关键词: 30CrNiMo钢, 冲击吸收能量, 沿晶断口, NbC, 晶界偏聚。

Abstract: 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.

Key words: 30CrNiMo steel, impact absorbed energy, intergranular fracture, NbC, grain boundary segregation