In-situ Study On The Effect Of Mixed Crystal On The Deformation Coordination Mechanism Of Austenitic Stainless Steel

In the hot forming of nuclear power main pipe material X2 CrNiMo18.12 austenitic stainless steel,mixed crystal structure often occurs,which seriously damages the mechanical properties of the material,and the mechanical properties of the material are closely related to the uncoordinated deformation behavior.However,there is a lack of systematic research on the deformation coordination of mixed crystal structure of X2 CrNiMo18.12 austenitic stainless steel.Therefore,it is a problem worthy of attention in this field to clarify the influence of mixed crystal on the coordinated deformation of structure.In this paper,the as-forged X2 CrNiMo18.12 austenitic stainless steel was used as the original material,and three kinds of mixed crystal structures were obtained by different thermal deformation + heat treatment tests.The in-situ tensile tests of the three structures were carried out at room temperature.Combined with electron scanning and electron backscatter diffraction techniques,the slip trace lines,crystal orientation,grain boundary orientation difference,local strain distribution and other information of the three structures were obtained.The grain rotation and slip opening of different mixed crystal structures during tensile process at room temperature were analyzed to clarify the stress and strain distribution of mixed crystal structures during tensile process.In the deformation process of mixed crystal structure of X2 CrNiMo18.12 austenitic stainless steel,most of the grains larger than 100μm have slip traces when the displacement is 640μm,while the slip traces of grains smaller than 100μm appear later,and some grains appear slip traces when the displacement is 7050μm.The orientation of the crystal accelerates with the increase of the stretching amount.The grains less than100μm rotate at a larger angle during the stretching process,but there is only one rotation path.The rotation angle of grains larger than 100 μm is smaller,but the rotation path is more than two.With the tensile process,the area of stress concentration in the microstructure gradually increases.The stress concentration at the grain boundary of the grains larger than 100μm is more serious during the tensile process,but there is no obvious stress concentration inside the grains.The stress concentration phenomenon occurs at the grain boundary and inside the grains of less than 100μm during the tensile process.By comparing and analyzing the in-situ test data of three mixed crystal structures,it is found that the mixed crystal has a certain influence on the coordinated deformation behavior,and the strain distribution is also different.In different mixed crystal structures,the slip plane of grain activation is {111} crystal plane family,and the slip direction is crystal orientation family.In different mixed crystal structures,the larger the mixed crystal degree is,the larger the rotation angle of the grains is,that is,the higher the mixed crystal degree of the structure is,the more obvious the orientation change of the grains is.However,in different mixed crystal structures,most of the grain orientations move towards the [111] direction.In different mixed crystal structures,the larger the mixed crystal degree,the more uneven the strain distribution of the structure during the tensile process,and the more serious the stress concentration at the abnormal grain boundary.