Effect Of Grain Size On Deformation Mechanism And Mechanical Properties Of 316L Stainless Steel

Because of its excellent mechanical properties,316 L stainless steel has been widely used in industrial production.With updating industrialization demands and increasing progress of science and technology,the in-depth study of 316 L stainless steel and its properties and deformation mechanism is of high significance.Especially,the grain size of materials on their tensile properties and impact fracture morphology,the study of material rolling deformation mechanism,the analysis of the impact toughness at room temperature and liquid nitrogen temperature,the tensile properties of heterogeneous stainless steel under low temperature,and coordination of deformation mechanism research have important attracted lots of attention,both from academic and technological point of view.In this paper,the homogeneous structure and layered heterogeneous structure of 316 L stainless is obtained by traditional cold rolling + annealing process.The evolution of microstructures and mechanical properties of 316 L stainless were studied by optical microscope,scanning electron microscopy,X-ray diffraction,electron backscatter diffraction,transmission electron microscopy,microhardness tester,uniaxial tensile test and Charpy impact test.The main conclusions of the paper were as follows:(1)The third chapter of this paper explores the relationship between yield strength and fracture morphology and grain size.The yield of equiaxed 316 L stainless steel with different grain sizes prepared by cold rolling + annealing has approximately-1/2 exponential relationship of the grain size.When the grain size decreases,the number of grains contained in the same space increases,so the grain boundary density increases,where the energy is higher,and it is difficult to pass through the grain boundary when the dislocation slips,so it is packed near the crystal boundary,thereby enhancing strength.Secondly,the average diameter of dimples and grain size also show a positive correlation with 1/2 power.It shows that as the grain size increases,the average diameter of dimples gradually increases.These larger dimples usually cause severe plastic deformation during the fracture process,indicating an increase in ductility.(2)The fourth chapter of this paper explores the influence of grain size on the rolling deformation mechanism of 316 L stainless steel at 20% reduction.During the deformation process,dislocations proliferate significantly in samples with a grain size less than 12μm,while deformation twins are mainly used to coordinate the deformation in larger grain samples.However,the strain condition in the deformation process is not sufficient to induce martensitic transformation.(3)The fifth chapter of this paper mainly explores the influence of 316 L stainless steel grain size and macroscopic geometric size on impact toughness.It found that the larger the macroscopic size of the impact sample,the greater the proportion of the plane strain area in the impact fracture due to the almost uniform thickness of the shear lip,the more impact energy absorbed during the impact,and the better the impact toughness of the sample;The larger the size of the grains,the easier it is to form larger dimples when cracks propagate during the impact process,which increases the contribution to impact energy consumption and makes the impact toughness more excellent.(4)The sixth chapter of this paper mainly explores the mechanical properties and deformation mechanism of layered heterogeneous 316 L stainless steel at room temperature and liquid nitrogen.It found that the yield strength at room temperature depends on the presence of high hetero-deformation induced stress at the soft/hard interface;at the same time,a large number of geometric necessary dislocations and stacking faults generated in micron recrystallization near the soft/hard interface are increased The uniform elongation of the layered heterogeneous 316 L stainless steel improves the coordinated deformation ability;the layered heterogeneous 316 L stainless steel shows better performance in a liquid nitrogen environment than it in a normal temperature environment.The generation of macroscopic strain in the low temperature environment promotes the generation of stress-induced martensitic transformation,and the generation of the Lüders band causes uniform deformation of the sample while increasing the elongation;when the Lüders band extends to both sides of the gauge section After that,the phase transformation induces the martensite transformation and at the same time,the dynamic recovery is suppressed during the low temperature hardening process.A large number of dislocations accumulate in the ultrafine-grained martensite,which increases the elongation of the material while also increasing the strength.