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In practice, the wear resistance, lifetime and capability of components and tools to resist loading greatly depend on the residual stress field in the material. This is especially true for hot-rolling applications, which require rolls with hard, heat- and wear-resistant surfaces, a tough core and the proper compressive residual stress level to resist Hertzian cyclic loading. If the casting, heat treatment, cooling process and surface machining and grinding are not done properly, a very high and uneven tensile residual stress field may occur, causing a drop in the wear resistance, cracking or even fracture of the roll. The aim of this investigation was to determine the impact of various heat treatments of double-layer cast rolls on the values and distribution of residual stresses in the rolls made from semi-high-speed steel with a high content of chromium (SHSS HCS). Using the hole-drilling method, the residual stress depth distribution was measured circumferentially and transversely on the double-layer cast roll surface after casting, heat treatment, turning and grinding. Furthermore, using different turning and grinding parameters (speed, feed), and heat-treatment parameters (temperature, time), the influence of these parameters on the residual stress level and the wear resistance of roll's outer layer were determined. V praksi je odpornost proti obrabi, trajnostna doba in sposobnost komponent ter orodij, da se uprejo obremenitvi, močno odvisna od zaostalih napetosti v materialu. To še posebej velja za aplikacijo vročega valjanja, kjer se od valjev zahteva, da imajo trdo, toplotno in obrabno odporno površino, žilavo jedro in ustrezen nivo tlačnih zaostalih napetosti, ki so se sposobne upreti Hertzovem cikličnem utrujanju. Če so postopki litja, toplotne obdelave, proces ohlajanja, površinske obdelave in brušenja opravljeni nepravilno, lahko to privede do zelo visokih in neenakomernih nateznih zaostalih napetosti, kar povzroči padec odpornosti proti obrabi, razpoke ali celo lom valja. Cilj raziskave je bil ugotoviti vpliv različnih toplotnih obdelav dvoslojno litih valjev na vrednosti in porazdelitve zaostalih napetosti v valjih, izdelanih iz hitroreznega jekla z visoko vsebnostjo kroma (SHSS HCS). Z uporabo metode vrtanja luknjice je bila izmerjena porazdelitev zaostalih napetosti z globino. Meritve so bile opravljene po obodu in prečno na površini dvoslojno litega valja po ulivanju, toplotnih obdelavah, struženju in brušenju. Poleg tega so bili z uporabo različnih parametrov struženja in brušenja (hitrost, pomik) ter parametrov toplotne obdelave (temperatura, čas) ugotovljeni vplivi teh parametrov na porazdelitev zaostalih napetosti in odpornost zunanje plasti valjev proti obrabi. |
