Studies and Researches on Heating Microstructures of Some Steels

An important category of widely used steels is chromium alloy improvement steels (STAS 9382/4-89) intended for the execution of shafts, axles, cams, sprockets and sprockets subjected to operation at important demands. The properties of these steels are determined both by the chemical composition and by the way of plastic elaboration and deformation, but also by the way in which the structural transformations to the thermal treatments of tempering and recovery result. The properties of a certain steel are largely determined by the granulation size of the secondary structure, which in turn is dependent on the size of the austenitic granulation, respectively the hereditary granulation. At a given steel mark, the mode of heating (slow or fast) at the austenitization temperature is decisive regarding the dimensions of the austenitic grain respectively of the nature of the secondary granulation and of the operating properties. Studies and research were conducted on steels with an average content of 0.5% C (OLC 50, 40Cr10, 40Cr30), respectively alloys and chromium alloys. The experimental results show that the number of germs increases with the increase of the heating rate at austenitization. Along with the influence it has on the number of germs, the speed of heating manifests its effects on the critical temperatures of transformation. The presence of chromium additions is manifested by phenomena of carbide stabilization.