一种Nb⁃Ti微合金化贝氏体钢等温转变研究

Isothermal transformation study of a Nb⁃Ti micro⁃alloyed bainitic steel

对一种Ni,Cr,Cu复合强化、Nb⁃Ti微合金化处理的贝氏体钢进行了热模拟研究。分别在贝氏体转变区600,550,500℃三个温度点等温处理90 s,得到了三种不同的微观组织。在上温度点等温处理,贝氏体转变表现出不完全的特征,在随后冷却过程中仍有相变发生;在中间温度点等温处理,剩余未转变的奥氏体相变导致的膨胀率仅有10%左右,贝氏体组织明显细化,组织强度最高;在下温度点等温处理,相变已接近全部完成,组织得到明显细化,生成的大量奥氏体⁃马氏体(MA)岛造成强度下降。

A thermal simulation of a Ni,Cr and Cu composite strengthened,Nb-Ti micro-alloyed treated bainitic steel is carried out.Three different microstructures are obtained after isothermal treat⁃ment at 600,550 and 500℃for 90 seconds respectively in the bainite transformation temperature range.After isothermal treatment at the upper temperature point,the bainite transformation shows in⁃complete characteristics,and there is still phase transformation in the subsequent cooling process.Iso⁃thermally treated at the middle temperature point,the expansion rate caused by the transformation of residual austenite remaining untransformed is only about 10%,the bainite structure is obviously re⁃fined,and the strength of the structure is the highest.After isothermal treatment at the lower tempera⁃ture point,the phase transformation is nearly completed,and the structure is obviously refined.Mean⁃while,a large amount of austenite-martensite(MA)islands are generated,which results in a decrease in strength.