Research On Hot Deformation Behavior And Microstructure Evolution Of ESR Mn18Cr18N Austenitic Stainless Steel

Mn18Cr18N is used as the power equipment large generator ring steel,it belongs to high-nitrogen austenitic stainless steel and has good comprehensive performance and stress corrosion resistance.At present,Mn18Cr18N electroslag remelting ingot is used to produce guard ring,which has high purity and good compactness.However,quality problems such as uneven microstructure and properties will be found in forgings because of the developed columnar crystals,coarse,mixed crystals,etc.In this paper,Mn18Cr18N electroslag remelting ingot as the research object,the methods of thermal simulation,test analysis and numerical simulation were adopted to study the thermal deformation behavior and microstructure evolution of ESR Mn18Cr18N steel,establish the constitutive equation of thermal deformation and the microstructure evolution model and analyze the numerical simulation of the process.All these means were carried out to provide theoretical basis and key technical parameters for the microstructure and properties of ESR Mn18Cr18N steel ring forgings.Firstly,thermal deformation stress-strain curve of Mn18Cr18N steel was carried out under the condition of the temperature range from 950?C to 1200?C and strain rate range of 0.001-1s^-1 and true strain 0.69 by using Gleeble-1500D thermal simulation testing machine.On this basis,the thermal deformation behavior and characteristic parameters of the steel were analyzed.The hot deformation activation energy of the steel was calculated as high as 637.35KJ/mol,which indicates that the dynamic recrystallization of the steel is slow.The strain index of 4.95 suggests that hot deformation of the steel is mainly controlled by dislocation climb.By analyzing and modeling the characteristic points of the rheological curve,the two-stage Laasraoui equation was used to establish the flow stress equation of the steel.The microstructure evolution of dynamic recrystallization under thermal deformation was obtained and the dynamic recrystallization kinetics and grain size evolution model were established by Metallographic method and analyzed the microstructure evolution of ESR Mn18Cr18N steel during thermal deformation,which provided the microstructure evolution model for the numerical simulation of the microstructure of hot deformation of the steel.The microstructure evolution model of thermal deformation of ESR Mn18Cr18N steel was guided into Deform-3D simulation software to simulate and analyze the thermal parameters and microstructure evolution in the process of one large deformation upsetting and three small deformation accumulative upsetting,and the experimental verification was carried out.The results show that the fine and uniform grain structure can be obtained,and the high-temperature ferrite can be dispersed and dissolved into the matrix structure to obtain higher comprehensive mechanical properties by forging the ESR Mn18Cr18N steel with three small deformation accumulative upsetting process.