Mak-Mak N. Creation of metastable states and strengthening of structural steels by means of heat and chemical treatment

The work’s aim is the operational longevity improvement of parts, made of structural steels that have to work under different wear conditions by means developing surface hardening, complex processes that ensure receiving metastable phase-structural gradient states and modifications with self-strengthening effect at their exploitation. The investigation’s object is structural steels’ surface layers, strengthened by chemical-thermal, bulk and surface heat treatment methods. The investigation’s subject is gradient phase-structural state and the low-carbon structural steels surface layers properties after chemical-thermal and heat treatment. Methods of investigation include optical and electronic microscopy, micro-X-ray spectral analysis, X-ray structural phase analysis, quantitative metallography, spectral analysis, 3D micro-fractography of worn-out surfaces, measuring of hardness and micro-hardness, abrasive and shock-abrasive dry and sliding wear testing, mathematical simulation and treatment of experimental data. New methods and ways of volume-surface and surface hardening (HTTCT, LTTCT, plasma quenching and RTCN) of the carbonized low carbon structural steels series were developed. The proposed methods and technologies for volume-surface and surface hardening provides the regulation for metastable austenite gradient modifications, wear resistance increase in under various wear conditions by 2.5 6 times. The developed surface hardening methods ensured the machined parts (blades of shot blasting machines of the grain crusher tool, gears) durability increase in by 1.7-2; 2.6-3; 1.3-1.5 times, respectively, compared with the serial. The developed surface hardening methods were introduced into production at PJSC «Azovmash», at the industrial enterprise «Victor» and recommended for introduction at the machine-building enterprise «MAGMA» with a total economic effect of 92800 UAH.