Nb和Cu在低碳微合金钢回火过程中的析出行为

Precipitation Behavior of Nb and Cu During Tempering in Low Carbon Micro-alloyed Steel

利用金相技术、硬度测量及透射电子显微术,研究了Nb钢及Nb-Cu钢在525℃回火过程中的析出行为。结果表明:两种实验钢在850℃奥氏体化淬火后,组织类型类似,525℃回火20h后,显微组织没有发生明显变化。Nb-Cu钢在回火的初始阶段硬度下降迅速,15 min后硬度上升,90 min左右到达峰值,Cu的析出快于Nb;而在随后的回火过程中因为Nb的析出导致硬度变化平缓。通过对比Nb钢的硬度曲线及透射电镜观察,认定ε-Cu的析出和NbC的析出是独立进行的,采用相同工艺回火的C-Mn钢硬度变化曲线进一步证实了这一点。

The precipitation behavior at 525℃ in two low carbon micro-alloyed steels containing Nb and Nb-Cu elements was studied by metallographic observation, hardness measurement and TEM technique. The experimental results show that the microstructure of tested steels are similar and stable even though tempered at 525℃ for 20 h after austenization at 850℃ and quenching. The hardness of Nb-Cu steel decreases rapidly at the beginning of tempering. After 15 min, the hardness of Nb-Cu steel increases gradually and at about 90 rain, the peak hardness is observed. The precipitation of Cu is faster than that of Nb. However, the hardness curve decreases slowly with tempering time prolonging due to compensation effect of the NbC precipitation. By comparing the hardness curve of C-Nb steel and the aid of TEM observation results, it is concluded that the occurrence of ε-Cu and NbC precipitates are relatively independent. Furthermore, the experiment results of C-Mn steel adopting the same processes confirm the same conclusion.