30CrNiMo铸钢件冲击性能不合格原因分析

针对30CrNiMo铸钢件调质后冲击吸收能量不合格的问题,通过断口分析、金相检验、硬度测试、化学成分分析等方法对30CrNiMo铸钢件冲击吸收能量不合格原因进行了分析。结果表明,30CrNiMo铸钢件冲击断口为沿晶断口。金相检验发现淬火态晶粒不均匀,存在混晶现象。Nb在原奥氏体晶界处偏聚形成NbC,一方面能降低晶界的活动性,对晶界迁移起阻碍作用,另一方面,形成较多的第二相粒子起钉扎晶界、巩固晶界遗传的作用,最终导致奥氏体晶粒粗化后,钢的韧性—脆性转变温度升高,钢在室温进行冲击时得到脆性穿晶断口和低的冲击性能。

Analysis of unqualified impact property of 30CrNiMo steel castings

In view of the unacceptable impact absorbed energy of 30CrNiMo steel casting after quenching and tempering, the main influence factors of which were analyzed through fracture analysis, metallography, hardness testing and chemical composition analysis. The results show that there are intergranular fracture of impact specimen of the 30CrNiMo steel castings, and the quenched specimen appears mischcrystal structure. Furthermore, a large number of NbC phases segregate at the grain boundary, which impedes the movement of grain boundary effectively. At the same time, abundant NbC phases also consolidate the inheritance phenomenon of grain by the pinning effect, which enhances ductile-brittle transition temperature significantly after the austenite grain coarsening. Ultimately, brittle transgranular fracture and low impact property are obtained when the specimen is impacted at room temperature.