Transformation Behavior of Austenite of Nb-bearing Micro-alloyed Low Carbon Steel During Continuous Cooling

The transformation behavior of Nb-bearing micro-alloyed low carbon steel during continuous cooling was investigated by means of MMS-300 thermomechanical simulator. The CCT curves under deformed and un-deformed conditions were obtained by thermal dilation and metallography. The effects of hot deformation and accelerated cooling on microstructure transformation were studied. The experimental results show that the dynamic CCT diagrams shift to the left and upper compared with the static ones,and the onset temperature of γ→α transformation is gradually lower with the increase of cooling rate. The transformation of ferrite and pearlite is accelerated and the transformation of bainite is retarded by high temperature deformation,so the transformation range of ferrite increases; the deformation of austenite has double effects on the transformation of bainite:the deformation inhibits bainite transformation at low cooling rate and promotes bainite transformation at high cooling rate.