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利用光学显微镜、扫描电镜、透射电镜和硬度测试等方法研究了再结晶退火与热装等温退火工艺对COST-FB2钢显微组织及硬度的影响。结果表明:采用650~700℃再结晶退火,随着退火温度提高,马氏体板条逐渐回复,M23C6型碳化物尺寸增大,硬度下降;750~800℃区间发生再结晶,硬度最低;850℃退火时进入二相区,冷却过程产生二次马氏体,硬度显著回升。延长700℃再结晶退火时间,硬度缓慢下降,16 h后基本保持不变。采用700℃热装等温退火时,8 h后开始发生铁素体转变,硬度明显下降,100 h后铁素转变完全,硬度最低,随后基本保持稳定。热装退火的软化效果优于再结晶退火。
The effects of recrystallization annealing and hot isothermal annealing on the microstructure and hardness of COST-FB2 steel were studied by means of optical microscope, scanning electron microscope, transmission electron microscope and hardness test. The results show that the martensite lath gradually recovers with annealing temperature increasing from 650 ℃ to 700 ℃, the size of M23C6 carbides increases and the hardness decreases. The recrystallization recrystallization occurs at 750 ~ 800 ℃ and the hardness is the lowest. ℃ annealing into the two-phase zone, the secondary martensite produced during cooling, the hardness rebounded significantly. Extend 700 ℃ recrystallization annealing time, the hardness decreased slowly, remained basically unchanged after 16 h. Ferrite transformation began to occur at 8 h after hot isothermal annealing at 700 ℃, and the hardness decreased obviously. After 100 h, the ferrite transformation was complete and the hardness was the lowest, then remained basically stable. The softening effect of hot-rolled annealing is better than recrystallization annealing.