Ductility and fracture models of G20Mn5 cast steel

Abstract

Steel castings are capable of avoiding welding residual stress as well as facilitating easy on-site construction, and therefore are being increasingly used in modern building structures. However, due to the existence of microscopic coarse grains and discontinuities generated during the casting process, cast steel material exhibits highly variable ductility. The lack of knowledge on this front forces engineers to adopt a considerable margin of safety in order to prevent premature material fracture, leading to design of bulky and unnecessarily heavy castings. To overcome this, this study carried out an investigation to evaluate the inherent variability in the ductility of G20Mn5 cast steel. A total of 364 coupons were tested, including 284 simple tension coupons, 40 notched round coupons, and 40 shear coupons. The coupon tests and the complementary finite-element investigations reflected, in a comprehensive way, the ductility of G20Mn5 and its dependence on the heat treating method, casting thickness, and distance from casting surface, as well as the stress state that the material is subjected to. The notable influence of the effective material volume of the coupons, defined as the volume where fracture can potentially occur, was revealed and discussed. Finally, fracture models were proposed for estimating the fracture strain of G20Mn5 at all stress states. This study provides a fundamental databank for the analysis and design of constructional steel castings.