Elevated temperature material properties of advanced high strength steel alloys

Abstract

Advanced High-Strength Steels (AHSS) have high potential to be adopted in future innovative infrastructure. However, the material properties of AHSS at elevated temperature, which are necessary for analysis and design in the fire situation, are not yet specified in design codes or literature. An experimental investigation is carried out on cold-formed steels with nominal yield stress ranging from 340 MPa to 1200 MPa. The tested materials include two types of advanced high-strength steels (dual-phase (DP) and martensitic (MS) steel) and two conventional steels (high-strength low-alloy (HSLA) and mild steel). 88 tensile specimens are tested in steady-state and transient-state conditions at temperatures up to 700 °C. Material properties are obtained from the tests including elastic modulus, 0.2% proof stress, yield stresses at strain levels of 0.5%, 1.5%, and 2%, ultimate stress, and elongation at fracture. The test results are compared with the design codes provisions in Eurocode 3 and AISC 360, and with data from existing literature. Comparisons show that cold-formed DP and MS steels exhibit relatively larger reduction in stiffness and strength than conventional cold-formed steels at elevated temperature, which warrant the development of specific provisions. It is also found that transient-state tests at 5 °C/min heating rate yield approximately similar yield stress retention factors as steady-state tests but yield lower values of elastic modulus retention factors. New predictive models are proposed to determine the mechanical properties at elevated temperature of the cold-formed advanced high-strength steels with nominal yield stress up to 1200 MPa.