Preparation And Properties Study Of Gradient Nanostructured And Heterostructured Duplex Stainless Steel

In this paper,the plastic deformation treatment of 2205 and 2507 duplex stainless steel is mainly performed by rotational accelerated shot peening and forging + rolling + annealing.Through various analysis and testing methods,the phase changes and mechanics of duplex stainless steel in different plastic deformation processes are systematically studied.The evolution of performance and microstructure mainly has the following conclusions:(1)After being treated by RASP,severe plastic deformation and significantly increased roughness occurred on the surface of 2205 duplex stainless steel.The gradient nanostructure was introduced on the surface of the material,and the surface grain refining effect was obvious.The most surface was ultra-fine grain,and the grain size gradually increased with the increase of depth.The surface hardness increased significantly,and the hardness changed along the depth direction.The e projectile diameter and shot peening speed all affect the performance of 2205 duplex stainless steel.(2)After being treated by RASP,2507 duplex stainless steel introduced gradient nanostructures in the depth of tens of microns on the surface layer.The gradient nanostructures include gradient distribution of grain size,dislocation and twin density.The most surface layer of the sample is the fine grain layer.The grain refining effect is obvious.After that,the grain size gradually increases.Shot peening speed,time and sample thickness all affect the material performance effectively,and the proportion of gradient structure in the material affects the overall performance.(3)Hot forging and cold rolling made the 2507 duplex stainless steel plate undergo severe plastic deformation,but no phase transition occurred,and the strength was obviously improved.For forging + rolling 2507 duplex stainless steel annealing,short annealing did not see precipitation phase.Austenite is more stable than ferrite when annealing in biphase steel after large plastic deformation: the morphology of twin crystals in austenite is basically unchanged under short annealing condition,but the dislocation density of twin crystals decreases.Ferrite grains are prone to partial recrystallization,which leads to the formation of heterogeneous structures and the formation of recrystallized grains with time growth.(4)The fracture mode of duplex stainless steel after rotational accelerated shot peening,forging and rolling is ductile fracture,and the fracture surface shows typical dimple characteristics.With the strain increases,the dimple becomes smaller and shallower.The fracture modes of the materials are different when annealing with different parameters: short time annealing,the materials are all ductile fracture.