Gas-cycling processes of chemical and thermal treatment: regulation of the nitride layer structure for iron and steel

Abstract

The relevance of the research is determined by the needs of mechanical engineering in the development of inexpensive and effective technologies for surface hardening of steel products, which include gas nitride hardening. The aim of the work is to study the effect of nitride hardening in the gas-cyclic regime on the kinetics of growth of diffuse layers and their phase composition in case of iron and steel: ChWMn tool steel and corrosion-resistant maraging steel 03Ch11Ni10Mo2Ti (WSTST17). In addition to isothermal processes (at 520 ℃ and 620 ℃), processes with temperature changes at active and passive stages (thermal cycling 520 ℃ / 620 ℃) have been studied. It has been found that gas and thermal cycling significantly increases the thickness of the diffusion layer in iron compared to traditional nitride hardening in ammonia, and this is mainly due to the growth of the internal nitriding zone. Processes with multitime repeat short half-cycles, which end in an active saturation stage in ammonia and contribute to the formation of a developed nitride zone. The formation of surface layers in iron without an ε -phase occurs in two-stage processes with a final passive stage. It is shown that thermo-gas cyclic processes provide a multiple increase in the thickness of the internal nitriding zone in ChWMn steel. Processes with a duration of half cycles of 1 and 1,5 hours with the final stage of denitration contribute to the predominance of the γ' phase in the carbonitride zone, which explains the increase in wear resistance. A thermal gascyclic process of 530 ℃ / 580 ℃ in a pulsating ammonia-air mixture with a final passive stage is used to form a junction zone based on the γ'- phase in steel 03Ch11Ni10Mo2Ti (WSTST17).