中文摘要：

研究了系列低碳微合金Ti-Nb可焊钢中的N含量对模拟焊接热影响区（HAZ）高温奥氏体晶粒尺寸和冲击韧度的影响及其第二相粒子的作用.对试样进行了大热输入焊接热模拟,测定了高温奥氏体晶粒尺寸和焊后试样中的冲击韧度值,并用透射电子显微镜萃取复型法观察了典型试样中第二相粒子（Ti,Nb）N的形态及分布特征.结果表明,钢中Ti、N含量及第二相粒子的尺寸和数目与高温奥氏体晶粒尺寸及冲击韧度值具有很好的对应关系;钢中的N由于生成了细小弥散分布的第二相粒子（Ti,Nb）N而细化了高温奥氏体晶粒,改善了焊后韧性.低碳微合金Ti-Nb钢中适宜的含氮量有一个范围.

英文摘要：

The effects of nitrogen content on austenite grain size at high temperature and impact toughness of simulated welding HAZ and actions of second phase particles (Ti, Nb)N in series low carbon Ti-Nb microalloyed weldable steels were studied. The simulated weld with great heat input had been carried out. The austenite grain size at high temperature was measured and impact toughness after welding was tested. Morphology and distribution characteristics of second phase particles (Ti, Nb)N in typical specimens had been observed by using transmission electron microscope by means of carbon extraction replicase technique. The results showed that there is good correspondence among Ti and N content, size of particles (Ti, Nb)N, austenite grain size and impact toughness. Toughness after welding is improved because of formation of fine and dispersive second phase particles (Ti, Nb)N which refines austenite grain size at high temperature. There is a scope of rational N content in low carbon Ti-Nb microalloyed weldable steels.