temperature of the forging billet reaches 80℃~180℃. Step 6) Temperature-controlled tempering: After air cooling, the forging billet is placed in a heating furnace at 80℃~200℃ and kept at that temperature for 1h~10h. Step 7) Annealing: Heat to 600℃~650℃ at a heating rate of ≤50℃ / h, hold for 1h~10h, after holding, furnace cool to 480℃~530℃ at a cooling rate of ≤30℃ / h, hold for 2h~30h, after holding, furnace cool to below 200℃ at a cooling rate of ≤30℃ / h, remove from furnace and air cool to room temperature.

[0005] The process method for quality control of 1.4418mod forging blanks according to the present invention is applicable to forging blanks with an outer diameter ≤350mm. Compared with the prior art, the process of the present invention has the following advantages: 1. The invention firstly developed a composite process of manufacturing an intermediate billet with a certain forging ratio, followed by intermediate billet normalizing, air cooling, hydrogen diffusion annealing, surface temperature control of the forging billet, rate-limited heating and stepped heat preservation, normalizing, temperature-controlled cooling to promote microstructure transformation, and high-temperature tempering and isothermal transformation, which effectively improves the overall quality of the forging billet. 2. After forging, temperature-controlled cooling promotes the transformation of the forging structure and residual heat tempering, providing a good foundation for subsequent microstructure refinement; 3. After high-temperature normalizing, the surface temperature is pre-cooled to a certain temperature and held at this temperature to promote microstructure transformation and reduce microstructure stress to prevent the forging billet from cracking. 4. By annealing the intermediate billet and the forging billet twice, the hydrogen content inside the forging billet is effectively reduced, providing a good foundation for improving the impact toughness of the quenched and tempered heat treatment. 5. By using furnace-controlled temperature cooling and residual heat self-tempering, the temperature difference between the inside and outside of the forging billet is reduced, thereby reducing thermal stress and structural stress and ensuring the quality of the forging billet. 6. Through composite treatment, the abnormal structure of this material, which is Ni-containing martensitic steel, was eliminated, the internal structure and grain size of the forging billet were refined, and the product quality was guaranteed. 7. The number of forging heating cycles is reduced, which not only saves production costs but also improves production efficiency. The high-chromium, high-nickel, nitrogen-containing stainless steel forgings produced according to this invention meet production requirements in terms of product quality. Detailed Implementation

[0006] This invention is a composite process that first manufactures an intermediate billet with a certain forging ratio, then normalizes the intermediate billet, air-cools it, anneals it with hydrogen diffusion, controls the surface temperature of the forging billet, increases the heating rate by a limited rate and holds it in a stepped manner, normalizes it, cools it with controlled temperature to promote microstructure transformation, and then tempers it at high temperature and performs isothermal transformation. This process not only reduces the number of forging heating processes and saves production costs, but also effectively improves the overall quality of the forging billet. The high-chromium, high-nickel, nitrogen-containing stainless steel forging billets produced according to this invention meet production requirements.

[0007] Example 1: A quality control method for high-chromium, high-nickel, nitrogen-containing stainless steel forging billets. Billet specifications: Φ160mm*L; 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%.

[0008] The manufacturing control methods are as follows: Step 1) High-temperature normalizing of intermediate billet: First, manufacture intermediate billets with a forging ratio of 2.3. After forging, the intermediate billets are placed in a heating furnace at 800°C for waiting. After waiting, the temperature is increased to 970°C at a heating rate of 100°C / h and held for 4.5h. After holding, the billets are removed from the furnace and air-cooled until the surface temperature of the intermediate billets reaches 160°C. Step 2) Temperature-controlled tempering: After air cooling, the intermediate billet is placed in a heating furnace at 150℃~200℃ and kept at that temperature for 4 hours. Step 3) Annealing: After holding at the temperature, heat the temperature to 630℃ at a rate of 100℃ / h and hold for 20h. After holding, cool the temperature in the furnace to 195℃ at a rate of 30℃ and then air cool it to room temperature. After that, heat it to forge it into the final forging billet. Step 4) Pre-cooling after forging: After forging, place the forging billet in the air cooling zone for air cooling until the surface temperature of the forging billet reaches 185℃. Step 5) High-temperature normalizing: After air cooling, the forging billet is placed in a heating furnace at 210℃~240℃ and held for 3 hours. After holding, the temperature is increased to 600℃ at a heating rate of 80℃ / h and held for 3 hours. Then, the temperature is increased to 950℃ at full power and held for 4.5 hours. After holding, the billet is removed from the furnace and air-cooled until the surface temperature of the forging billet reaches 170℃. Step 6) Temperature-controlled tempering: After air cooling, the forging billet is placed in a heating furnace at 150℃~200℃ and kept at that temperature for 4 hours. Step 7) Annealing: Heat to 630℃ at a heating rate of 50℃ / h, hold for 5h, then furnace cool to 500℃ at a cooling rate of 30℃ / h and hold for 15h. After holding, furnace cool to 197℃ at a cooling rate of 30℃ / h and air cool to room temperature.

