材料期刊网

对热轧铁素体贝氏体双相钢 FB60、铁素体马氏体双相钢 DP600和铁素体珠光体钢SPFH590等三种汽车用高强钢板进行了扩孔试验,利用光学显微镜观察了扩孔裂纹的萌生和扩展,研究了不同钢的扩孔性能及开裂机理。结果表明：FB60钢的扩孔性能最优,DP600钢的最差；SPFH590钢与FB60钢具有相同的屈强比,但其扩孔性能却不及FB60钢的；组织对扩孔性能的影响与扩孔裂纹的萌生和扩展有关,FB60钢的裂纹萌生于铁素体内以及铁素体与贝氏体晶界,绕过贝氏体穿过铁素体扩展；SPFH590钢的裂纹萌生于铁素体与珠光体边界、珠光体内铁素体与渗碳体界面和铁素体内,极易沿铁素体与渗碳体片层扩展；DP600钢的裂纹萌生于铁素体与马氏体晶界,并沿晶界扩展。

Hole expansion tests were conducted for hot-rolled ferrite-bainite dual phase steel FB60,ferrite-martensite dual phase steel DP600 and ferrite-pearlite steel SPFH590.Optical microscope was used to observe formation and propagation of expansion cracks and analyze the hole expansion property and cracking mechanism of the steels.The results show that the FB60 steel exhibits the best hole expansion property,and DP600 steel exhibits the worst hole expansion property.However,the yield ratio of SPFH590 steel was equal to that of FB60 steel,but the hole expansion rate of SPFH590 steel less than that of FB60 steel.The effect of microstructure on hole expansion property was related to the formation and propagation of expansion cracks.The cracks formed not only at ferrite-bainite interfaces but also within ferrite grains in FB60 steel,and propagated along the phase interface between ferrite and bainite and by cutting off ferrite grains.The expansion cracks formed at ferrite-pearlite interfaces,ferrite-cementite interfaces within pearlite and within ferrite grains in SPFH590 steel,and propagated easily along the ferrite-cementite interface.The cracks formed at ferrite-martensite interfaces in DP600 steel,and propagated along the phase interface between ferrite and martensite.