运用热模拟方法,结合萃取复型、硬度测量及透射电子显微镜观察(TEM)等方法,研究了含Nb微合金钢经850℃热变形并弛豫不同时间后、水淬并在525℃时效时的硬度变化及析出行为.结果表明:变形奥氏体弛豫一定时间淬火后,在时效过程中出现双硬化峰现象;而奥氏体变形后直接淬火或长时间弛豫(1000s)则没有第一个硬化峰出现.对比C-Mn钢的分析结果证明Nb是产生硬化峰的重要原因.电镜观察的初步结果显示,变形奥氏体中形成的细小析出在时效过程中逐渐长大,已粗化的析出颗粒在525℃等温时效时变化不明显;而经过γ→α相变后α相中过饱和的Nb在时效时会重新析出,形成第二个硬化峰.
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