辊皮铸钢件热处理开裂失效分析

Failure analysis of heat treatment cracking of large steel cast roll sleeve

35SiMn大型工矿用铸钢件辊皮产品,经过铸造、正火及调质处理后,发现整个缸体内外壁和端面,都出现严重的龟斑裂纹。通过对化学成分、力学性能及金相组织检测和对该失效件进行分析,结果表明在正常加热温度的正火处理过程中,由于加热速度过快,工件内外温差过大,热膨胀系数不一致,在工件的次表层产生极大的热应力,在静置过程中热应力的释放,铸钢件的表面产生大量的裂纹。采用高温扩散退火加完全退火后,工件的组织得到细化强韧性提高。同时采用阶梯式缓慢加热的方式降低热应力,工件表面开裂倾向显著减少。经过工艺改进,工件表面开裂率由原来的65%左右降低为现在不到2%,极大地提高了生产效率和控制了生产成本。

Serious cracks appeared throughout the cylinder wall and the end face of the 35 SiMn large-scale mining cast steel roller sleeve after casting,normalizing and tempering processes. Through the test of chemical composition,mechanical properties and microstructure,the failure was analyzed. The results show that in the process of normalizing at the normal heating temperature,temperature difference inside the workpiece is too large due to the higher heating speed. The coefficient of thermal expansion is not consistent in the workpiece which induces a great thermal stress. Crack generated at the surface of the steel part. High temperature diffusion annealing plus complete annealing,the microstructure and toughness is improved. At the same time,slowly heating method can reduce the thermal stress,surface cracking tendency of decrease. Through improved technology,surface cracking rate of the workpiece reduced from 65% down to less than 2%,which greatly enhanced the production efficiency,and production costs are controlled.