The Rare Earth On The Mn-re, Bainitic Steel Phase Transformation Kinetics And Organizations

The effect of RE on phase transformation kinetics and morphology in Mn-RE bainite steel during isothermal transformation and continuous cooling transformation has been investigated systematically.On the base,the TTT diagrams and the CCT diagrams were obtained.Which laid the foundation for the establishmen between the problems of organization and sub-structure and the relationship of strength and toughness in the process of heat processing in Mn-RE bainite steel.Rare Earth have a greater effect on isthermal quenched mincrostructure in Mn-RE bainite steel.When the isthermal temperature from Mf to Ms,RE can ease to forme fascicular plates bainite.Rare Earth not only hinder the formation of granular bainite,but also refine the isthermal quenched mincrostructure with the increase of isthermal temperature.It is begining to transform the island bainite at 500℃.The effects of rare earth on bainitic transformation were vestigated by interruption quenched during continuous cooling in Mn-RE bainitic steel.With the increase of RE content,Bs point from 380℃to 350℃,residual austenite amount of the increased,bainitic ferrite instead of the volume fraction decreased,microhardness slightly bigger.Rare earth content has had a significant impact between the level of competition of sympathetic nucleation and ledgewise growth of Bainite.Substructure in bainitic is finer with the mixed rare earth content increasing.The bainite steel are divided by stable residual austenites between subplates and subunits,and eventually formed multi-level fine mincrostructure of bainite.When the quantity of RE elements was added,the CCT diagrams are shifted to righ and to down,the hardenability was increased.During transformation of bainite,ferrite fraction of 1~# steel decreased sharply with cooling rate increasing,carbon-free bainite fraction raised.When the cooling rate higher than 40℃per minute,carbon-free bainite transform to lath bainite.However, cooling rate has less effect on ferrite fraction of 2~# steel,which transform to lath bainite.The structure of bainite was fined remarkable.Rare Earth can Increase the value of the phase structural factor(n_A & F_C~D),and form the segregation unit as the center of RE;In the process of transformation,Rare Earth impede the proliferation of carbon and increase the resistance of transformation caused by Fe-C-M segregation unit.Thus the bainite transformation has been postponed and the mincrostructure of bainite has been fined.