30 KB193 KB29 KB200020242006Leskovšek, VojtehNolan, James DavidŠuštaršič, Borivojletnik:40številka:56 stranistr. 179-184ISSN:1580-2949COBISSID:576682URN:URN:NBN:SI:doc-E0LZJSQXenInštitut za kovinske materiale in tehnologijeMateriali in tehnologijelomna žilavostmikrostrukturanitriranjeorodna jeklatoplotna obdelavatrdotaThe application of linear elastic fracture mechanics to optimize the vacuum heat treatment and nitriding of hot-work tool steels|Linear elastic fracture mechanics was used to optimis(!)e the vacuum-heat-treatment procedure for conventional hot-work AISI H11 tool steel. The fracture toughness was determined with non-standard, circumferentially notched and fatigue-precracked tensile-test specimens. The fracture-testing method is sensitive to changes caused by variations in the microstructure due to the austenitizing and tempering temperature as well as the homogeneity of the material itself. The combined tempering diagram - Rockwell-C hardness, fracture toughness, Ksub(Ic), tempering temperature - was used to help choose the vacuum-heat-treatment parameters, aimed at obtaining the best properties for a given application with respect to the investigated steel. Nitriding treatments are established methods for improving the wear performance of tools and dies from H11 hot-work tool steel. However, the understanding of the relationship between the nitriding process parameters, on the one hand, and the microstructure and fracture behaviour of the surface layers, on the other, is far from complete. Vickers hardness indentations can generate radial fractures in brittle surface layers, and it has been shown that these cracks can be used to provide reliable information about the fracture toughness of these layers. The results suggest that for a sufficiently thick compound layer, this method has the potential to be applied as a pseudo non-destructive method of monitoring the fracture properties of treated surfaces on actual tool parts. The use of Vickers indentations for fracture toughness would give a useful insight into the fracture properties of nitride layers and their likely response to the application conditions involving high shear or impact loading. This could be very useful for investigations and quality control tool for industrial surface engineering applicationsPri optimiranju vakuumske toplotne obdelave konvencionalno izdelanega orodnega jekla za delo v vročem AISI H 11 smo uporabili princip linerne elastomehanike loma. Lomno žilavost smo določili z nestandardnimi cilindričnimi nateznimi preizkušanci z zarezo po obodu in utrujenostno razpoko v konici zareze. Metoda je občutljiva za spremembe v mikrostrukturi, ki so povezane s temperaturo avstenitizacije in popuščanja, kot tudi na homogenost samega jekla. Za izbiro parametrov vakuumske toplotne obdelave smo uporabili kombiniran diagram popuščanja - trdota Rockwell-C, lomna žilavost Kspodaj(Ic), temperatura popuščanja - z namenom, da bi dobili najprimernejše lastnosti preiskovanega jekla za specifično uporabo. Z modificiranjem delovnih površin povečamo orodju iz jekla za delo v vročem AISI H11 obrabno odpornost. Nitriranje v pulzirajoči plazmi je uveljavljen postopek s katerim delovnim površinam takemu orodju povečamo odpornost proti obrabi. Vendar pa odnosi med parametri nitriranja in mikrostrukturo ter lomnimi lastnostmi modificiranih plasti še niso dovolj raziskani. Posledica vtiskovanja Vickersove piramide v trde krhke površinske plasti so radialne razpoke, na osnovi katerih lahko pridobimo zanesljive informacije o lomni žilavosti teh plasti. Iz rezultatov je razvidno, da lahko uporabljeno neporušno metodo uporabimo za ugotavljanje lomnih lastnosti modificiranih površin orodij, če je spojinska plast dovolj debela. Uporaba vtiskovanja Vickersove piramide za določevanje lomne žilavosti omogoča boljše razumevanje lomnih lastnosti nitridnih plasti in njihov verjeten odziv na specifične pogoje uporabe pri velikih strižnih in/ali udarnih obremenitvah. To bi lahko bila tudi zelo uporabna raziskovalna in kontrolna metoda, ki bi jo uporabljali pri aplikacijah inženirstva površin v industrjiTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaInštitut za kovinske materiale in tehnologije