ASSESSMENT OF THE INFLUENCE OF HEAT TREATMENT MODES USING NEGATIVE TEMPERATURES ON THE MECHANICAL PROPERTIES OF ShKh15 STEEL. PART II: THE INFLUENCE OF HEAT TREATMENT MODES ON THE STRUCTURAL-PHASE STATE AND MICROSTRUCTURE
10.25712/ASTU.1811-1416.2024.02.014
Keywords:
structural bearing steel ShKh15, heat treatment, microstructure, tensile strength, impact strength, hardness, austenite, martensiteAbstract
The presence of retained austenite is undesirable in the case of manufacturing precision parts from ShKh15 steel due to the fact that during operation its transformation into martensite is inevitable, which results in a change in the geometric dimensions of the parts, which ultimately can lead to jamming of precision pairs, or the formation of cracks and failure building a precision unit or assembly. This study shows the change in the structural-phase state and microstructure of hardened structural steel ShKh15 depending on the temperature regime of tempering and cold treatment. It has been established that stimulation of martensitic transformation by cold treatment or cryogenic treatment leads to fragmentation of austenite inclusions, while slightly reducing the total content of retained austenite. The size of carbide inclusions in the case of cold treatment or cryogenic treatment can be considered invariant, while the total number of particles of carbide precipitates increases by 6.5 and 8.4 times, respectively, in the case of cold treatment at -60 °C and cryogenic treatment at -196 °C compared to traditional heat treatment.