28 KB713 KB22 KB200020242010Pellizzari, Massimoštevilka:3letnik:44str. 121-127ISSN:1580-2949COBISSID:815274URN:URN:NBN:SI:doc-UIRFCOTHenInštitut za kovinske materiale in tehnologijeMateriali in tehnologijehitrorezno jeklokarbidikromlitinemodeliranjestrjevanjetermodinamikaThermodynamic modeling for the alloy design of high speed steels and high chromium cast irons| Termodinamično modeliranje načrtovanja sestave hitroreznih jekel in litine z veliko vsebnostjo kroma|In recent years, Thermo-Calc was successfully used by the author for the development of as-cast High Speed Steels and High Chromium Irons. The correlation between solidification process and microstructure was studied in view of influence of alloying elements introduced to promote carbide precipitation. The solidification process occurs under non-equilibrium conditions, because of microsegregation phenomena connected with the solidification structure: the liquid between dendrites becomes progressively enriched in solute and its composition increasingly differs from that predicted by the equilibrium diagram. This behavior can be studied with good approximation by using the model proposed by Scheil and Gulliver. In this way it was possible to refine the phase constitution of High Speed Steels, even if kinetic-related phenomena still limit its correct prediction. Present results also show that microstructural tailoring is possible looking at the correlation existing between the fraction of liquid phase at eutectic MC carbides precipitation. The morphology of V-rich particles changes from a continuous interdendritic network to a globular dissociated eutectic, showing higher toughness. The composition of HiCrI should result as near as possible to the eutectic, to maximize eutectic carbide amount. Calculations allowed to define the parameter TL-TEi (TL = liquidus temperature; TEi = eutectic start temperature) as representative of the material hypoeutecticity, and, on the basis of experimental results, a value of 20 °C was safely established in the development of the new compositionZadnja leta je avtor uspešno uporabil Thermo-Calc za razvoj hitroreznih jekel (HSS) in veliko vsebnostjo litine kroma (HiCrI). Raziskana je bila korelacija med procesom strjevanja in mikrostrukturo z vidika legirnih elementov, ki so bili dodani za povečanje precipitacije karbidov. Proces strjevanja je neravnotežen zaradi povezanosti med strjevalno strukturo in mikrosegregacijo: talina med dendriti postopno postane obogatena s topljencem, njena sestava pa se naraščajoče razlikuje od tiste, ki jo napoveduje ravnotežni diagram. Tako vedenje je mogoče raziskati z zadostnim približkom, če uporabimo model, ki sta ga predlagala Scheil in Gulliver. Tako lahko izboljšamo fazno sestavo hitroreznih jekel, čeprav kinetični pojavi omejujejo natančno napoved. Prikazani rezultati dokazujejo, da je mogoče krojiti mikrostrukture z opazovanjem korelacije med deležem taline pri precipitacijo MC-karbidov. Morfologija zrn, bogatih z V, se spremeni od povezane interdritske mreže v globularni disociirani evtektik in dobi večjo žilavost. Sestava litine z veliko vsebnostjo kroma (HiCrI) naj bo čim bližja evtektični, da se tako poveča delež evtektičnih karbidov. Z izračuni je bil določen parameter TL - TEi (TL = likvidis temperatura; TEi = temperatura začetka evtektika), ki je merilo hipoevtektičnosti. Na podlagi eksperimtalnih rezultatov je bila opredeljena vrednost parametra 20 °C za razvoj novih sestavTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaInštitut za kovinske materiale in tehnologije