Abstract

The aim of this work is to study the effect of cold forming on the mechanical properties and microstructure of a steel grades used in manufacturing of rectangular hollow sections. Conventional and a direct-quenched steel sections in 500 MPa strength level are compared. Tensile properties and Charpy-V impact toughness were determined for the flat side and corner of hollow section. The results show that the strength in corner area is approximately 50 MPa higher and the elongation at fracture 4 % lower compared to flat side area, revealing the work hardening and the effect of higher cold deformation rate in corner areas. The impact energies of sub-sized samples (5 mm x 10 mm x 55 mm) were at high level at -40 °C and -60 °C in both steels. However, the direct-quenched steel had improved impact toughness when testing temperature decreased. It is also notable that no differences in CV values between the flat and corner samples were observed. EBSD results showed compressed microstructure in inner corner radius and the outer was stretched in correspondingly. This resulted inner corner area having the smallest grain sizes. Additionally, a brief discussion between the mechanical properties of structural rectangular hollow sections is presented.