Transformation of Ferrite in Lower Bainite of 1.5%C UHCS During Tempering Process
Fe-1.5C-1.5Cr-2.0Al UHCS austempering at 300℃ was treated with tempering treatment at 400-550℃.The microstructure was observed by SEM and the micro-zone composition was analyzed by EDS,transformation of ferrite in lower bainite and composition changes during temper process were studied.The results indicate that the dislocations between pieces and pieces of lower bainite disappeares firstly when the Fe-1.5C-1.5Cr-2.0Al UHCS austempering was treated by temper process,most of these dislocations comes into cystiform structure,and the lower bainite pieces broadens and merges to polygon ferrite,this kind of complex phases microstructure is completely changed to precipitated phase and matrix finally.Nonisometric blocky ferrite and polygon ferrite appears during the tempering process,the blocky ferrite comes from the decomposition of retained austenite,and the polygon ferrite comes from the lower bainite pieces.