Research On Grain Refinement During Hot Deformation Of Duplex Stainless Steel

As a special kind of stainless steel,duplex stainless steel(DSS)is characterized by its dual phase structure,that is,austenite and ferrite.Combing the advantages of austenitic stainless steel and ferrite stainless steel,with excellent corrosion resistance,high strength,good toughness and weldability.It is widely used in deep-sea pipeline,petrochemical,shipbuilding and papermaking industries,so as to become the mainstream steel in the 21~stt century.The forming characteristics of a duplex stainless steel were studied in this paper.The single pass thermal compression test of duplex stainless steel was carried out with Gleeble-1500D thermal simulator.The evolution of microstructure during hot deformation was observed,the effect of deformation temperature and strain rate on flow stress was analyzed,and the grain refinement mechanism of duplex stainless steel during hot deformation was discussed.Constitutive relation of hyperbolic sinusoidal equation based on Arrhhenius type is constructed by Z parameter method,and the calculated results are in good agreement with the experimental results.At the same time,the hot machining diagram based on dynamic material model and Prasad model instability criterion is established to analyze the power dissipation rate and instability range of different deformation parameters in different true strain range.To provide guidance for hot working parameters of duplex stainless steel.The main conclusions are as follows:(1)Dynamic softening mechanism exists during hot deformation of duplex stainless steel.The higher the deformation temperature and the lower the strain rate,the longer the steady-state region,the dynamic softening mechanism is more obvious.When the deformation temperature is high,fine austenite grains appear in the microstructure,and the ferrite grain boundaries are gradually bent and the grains are gradually refined.When the strain rate is low,the content of austenite in the microstructure increases,but the dynamic recrystallization is caused by the insufficiency of ferrite bearing most of the strain.With the increase in strain rate,promotes the formation of dynamic recrystallization,dynamic recrystallized grains were refined because of the late recovery and grow.(2)Based on the constitutive equation of Arrhenius type hyperbolic sinusoidal equation.The analysis of absolute error and correlation shows that:the experimental results are in good agreement with the predicted values.The model can predict the flow stress of duplex stainless steel under different deformation parameters during hot deformation.(3)According to the established hot working diagram,the optimum parameters selection range for hot working of duplex stainless steel.The region is unstable and energy dissipation is high,which provides the system with high energy for microstructure evolution.The system can be fully dynamically recovered and recrystallized.