改进型4Cr5Mo2MnV1Si压铸模块钢的球化处理

改进型4Cr5Mo2MnV1Si压铸模块钢采用传统“余热退火+正火+等温球化退火”工艺球化处理后，组织未达到技术要求，对其传统球化处理工艺做了改进，并对改进工艺处理试样的组织、硬度进行检测。结果表明，试验钢余热退火+正火+等温球化退火后，再经1010℃保温0.5 h炉冷至不同温度(820、790和760℃)保温1 h空冷处理后，显微组织均呈板条马氏体形态，基体上均匀弥散分布有碳化物颗粒，但硬度均高于400 HBW,未达到硬度小于240 HBW球化组织的要求。而经1010℃保温0.5 h空冷至室温，再820、790和760℃保温1 h回火空冷处理后，组织均为等轴铁素体上均匀分布着质点状碳化物，硬度分别为321、235和245 HBW,其中790℃回火效果最好，球化组织级别达到GB3,硬度小于240 HBW。因此，采用余热退火+正火+高温回火(790℃)代替余热退火+正火+等温球化退火可实现改进型4Cr5Mo2MnV1Si压铸模块钢的锻后球化处理。

Spheroidizing of modified 4Cr5Mo2MnV1Si die-casting module steel

Spheroidized microstructure of modified 4Cr5Mo2MnV1Si die-casting module steel didn't meet the technical requirements by the traditional spheroidizing treatment of “residual heat annealing+normalizing+isothermal spheroidizing annealing”, then the traditional spheroidizing process was improved, and the microstructure and hardness of the specimens treated by the improved process were tested. The results show that after residual heat annealing+normalizing+isothermal spheroidizing annealing, and then heated at 1010 ℃ for 0.5 h by furnace cooling to different temperatures (820, 790 and 760 ℃) held for 1 h by air cooling, the microstructure of the steel is lath martensite and carbide particles uniformly dispersed on the matrix, but the hardness is higher than 400 HBW, which can not meet the requirement of spheroidizing structure with hardness less than 240 HBW. However, when heated at 1010 ℃ for 0.5 h air-cooled to room temperature and then tempered at 820, 790 and 760 ℃ for 1 h, the microstructure is equiaxed ferrite with particle-like carbides uniformly distributed, the hardness is 321, 235 and 245 HBW respectively. And the tempering effect at 790 ℃ is the best, the spheroidization grade reaches GB3, the hardness is less than 240 HBW. In conclusion, the spheroidizing treatment after forging of the modified 4Cr5Mo2MnV1Si die-casting module can be realized by using residual heat annealing+normalizing+high temperature tempering (790 ℃) instead of residual heat annealing+normalizing+isothermal spheroidizing annealing.