热轧Nb微合金化TRIP钢高温区变形过程中Nb的析出行为

通过Gleeble热模拟实验研究了含0.038% Nb (质量分数)的热轧TRIP钢在高温奥氏体区的热加工工艺，借助光学显微镜、扫描电镜和透射电镜分析了组织演变和Nb的析出行为，并利用电感耦合等离子体发射光谱仪定量分析了Nb的固溶/析出程度.在1250℃奥氏体化5 min后添加Nb有70%固溶于奥氏体.在1000℃以上的奥氏体再结晶区变形过程中Nb的析出量仅占总固溶量的3%，不能有效抑制静态再结晶，奥氏体晶粒得到明显细化.在900℃的奥氏体未再结晶区变形前析出Nb量已达到总固溶量的9%，再结晶被抑制而获得拉长状奥氏体.奥氏体未再结晶区变形可促进铁素体转变并细化铁素体晶粒.再结晶奥氏体或形变奥氏体状态下冷却至650℃时分别有占总添加量的48%和40%的Nb仍以固溶态存在.

Precipitation behavior of Nb in hot-rolled Nb-microalloyed TRIP steel during high-temperature deformation

ABSTRACT Hot-rolled TRIP steel with 0.038% Nb was thermomechanically processed on a Gleeble simulation test machine. The microstructural evolution and the precipitation behavior of Nb were analyzed by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The amount of Nb in solution/precipitation was quantitatively measured by inductively coupled plas-ma optical emission spectrometry ( ICP-OES) . After austenization at 1250℃ for 5 min, about 70% of added Nb is dissolved into aus-tenite. During hot deformation in the austenitic recrystallized region above 1000℃, only 3% of dissolved Nb precipitates, which is too little to retard static recrystallization of austenite, and then the austenite grain size is markedly refined. Before hot deformation in the austenitic non-recrystallized region at 900℃, the fraction of precipitated Nb is up to 9%, which retards static recrystallization of aus-tenite after hot deformation and results in pancaked austenite grains. Hot deformation in the austenitic non-recrystallized region accel-erates the γ→αtransformation and refines the ferrite grains. After controlled-cooling to 650℃, there are still 48% and 40% of added Nb in solution after thermomechnical processing for recrystallized austenite and deformed austenite, respectively.