Equal Channel Angular Pressing Process Of Cast Stainless Steel Structure Evolution And Mechanical Properties Study

With the help of optical microscope (OM), scanning electronic microscope (SEM), X-ray diffraction (XRD)and transmission electronic microscope (TEM) et al, casting 304L austenitic stainless steels by equal channel angular pressing (ECAP) of sever plastic deformation (SPD) were investigated at different temperature, including the mechanism and the mechanical properties of the refinement of grains. In addition, The influence of originality structure to equal channel angular pressing was discussed by investigating the microstructure evolution of casting and solution 304L austenitic stainless steel during equal channel angular pressing.The refinement mechanical of grains can be fulfilled by three mechanisms during ECAP: the first is the movement of dislocation in which the dislocations come into being dislocation cells or dislocation walls and then become subgrain boundaries which will give rise to high angle boundaries during ECAP. The second is grains are refined by the twinning during ECAP. The third is strain induced martensite which come into being new grains which will give rise to ultrafine-grained during ECAP. But the procedure will be occurrenced only at low temperature.The fir-tree of casting 304L austenitic stainless steel are broke and diffusion in basal body at 200 ℃ during 1-4 passes ECAP. Because of slipping and twinning refinement, ultra-fine with mean grain size of ～202nm were obtained after 4 passes. The yield strengths, ultimate strengths and microhardness of ECAPed 304L increased sharply during the beginning passes, but the uniform elongation and Work-harding exponential decreased rapid (the uniform elongation of <3%, work-harding exponential of 0.060 after 4 passes) during 1～4 passes.The fir-tree of casting 304L austenitic stainless steel are broke and diffusion in basal body at 200℃ during 1～4 passes ECAP. Because of slipping and twinning refinement, ultra-fine with mean grain size of ～202nm were obtained after 4 passes. The yield strengths, ultimate strengths and microhardness of ECAPed 304L increased sharply during the beginning passes, but the uniform elongation and Work-harding exponential decreased rapid (the uniform elongation of <3% , work-hardingexponential of 0.060 after 4 passes) during 1～4 passes.The deformation mechanical of casting 304L austenitic stainless steel can be fulfilled by three form at RT～800℃ during ECAP: The first is strain induced martenstie which give rise to grains refine except slipping and twinning at low temperature. The second is mostly slipping and little twinning at middle temperature during equal channel angular pressing. The third is all of deformation mechanical is slipping at high temperature. Along with deformation temperature increase, the broken degree the fir-tree of casting 304L decrease.The number of twinning is more than the casting during the solution of 304L austenitic stainless steel ECAPed. The coarse grains are refined by slipping and twinning during the solution ECAPed. the deformation mechanism of casting 304L austenitic stainless is mostly slipping and little twinning during equal channel angular pressing. The yield and ultimate strengths of casting and solution 304L increased sharply during the beginning passes, but the uniform elongation and work-harding exponential decreased rapid during equal channel angular pressing. Compared casting with solution ECAPed, the strengths of two states are base homology, but the elongation of solution is twice than casting.