Studying On Grain Growth Behavior And Mechanical Properties Of Ultrafine Grained 304 Stainless Steel

Effect of the experiment on the grain growth behavior of ultrafine grained 304 stainless steel during annealing temperature and annealing time on the mechanical properties and tensile properties were studied respectively,calculation and measurement of the grain growth activation energy,stress-strain curve and friction temperature spectra,and reveal the grain from the atomic level the mechanism of growth and.The main results are as follows:(1)The growth behavior of ultrafine grained 304 stainless steel has been studied.The results show that the grain size increases with the increase of annealing time and annealing temperature.In the same holding time,the grain size increase is not obvious when the annealing temperature is lower than 400,and the increase of grain size becomes larger when the annealing temperature is increased to 500.Under the conditions of the annealing temperature,the grain growth trend is decreased with the increase of annealing time,that is to say,the annealing temperature has a great influence on the grain growth.Grain growth exponent n value increases with the increase of annealing temperature,the calculated value of grain size is linear with the measured value,and the grain growth pattern is consistent with the Beck equation of grain growth dynamics.The calculated austenite grain growth activation energy close to the size of the grain boundary relaxation activation energy can be calculated with the increase of annealing temperature.(2)The effect of ultrafine grain growth behavior of 304 stainless steel has been studied.The results show that the mechanical properties of ultrafine grained 304 stainless steel yield strength,hardness and grain size is consistent with the Hall-Petch relationship,namely strength with grain size increased.Overall,the P1 peak first increased and then decreased,the P2 peak first decreased and then increased,and the P3 peak was decreased.With increasing annealing temperature and time,the excitation effect of interstitial atom is increasing and constant.The higher the annealing temperature,interstitial atoms at the edge of saturated with aggregation time shorter,by pinning the earlier interstitial supersaturation of the formation of the second phase precipitation dislocation,influence of dislocation mobility more in advance,with the annealing of second phase coarsening of dislocation pinning effect weakened,dislocation mobility enhanced.With the increase of annealing temperature,the strength and hardness of the first slow down and then decreased sharply;with the increase of annealing time,the two showed the opposite.(3)Ultrafine grains with different grain sizes of 304 stainless steel at room temperature tensile test showed that: coarse grain and ultra-fine grain sample flow stress were increased with the strain rate increase,the strain rate sensitivity of ultrafine grained samples are higher than that of the coarse grain specimens.With the grain size increase,sample flow stress decreases,elongation increases,the work hardening rate is low,indicating that the deformation mechanism of grain boundary sliding was weakened and role of based on dislocation motion during plastic deformation was enhanced.The peak of P2 and P1 increased with the increase of the deformation,and the peak height reached saturation at a certain time,and the saturation of P2 and P1 increased with the increase of grain size.The larger the grain size is,the larger the deformation capacity of P1 and P2 peak reaches saturation,which indicates that the density of a certain grain size reaches a certain limit after the dislocation multiplication.When the grain size is larger than 400 nm,the smaller the grain size is,the shorter the saturation time of the plastic deformation is,the larger the grain boundary sliding resistance is,the more obvious the hardening phenomenon is.In the later stage of plastic deformation,dislocation caused by dynamic recovery at grain boundary deformation,dislocation generation and devoid of balance,the dislocation production and disappear reached a state of equilibrium.