超细化低碳贝氏体钢的回火组织及力学性能

TEMPERING MICROSTRUCTURES AND MECHANICAL PROPERTIES OF AN ULTRA-FINE LOW CARBON BAINITIC STEEL

研究了弛豫-析出控制相变(RPC)技术参数(弛豫时间)对超细化低碳贝氏体钢回火后组织与性能的影响,同时与控轧后空冷(AC)以及传统的再加热淬火工艺(RQ)得到的回火组织及性能进行了比较.不同RPC技术参数得到的钢板经300-700℃回火1h后,随温度升高均呈现软化-硬化-再软化的变化规律,只是变化速度及硬度值有所不同.经过AC工艺得到的钢板在回火后硬度和强度变化不明显,而经过RQ处理后的钢板随回火温度升高强度和硬度单调下降 回火前RPC和RQ两种工艺得到的钢板组织均为板条状贝氏体和少量粒贝的复合组织.回火后RPC工艺钢组织变化不明显,只是弛豫不同时间的试样组织粗化速度不同,而RQ工艺钢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.实验结果表明,利用RPC工艺得到的高强韧性钢板具有良好的热稳定性.

Effect of the parameter of RPC (relaxation-precipitation controlling phase transformation) technology on the microstructures and mechanical properties of an ultra fine low carbon bainitc steel tempered at 300-700 degreesC was investigated, and compared with those of same composition steels processed by RQ (reheating and quenching) and AC (controlled rolling and air cooling). Afters tempered at 300-700 degreesC for 1 h, the hardness and strength of all the RPC plates demonstrate a softening-hardening-softening phenomenon, but the rate of-hardness change and the effect of hardening are different in samples relaxed for different times. The hardness and strength of AC plate are not obviously changed and those of RQ plate decrease faster with increasing temperature. The main microstructures of RPC steel and RQ steel both are lath-like bainite and little granular bainite before tempering. The microstructure of RPC steel does not change obviously after tempering, except the rate of microstructures coarsening are different in samples relaxed for different times. Otherwise, the boundaries of bainitic laths in RQ steel disappear quickly and finally a polygonal ferrite formed. These results indicate that the high strength and toughness steels manufactured by RPC technique possess high thermo-stability, which is caused by the different states of dislocation and precipitates interaction in steels treated by various processes.