热变形工艺参数对超低碳贝氏体钢转变行为和显微结构的影响

Effect of Hot Rolling Schedules on the Transformation Behavior and Microstructure in Mn-Mo-Nb-B Ultralow Carbon Bainitic Steel

研究了超低碳贝氏体钢在 1 2 0 0～ 40 0°C范围内 ,用常规轧制工艺 ( CCR)、再结晶控制轧制 ( RCR)和动态再结晶控制轧制 ( DRCR) 3种热模拟变形工艺进行变形后再进行连续冷却转变行为 .结果发现 ,3种变形工艺均可细化奥氏体的晶粒 ,而且细化晶粒程度的变形工艺顺序依次为DRCR、RCR和 CCR.此外 ,奥氏体的转变行为受到 CCR、RCR和 DRCR工艺的影响 .同一冷却速度下 ,3种不同的变形工艺获得过冷奥氏体发生贝氏体转变的开始温度不同 .显微结构观察表明 ,在试验冷却速度下 ,用 CCR工艺变形 ,全部获得铁素体且存在少量的化合物 ;用 RCR和 DRCR工艺变形 ,全部获得贝氏体 ,贝氏体呈板条状 ,其尺寸随冷速的增大而减小 。

The effect is investigated by means of continuous cooling torsion test (CCT) using conventional controlled rolling (CCR), recrystallization controlled rolling (RCR) and dynamic recrystallization controlled rolling (DRCR) at 1200-400°C. It is found that the austenite grains are refined by three rolling schedules, the refinement degree of which is DRCR, RCR and CCR. At the same cooling rate, the bainite transformation temperature of deformed specimens with the three schedules is different. The final structure obtained from the CCR is ferrite and some little compounds, whereas the bainite structure is obtained by the schedules of RCR and DRCR which takes the morphology of plate-like. The size and fraction of bainite structure are changed with cooling rate.