17 KB55 KB15 KB199219991999Grabke, Hans JürgenHomolová, VieraJanovec, JozefPerháčová, JanaŠevc, PeterVýrostková, Annaletnik:334 straništevilka:6str. 423-426ISSN:1318-0010COBISSID:202922URN:URN:NBN:SI:doc-PEYQEQ0BenInštitut za kovinske materiale in tehnologijeŽelezarna JeseniceŽelezarna RavneŽelezarna ŠtoreKovine zlitine tehnologijefosforkarbidikristalizacijalegirano jekloprecipitacijasegregacijaSome aspects of carbide precipitation and phosphorus grain boundary segregation in Cr-V low alloy steels| Nekatere značilnosti tvorbe karbidov in segregacij na kristalnih mejah pri malolegiranih CrV jeklih|Phosphorus grain boundary segregation was investigated at 773 and 853 K for three Cr-V low alloy steels with different vanadium contents. AES and TEM methods were used for determination of the segregating elements enrichment on grain boundaries and phase identification, respectively. Phosphorus segregation enthalpy and entropy, as well as the phase equilibria for both temperatures, were determined by means of thermodynamic calculations. Aging upto 1000 hours was sufficient to achieve the equilibrium state of phosphorus segregation at the ageing temperatures. In agreement with Langmouir-McLean theory, the phosphorus grain boundary equilibrium concentration decreases with the temperature. The ageing conditions, however, were not sufficient to achieve the phase equilibrium. According to thermodynamic calculations, the steels should consist of ferrite, ?M_7C_3$? and MC (?$M_7C_3$? only in one state at higher ageing temperature) were found experimentally. Chemical composition changes of analysed carbides also confirmed the non-equilibrium state of precipitation. The changes accompanying the non-equilibrium development of phases show a direct influence on phosphorus segregation, specially at 773 K. As a consequence, the supporting effect of vanadium on phosphorus segregation, observed at 853 K is not clear at this low temperatureRaziskana je bila segregacija fosforja na kristalnih mejah pri 773 in 853 K pri treh malolegiranih jeklih z nizko vsebnostjo vanadija. Uporabljeni sta bili AES in TEM metodi. Entalpija in entropija segregacije ter fazna ravnotežja so bila termodinamično izračunana. Staranje 1000 ur je bilo zadostno za doseganje ravnotežne segregacije fosforja. V soglasju s teorijo Langmouir-McLeana je ravnotežna segregacija fosforja manjša pri nižji temperaturi. Staranje v trajanju 1000 ur pa ni bilo zadostno za doseganje faznega ravnotežja. Na osnovi termodinamskih izračunov je pričakovana fazna sestava jekla ferit, ?$M_7C_3$? in MC, eksperimentalno pa so najdeni ferit, ?$M_3C$? ter ?$M_7C_3$? samo po žarjenju pri višji temperaturi. Tudi kemična sestava izločenih karbidov je dokazala neravnotežno izločanje. Nastanek neravnotežnih konstituent mikrostrukture kaže na neposreden vpliv segregacije fosforja, posebno pri 773 K. Kot posledica se pri nižji temperaturi ni jasno pokazal pospeševalen vpliv vanadija na segregacijo fosforjaTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaInštitut za kovinske materiale in tehnologije