P20钢变形奥氏体连续冷却时的相变规律

CONTINUOUS COOLING TRANSFORMATION BEHMIOUR OF DEFORMED AUSTENITE FOR PLASTIC DIE STEEL P20

采用膨胀法结合金相分析建立了P20钢的CCT曲线,根据动态CCT曲线，提出P20钢轧后控冷预硬化工艺．与常规热处理条件相比，形变热处理条件下的奥氏体具有较高的稳定性.变形后以0．2—0．02℃／s连续冷却时，主要发生贝氏体相交，而多边形铁素体相变被抑制．变形可使奥氏体机械稳定化，阿氏体相变推迟至较低温度下完成.P20钢轧后在贝氏体相变区缓冷获得粒状贝氏体组织，实现在线预硬化，硬度达到35—38．

The continuous cooling transformation (CCT) diagrams of austenite in various states for steel P20 were constructed by means of the combined method of dilatometry and metallography. The influence of deformation process on the transformation behaviour and microstructure was investigated. The thermomechanically processed austenite was more stable than that treated by conventional hardening process. Polygonal ferrite transformation did not occur during continuous cooling at rate ranging from 0.2℃/s to 0.02℃/s. Deformed austenite caused itself mechanical stabilization, hence retarded the bainitic transformation to lower temperature.The experlinental results manifest that steel P20 treated by slowly continuous cooling through bainitic transformation region after hot rolling can produce granular microstructure and reveal hardness of HRC 35-38.