The master's thesis was carried out with the aim of determining the influence of different heat treatment parameters on the retained austenite content in induction hardened steels. The experiments were performed on three different steels: OTV1B, OTV1 and OHV5. Hardening was performed on a BIKS 750 induction machine, and the samples were in the form of cylinders with dimensions Ø 193 mm × 540 mm. After hardening, the selected samples were tempered at temperatures from 100 °C to 650 °C. Tempering lasted 30 hours at temperatures up to 300 °C and 2 hours at higher temperatures. After completion of the heat treatment, we measured the hardness on the surface of the samples and drew hardness-temperature diagrams. Another set of samples was cooled after hardening to temperatures of –70 °C, –100 °C and –130 °C, and then tempered at 120 °C for 30 hours. X-ray diffraction was used to determine the retained austenite content for all three steel grades, while the metallographic analyses were performed for the microstructure characterisation. The results of X-ray diffraction showed us that the initial percentage of retained austenite after hardening for all three steels was around 22 vol. %. During tempering, the amount of retained austenite remained the same up to a certain temperature. This was different for individual steels. In the case of steel OTV1B, the retained austenite remained up to 350 °C, while in the case of steels OTV1 and OHV5, the retained austenite content started to decrease at tempering temperatures between 150 and 250 °C. At higher temperatures, the proportion of retained austenite dropped below 1 vol. % in all steels. For cooled samples, the values for retained austenite ranged between 9 and 12 vol. % and varied only slightly as a function of the cooling temperature.
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