Study On Hot Deformation Behavior Of High Nitrogen Austenitic Stainless Steel

The use of nitrogen instead of nickel in highnitrogen austenitic stainless steel can not only reduce the cost,but also improve the strength and corrosion resistance of the material without too much reduction in plasticity.However,there is also a phenomenon of recovery retardation,which tends to cause stress concentration and cracking during the rolling process.Therefore,the hot deformation behavior of high nitrogen austenitic stainless steel was studied.In this paper,single and doublepasshotcompression experiments of high nitrogen austenitic stainless steel were carried out by using thermal simulation test machine Gleeble-3500.The deformation temperature and strain rate of single pass hot compression are 950?,1000?,1050?,1100?and 0.01s^-1?0.1s^-1?0.5s^-1?1s^-1,respectively.The effects of deformation conditions on flow stress and microstructure were analyzed.The high temperaturehotdeformation equation and the dynamic recrystallization kinetics model were established,and the hotprocessing maps with different amount ofdeformation were drawn.The deformation temperaturesof the double pass experiments are the same as that of the single pass.The strain rate is 1s^-1,and the residence time between intermediate passes is 5²0s.The metadynamic recrystallization kinetics model was established by analyzing the effects of temperature change and residence time on the flow stress and microstructure.The research results are as follows:1.The original data of the single-pass hot compression experimentswas fitted with the origin software.The influencesof experimental temperature andstrainrate onflow stress curves were analyzed.The microstructure wasobserved and analyzed by means of metallographic microscope and scanning electron microscopy.Conclusions are as follows:with the constant strain rate,the flow stress decreases with the increase of deformation temperature;with the constant deformation temperature,the flow stress increases with the increase of strain rate.The thermal activation energy is 574.694KJ/mol,and the correlation coefficient between the predicted value and the actual value of the established constitutive equation is99.998%.The main softening mechanism of the high nitrogen austenitic stainless steel is dynamic recrystallization,and a dynamic recrystallization kinetics modelwas established.Based on the dynamic material model,hot processing mapsof high nitrogen austenitic stainless steelwere obtained by power dissipation diagramsand rheological instability diagrams.The optimum thermal processing parameters range from 980 to 1040?and strain rate range from 0.05 to 0.24s^-1.2.Flow stress curves were analyzed and fitted after double pass hot compression on high nitrogen austenitic stainless steel,and the microstructure after hot compression was observed.The metadynamic recrystallization volume fraction increase with the prolongation of the residence time between the passes and the increase of the deformation temperature.The residence time of metadynamic recrystallization volume fraction reached 50%was obtained by linear regression analysis.The metadynamic recrystallization activation energy was obtained and the metadynamic recrystallization kinetics equation was constructed.