A heat treatment process for controlling the quality of 14Cr12Ni3Mo2VN forging blank

Abstract

The application relates to a heat treatment process for controlling the quality of a 14Cr12Ni3Mo2VN forging blank. 23 C6 organization spheroidization grows, reduces the transformation amount of martensite, thereby reducing or avoiding the cracking phenomenon caused by excessive forging blank organization stress; through furnace temperature control cooling, not only the internal and external temperature difference of the forging blank is reduced, but also the transformed martensite is promoted to self-tempering, thereby reducing the thermal stress and organization stress, and ensuring the forging blank quality; since the material belongs to a Ni-containing martensite steel, no stable organization transformation occurs under high-temperature slow cooling, and the final organization is carbide+martenite, at this time, the material is relatively brittle and easy to crack to generate waste products; through temperature control of the forging blank after annealing and high-temperature tempering, the internal stress of the forging blank is eliminated and the hardness is reduced, thereby ensuring subsequent processing; through low-temperature two-phase zone heating temperature control, the grain size is refined, and the product quality is ensured.

Description

Technical Field

[0001] This invention belongs to the field of metal heat treatment technology, and specifically relates to a heat treatment process for controlling the quality of 14Cr12Ni3Mo2VN forging billets. Background Technology

[0002] 14Cr12Ni3Mo2VN is a high-performance martensitic heat-resistant stainless steel with excellent comprehensive mechanical properties, good corrosion resistance, and oxidation resistance. It is widely used in high-end manufacturing fields such as aerospace and energy equipment. However, due to its high alloy content, low high-temperature transformation point, and high Ni content, residual austenite and martensite inversion into austenite occur during cooling and heating. This can easily lead to mixed grain size, excessive thermal stress and structural stress in the forged billet, resulting in cracking and scrapping. Steel companies typically use conventional annealing processes after forging, which is insufficient to solve these quality problems, resulting in significant scrap losses and impacting the production schedule and market orders for 14Cr12Ni3Mo2VN forged billets. Therefore, a new heat treatment process is needed to improve the quality of the forged billets, ensure a uniform and fine microstructure, and prevent post-production cracking. How to control the surface temperature after forging to keep the core temperature in the two-phase region, promote the spheroidization and growth of Cr23C6 microstructure, reduce the amount of martensite transformation and self-tempering, thereby reducing or avoiding excessive stress in the forging billet and cracking, and promote grain refinement by controlling the heating temperature in the low-temperature two-phase region to ensure that the product has a uniform and fine microstructure are urgent problems to be solved. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a heat treatment process for controlling the quality of 14Cr12Ni3Mo2VN forging billets that can solve the problem of forging billet cracking and scrapping, promote grain refinement, and improve product quality. By controlling the surface temperature after forging to keep the core temperature in the two-phase region, the process promotes the spheroidization and growth of Cr23C6 microstructure, reduces the amount of martensite transformation and self-tempering, thereby reducing or avoiding excessive stress in the forging billet microstructure that causes cracking. Furthermore, by controlling the heating temperature in the low-temperature two-phase region, the process promotes grain refinement and ensures that the product microstructure is uniform and fine.

[0004] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A heat treatment process for controlling the quality of 14Cr12Ni3Mo2VN forging billets, the process being carried out according to the following steps: Step 1) Post-forging temperature control: After forging, the forging billet is hoisted to the unloading area for air cooling until the surface temperature of the forging billet is 500℃~600℃; Step 2) Low-temperature annealing: After air cooling, the forging billet is loaded into the heating furnace and heated to 725℃~800℃ at a heating rate of ≤80℃ / h. It is held for 2h~20h. After holding, it is furnace cooled to below 200℃ at a rate of ≤30℃ and then air cooled. The forging surface temperature is air cooled to 30℃~70℃ and then put back into the furnace, with the highest point temperature of the forging billet as the reference. Step 3) High-temperature tempering: Increase the temperature to 650℃~700℃ at a rate of ≤80℃ / h, hold for 5 h~50h, remove from the furnace and air cool to room temperature after holding. Compared with the prior art, the process of this invention has the following advantages: 1. By controlling the surface temperature after forging to keep the core temperature in the two-phase region, the spheroidization and growth of Cr23C6 microstructure is promoted, the transformation of martensite is reduced, thereby reducing or avoiding the phenomenon of cracking caused by excessive stress in the forging billet microstructure. 2. By controlling the temperature of the furnace during cooling, not only is the temperature difference between the inside and outside of the forging billet reduced, but the transformed martensite can also be self-tempered, thereby reducing thermal stress and structural stress and ensuring the quality of the forging billet. 3. Since this material is a Ni-containing martensitic steel, it does not undergo a stable structural transformation under high temperature and slow cooling. The final structure is carbide + martensite. At this time, the material is relatively brittle and prone to cracking, resulting in scrap. Therefore, by controlling the temperature of the forging billet after annealing and combining it with high temperature tempering, the internal stress of the forging billet is eliminated and the hardness is reduced, ensuring subsequent processing. 4. Temperature control through low-temperature two-phase heating promotes grain refinement and ensures product quality. Detailed Implementation

