微合金元素Nb对低碳铸钢强度和冲击韧性的影响

采用中频炉冶炼制备不同Nb含量的微合金低碳铸钢,用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、液压万能强度试验机、半自动冲击试验机等手段研究了Nb微合金化对低碳铸钢显微组织、强度和冲击韧性的影响.结果表明,添加合适的微合金元素Nb可以使低碳铸钢的晶粒尺寸减小20.8％～34.6％,同时促进细小NbC析出相的形成,能有效提高低碳铸钢的强度和冲击韧性,晶粒细化和析出强化为其主要的强韧化机制.其中,含Nb量为0.044％的微合金铸钢屈服强度为350 MPa,抗拉强度为520 MPa,室温冲击功为119.7 J.与普通低碳铸钢相比,其塑性基本保持不变,但屈服强度、抗拉强度和室温冲击功分别提高了20.7％、7.2％和25.6％.

Effect of Microalloying Element Niobium on the Strength and Toughness of Low Carbon Cast Steels

Microalloyed cast steels with different amount of niobium (Nb) were produced by medium frequency induction furnace.Optical microscopy (OM),scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to investigate the effect of microalloying element Nb on microstructure,strength and toughness of low carbon cast steels.The results indicated that the grain size of low carbon cast steels were refined by 20.8％-34.6％ and fine NbC particles were formed by niobium addition.Meanwhile,yield strength (YS),ultimate tensile strength (UTS) and room temperature toughness of the microalloyed steels were improved significantly.Grain refining and precipitation were proved to be the main strengthening mechanisms.When the content of Nb was 0.044 wt％,the YS,UTS and impact energy of the microalloyed steel were 350 MPa,520 MPa and 119.7 J,respectively.They were improved by 20.7％,7.2％ and 25.6％ with retained ductility,respectively,as compared to Nb-free steel.