INVESTIGATION OF THE INFLUENCE OF THE INITIAL MICROSTRUCTURE UNDER DIFFERENT REGIMES OF HEAT TREATMENT ON THE MECHANICAL PROPERTIES OF 42CrMо4 STEEL

In this article, the impact of heat treatments - normalization and a combination of normalization, quenching and high-temperature tempering - on the microstructure and mechanical properties of 42CrMo4 steel specimens is investigated. Three groups of samples were studied: 1) as received; 2) after normalization at temperature of 860° С with holding time of 20 minutes and cooling in air; 3) after normalization (860°С/20 minutes), quenching at 850°С in oil and then tempered at 590°С, followed of cooling in air. The phase and microstructural analysis revealed the presence of retained austenite in the samples subjected to normalization. The resulting microstructure is ferrite-sorbite, containing about 10% retained austenite. The mechanical properties for the three investigated groups of samples showed the highest values for tensile strength (Rm=1147 MPa) and hardness (324 HBW) after normalization, and the highest elongation (12.9%) was obtained with the combination of normalization, quenching and high temperature tempering.