钒和铬对贝氏体车轮钢回火组织与性能的影响

Microstructure and Mechanical Properties of Tempered Bainitic Railway Wheel Steels with Addition of V and Cr

贝氏体车轮钢开发已经成为国际研究热点。新近开发的空冷型锰—硅系贝氏体车轮显示了良好的应用前景,但其成分和热处理工艺有较大改进空间。本文通过扫描电镜(SEM)、透射电镜(TEM)观察和力学性能测试等系统研究了钒和铬对该系贝氏体钢,回火组织与力学性能的影响。结果表明,实验钢在空冷+低温回火后都可获得板条贝氏体+粒状贝氏体+残余奥氏体的组织。其中铬的添加可降低钢的贝氏体转变温度,在提高残余奥氏体的稳定性的同时,有利于贝氏体车轮钢强度和低温韧性提升。钒的添加可通过V(C,N)沉淀强化作用,使贝氏体车轮钢的屈服强度在480~560℃回火温度范围提高,得到显著的二次强化效果。但当铬与钒同时添加时,V(C,N)析出会受到抑制,二次强化效果明显减弱。此外,实验钢在400℃以上回火时会出现明显回火脆性,冲击功大幅下降。因此,在锰-硅系贝氏体车轮钢中添加钒和铬并在320℃回火时可以获得优化的强韧性能匹配。

Bainitic wheel steels have drawn high attentions in the world.A new Mn-Si bainitic wheel steel developed recently demonstrates excellent general properties,while it is noted that this new bainitic steel could be highly elevated by adjustment of chemical composition and heat treatment.In this work,the influence of vanadium and chromium addition on tempered microstructure and mechanical properties of these steels were studied through scanning electron microscopy(SEM),transmission electron microscopy(TEM)and mechanical properties tests etc.The results showed that the microstructures of all experimental steels after low temperature tempering were mainly lath bainite,granular bainite and retained austenite.Cr addition had significant effect on reducing bainitic transformation temperature as well as enhancing the retained austenite’s thermal stability,which benefited in the increment of hardness and low temperature toughness.V addition could enhance the yield strength through precipitation strengthening of V(C,N)when it was tempered at 480~560℃,presenting remarkable secondary strengthening.But when V and Cr were added simultaneously,this strengthening would be weakened because of the restraint of V(C,N)precipitation.Moreover,when tempering temperature exceeded 400℃,temper embrittlement occurred for both experimental steels and the impact energy greatly declined.So bainitic wheel steels containing V and Cr would reach the best match of strength and toughness when it was tempered at 320℃.