This master thesis was written as part of the development program of the company Sorbit Valji d.o.o. The company produces conventional hardened rolls for cold rolling. In recent years, the production program has been expanded into the production of surface hardened rolls. The goal of this master’s work was to determine the influence of inductor frequency during induction hardening on hardening depth for medium alloyed steel with 5 wt. % chromium. The heat treatment was performed with a BIKS 750 induction machine on cylindrical OTV1B samples, measuring 400 mm in diameter. The test pieces were heated to the austenitization temperature using electromagnetic induction of different frequencies. After being heated to the set temperature, the test pieces were quenched in water to achieve the desired hardening effect. The use of different frequencies leads to a change in the temperature profile across the cross-section of the specimen, which subsequently changes the hardening depth. Afterwards, the test pieces were cooled (cryogenically treated) to –130 °C to eliminate residual austenite and then tempered at 160 °C to release internal stresses. Based on the hardness tests, we determined the depth of the minimal useful hardness of cold rolling mills. We performed metallographic analyzes and X-ray diffraction to determine the proportion of retained austenite. From the results, we can conclude that at higher frequencies (350–650 Hz), the depth of the hardened layer does not change significantly with frequency, while at lower frequencies (80–200 Hz) this depth increases exponentially. A hardening depth of 15 mm can be achieved with higher frequencies, while lower frequencies must be used to achieve a deeper hardening depth between 20 and 30 mm.
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