304 austenitic stainless steel cold hardening and annealing softening
|School||Central South University|
|Course||Materials Processing Engineering|
|Keywords||304 austenitic stainless steel work hardening softening deformation twinning strain-induced martensite|
Cracking failure is a great technological problem in sheet metal forming of stainless steel. The persent thesis investigated a kind of deep-drawing part of 304 austenitic stainless steel sheet made by Hunan the safe of coal mine Co.,Ltd, aimed to prevent cracking during forming process, Systemic tests were conducted to study the law and mechanics of work hardening and annealing softening behaviors of 304 austenitic stainless steel, and a reasonable annealing procedure was put forward through experimental research. The main contents of study and conclusions are as follows:(1) Work hardening of 304 austenitic stainless steel was researched by means of tensile testing at room temperature; On the basis of the precision for description and the law on change in the work hardening rate with true strain, the work hardening curves for the alloys maybe expressed as: a = Kεn1+n2+nεThe results of microstructure analyzing of 304 austenitic stainless steel showed that when it was deformed at room temperature, obvious work hardening was caused by the changes in structure during deformation. The strain-induced a-martensite, e-martensite and deformation twins enhance flow stress obviously, which is the main reason for the strong work hardening in FCC metals and alloys with low stacking fault energy as 304 austenitic stainless steel.(2) The rules and mechanics of softening behavior of this alloy were studyed by the annealing testing, and the best parameters of the annealing prcess were determined. The results demonstrated that mechanical properties changed slightly after annealing at low temperature(100~480℃), indicating that the effects of softening was not obvious at this annealing temperature; in contrast, annealing at high temperature(850℃’-~1050)℃ for 3min~~10min, and cooling rapidly, obvious effects of softening was obtained. Considering the oxygenization and labor efficiency of workpiece full-scale, it can be concluded that the best procedure of annealing of 304 austenitic stainless steel cold working parts is bright annealing at 1050# for 3min and rapid cooling (the cooling speed>180℃/min) in the protective atmosphere until the temperature below 500℃.