The effect of annealing time on properties of austenitic stainless steel

U ovom radu provedena je mikrostrukturna analiza, ispitivanje mikrotvrdoće i udarne radnje loma austenitnog nehrđajućeg čelika AISI 316L. Ispitivanja su provedena prije i nakon žarenja na 850 °C. Vrijeme žarenja tijekom ispitivanja je bilo od 30 do 90 minuta. Nakon žarenja, uzorci su ohlađeni na sobnoj temperaturi. Mikrostrukturna analiza ispitivanih uzoraka provedena je optičkom mikroskopijom (OM) i pretražnom elektronskom mikroskopijom (SEM) opremljenom uređajem za energetsko disperzijsku spektroskopiju (EDS). Ispitivanja udarne radnje loma provedena su na uređaju Charpyju na sobnoj temperaturi. Početno valjano stanje ispitivanog čelika pokazalo je prisutnost tipičnih izduženih poligonalnih zrna austenita i delta ferita, dok uzorci nakon žarenja pokazuju prisutnost i razvoj sigma faze u mikrostrukturi tijekom žarenja. Mikrotvrdoća je mjerena Vickersovom metodom te je utvrđeno da porast vremena žarenja nema značajniji utjecaj na mikrotvrdoću. Porastom vremena žarenja smanjila se udarna radnja loma što se može povezati s mikrostrukurnim promjenama. Nakon ispitivanja udarne radnje loma provedena je fraktografska analiza prijelomnih površina pomoću pretražnog elektronskog mikroskopa.In this paper, microstructural analysis, microhardness testing and fracture impact tests of austenitic stainless steel AISI 316L were performed. Investigations were performed before and after annealing at 850 °C. The annealing time during the investigation was 30 to 90 minutes. After annealing, the samples were cooled down to room temperature. Microstructural analysis of the investigated samples was performed by optical microscopy (OM) and scanning electron microscopy (SEM) equipped with device for energy dispersive spectroscopy (EDS). Impact energy tests were performed on a Charpy device at room temperature. The initial rolled state of the test steel showed the presence of typical elongated polygonal grains of austenite and delta ferrite, while after-annealing samples showed the presence and development of sigma phase in the microstructure during annealing. Microhardness was measured by the Vickers method and it was found that an increase in annealing time had no significant effect on microhardness. With increasing annealing time, the impact energy, which can be associated with microstructural changes, has decreased. After impact energy testing, fractographic analysis of fracture surfaces was performed using a scanning electron microscope