Heat treatment process for improving grain size of XCr5MoVE forging stock

Abstract

The invention relates to a heat treatment process for improving the grain size of an XCr5MoVE forging stock, which can effectively improve the internal structure of the forging stock, refine grains, remove internal stress, avoid cracking of the forging stock, obviously improve the product quality and obtain a good quality basis for subsequent quenching and tempering heat treatment. Partial structure transformation is promoted, and grain recovery and regrowth are avoided; the temperature difference from the surface of the forging stock to the core part is reduced through stepped preheating and speed-limiting temperature rise, and forging stock cracking caused by overlarge thermal stress is avoided; through forging stock temperature and heat preservation control, transformation to a pearlite structure is promoted, so that a balanced structure is obtained, and basic preparation is made for subsequent heat treatment and grain refinement; forging stock temperature control, stepped preheating, speed-limiting temperature rising, normalizing and isothermal annealing processes are effectively combined, refining and homogenization of the grain size in the forging stock can be guaranteed through repeated structure transformation, and the situation that the forging stock produced according to a conventional annealing process only plays a role in spheroidizing but does not play a role in refining the grain size in the forging stock is avoided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal material heat treatment, and particularly relates to a heat treatment process for improving the grain size of XCr5MoVE forging blank, which can effectively improve the internal organization of the forging blank, refine the grains, remove internal stress and avoid cracking of the forging blank, and significantly improve the product quality, thereby providing a good quality basis for subsequent quenching and tempering heat treatment. BACKGROUND

[0002] The XCr5MoVE material mainly contains about 0.4% of C, about 5% of Cr, about 0.5% of Mo and about 0.32% of V, and belongs to the hot die steel class. Currently, the material is mainly applied to industrial forgings. During forging, the upsetting and elongation deformation mode is adopted to ensure the compaction effect of forging due to the large cross-sectional size. Due to the control of forgeable temperature range, multiple forging times are required during production, which leads to uneven and coarse internal organization of the forging blank. Therefore, in order to improve the organization uniformity and refinement, the conventional heat treatment process of ultra-refinement + high-temperature tempering or isothermal annealing is adopted after forging. After production, it is found through detection of the forging blank that the grain size of the forging blank is coarse or mixed crystal, and the grain size is basically at the level of 1-4. The product quality is affected in the subsequent quenching and tempering heat treatment. Therefore, in order to improve the grain size of the XCr5MoVE forging blank and ensure the overall quality of the forging blank, a heat treatment process is urgently needed to solve the above problems. SUMMARY

[0003] The present application aims to overcome the deficiencies in the prior art and provide a heat treatment process for improving the grain size of XCr5MoVE forging blank, which can effectively improve the internal organization of the forging blank, refine the grains, remove internal stress and avoid cracking of the forging blank, and significantly improve the product quality, thereby providing a good quality basis for subsequent quenching and tempering heat treatment.

[0004] To achieve the above-mentioned application purposes, the present application adopts the following technical solutions: A heat treatment process for improving the grain size of XCr5MoVE forging blank, the chemical composition of the XCr5MoVE forging blank is as follows in terms of mass percentage: C: 0.35%-0.42%, Si: 0.9%-1.10%, Mn: 0.2%-0.40%, Cr: 4.5%-5.20%, Ni≤0.50%, S≤0.008%, P≤0.020%, V=0.33% and Mo=0.50%-0.60%. The specific process is as follows: Step 1), cooling after forging: after the end of forging, the forging blank is placed in the cooling zone for air cooling, and the air cooling is performed until the surface temperature of the forging blank reaches 450-550℃, and then the forging blank is placed in the heating furnace for preparing to perform normalizing; Step 2) Normalizing: Place the forging billet in a heating furnace at 600℃~700℃ and hold for 1h~15h. After holding, raise the temperature to 990℃~1020℃ at a heating rate of ≤100℃ / h and hold for 2h~30h. After holding, remove from the furnace and air cool or air cool until the surface temperature of the forging billet reaches 200℃~300℃. After cooling, prepare to remove from the furnace for isothermal annealing. Step 3) Isothermal annealing: Place the forging billet in a heating furnace at 400℃~600℃ and hold for 1h~20h. After holding, heat it to 840℃~880℃ at a heating rate of ≤100℃ / h and hold for 5h~50h. After holding, air cool or turn off the power and cool it in the furnace, or cool it in the furnace at a cooling rate of ≤30℃ / h to 650℃~750℃. Hold it in this temperature range for 5h~50h. Then cool it in the furnace at a cooling rate of ≤20℃ / h to below 500℃ and air cool it to room temperature.

[0005] Compared with existing technologies, the process of this invention has the following advantages: 1. After forging, pre-cooling with controlled temperature is performed to ensure the release of temperature in the core of the forging billet, promote partial microstructural transformation, and prevent grain regeneration and regrowth. 2. By using stepped preheating and limited-rate heating, the temperature difference between the surface and core of the forging billet is reduced, thus avoiding excessive thermal stress that could cause the forging billet to crack. 3. By controlling the temperature and holding time of the forging billet, the transformation to pearlite structure is promoted, thereby obtaining a balanced structure and laying the foundation for subsequent heat treatment to refine the grains. 4. By effectively combining the processes of temperature control, stepped preheating, rate-limited heating, normalizing, and isothermal annealing of the forging billet, repeated microstructural transformations ensure the refinement and homogenization of the internal grain size of the forging billet. This avoids the situation where forging billets produced by conventional annealing processes only achieve spheroidization without refining the internal grain size. XCr5MoVE forging billets produced according to this invention effectively improve the internal microstructure, refine the grain size, and remove internal stress to prevent cracking, significantly improving product quality and providing a good quality foundation for subsequent quenching and tempering heat treatment. Detailed Implementation

