Uticaj mikrostrukture na prelaznu temperaturu ADI materijala

Abstract

U disertaciji je izvršena karakterizacija mikrostrukture i mehaničkih osobina nelegiranog austemperovanogi nodularnog liva (ADI materijala), kao i uticaja mikrostrukture na prelaznu temperaturu u intervalu od -196 do +100°C. Utvrđeno je da mehaničke osobine ADI-ja zavise od morfologije ausferitne mikrostrukture i količine zadržanog austenita, tj. parametara austemperovanja. Na osnovu mehaničkih osobina utvrđen je i opseg procesiranja u skladu sa standardima ASTM, ISO i EN. Zaključeno je da prelazna temperatura ADI materijala zavisi od količine i stabilnosti zadržanog austenita. U višem temperaturnom opsegu (iznad cca. -25°C) dominantna je količina zadržanog austenita, dok na nižim temperaturama, stabilnost. Visoka obogaćenost ugljenikom, stabilnog zadržanog austenita sprečava stvaranje martenzita na niskim temperaturama, a time i pojavu krtosti kod ADI-ja.

The object of this thesis was to characterize microstructure and mechanical properties of the unalloyed ADI material (Austempered Ductile Iron). In addition, the influence of microstructure on the ductile to brittle transition temperature (DBTT) by Charpy impact test in temperature interval from 196 to +100°C has been studied. The all properties obtained depend on the morphology of microstructure and the amount of retained austenite, i.e. on the austempering parameters. According to the mechanical properties and standard requirements (ASTM, ISO and EN) the processing window has been proposed, also. It was found that DBTT is influenced by amount and stability of retained austenite. In upper temperature range (above cca. 25°C) the most influence factor on DBTT is amount of retained austenite, while at the lower temperatures the stability is more prominent. Stability of high carbon retained austenite at lower temperatures prevents transformation to martensite and thus the embrittlement of ADI.