The Macro And Micro Research On304Stainless Steel In The Processes Of Profile Preparation And Parts Forming

304stainless steel is the austenitic stainless steel, which has good corrosionresistance, low temperature strength and good mechanical properties, it has beenwidely used in automobile, shipbuilding, aerospace and medical apparatus etc. Butbecause the304stainless steel belongs to the face centered cubic structure with lowstacking fault energy, the low stacking fault energy leads that full dislocation easilydecomposed into extended dislocation with greatly width of stacking fault, whileextended dislocation is not conducive to recovery, therefore, its softening mechanismis mainly through recrystallization, although in the hot forming process, it can softenand remove the work hardening through recrystallization, the surface quality ofproducts is poor and the size accuracy is low, that restricts its industrial application.While the cold forming technology has the advantage of high size accuracy, goodsurface quality and good comprehensive mechanical property which can meet therequirements of precision and quality, but the work hardening phenomenon is veryobvious in cold forming process, which can affect the processing efficiency and thedie life, and the product is prone to crack, therefore, researching on the macro andmicro changes of304stainless steel in the process of forming has great significancefor process improvement and guiding production.In this paper, the preparation of304stainless steel profile and the forming of theparts has been taken as a research object, the experimental method and the numericalsimulation method has been combined to research the macro and micro change in theprocess of profile preparation, parts forming and material fracture. As for the processof the profile preparation, in order to verify the reliability of the simulation of heattreatment, the simulation and the experiment of upsetting and annealing has beendone for the original specimen. As for the process of the parts forming, bothsimulation and experiment have been done for the extrusion. As for the fractureprocess of the material, the micro changes of voids initiation and growth duringtensile experiment of the304stainless steel have been researched. The results showthat: the deformation induced martensite during the upsetting process of the originalspecimen, which led the micro hardness increased from247.2HV to444.0HV. Recrystallization was happened for the specimen after upsetting in the annealingprocess with the temperature of1100℃, finally the irregular austenitic grain size wasgot, the average grain size was96.86um, which was consistent with the simulationresults. The hardness of the material after annealing declined to180.0HV, and themartensite which was induced by the deformation also disappeared. During theformation process of the parts, the extrusion test has been done after drawing andannealing, and the obviously fibrous tissue along the extrusion direction has beenfound in the place where was large deformed in the extrusion process, while the grainsize changed little in the place where was small deformed, which was consistent withthe simulation. During the fracture of the material, with the tension beginning, thedislocation density accumulated and the slip band which was made up of slip linewith the same direction appeared in the grain interior, and the direction of the slipband was different with different grains. With the increase of the tension, the grainorientation changed obviously, and the grain near the gap rotated which led to thepeel fold emerging on the surface of the specimen. Many micron voids near the gapwere found after stretching0.4mm through the SEM track, and with the increase ofthe tension, the micron void were elongated along the tensile direction, while thegrowth rate of the void was trend to moderate with the increasing tensile elongation.