[0006] Example 1: A heat treatment process for improving the grain size of XCr5MoVE forging billets. The chemical composition of the XCr5MoVE forging billets, by mass percentage, is: C=0.40%, Si=1.04%, Mn=0.31%, Cr=4.91%, Ni=0.24%, S=0.001%, P=0.009%, V=0.33%, Mo=0.57%; specifications: Φ465mm * 4700mm; manufacturing process is as follows: Step 1) Post-forging cooling: After forging, the forging billet is placed in the cooling zone for air cooling until the surface temperature of the forging billet reaches 520°C. Then, the forging billet is placed in the heating furnace to prepare for normalizing. Step 2) Normalizing: Place the forging billet in a heating furnace at 650℃ and hold for 10 hours. After holding, raise the temperature to 1000℃ at a rate of 100℃ / h and hold for 8 hours. After holding, remove the billet from the furnace and air cool until the surface temperature of the forging billet reaches 280℃. After cooling, prepare to remove the billet from the furnace for isothermal annealing. Step 3) Isothermal annealing: Place the forging billet in a heating furnace at 450℃ and hold for 5 hours. After holding, heat the billet to 860℃ at a heating rate of 100℃ / h and hold for 10 hours. After holding, cool the billet in the furnace at a cooling rate of 30℃ / h to 680℃, then hold for 20 hours, and then cool the billet in the furnace at a cooling rate of 20℃ / h to 495℃. Remove the billet from the furnace and air cool it to room temperature. The test results after production according to the above heat treatment process are shown in Table 1: Table 1 Test Results Internal control grain size ≥ 4 Actual test 7.5 After production using the heat treatment process of the present invention to improve the grain size of XCr5MoVE forging billets, the grain size is effectively refined, providing a good quality foundation for subsequent quenching and tempering heat treatment.

[0007] Example 2: A heat treatment process for improving the grain size of XCr5MoVE forging billets. The chemical composition of the XCr5MoVE forging billets, by mass percentage, is: C=0.37%, Si=1.01%, Mn=0.27%, Cr=4.93%, Ni=0.20%, S=0.001%, P=0.008%, V=0.33%, Mo=0.56%; specifications: Φ465mm * 4700mm; manufacturing process is as follows: Step 1) 35℃, then place the forging billet in the heating furnace to prepare for normalizing; Step 2) Normalizing: Place the forging billet in a heating furnace at 650℃ and hold for 10 hours. After holding, raise the temperature to 1000℃ at a rate of 100℃ / h and hold for 8 hours. After holding, remove the billet from the furnace and air cool until the surface temperature of the forging billet reaches 260℃. After cooling, prepare to remove the billet from the furnace for isothermal annealing. Step 3) Isothermal annealing: Place the forging billet in a heating furnace at 450℃ and hold for 5 hours. After holding, heat the billet to 860℃ at a heating rate of 100℃ / h and hold for 10 hours. After holding, cool the billet in the furnace at a cooling rate of 30℃ / h to 680℃, then hold for 20 hours, and then cool the billet in the furnace at a cooling rate of 20℃ / h to 497℃. Remove the billet from the furnace and air cool it to room temperature. The test results after production according to the above heat treatment process are shown in Table 2: Table 2 Test Results Internal control grain size ≥ 4 Actual test 7.5-4.5 After production using the heat treatment process of the present invention to improve the grain size of XCr5MoVE forging billets, the grain size is effectively refined, providing a good quality foundation for subsequent quenching and tempering heat treatment.

Claims

1. A heat treatment process for improving the grain size of XCr5MoVE forging billets, characterized in that: The The chemical composition of the XCr5MoVE forging billet, by mass percentage, is: C: 0.35%~0.42%, Si: 0.9%~1.10%, Mn: 0.2%~0.40%, Cr: 4.5%~5.20%, Ni≤0.50%, S≤0.008%, P≤0.020%, V=0.33%, Mo=0.50%~0.60%; the specific process is carried out according to the following steps: Step 1) Post-forging cooling: After forging, the forging billet is placed in the cooling zone for air cooling until the surface temperature of the forging billet reaches 450℃~550℃; Step 2) After completing Step 1), normalizing is performed: the forging billet is placed in a heating furnace at 600℃~700℃ and held for 1h~15h. After holding, the temperature is increased to 990℃~1020℃ at a heating rate of ≤100℃ / h and held for 2h~30h. After holding, the billet is removed from the furnace and air-cooled or air-cooled until the surface temperature of the forging billet reaches 200℃~300℃. Step 3) After completing Step 2), perform isothermal annealing: Place the forging billet in a heating furnace at 400℃~600℃ and hold for 1h~20h. After holding, heat the billet to 840℃~880℃ at a heating rate of ≤100℃ / h and hold for 5h~50h. After holding, air cool or turn off the power and cool in the furnace, or cool in the furnace at a cooling rate of ≤30℃ / h to 650℃~750℃. Hold in this temperature range for 5h~50h. Then cool in the furnace at a cooling rate of ≤20℃ / h to below 500℃ and air cool to room temperature.