Study On Intergranular Corrision And Grain Boundary Characteristic Distribution Of TP321 Austenitic Steel

TP321 austenitic stainless steel has good comprehensive mechanical properties,easy processing and corrosion resistance,and is widely used in petroleum,chemical,marine and other harsh environments.As the weak link of polycrystalline materials,grain boundary often becomes the breach of austenitic stainless steel corrosion and inter-granular corrosion occurs.By increasing the proportion of special grain boundaries in austenitic stainless steel and breaking the network connectivity of large angle grain boundaries,the optimization of grain boundary characteristic distribution can be realized and the inter-granular corrosion resistance of materials can be improved.In this paper,the influence factors of inter-granular corrosion of TP321 austenitic stainless steel are studied,the influence of single cold rolling annealing and cyclic compression heat treatment on the grain boundary characteristic distribution of TP321 austenitic stainless steel was analyzed.The microstructure evolution law in the optimization of the grain boundary characteristic distribution of TP321 austenitic stainless steel was discussed.The results show that the most sensitive temperature of intergranular corrosion of TP321 austenitic stainless steel is 700? in 48 h when the sensitization time is fixed,and the longer the sensitization time is,the more serious the intergranular corrosion of TP321 austenitic stainless steel is.During the stabilization treatment at 900?,the susceptibility of TP321 stainless steel to intergranular corrosion was reduced,and a large number of Ti C particles were precipitated during the stabilization treatment,which consumed the C atom of solid solution.With the increase of stabilization time,the re activation rate RA decreased,the sensitivity of intergranular corrosion decreased,and it was in a good passivation state.After single pass cold rolling with small deformation(6.5%),TP321 austenitic stainless steel was annealed at 900? for 12 hours,which was insufficient to trigger recrystallization.The proportion of special grain boundaries increased with the increase of annealing time.After 72 hours annealing,the proportion of special grain boundaries increased from 35.6% to60.2%.However,the recrystallization can be completed rapidly in the material with large deformation(50%)and the proportion of special grain boundary changes little with the increase of annealing time.However,in the single 3?12% cyclic deformation heat treatment,with the increase of the number of cycles,the larger the average grain size is,the more abnormal the grain growth trend is.The larger the deformation is,the higher the strain inhomogeneity is,and the more obvious the abnormal grain growth is.In TP321 austenitic stainless steel,the formation of special grain boundaries mainly occurs in the recrystallization process of annealing,and the proportion of special grain boundaries is related to the degree of strain inhomogeneity,abnormal grain growth and recrystallization,among which the main factor is the degree of crystallization.Under the combined action of deformation,heat treatment and heat treatment temperature / time,the higher the recrystallization degree of austenitic stainless steel,the greater the proportion of special grain boundaries.