淬火纵向裂纹的有限元模拟

Finite element simulation of longitudinal quenching crack

淬火纵向裂纹在热处理工业中十分常见。本工作结合实验和有限元模拟的方法对16 mm直径的42CrMo圆柱件在不同的淬火介质(清水、油、盐水单液淬火和清水-油双液淬火)及淬火工艺下的淬火开裂现象进行了研究。经过清水淬火后的圆柱件均出现了纵向裂纹,但经油、盐水和清水-油双液淬火后的试样均未出现裂纹。通过有限元方法对以上不同淬火工艺的淬火应力进行了计算,根据计算结果对全淬透淬火件的淬火应力分布进行了分析。残余应力计算结果表明,42CrMo圆柱件在清水中淬火开裂的原因是由其表面较高的拉应力引起;经盐水淬火后的试样表面应力状态为压应力,其对淬火开裂的预防具有有益作用。基于淬火开裂实验和热应力及相变应力的计算结果,提出了两种预防全淬透件纵向开裂的方法。通过分析样品在清水淬火时的瞬时应力,对淬火开裂时的时间进行了估计。

Longitudinal quenching cracks are very common in heat treatment industry. In this paper, the quenching cracking of 42 CrMo bars with 16 mm diameter under different quenchants(water, oil, brine and water-oil double liquid quenching) and quenching process was studied by means of experiment and finite element simulation. After quenching with water, longitudinal cracks were found in all the samples, but no cracks were found in the samples quenched by oil, brine and water-oil. The quenching stress of different quenching processes was calculated by finite element method, and the quenching stress distribution of through-hardened quenched parts was analyzed according to the calculation results. The results of residual stress calculation show that the reason of quenching cracking of the 42 CrMo bars quenched in water is caused by the higher tensile stress on the surface, and the surface stress state of the specimen after quenching with brine is compressive stress, which is beneficial to the prevention of quenching cracking. Based on the experimental results of quenching cracking and the calculated results of thermal stress and phase transformation stress, two methods to prevent longitudinal cracking of the through-hardened quenched parts are proposed. The time of quenching cracking is estimated by analyzing the instantaneous stress of the sample during water quenching.