中文摘要：

利用Gleeble-3500热模拟试验机、扫描电镜、透射电镜、电子背散射衍射技术等手段研究V对700 MPa级高强度汽车大梁钢组织细化的影响.在冷却速度2~7℃·s-1时,显微组织为针状铁素体＋粒状贝氏体组织.V添加提高粒状贝氏体体积分数,细化粒状贝氏体组织,并明显降低粒状贝氏体中M/A岛的尺寸.与无V钢相比,含V钢中大角度晶界比例提高18.2%,对提高钢的韧性有利.由于C含量过低,在实验钢中未观察到单独的VC析出,由此推测V主要固溶在基体中,以合金化方式促进钢的贝氏体相变,使组织得到有效细化.

英文摘要：

The effects of vanadium on the microstructure refinement of automobile beam steel with a yield strength of 700 MPa were investigated by Gleeble- 3500 Thermo Simulator, scanning electron microscopy, transmission electron microscopy and electron back-scattered diffraction. The results show that a mixture structure of acicular ferrite and granular bainite can be obtained in a cooling rate range of 2 to 7 ℃ · s - 1. It is recognized that the volume fraction of granular bainite increases and the microstructure can be refined by adding vanadium. After the addition of vanadium, the size of M/A islands decreases obviously. Compared to the V-free steel, high angle grain boundaries in the V-bearing steel increases by 18.2% , indicating a potential improvement in toughness. No VC precipita- tion is observed in the tested steel due to low carbon content, so it can be deduced that V in the solid solution can promote the bainite transformation and refine the microstructure.