Toughening and Embrittlening of Si-Mn-Mo-V Steels in Quenched and lowTemperature Tempered Condition

The influence of Si and Mn on the toughening and embrittlening of Si-Mn-Mo-V steels in the quenched and low temperature tempered condition has been studied in this paper. Experimental results indicate that the segregation of P at austenite grain boundaries is seriously promoted by the Mn addition in-the steel without Si. The segregation of P may be occured during the austeni tizing and subsequent cooling by the co-segregation of Mn and P.The steel at quenched and low temperature tempered condition is offen failed by intergran ular fracture, with low impact toughness because of P segregation.The segregation of P and Mn at the austenite grain boundaries is significantly decreased by the addition of Si in the steel which has been embrittled by Mn (about 2%).Auger Spectromicroscope analyses show there is an obvious segregation of Si at the austenite grain boundaries of the Si bearing steels.It is well known that Si and P have a nagative interaction coefficient,sip<0.For this reason,P was repelled away from the austenite grain boundaries where si has been alread segregated and then the concentration of P at the grain boundaries is decreased.For reasons given above,the grain boundar ombrittlernent and in-tsrgranular fracture are suppressed and then the impact touphnese is markedly increased.
The effects of si and Mn on low temperature tempered embrittlement(LT-TE), or 350℃-embrittlement as it called, of Si-Mn-Mo-V steels have been a-Iso studied in this work. Experimental results indicate that the LTTE is associated both with the impurities segregation at grain boundaries and with the transition of epsilon carbide to cementite which usually precipitated as thin film at the austenite grain boundaries. The segregation of impurities, especially P and the carnbide transition are both significantly influenced by si and Mn. Therefore, the temperature and the intensity of LTTE occured in these steels are also strongly influenced by si and Mn.