Effect of carbonitriding on the structure and properties of carbon structural steel 45

In modern mechanical engineering, the task of comprehensive improvement of the operational properties of metallic materials is largely associated with the development of new technological processes for surface hardening of parts made from them. Liquid carbonitriding processes are characterized by high efficiency, simplicity and technological flexibility. The essence of carbonitriding or the method of “liquid” nitriding is to harden the surface layer of steel and cast iron products by the method of diffusion saturation with nitrogen and carbon in a melt of salts synthesized from ammonium carbon compounds (melamine, melon, dicyandiamide), at a temperature of 540-580 °C. Since this process involves simultaneous saturation with both nitrogen and carbon, carbonitride phases are formed in the surface layer of the metal, which are more plastic and do not have such fragility as pure nitride phases obtained by gas nitriding, which is the closest analogue of the described method. After carbonitration, a hardened layer consisting of several zones is formed on the surface. The upper layer ε a carbonitride of Fe3 type (N, C). Under the carbonitride layer there is a zone of γ “- phase of Fe4 type (N, C), under which there is a diffusion zone (heterophase layer) consisting of a solid solution of carbon and nitrogen in iron with inclusions of carbonitride phases, the hardness of which is much higher than the hardness of the core.