AISI 304不锈钢中δ→γ相变的原位观察

IN SITU OBSERVATION O Fδ→γ TRANSFORMATION IN THE STAINLESS STEEL AISI304

利用共焦激光扫描显微镜原位观察了AISI304不锈钢冷却过程中高温铁素体(δ)→奥氏体(→)相变的过程及其特征．结果表明,γ相优先在δ晶界处形成；冷却速率影响γ相的生长形态,典型形态分为块状、圆形、树枝状等；“游离”γ枝晶发生粗化,并和周围的γ枝晶聚合；相同冷却条件下,δ晶界处的γ枝晶聚合程度明显高于δ晶粒内部；二次枝晶在冷却过程中粗化,并竞争生长．利用ThermoCalc计算C元素在δ→γ相变过程中的偏析系数,以此求解δ→γ相变数学模型．

The process and characteristics of high-temperature ferrite （δ） → austenite （γ） transformation during cooling of the stainless steel AISI304 have been observed in situ by using a confocal laser scanning microscope. The results show that the γ phase appeared prior at the δ grain boundaries; The cooling rate affects the growth morphology of γ phase which includes block-like, round, and dendritic; The independent γ dendrite becomes coarse, and may also aggregate with surrounding γ dendrites, the aggregate degree at δ grain boundary is obviously higher than that within the grain at the same cooling rate; The secondary dendrites became coarse, and grew competitively during cooling. Based on the calculated partition ratio of C during δ→γ transformation by using ThermoCalc, the mathematical model of δ→γtransformation is solved.