The study shows the numerical investigation on flat oval hollow section members of cold-formed carbon steel and lean duplex stainless steel (LDSS) subjected under torsional loading using the finite element software, Abaqus. Parametric studies of the flat oval section have been performed for various slenderness ranging from slender to stocky sections. The flat-oval member length has been considered as three times that of the flat length of the member cross-section. On the basis of the finite element analyses, it can be observed that the torsional capacity of the LDSS section has higher capacity in comparison with the carbon steel in the ranges of 70–100% as thickness varies from 3 to 20 mm, even though the variation in the yield stress is around 87%. There is a linear increase of torsional capacity as the thickness increases for both the carbon and stainless steel but the stiffness of stainless steel is higher. The torsional capacity of the member decreases with an increase in the slenderness ratio of the member cross-section.