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Namen diplomske naloge je optimizacija indukcijskega kaljenja orodnega jekla K313 s 5 mas. % kroma za izdelavo kovanih valjev za hladno valjanje z enojnim induktorjem frekvence 400 Hz. Pri preizkusih sem opisal in analiziral toplotno obdelavo na osnovi kalilne vrste in popuščnih diagramov. Najprej sem opravil poskuse na vzorcih, dimenzij 20 mm × 20 mm × 80 mm, ki so bili segreti v elektrouporovni komorni peči in na zraku kaljeni do sobne temperature. Rezultati tega so osnova za toplotno obdelavo konvencionalno kaljenih valjev. Poskuse indukcijskega kaljenja sem opravil na preizkušancih, dimenzije ??240 mm × 600 mm. Vsi preizkusi so se vršili na indukcijskem stroju BIKS 750, ki je namenjen za indukcijsko kaljenje valjev z enojnim ali dvojnim induktorjem. Na vzorcih kalilne vrste smo analizirali mikrostrukturo in izmerili delež zaostalega avstenita. Na podlagi teh rezultatov smo določili optimalno temperaturo avstenitizacije za izdelavo popuščnih diagramov. Na vzorcih za popuščni diagram smo izmerili trdote in delež zaostalega avstenita. Preizkuse smo izvedli tudi na vzorcih, ki so bili po kaljenju še podhlajeni (kriogeno ohlajeni) na –130 °C. Opisal in analiziral sem tudi mehanske lastnosti (žilavost) in mikrostrukturo, kar je potrebno za kontrolo uspešnosti toplotne obdelave. Iz rezultatov preiskav zaključujemo, da so najprimernejše temperature avstenitizacije za jeklo K313 med 1000 in 1040 °C. Za doseganje trdot do 62 HRC je najprimernejša tehnologija brez podhladitve, nad 62 HRC pa s podhlajevanjem. The purpose of my diploma thesis was to optimise the process of induction hardening K313 tool steel with 5 wt. % chromium, using a single inductor with 400 Hz frequency for the production of forged rolls for cold rolling. In the tests, I described and analyzed heat treatment based on the results of hardenability tests (sensitivity-to-grain growth) and tempering diagrams. I first performed experiments on samples with dimensions 20 mm × 20 mm × 80 mm, which have been heated in an electric resistance chamber furnace and then hardened with air to room temperature. The results from these tests provide the basic understanding of conventional heat treatment. The experiments for induction hardening were performed on samples, measuring Φ 240 mm × 600 mm. All tests were performed on the induction machine BIKS 750, which is designed for induction hardening of steel rolls with single or double inductors. We analyzed the microstructure and measured the content of retained austenite on the samples from the hardenability test to determine the optimal austenitisation temperature, which we used to make tempering diagrams. We then measured the hardness and proportion of retained austenite on the samples for the tempering diagrams. The same tests were performed on samples, that were cooled to –130 °C after being hardened. I also described and analyzed mechanical properties (toughness) and microstructure, which is required to control the performance of heat treatment. From the results we conclude, that the most suitable austenitisation temperatures for K313 steel are between 1000 and 1040 °C. To achieve hardness up to 62 HRC the most suitable technology is without cryogenic treatment, and to reach hardness above 62 HRC it is better to use cryogenic treatment. |
