冷速对含硅低碳钢高温δ→γ相变的影响

摘要

High temperature ferrite （δ）→austenite （γ） phase transformation in a low carbon silicon-bearing steel （0. 98% Si） was observed by in situ using a confocal scanning laser microscope（CSLM） at three different cooling rates（1,10,30 ℃ · s-1）. The effect of cooling rate on the transformation was analyzed. The results show that the undercooling increased and the starting transformation temperature lowered with increasing the cooling rate. At lower cooling rate, the T phase nucleated only at the δ grain boundaries, but not happened inside the grains. While at higher cooling rate, the γ phase precipitated both at the δ grain boundaries and inside δ grains, and deeper undercooling was needed when inside the grains. The γ boundaries nibbled the δ matrix phase with plana-like patterns during its growth process. The migration velocity of the grain boundary increased with increasing the cooling rate.%利用共聚焦激光扫描显微镜原位观察了含硅低碳钢（0．98％硅）在三种不同冷速（1，10，30℃·s-1）下高温铁素体（δ）→奥氏体（γ）相变的过程，分析了冷速对该相变的影响。结果表明：随冷速的增加，过冷度增大，相变点下降；在慢冷速下，新相γ仅在δ晶界处形核，而在晶粒内部没有发现形核；在快冷速下，新相在晶界和晶粒内部形核，并且在晶粒内部形核需要更大的过冷度；新相γ在长大过程中是γ晶界以平面状迁移的方式“蚕食”δ母相。随冷速增加，晶界迁移速度增大。