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针对40Cr钢出现冲击值降低的问题,运用实践——认识——实践掌握客观规律的方法,研究了几个炉号的钢材,得出其中元素偏析是影响冲击值降低的原因。在所研究的炉号中,微量元素磷和锡在正常的热处理工艺条件下偏析于奥氏体晶界;偏析程度可因其它合金元素的偏析而加剧。磷和锡的偏析引起原奥氏体晶界相间结合力减弱,导致冲击值降低。通过正火和不完全淬火以改变磷和锡的分布,使冲击值显著提高,并保证其它机械性能满足要求。在生产过程中,不宜采用不完全淬火时,应当控制原材料的成分和冶炼工艺,使微量有害元素的含量降至一定限度以下。
Aiming at the problem of reducing the impact value of 40Cr steel, the practice of - understanding - practice to grasp the objective law has been studied. In the furnace number studied, the trace elements phosphorus and tin segregated at the austenite grain boundaries under normal heat treatment conditions; the degree of segregation may be exacerbated by the segregation of other alloying elements. The segregation of phosphorus and tin causes the original austenite grain boundary to weaken the binding force between phases, resulting in a reduction of the impact value. By normalizing and incomplete quenching to change the distribution of phosphorus and tin, the impact value is significantly increased and other mechanical properties are guaranteed to meet the requirements. In the production process, should not be used when incomplete quenching, should control the composition of raw materials and smelting process, so that the amount of trace harmful elements below a certain limit.