[0009] After production according to the above process, the test results are shown in Table 1: Table 1 Test Results Actual testing Level 4 qualified After production using the quality control method for high-chromium, high-nickel, nitrogen-containing stainless steel forging billets of this invention, the grain size is refined, the surface quality of the forging billets is qualified, and the production needs are met.

[0010] Example 2: A quality control method for high-chromium, high-nickel, nitrogen-containing stainless steel forging billets. Billet specifications: Φ160mm*L; 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%; The manufacturing method is as follows: Step 1) High-temperature normalizing of intermediate billet: First, manufacture intermediate billets with a forging ratio of 2.3. After forging, the intermediate billets are placed in a heating furnace at 800°C for waiting. After waiting, the temperature is increased to 970°C at a heating rate of 100°C / h and held for 4.5h. After holding, the billets are removed from the furnace and air-cooled until the surface temperature of the intermediate billets reaches 175°C. Step 2) Temperature-controlled tempering: After air cooling, the intermediate billet is placed in a heating furnace at 150℃~200℃ and kept at that temperature for 4 hours. Step 3) Annealing: After holding at the temperature, heat the temperature to 630℃ at a rate of 100℃ / h and hold for 20h. After holding, cool the temperature in the furnace to 192℃ at a rate of 30℃ and then air cool it to room temperature. After that, heat it to forge it into the final forging billet. Step 4) Pre-cooling after forging: After forging, place the forging billet in the air cooling zone for air cooling until the surface temperature of the forging billet reaches 190℃. Step 5) High-temperature normalizing: After air cooling, the forging billet is placed in a heating furnace at 210℃~240℃ and held for 3 hours. After holding, the temperature is increased to 600℃ at a heating rate of 80℃ / h and held for 3 hours. Then, the temperature is increased to 950℃ at full power and held for 4.5 hours. After holding, the billet is removed from the furnace and air-cooled until the surface temperature of the forging billet reaches 175℃. Step 6) Temperature-controlled tempering: After air cooling, the forging billet is placed in a heating furnace at 150℃~200℃ and kept at that temperature for 4 hours. Step 7) Annealing: Heat to 630℃ at a heating rate of 50℃ / h, hold for 5h, then furnace cool to 500℃ at a cooling rate of 30℃ / h and hold for 15h. After holding, furnace cool to 197℃ at a cooling rate of 30℃ / h and air cool to room temperature.

[0011] After production according to the above process, the test results are shown in Table 2: Table 2 Test Results Actual testing Level 4.5 qualified After production using the quality control method for high-chromium, high-nickel, nitrogen-containing stainless steel forging billets of this invention, the grain size is refined, the surface quality of the forging billets is qualified, and the production needs are met.

Claims

1. A quality control method for high-chromium, high-nickel, nitrogen-containing stainless steel forging billets, characterized in that: This method is performed according to the following steps: Step 1) High-temperature normalizing of intermediate billet: First, manufacture intermediate billets with a forging ratio of 2.0 to 3.

0. After forging, the intermediate billets are placed in a heating furnace at 750℃ to 850℃ to wait for material. After the material is waiting, the temperature is raised to 960℃ to 980℃ at a heating rate of ≤100℃ / h and held for 1h to 15h. After the holding time, the billets are removed from the furnace and air-cooled until the surface temperature of the intermediate billets reaches 90℃ to 180℃. Step 2) Temperature-controlled tempering: After air cooling, the intermediate billet is placed in a heating furnace at 80℃~200℃ and kept at that temperature for 1h~10h. Step 3) Annealing: After holding at the temperature, heat the temperature to 600℃~650℃ at a heating rate of ≤100℃ / h, hold for 5h~40h, and after holding, cool the furnace at a cooling rate of ≤30℃ to below 200℃, then air cool to room temperature, and then heat forging to form the final required forging billet. Step 4) Pre-cooling after forging: After forging, place the forging billet in the air cooling zone for air cooling until the surface temperature of the forging billet reaches 150℃~200℃. Step 5) High-temperature normalizing: After air cooling, the forging billet is placed in a heating furnace at 200℃~250℃ and held for 1h~10h. After holding, the temperature is increased to 550℃~650℃ at a heating rate of ≤80℃ / h and held for 1h~5h. Then, the temperature is increased to 930℃~960℃ at full power and held for 1h~15h. After holding, the billet is removed from the furnace and air-cooled until the surface temperature of the forging billet reaches 80℃~180℃. Step 6) Temperature-controlled tempering: After air cooling, the forging billet is placed in a heating furnace at 80℃~200℃ and kept at that temperature for 1h~10h. Step 7) Annealing: Heat to 600℃~650℃ at a heating rate of ≤50℃ / h, hold for 1h~10h, after holding, furnace cool to 480℃~530℃ at a cooling rate of ≤30℃, hold for 2h~30h, after holding, furnace cool to below 200℃ at a cooling rate of ≤30℃, remove from furnace and air cool to room temperature.

2. The quality control method for a high-chromium, high-nickel, nitrogen-containing stainless steel forging billet according to claim 1, characterized in that: Applicable to forging blanks with an outer diameter ≤350mm.