含钼双相钢DP600相变研究和工艺实践

采用热模拟试验研究了含钼双相钢DP600在不同冷却模式、转变温度和冷却速率时的显微组织转变，分析了相变后的马氏体比例和晶粒度级别，根据热模拟结果设计了DP600钢的生产工艺，并探讨了钼元素对双相钢的影响。结果表明，DP600钢在热轧组织转变时，两段式冷却工艺比一段式工艺形成的马氏体细小，且晶粒度提升1级。奥氏体向铁素体转变过程中，存在最佳相变温度平衡点；590 ℃以上减缓DP600钢铁素体＋珠光体的过冷转变速率，可以细化晶粒、增加马氏体比例。生产的DP600钢金相显微组织为铁素体＋马氏体，马氏体比例为17%，晶粒度为11级；纵向、横向抗拉强度分别为592和620 MPa，伸长率分别为28.5%和26.5%。钼元素可以强烈抑制C- Si- Mn- Cr- Mo系DP600钢的铁素体转变，缩小铁素体转变区。

Research of phase transition and process practice on DP600 dual phase steel with molybdenum

The microstructure transformations of the dual phase steel DP600 with Mo in different cooling modes, transition temperatures and cooling rates were studied by thermal simulation experiments. The proportions of martensite and the grain size levels were analyzed after phase transition, and the production process of DP600 was designed on the basis of the experiments, while the influence of Mo element on dual phase steel was also discussed. The results showed that the martensite formed by the two- stage cooling process was smaller than that by the one- stage process, and the grain size was improved one level after the change of hot rolling microstructure was finished for DP600 steel. There was a good phase transition balance temperature in the process of transformation from austenite to ferrite. Reducing the overcooling transition rate of ferrite and pearlite in the DP600 steel over the temperature of 590 ℃ would refine grain size and increase the proportion of martensite. The microstructure of the DP600 steel obtained by production was ferrite and martensite. Meanwhile, the martensitic ratio was 17% and the grain size was 11 level. The tensile strength in vertical and horizontal direction was 592 and 620 MPa, respectively, and the elongation was 28.5% and 26.5%, respectively. The Mo element could strongly inhibit the transformation of ferritic and reduce the ferrite transition zone for the C- Si- Mn- Cr- Mo DP600 steel.