Abstract: The microstructure and mechanical properties of V-Ti,Nb-V-Ti microalloyed non-quenched and tempered steel were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy. The results show that the impact toughness can reach 50 J when rolling ratio is greater than or equal to 10 in the Nb-V-Ti microalloyed non-quenched and tempered steel. While the similar impact toughness is achieved when the rolling ratio reach and more than 15 in V-Ti non-quenched and tempered steel. According to the same rolling ratio, it can be found that impact toughness of Nb-V-Ti microalloyed steel is better than V-Ti non quenched and tempered steel. Niobium addition could raise the coarsening temperature of austenite, effectively inhibit quick growth of austenite, and reduce the grain size and space of pearlite lamellar. The rod cemenite gradually transformed into granular of spherical cemenite. Additionally, Nb could promote the precipitation of fine-dispersed carbides in V-Ti alloyed non-quenched and tempered steel. Therefore, after non-re- crystfdlization region deformation, the Nb-V-Ti alloyed steel could obtain the fine dual phase structure with ferrite and pearlite, and the relatively 900 ℃ temperature large deformation could further improve the strength and toughness of Nb-V- Ti non-quenched and tempered steel.

摘要： 通过金相、扫描、透射电镜研究不同轧制比工艺下V-Ti、Nb-V-Ti两种微合金化非调质钢的微观组织及机械性能。结果显示:Nb-V-Ti非调质钢轧制比大于10时,冲击韧性值可以达到50 J,而V-Ti非调质钢的轧制比却需要大于15以上,才能达到类似的冲击韧性值。从相同轧制比对比也可以发现,Nb-V-Ti非调质钢的冲击性能明显优于V-Ti非调质钢,这是因为Nb能够显著提高非调质钢的奥氏体粗化温度,有效阻止奥氏体晶粒的快速长大,细化非调质钢晶粒,降低珠光体片层间距,使渗碳体呈粒状或球状分布;另外,Nb能促进V-Ti非调质钢中细小含铌碳化物的弥散析出,细化基体组织,同时提高非调质钢的强度。因此,Nb-V-Ti复合非调质钢经过未再结晶区变形后可获得均匀细小的铁素体-珠光体组织,且在900℃未再结晶区进行大轧制比变形能够有效改善Nb-V-Ti非调质钢的强韧性。

关键词: 微合金非调质钢, 铌, 未再结晶区, 大轧制比