Study On The Influence Of Loading Direction On The Hot Deformation Behavior Of Cr20Mn2Ni2 Duplex Stainless Steel

Duplex stainless steel has a two-phase microstructure consisting of both ferrite and austenite phases.Due to its high strength,exceptional toughness,superior thermal conductivity and robust corrosion resistance,it has always been one of the main areas of focus in the development of corrosion resistant metals.Economical duplex stainless steel mainly replaces the Ni and Mo elements of conventional duplex stainless steel with N and Mn elements,which significantly reduces production costs while maintaining excellent overall properties and offering great development potential.However,the incorporation of the N element in this material increases the high-temperature strength of the austenite phase,leading to an increased disparity in mechanical properties between the two phases at elevated temperatures.This results in material deformation incompatibility,strain and stress concentration during hot working,ultimately leading to material failure.Therefore,investigating the hot deformation behaviour of low cost duplex stainless steel and analysing the stress and strain distribution patterns of the two phases during deformation is of great importance for the development of the material.In this thesis,we used an independently developed forged economic duplex stainless steel as the subject of our research.Through hot compression tests,we obtained the true stress-strain curve of the material under various strain rates(0.01～10s^-1)and deformation temperatures（1000℃～1200℃）,and then established the hot deformation constitutive equation of the material.Based on the rheological curve of the material under longitudinal loading,we developed the peak strain model,the dynamic recrystallisation critical strain model and the dynamic recrystallisation volume fraction model.Using the dynamic material model theory and the Prasad instability criteria,we plotted the hot working maps of the material for different amounts of deformation under two loading directions.We also analysed the hot working performance and microstructure evolution patterns of the material under different conditions,using microstructure analysis to determine the optimum hot working process conditions for economical duplex stainless steel.Based on the mixed law,we established stress distribution models,strain distribution models and finite element models for the experimental steel under two loading directions.We analysed the stress and strain distribution patterns for the experimental steel under both loading directions and found that under longitudinal loading,the two phases exhibit coordinated deformation,resulting in enhanced material plasticity.Conversely,under transverse deformation,the strain distribution of the two phases is uneven,with the ferrite phase bearing the majority of the deformation.However,as the amount of deformation increases,the deformation of the two phases becomes progressively more coordinated.