低碳钢中微细非平衡组织的热稳定性

研究了同一成分的钢经过弛豫-析出控制相变RPC和再加热淬火RQ两种工艺处理后在500到700℃同火过程中组织与性能的演变.经过RPC处理后的钢板随回火温度的升高硬度降低不明显.在600到650℃温度回火时硬度还有所回升:经过RQ处理后的钢板同火前硬度虽然较低,但软化速度非常快.回火前两种钢板组织均为贝氏体和马氏体的复合组织,经RPC处理后的钢板随回火温度的提高组织没有明显变化,只是一些板条出现合并现象,而经过RQ处理后的钢板随回火温度的升高板条很快消失最终演变成多边形铁素体,硬度也随之大幅度下降.以上结果表明微细非平衡组织的热稳定性与其热历史密切相关.

Thermo-Stability of Fine Non-Equilibrium Microstructure in Low Carbon Steel

The evolution of microstructure and hardness of low carbon plate steel during tempering at 500-700℃ was investigated. The steel was manufactured by RFC (Relaxation-Precipitation Controlling phase transformation) technique. A part of the plate was reheated to 930℃ and held for 1 h before quenched into water (RQ) as a comparison. RFC plate softened slowly with the increase of tempering temperature and even became harder between 600 and 650℃. Despite of a lower original hardness of RQ plate it softened faster during tempering. RPC steel and RQ steel are constituted by bainite and martensite microstructures before tempering. The microstructure of RFC steel did not change obviously except some bainitic laths coalescing were detected by means of SEM during tempering, while the boundary of bainitic laths of RQ steel disappeared quickly and finally formed polygonal ferrite forms accompanied a dramatic decrease in hardness. These results indicate that the thermo-stability of fine non-equilibrium microstructure is tightly related to their history.