Effect of hydrogen embrittlement and non-metallic inclusions on tensile fracture properties of 55CrSi spring steel

Abstract

The tensile fracture behavior of 55CrSi spring steels were investigated. The results demonstrate that interior inclusion and hydrogen level has a significant effect on ductility and a minimal effect on tensile strength of the spring steel. It was due to the effect of cracking from MgO-Al2O3 spinel inclusion or the inclusions with a mixture of CaO, SiO2 and part of Al2O3 due to hydrogen. The results of SEM showed that the ductility reduction is connected with the formation of 'fisheye' which formed under the influence of mobile hydrogen. For the specimen containing MgO-Al2O3 spinel inclusion, the fracture surface in the 'fisheye' area is mainly composed of three regions including typical quasi-cleavage mixed intergranular fracture, dimple mixed transgranular fractures and ductile fracture from the interior to the edge, whereas there is no obvious transition zone from brittle fracture to dimple fracture in the 'fisheye' area of the specimen containing inclusions with a mixture of CaO, SiO2 and part of Al2O3