Abstract
The effect of nitrogen on deformation-induced martensitic transformation (DIMT) in metastable 301 austenitic stainless steel has been studied based on the inelastic deformation theory. DIMT is regarded here as continuous relaxation process of internal strain energy accumulated during inelastic deformation. Using the kinetics equation based on the inelastic deformation theory the relationship between the volume fraction of transformed martensite and inelastic strain for DIMT has been successfully verified with the parameter representing the stability of austenite. The addition of nitrogen is experimentally found to increase austenite stability and the critical inelastic strain below which any DIMT is not observed to occur and to decrease the saturation volume fraction of α’ martensite. On the other hand, DIMT has been analyzed with its effect on stress-strain curve shape and mechanical properties in relation to the addition of nitrogen. The characteristic transition from sigmoidal to parabolic curve shape in stress-strain response has disappeared with the addition of nitrogen.
Highlights
Deformation induced martensitic transformation (DIMT) has recently generated great interest in steel and automobile industries due to its role on achieving high strength steels with high ductility, so called transformation-induced plasticity (TRIP) steels
deformation-induced martensitic transformation (DIMT) phenomenon has been analyzed in terms of either transformation kinetics or stress-strain response [4,6,7,8,9,10,11,12,13,14,15,16,17]
The transformation kinetics of DIMT prescribes the relation between the volume fraction of transformed martensite and plastic strain, while the change in deformation behavior due to DIMT has been analyzed in relation to the variation of stress-strain curve and mechanical properties [1,10,13,18]
Summary
Deformation induced martensitic transformation (DIMT) has recently generated great interest in steel and automobile industries due to its role on achieving high strength steels with high ductility, so called transformation-induced plasticity (TRIP) steels. DIMT is known to take place when austenite is deformed at temperatures below Md , which could be well above the transformation start temperature of martensite, Ms. Generally, the Md temperature strongly depends on chemical compositions, strain rate, and loading temperature. DIMT phenomenon has been analyzed in terms of either transformation kinetics or stress-strain response [4,6,7,8,9,10,11,12,13,14,15,16,17]. The transformation kinetics of DIMT prescribes the relation between the volume fraction of transformed martensite and plastic strain, while the change in deformation behavior due to DIMT has been analyzed in relation to the variation of stress-strain curve and mechanical properties [1,10,13,18]
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