LAUSR

Abstract The suitability of using high performance steel (S700MC) for road restraint systems (RRS) under very high containment level was evaluated in this study. To investigate the influence of the crash on the mechanical behaviour of the steel, different test pieces were tested by tensile and hardness testing, and examined by scanning electron microscopy (SEM). The tensile test results of S700MC showed a noticeable increase in yield strength at 0.2% elongation (Rp0.2) from 744 to 935 MPa, and ultimate tensile strength (UTS) from 810 to 1017 MPa, before and after crash tests (BC and AC, respectively). S700MC showed ~9% lower elongation at fracture value in comparison with S275JR and S355JR steels. Besides, fracture toughness, was significantly higher for S700MC (133 and 148 MJ/m3 for BC and AC, respectively) compared to conventional mild steels (108–118 MJ/m3). Microstructural observations of head-part of all S700MC samples revealed equi-axed grains. The fracture surface of tensile tested samples before crash, showed elongated grains accompanied by pore formation. Among after crash samples, one test piece showed intergranular cracks while no intergranular cracks were observed for the other crashed pieces which resulted in the lower Rp0.2 (813 MPa) and UTS strength (847 MPa) and fracture toughness (125 MJ/m3). The results showed that although RRS manufactured with S700MC undergoes severe mechanical deformation, the risk of brittle fracture is very low and this is beneficial from industrial as well as social point of view.