Evaluation of Mechanical Properties of Medium Carbon Steel by Dislocation Microstructure Analysis

Abstract

Carbon steels realize high strength by quenching, which are used for mechanical elements such as gears and bearings. Martensitic transformation makes harder due to high dislocation density and fine crystal grains. The mechanical performance increase in proportion to their hardness. However, in the case of medium carbon steels, steels quenched and tempered at 290℃ have better mechanical properties than as quenched steels. There are some factors for decrease of mechanical properties such as dislocation density and retained austenite, this study focused on dislocation microstructure. To obtain their dislocation microstructure, line profiles from neutron diffraction were analyzed using convolution multiple whole profile (CMWP) fitting method. It is known that there are as proportional relationships between the square root of dislocation density and yield stress, but the analysis results show no proportional relationship. Therefore, we employed dislocation arrangement parameter to take into account mobile and immobile dislocations. Thus, effective dislocation density was introduced and may be able to explain the relationship with yield stress.