Modeling the Tensile Strain Hardening Behavior of a Metastable AISI 301LN Austenitic Stainless Steel Pre-strained in Compression

Abstract

Boltzmann-type sigmoidal equations to model the tensile strain hardening and flow stress behavior of a metastable AISI 301LN austenitic stainless steel subjected to prior cold deformation have been developed. This model can be used in the numerical simulation of the energy absorbed by structures fabricated using this steel during collision events. In addition, it can also be used to establish the maximum allowable prior compressive strain through cold rolling which will result in a steel capable of adequate energy absorption. It was found that the compressive pre-strain had a strong effect on increasing the initial martensite content, increasing the tensile yield strength but reducing the ability of the material to absorb energy during subsequent tensile straining. In order to produce AISI 301LN crash-relevant structures for a vehicle, a cold rolling thickness reduction in the order of 20 pct or lower must be employed. This will result in the mechanical energy absorbed by the material of at least 210 MJ/m³ in the event of a collision. The tensile strain hardening curves established for the pre-strained steel confirmed a high-strength coefficient value in the range of 1770 to 1790 MPa for the AISI 301LN steel at 30 °C. Neutron diffraction work, coupled with Electron backscatter diffraction (EBSD) analyses, studied the γ → α′ and ɛ martensitic transformation during compressive pre-straining, in order to explain the subsequent tensile strain hardening effects observed.