Heat treatment process for improving quality of 1Cr17Ni2 forging

Abstract

The invention relates to a heat treatment process method for improving the quality of a 1Cr17Ni2 forge piece, which is suitable for a round bar forge piece with the outer circle diameter less than or equal to 300mm, and is characterized in that the two ends of the forge piece are chopped after the forging is finished, so that the forge piece is prevented from generating stress concentration along the shrinkage cavity positions at the two ends to cause the longitudinal crack of the forge piece; a low-temperature annealing and high-temperature tempering mode is adopted, the hardness of the forge piece is reduced, it is guaranteed that residual austenite is fully converted into a martensitic structure, and forge piece cracking caused by too large stress due to the existence of the unstable martensitic structure in subsequent machining is avoided; complete austenitizing is guaranteed through high-temperature heating, existence of undissolved carbides is avoided, the quenching effect is guaranteed, and the forging quality is improved; the staying time of a tempering brittle zone at 360-560 DEG C is avoided through a stepped rapid cooling mode in high-temperature performance tempering, the toughness of the forge piece is improved, and the internal stress is effectively removed; and by means of thermal correction and high-temperature tempering, the straightness of the forge piece is guaranteed, internal stress removal is corrected, and the quality stability of the forge piece is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat treatment of metal materials, and particularly relates to a heat treatment process for improving the quality of 1Cr17Ni2 forgings, which can effectively ensure the overall quality improvement of 1Cr17Ni2 forging blanks. Background Art

[0002] The 1Cr17Ni2 material belongs to martensitic stainless steel, with relatively high alloy content, C: 0.11% - 0.17%, Ni: 1.5% - 2.5%, Cr: 16.0% - 18%, having characteristics such as high density, high strength, low weight, and high corrosion resistance. It is mainly used for manufacturing automotive parts, aerospace components, containers, ships, valves, pipelines, etc. When our company produces products of this material, it is mainly used for producing round bar forging products. Due to the relatively high Cr alloy content of this material, strict requirements are imposed on the processability, and the production process is difficult to control. There are often the following problems: 1. During the post-forging heat treatment process, partial transformation of austenite to martensite occurs, generating relatively large transformation stresses, resulting in stress concentration at the shrinkage holes at both ends of the forging, causing the forging to crack; 2. In terms of the control of the fully austenitizing temperature, if the heating temperature is controlled too low, undissolved carbides will appear, affecting the plasticity and toughness of the forging. If the heating temperature is controlled too high, the grain size will become coarser as the temperature increases, and at the same time, a certain amount of high-temperature δ-ferrite will be formed, affecting the strength, plasticity, and toughness of the forging; 3. This material has a certain temper embrittlement zone. If not properly controlled, temper embrittlement is likely to occur, reducing the impact toughness of the forging and resulting in unqualified phenomena; 4. Since the forging will undergo a certain amount of deformation after heat treatment, straightness correction is required to ensure it. However, the plastic and toughness of this material are relatively poor, and at the same time, it has a temper embrittlement zone within a certain temperature range, which is difficult to control and is prone to fracture during the correction process, resulting in scrap. Based on the above situation, in order to improve the quality of forgings and avoid certain scrap losses, a heat treatment process for improving the quality of 1Cr17Ni2 forgings is urgently needed. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies existing in the prior art and provide a heat treatment process for improving the quality of 1Cr17Ni2 forgings, which not only ensures complete tissue transformation, prevents the martensite transformation of retained austenite, and avoids the risk of cracking during processing, but also through full austenitization by high-temperature heating and stepwise rapid cooling after tempering, avoids the existence of undissolved carbides and the influence of temper embrittlement, and improves the toughness of the forging and the removal of internal stress.

