Research On Effect Of Cerium On Hot Deformation Behavior Of Super Austenitic Stainless Steel 654SMO

With the rapid development of high-end equipment in the fields of energy conservation and environmental protection,marine engineering and petrochemical industry,the demand for key materials is also increasing.Super austenitic stainless steel has attracted much attention due to its outstanding corrosion resistance,excellent comprehensive mechanical properties and relatively low cost.However,high alloy content of super austenitic stainless steel leads to high precipitation sensitivity,poor hot ductility,high hot deformation resistance,narrow hot working range and easy rolling cracking,which seriously restricts its industrialization process.At present,the high grade super austenitic stainless steel 654SMO,is still in the research stage.Rare earth plays an important role in purifying molten steel,modifying inclusions,refining grains and improving precipitation.It is expected that the hot working problems will be improved if rare earth is introduced into super austenitic stainless steel.Therefore,it is of great practical significance to explore the effect of rare earth on the hot deformation behavior of super austenitic stainless steel 654SMO.In this study,single pass hot compression experiments were carried out on a Gleeble-3800 thermal simulator.The influence of Ce on the hot deformation behavior of 654SMO was systematically analyzed.The Arrhenius constitutive model and hot working diagram were constructed.Combined with the microstructure analysis,the influence mechanism of Ce on thermal deformation resistance,microstructure evolution and hot working range was clarified.The main conclusions are as follows:The rheological curves of CeO and Ce24 steel show typical dynamic recrystallization characteristics.With the increase of deformation temperature or the decrease of strain rate,the hot deformation resistance of both steels decreases,and the hot deformation resistance of Ce24 steel is slightly higher than that of CeO steel;the constitutive equations of CeO and Ce24 steel with high prediction accuracy are constructed based on Arrhenius model,and the thermal deformation activation energies of the two steels are obtained as Q(Ce0)=621.46 kJ·mol-1 and Q(Ce24)=647.42 kJ·mol-1,respectively.With the increase of deformation temperature,the energy required for hot deformation is more sufficient,the grain boundary migration rate increases,the dislocation movement is accelerated,and the critical conditions of dynamic recrystallization are easier to meet.The dynamic recrystallization degree of CeO and Ce24 steel is improved.When the strain rate increases from 0.05 s-1 to 0.5 s-1,the deformation heat promotes the dynamic recrystallization,and the degree of recrystallization increases;when the strain rate increases from 0.5 s-1 to 5 s-1,the deformation time is shortened,the critical dislocation density increases,which hinders the dynamic recrystallization and reduces the recrystallization degree.Ce has dual effects on the dynamic recrystallization of 654SMO:on the one hand,Ce can refine the initial grains,increase the nucleation sites of dynamic recrystallization,and promote the dynamic recrystallization;on the other hand,Ce can reduce the stacking fault energy and increase the difficulty of dislocation movement;the refinement effect of Ce on the initial grains promotes the grain boundary precipitation and enhances the pinning effect;moreover,Ce atoms tend to segregate at the grain boundary and hinder the nucleation and growth of the dynamic recrystallization grains.Overall,the favorable effect of Ce on the initial grain refinement is dominant,which finally promotes the dynamic recrystallization.At low temperature and low rate deformation(950℃,0.05 s-1),low deformation temperature is the main factor of rheological instability:the lack of deformation energy leads to the difficulty of dislocation movement,which is not conducive to the occurrence of dynamic recrystallization.Under this condition,the promotion effect of Ce on dynamic recrystallization is difficult to play;At high temperature and low rate deformation(1150℃,0.05 s-1),low strain rate is the main factor of rheological instability:the deformation time at low speed is long,and the dynamic recrystallization grains squeeze each other to produce dislocations,which hinder the uniform development of dynamic recrystallization.While Ce reduces the non-uniformity of dynamic recrystallization,it is still in the unstable region.Ce has little effect on the hot working range of 654SMO,and the suitable hot working range of both steels is 1150～1200℃,0.5～4.0s-1.