中文摘要：

研究了经过弛豫-析出控制相变技术（RPC技术）生产的低碳微合金钢板在650 ℃回火过程中组织与性能的演变,同时与经过930 ℃保温1 h后再加热淬火（RQ）的钢板进行了对比.结果表明,回火前两种钢板的组织均为贝氏体＋少量马氏体,经过RPC技术生产的钢板回火0.5 h后,金相组织没有明显变化,但硬度下降幅度较大;在1～7 h的回火过程中部分组织出现板条合并现象,此阶段硬度值变化不明显;7 h之后某些区域组织的板条特征趋于消失,出现了少量多边形铁素体,硬度又明显下降;回火20 h后,约一半的组织转化为多边形铁素体.而经过再加热淬火处理后的钢板回火前硬度虽然较低,但回火过程中软化速度极快,板条组织很快消失.最终获得全部的多边形铁素体组织.因此超细组织的热稳定性取决于其热历史.

英文摘要：

The evolution of microstructures and hardness of low carbon microalloyed steel plate during tempering at 650℃ has been investigated. The steel plate was manufactured by RPC （relaxation-precipitation controlling phase transformation） technique. As a comparison a part of the plate was reheated at 930℃ holding for 1 h, then quenched （RQ）. The results show that the microstructures both of RPC steel and RQ steel are ultra-fine bainite with little martensite before tempering. No obvious change is detected by means of optical microscopy in RPC steel tempered for 0. 5 h ,while accom- panied by obvious drop of hardness. Bainite laths start to coalesce in some regions, but the sample hardness keeps nearly constant during tempering from 1 h to 7 h. With further tempering, polygonal ferrite forms in local regions while hardness decreased dramatically. Until tempering for 20 h, about half of bainite laths transform into ferrite. Despite that the RQ steels have lower original hardness, the samples soften faster during tempering. Boundaries of bainite laths of RQ steel disappear quickly and finally transform into polygonal ferrite completely. These results indicate that thermo-stability of ultra-fine microstructures is tightly dependent on their thermo-history.