Formation of proeutectoid ferrite during dynamic transformation of undercooled austenite in a eutectoid steel

The dynamic transformation of undercooling austenite under various strain rates was investigated using single pass isothermal hot compression experiments in eutectoid steel,and thermal-calc calculation was used to disscuss the mechanism governing the dynamic transformation process.The results show that proeutectoid ferrite forms firstly at the prior grain boundaries of austenite before pearlite transformation.The interlamellar space and the thickness of cementite lamellae of the pearlite formed by dynamic transformation of undercooled austernite are smaller than that of pearlite fromed by isothermsl transformation.Increasing the strain rate leads to the increase in the volume fraction of proeutectoid ferrite,the slight increase of the thickness of cementite lamellae and the decrease of the interlamellar space of pearlite formed by dynamic transformation of undercooled austenite.Thus,it is concluded that hot deformation of undercooled austenite leads to the right-shift of eutectoid point,which is different from the Fe-C equilibrium phase diagram.