[0004] To achieve the above invention purpose, the present invention adopts the following technical solutions: A heat treatment process for improving the quality of 1Cr17Ni2 forgings, the specific process steps are as follows: Step 1), chopping both ends of the forging: After forging, place the forging on the chopping tool, and use the hydraulic press to chop off the defective shrinkage cavity positions at both ends of the forging. After completing Step 1), load the forging into the heating furnace for low-temperature annealing; Step 2), low-temperature annealing: After forging, place the forging in a heating furnace with a furnace temperature of 650°C to 750°C to wait for the material. After waiting for the material, heat it up to 850°C to 880°C at a heating rate of 50°C / h to 200°C / h, hold for 5h to 30h, and then cool it in the furnace at a cooling rate of ≤30°C / h until it is below 300°C and then take it out for air cooling until it reaches room temperature. After completing Step 2), load the forging into the heating furnace for high-temperature tempering; Step 3), high-temperature tempering: Load the forging into a heating furnace with a furnace temperature of ≤450°C, heat it up to 600°C to 700°C at a heating rate of 10°C / h to 100°C / h, hold for 5h to 30h, and then cool it in the furnace at a cooling rate of ≤30°C / h until it is below 400°C and then take it out for air cooling until it reaches room temperature. After completing Step 3), load the forging into the heating furnace for high-temperature quenching; Step 4), high-temperature quenching: Load the forging into a heating furnace with a furnace temperature of ≤450°C, heat it up to 600°C to 700°C at a heating rate of 10°C / h to 80°C / h, hold for 1h to 8h. After holding, heat it up to 800°C to 900°C at a heating rate of 10°C / h to 80°C / h, hold for 1h to 8h. After holding, heat it up to 1000°C to 1050°C at full power, hold for 2h to 20h. After holding, take it out for quenching and cooling. First, pre-cool in the air for 50s to 200s, and then put the forging into N32 quenching oil with an initial temperature of 20°C to 70°C and cool for 15min to 150min. During the cooling process, start the compressed air to stir the quenching oil. After cooling, lift the forging out of the quenching oil. After completing Step 4), load the forging into a heating furnace with a furnace temperature of ≤450°C for one-time high-temperature tempering; Step 5), one-time high-temperature tempering: Heat it up to 600°C to 650°C at a heating rate of 10°C / h to 100°C / h, hold for 3h to 20h. After holding, take it out for hot straightening of the forging, and control the straightness within ≤3mm. After hot straightening, ensure that the surface temperature of the forging is ≥500°C. After hot straightening, air-cool it to room temperature. After completing Step 5), load the forging into a heating furnace with a furnace temperature of ≤450°C for secondary high-temperature tempering; Step 6), secondary high-temperature tempering: Heat it up to 570°C to 620°C at a heating rate of 10°C / h to 100°C / h, hold for 3h to 20h. After holding, take it out for stepped rapid cooling. Put the forging into N32 quenching oil with an initial temperature of 20°C to 70°C and cool until the surface temperature of the forging reaches 250°C to 300°C, and then lift the forging out of the quenching oil for air cooling until it reaches room temperature.

[0005] The process of the present invention is applicable to 1Cr17Ni2 forgings with an outer diameter ≤ φ300mm. Compared with the prior art, it has the following advantages: 1. After forging, the two ends of the forging are chopped to avoid stress concentration at the shrinkage cavity positions at both ends of the forging, which may cause longitudinal cracking of the forging; 2. The low-temperature annealing + high-temperature tempering method is adopted, which not only reduces the hardness of the forging, but also ensures the full transformation of retained austenite into martensite structure, avoiding excessive stress caused by the unstable martensite structure during subsequent processing, which may lead to forging cracking; 3. Complete austenitization is ensured by high-temperature heating, avoiding the existence of undissolved carbides, ensuring the quenching effect and improving the quality of the forging; 4. The high-temperature performance tempering adopts a stepped rapid cooling method to avoid staying in the temper brittleness zone of 360°C to 560°C, improving the toughness of the forging and effectively removing internal stress; 5. Through the hot-state correction + high-temperature tempering method, the straightness of the forging and the removal of internal stress during correction are ensured, and the quality stability of the forging is improved. The overall quality of the 1Cr17Ni2 forgings produced according to the present invention is improved. Specific embodiments

