The effect of martensite transformation induced by plastic deformation on the stainless steels formability limits

摘要

Sheet metal forming processes are generally limited by plastic instability and tearing. The acceptable strain limits during such processing of sheet materials can be assessed by a forming limit diagram (FLD). In this research formability properties of stainless steels and the effect of martensite transformation during plastic deformation on this property are studied. The formability properties of austenitic and ferritic stainless steel are studied in both theoretical and experimental approaches, using the concept of forming limit diagram. In the theoretical approach a localized necking model and the Hill's quadratic anisotropy yield criterion are used and the material is considered to be strain hardened and sensitive to the strain rate. The experimental FLD are obtained using uniaxial tension test of notched strips and stretch forming test by hemispherical punch. The percent of martensite transformation induced by plastic deformation is measured using permeability factor and weighing method. The results show that the formability of austenitic stainless steels are better than ferritic ones. Also the formability of austentic stainless steels 304 because of martensite transformation that occurred during plastic deformation is better than 316 stainless steel.