汽车高强钢锻件淬火开裂分析与有限元模拟

Analysis and finite element simulation on quenching cracking for automotive high-strength steel forgings

某汽车高强钢锻件在生产中面临淬火开裂问题,急需从生产工艺上回溯开裂原因。对淬火后的某汽车高强钢锻件进行解剖,观察了裂纹形貌、金属流线、微观组织和元素分布,发现断裂处材料流动极不均匀,锻造变形时剧烈的滑移和剪切是导致开裂的主要原因。模拟了某SAE5137H汽车高强钢锻件在浓度为9%的PAG淬火液(聚烷撑乙二醇质量分数为9%的水性淬火介质)中淬火的过程,发现淬火开裂位置的最大等效应力远低于材料的抗拉强度,淬火应力较小。综合裂纹分析的试验结果和有限元分析结果可知,该锻件锻造过程中材料流动不均匀,局部产生剧烈滑移,使材料塑性下降,虽然在锻造后未直接开裂,但在淬火热应力的作用下因塑性不足而导致开裂。根据开裂原因,将位置A开裂处预锻模膛局部凹模圆角半径减小至R8 mm,并对锻件位置B处局部加热,锻件淬火开裂比例显著下降,解决了开裂问题。

High-strength steel forgings for an automobile face the problem of quenching cracking in production,and it is urgent to trace the cause of cracking from the production process.Therefore,the high-strength steel forgings after quenching for an automobile were dissected,and the crack morphology,metal streamlines,microstructure and element distribution were observed.Then,it was found that the material flow at the fracture was extremely uneven,and the severe slip and shear during the forging deformation were the main causes of cracking.Furthermore,the quenching process of an automotive SAE5137H high-strength steel forgings for an automobile in PAG quenching liquid with the mass fraction of 9%(water-based quenching medium containing 9%polyalkylene glycol)was simulated,and it was found that the maximum equivalent stress at the location of quenching cracking was much lower than the tensile strength of material,the quenching stress is low.Comprehensive crack analysis test result and finite element analysis result show that the material flow is not uniform during the forging process of forgings,and severe slip occurs locally,which reduces the plasticity of material.Although there is no direct cracking after forging,the lack of plasticity under the action of quenching thermal stress leads to cracking.According to the reason of cracking,by reducing the local die fillet of pre-forging mold cavity at cracking position A to R8 mm,and local heating at position B of the forgings,the quenching cracking ratio of the forgings is significantly reduced,and the cracking problem is solved.