送装工艺对板坯再加热过程奥氏体晶粒细化的影响

连铸坯下线至加热炉的温度制度及其表层组织演变与热送或粗轧裂纹密切相关.基于热模拟实验分析了送装工艺对奥氏体转变特征和再加热晶粒尺寸的影响.高温共聚焦激光扫描显微镜原位观察表明,含Nb J55钢在双相区700℃热装时,组织为晶界膜状先共析铁素体、魏氏体和大量残留奥氏体,再加热至1200℃,奥氏体晶粒大小、位置都不变;单相区600℃温装时,组织为大量铁素体+珠光体,再加热至1200℃时,奥氏体晶粒明显细化.马弗炉模拟SS400钢双相区不同热装温度发现,铁素体转变量至少达70%时才可细化再加热后的奥氏体晶粒.在临界转变量以上,基体中铁素体转变量越多晶粒细化程度越明显.

Effect of charging processes on the austenite grain refinement of continuously cast slabs during reheating

The thermal regime and structural control between continuous caster offline and a reheat furnace has a significant im-pact on the cracking problem occurring during hot charging or hot rolling. The effect of the charging process on the characteristics of austenite transformation and sizes of reheated grains was experimentally analyzed using thermal simulation. The in situ observation re-sults using a high-temperature confocal laser scanning microscope shows that film-like ferrite and Widmanst?tten ferrite are present along the grain boundary with amounts of retained austenite when hot charged at 700℃ in the dual phase region for J55 steel, and the size and location of the austenitic grain remain constant after reheating to 1200℃. When warm charged at 600℃ in the single phase region, large amounts of ferrite and pearlite are observed, and austenite grains are clearly refined after reheating to 1200℃. It is also found that the austenitic grain can only be visibly refined when the transformed ferrite fraction is higher than 70% for SS400 steel hot charged at different temperatures using a muffle furnace. The grain refinement is more obvious when the transformed ferrite fraction is higher than the critical value.