[0006] Example 1: A heat treatment process for improving the quality of 1Cr17Ni2 forgings, steel type: 1Cr17Ni2, Chemical composition: C = 0.15%, Si = 0.29%, Mn = 0.57%, Cr = 16.43%, Ni = 2.01%, S = 0.002%, P = 0.015%; Specification: Φ110*6970mm; The heat treatment process is as follows: Step 1). Chop the two ends of the forging: After forging, place the forging on the chopping knife and use a hydraulic press to chop off the defective shrinkage cavity positions at both ends of the forging; Step 2). After step 1) is executed, perform low-temperature annealing: After forging, put the forging into a heating furnace with a furnace temperature of 700°C to wait for the material. After waiting for the material, raise the temperature to 860°C at a heating rate of 80°C / h, hold for 6h, and then cool down with the furnace at a cooling rate of 20°C / h to below 290°C and take it out of the furnace for air cooling until it reaches room temperature; Step 3). After step 2) is executed, perform high-temperature tempering: Load the forging into a heating furnace with a furnace temperature of 310°C, raise the temperature to 650°C at a heating rate of 80°C / h, hold for 10h, and then cool down with the furnace at a cooling rate of 20°C / h to below 385°C and take it out of the furnace for air cooling until it reaches room temperature; Step 4), after Step 3 is executed, perform high-temperature quenching: Load the forging into a heating furnace with a furnace temperature of 271°C, heat it up to 620°C at a heating rate of 80°C / h, hold for 1 h, after holding, heat it up to 850°C at a heating rate of 80°C / h, hold for 1 h, after holding, heat it up to 1030°C at full power, hold for 3 h, and then take it out of the furnace for quenching and cooling. First, pre-cool in the air for 110 s, and then put the forging into N32 quenching oil with an initial temperature of 37°C and cool for 27 min. During the cooling process, start the compressed air to stir the quenching oil, and after cooling, lift the forging out of the quenching oil; Step 5), after Step 4 is executed, perform a high-temperature tempering: Load the forging into a heating furnace with a furnace temperature of 215°C, heat it up to 610°C at a heating rate of 80°C / h, hold for 6.5 h, after holding, take it out of the furnace for hot straightening of the forging, control the straightness within 3 mm, and after hot straightening, ensure that the surface temperature of the forging is 530°C, and then air-cool to room temperature after hot straightening; Step 6), after Step 5 is executed, perform a second high-temperature tempering: Load the forging into a heating furnace with a furnace temperature of 270°C, heat it up to 590°C at a heating rate of 80°C / h, hold for 6 h, after holding, take it out of the furnace for stepped rapid cooling, put the forging into N32 quenching oil with an initial temperature of 35°C and cool until the surface temperature of the forging reaches 272°C, and then lift the forging out of the quenching oil for air cooling, and air-cool to room temperature.

[0007] Table 1 Test Results Technical requirements σs (≥600 Mpa) σb (≥750 Mpa) δ (≥15%) Ψ ( / ) AKU ( / ) Actual detection 725 860 18 58 46 / 49 / 48 After being produced by the heat treatment process for improving the quality of 1Cr17Ni2 forgings of the present invention, the mechanical property test results are qualified and meet the customer's technical requirements.

[0008] Example 2: A heat treatment process for improving the quality of 1Cr17Ni2 forgings, steel type: 1Cr17Ni2; Chemical composition: C = 0.15%, Si = 0.29%, Mn = 0.57%, Cr = 16.43%, Ni = 2.01%, S = 0.002%, P = 0.015%; Specification: Φ110*6970 mm; The heat treatment process is as follows: Step 1), cut both ends of the forging: After forging, place the forging on the chopping knife and use a hydraulic press to cut off the defective shrinkage hole positions at both ends of the forging cleanly; Step 2), after Step 1 is executed, perform low-temperature annealing: After forging, put the forging into a heating furnace with a furnace temperature of 700°C to wait for the material, after waiting for the material, heat it up to 860°C at a heating rate of 80°C / h, hold for 6 h, and then cool it down in the furnace at a cooling rate of 20°C / h to below 293°C and take it out for air cooling, and air-cool to room temperature; Step 3): After step 2) is executed, perform high-temperature tempering: Load the forging into a heating furnace with a furnace temperature of 301 °C, heat it up to 650 °C at a heating rate of 80 °C / h, hold for 10 h, then cool it in the furnace at a cooling rate of 20 °C / h to below 393 °C and take it out of the furnace for air cooling until it reaches room temperature; Step 4): After step 3) is executed, perform high-temperature quenching: Load the forging into a heating furnace with a furnace temperature of 275 °C, heat it up to 620 °C at a heating rate of 80 °C / h, hold for 1 h, after holding, heat it up to 850 °C at a heating rate of 80 °C / h, hold for 1 h, after holding, heat it up to 1030 °C at full power, hold for 3 h, after holding, take it out of the furnace for quenching and cooling. First, pre-cool it in the air for 110 s, then put the forging into N32 quenching oil with an initial temperature of 39 °C and cool it for 27 min. During the cooling process, start the compressed air to stir the quenching oil. After cooling, lift the forging out of the quenching oil; Step 5): After step 4) is executed, perform a high-temperature tempering: Load the forging into a heating furnace with a furnace temperature of 215 °C, heat it up to 610 °C at a heating rate of 80 °C / h, hold for 6.5 h, after holding, take it out of the furnace for hot straightening of the forging. Control the straightness within 3 mm. After hot straightening, ensure that the surface temperature of the forging is 517 °C, and after hot straightening, air cool it to room temperature; Step 6): After step 5) is executed, perform a second high-temperature tempering: Load the forging into a heating furnace with a furnace temperature of 269 °C, heat it up to 590 °C at a heating rate of 80 °C / h, hold for 6 h, after holding, take it out of the furnace for stepped rapid cooling. Put the forging into N32 quenching oil with an initial temperature of 38 °C and cool it until the surface temperature of the forging reaches 276 °C, then lift the forging out of the quenching oil for air cooling until it reaches room temperature.

