The Effect Of Surface Nanocrystallization,Cold Rolling And Annealing On Microstructure And Properties Of 316L Stainless Steel

Aiming to obtain the 316L stainless steel having a good combination between strength,ductility and surface properties,in this paper,316L stainless steel was treated by plastic deformation and heat treatment through the compound process of surface nanocrystallization(Rotationally Accelerated Shot Peening),cold rolling and subsequently annealing.The surface morphology,phase transformation,microstructure and mechanical properties of the treated 316L stainless steel were systematically studied.The following results have been obtained:(1)A gradient nanostructured layer with a depth of several hundred micrometers in 316L stainless steel was observed after RASP,including the gradient distribution of grain size,phase composition,density of dislocation and twins along the depth.The grain refinement of 316L stainless steel was achieved by dislocation movement and mechanical twinning.(2)The deformation induced martensitic transformation occurred after plastic deformation and the martensite appeared.The volume fraction of martensite increased with the increase of strain.The martensite had a good thermal stability when the annealing temperature was below 500? and a reverse phase transformation began when the annealing temperature was above 500? and occurred entirely when the annealing temperature was above 730?.The speed of the reverse phase transformation was extremely fast.(3)The gradient nanostructured 316L stainless steel had not only a good combination between strength and ductility,but also the gradient hardness from surface to matrix.The mechanical properties could be controlled by parameters of RASP.(4)The gradient nanostructured layer could still be influenced by RASP when the rolling reduction was less than or equal to 20%.It indicated the gradient nanostructured layer had a good subsequent deformation stability.(5)The mechanical properties of the gradient nanostructured layer did not change at the annealing temperature which was below 500?,changed slowly at 500?700? and changed obviously at above 700?.It indicated the gradient nanostructured layer had a good thermal stability.