Mechanical properties of Q235∼Q460 mild steels at low temperatures

Abstract

Mechanical properties of mild steels (MSs) at varying temperatures are fundamental to structural design and numerical analysis. This paper studied mechanical properties of Q235∼Q460 mild steels used for the cold-region infrastructures and LNG tanks. To investigate the mechanical properties of mild steels at low temperatures, standard tensile tests on 12 Q235, 16 Q355 and 12 Q460 mild steel coupons in a cooling chamber were carried out at low temperatures of 20 ∼ -165℃. Test results showed that the yield and ultimate strength of mild steels increased with the decreasing temperatures. In addition, the ductility of MS was not compromised, and ductile failure occurred to MS at low temperatures. Furthermore, prediction equations on mechanical properties of MS at low temperatures were established by regression analyses. Finally, based on the predicted mechanical indexes, two- and three-stage constitutive models were proposed to describe the true stress–strain laws of Q355, Q460 and Q235 mild steels at 20 ∼ -165℃, respectively. Validations showed that the proposed constitutive model reasonably estimated the stress–strain behaviours of Q235 ∼ Q460 mild steels at low temperatures.