[0009] Table 2 Test Results Technical requirements σs (≥600 Mpa) σb (≥750 Mpa) δ (≥15%) Ψ ( / ) AKU ( / ) Actual detection 740 870 18 56 36 / 47 / 44 After being produced by the heat treatment process for improving the quality of 1Cr17Ni2 forgings of the present invention, the mechanical property test results are qualified and meet the customer's technical requirements.

Claims

1. A heat treatment process for improving the quality of 1Cr17Ni2 forgings, characterized in that: The specific process steps are as follows: Step 1), Chop both ends of the forging: After forging, place the forging on the chopping tool, and use the hydraulic press to chop off the defective shrinkage cavity positions at both ends of the forging cleanly. After completing Step 1), load the forging into the heating furnace for low-temperature annealing; Step 2), Low-temperature annealing: After forging, place the forging in a heating furnace with a furnace temperature of 650°C to 750°C to wait for the material. After waiting for the material, heat it up to 850°C to 880°C at a heating rate of 50°C / h to 200°C / h, hold for 5h to 30h, and then cool it in the furnace at a cooling rate of ≤30°C / h to below 300°C and take it out of the furnace for air cooling until it reaches room temperature. After completing Step 2), load the forging into the heating furnace for high-temperature tempering; Step 3), High-temperature tempering: Load the forging into a heating furnace with a furnace temperature of ≤450°C, heat it up to 600°C to 700°C at a heating rate of 10°C / h to 100°C / h, hold for 5h to 30h, and then cool it in the furnace at a cooling rate of ≤30°C / h to below 400°C and take it out of the furnace for air cooling until it reaches room temperature. After completing Step 3), load the forging into the heating furnace for high-temperature quenching; Step 4), High-temperature quenching: Load the forging into a heating furnace with a furnace temperature of ≤450°C, heat it up to 600°C to 700°C at a heating rate of 10°C / h to 80°C / h, hold for 1h to 8h. After holding, heat it up to 800°C to 900°C at a heating rate of 10°C / h to 80°C / h, hold for 1h to 8h. After holding, heat it up to 1000°C to 1050°C at full power, hold for 2h to 20h. After holding, take it out of the furnace for quenching and cooling. First, pre-cool it in the air for 50s to 200s, and then put the forging into N32 quenching oil with an initial temperature of 20°C to 70°C and cool it for 15min to 150min. During the cooling process, turn on the compressed air to stir the quenching oil. After cooling, lift the forging out of the quenching oil. After completing Step 4), load the forging into a heating furnace with a furnace temperature of ≤450°C for the first high-temperature tempering; Step 5), First high-temperature tempering: Heat it up to 600°C to 650°C at a heating rate of 10°C / h to 100°C / h, hold for 3h to 20h. After holding, take it out of the furnace for hot straightening of the forging, and control the straightness within ≤3mm. After hot straightening, it is necessary to ensure that the surface temperature of the forging is ≥500°C. After hot straightening, air-cool it to room temperature. After completing Step 5), load the forging into a heating furnace with a furnace temperature of ≤450°C for the second high-temperature tempering; Step 6), Second high-temperature tempering: Heat it up to 570°C to 620°C at a heating rate of 10°C / h to 100°C / h, hold for 3h to 20h. After holding, take it out of the furnace for step-by-step rapid cooling. Put the forging into N32 quenching oil with an initial temperature of 20°C to 70°C and cool it until the surface temperature of the forging reaches 250°C to 300°C, and then lift the forging out of the quenching oil for air cooling until it reaches room temperature.

2. The heat treatment process for improving the quality of 1Cr17Ni2 forgings according to claim 1, characterized in that: The present invention is applicable to round bar forgings with an outer diameter of ≤300mm.