Fracture behaviour and microstructural evolution of structural mild steel under the multi-hazard loading of high-strain-rate load followed by elevated temperature

This paper presents the mechanical properties, microstructure evolution and fracture behaviour of structural mild steel subject to the multi-hazard loading scenario of post-impact-fire. Two-phase tensile tests were conducted on mild steel coupons to assess the coupling effect of strain-rate and subsequent temperature at three pre-determined deformation levels. Stress-strain characteristics of pre-damaged steel at different temperatures have been interpreted using well known metallurgical concepts. Scanning Electron Microscopy (SEM) fractographs have been utilized to detect pertinent microstructural alterations. Results indicate that the strength, energy absorption and ductility of steel material at elevated temperatures largely depend on the pre-deformation history of the material caused by high strain rate loading, with this effect dwindling at very high temperatures.