重加热过程中含Nb微合金钢组织热稳定性

Thermo-stability of the Microstructure in a Nb-containing Microalloy Steel During Reheating

运用热模拟技术 ,结合金相和透射电子显微镜观察 ,研究了含Nb微合金钢在奥氏体区变形后等温弛豫不同时间再水冷得到的复合组织的热稳定性 ,发现在各样品的贝氏铁素体内部 ,位错组态与应变诱导析出颗粒的分布状态明显不同。在随后的 70 0℃重加热等温过程中 ,弛豫 6 0s的样品重加热时热稳定性明显高于弛豫 10 0 0s的样品。重加热前的预应变加速演化过程。这些现象表明 ,显微组织的热稳定性在很大程度上取决于它的形成历史。重加热等温过程发生的组织演化是以板条内位错摆脱钉扎发生多边形化 ,板条间小角倾转晶界通过位错攀移而逐渐消失和发生再结晶形成多边形铁素体的次序进行的。

Thermo-stability of the compound microstructures in a Nb-containing microalloyed steel cooled in water after isothermal relaxation of deformed austenite for different time was studied through thermal simulation test and along with metallographic and TEM observation. The results show that the dislocation configurations and the distribution of strain induced precipitates inside bainitic ferrite of samples relaxed for different time are distinct. When these samples are reheated and held at 650°C or 700°, the thermo-stability of the sample relaxed for 60 s is higher than that of the sample relaxed for 1000 s. The prestrain can accelerates the evolution process before reheating. Dislocations inside laths getting rid of the pinning of precipitates and their polygonization play a precursor to the evolution of microstructures during reheating and holding. Then the lath boundaries disappear gradually caused by dislocation climb. Finally, the recrystallization happens and polygonal ferrite appears.