[0005] Example 1: A heat treatment process for controlling the quality of 14Cr12Ni3Mo2VN forging billets, specifications: Φ160mm*L, manufacturing method as follows: Step 1) Post-forging temperature control: After forging, the forging billet is hoisted to the unloading area for air cooling until the surface temperature of the forging billet is between 550℃ and 585℃. Step 2) Low-temperature annealing: After air cooling, the forging billet is loaded into the heating furnace and heated to 770°C at a heating rate of 80°C / h. It is held for 5 hours. After holding, it is furnace cooled to 191°C at a rate of 20°C and then air cooled. The forging surface temperature is air cooled to 50°C~70°C and then put back into the furnace, with the highest point temperature of the forging billet as the reference. Step 3) High-temperature tempering: Heat to 690℃ at a rate of 80℃ / h, hold for 15 hours, remove from the furnace and air cool to room temperature.

[0006] The test results after production according to the above heat treatment process are shown in Table 1: Table 1 Test Results Technical Requirements Grain size ≥ 4 Surface hardness ≤287HB Actual testing Level 6-5 241 / 232 / 237 After production using the heat treatment process of the present invention for controlling the quality of 14Cr12Ni3Mo2VN forging billets, the results such as grain size and surface hardness meet the requirements.

[0007] Example 2: A heat treatment process for controlling the quality of 14Cr12Ni3Mo2VN forging billets, specifications: Φ160mm*L, manufacturing method as follows: Step 1) Post-forging temperature control: After forging, the forging billet is hoisted to the unloading area for air cooling until the surface temperature of the forging billet is 550℃~590℃; Step 2) Low-temperature annealing: After air cooling, the forging billet is loaded into the heating furnace and heated to 770°C at a heating rate of 80°C / h. It is held for 5 hours. After holding, it is furnace cooled to 195°C at a rate of 25°C and then air cooled. The forging surface temperature is air cooled to 50°C~70°C and then put back into the furnace, with the highest point temperature of the forging billet as the reference. Step 3) High-temperature tempering: Heat to 690℃ at a rate of 80℃ / h, hold for 15 hours, remove from the furnace and air cool to room temperature.

[0008] The test results after production according to the above heat treatment process are shown in Table 2: Table 2 Test Results Technical Requirements Grain size ≥ 4 Surface hardness ≤287HB Actual testing Level 6 221 / 215 / 207 After production using the heat treatment process of the present invention for controlling the quality of 14Cr12Ni3Mo2VN forging billets, the results such as grain size and surface hardness meet the requirements.

Claims

1. A heat treatment process for controlling the quality of 14Cr12Ni3Mo2VN forging billets, characterized in that: The process is carried out according to the following steps: Step 1) Post-forging temperature control: After forging, the forging billet is hoisted to the unloading area for air cooling until the surface temperature of the forging billet is 500℃~600℃; Step 2) Low-temperature annealing: After air cooling, the forging billet is loaded into the heating furnace and heated to 725℃~800℃ at a heating rate of ≤80℃ / h. It is held for 2h~20h. After holding, it is furnace cooled to below 200℃ at a rate of ≤30℃ and then air cooled. The forging surface temperature is air cooled to 30℃~70℃ and then put back into the furnace, with the highest point temperature of the forging billet as the reference. Step 3) High-temperature tempering: Heat to 650℃~700℃ at a heating rate of ≤80℃ / h, hold for 5 h~50h, remove from the furnace and air cool to room temperature after holding.