Influence of weldment microstructure of duplex stainless steels on wear resistance

U radu su opisani dupleks čelici, navedena je njihova podjela, najčešća područja primjene i svojstva, a posebna pozornost je posvećena zavarivanju dupleks čelika i mikrostrukturi zavarenog spoja. Opisano je nekoliko slučajeva trošenja koji se mogu očekivati obzirom na područje primjene dupleks čelika, te mehanizam nastanka i napredovanja rupičaste korozije. U eksperimentalnom dijelu rada napravljena je kvalitativna i kvantitativna analiza mikrostrukture uzoraka izrezanih iz valjane ploče čelika 1.4462 i toplinski obrađenih tako da im se mikrostruktura što više podudara sa mikrostrukturom realnog zavarenog spoja koja je također analizirana. Istraživan je utjecaj porasta volumnog udjela sigma faze (dobiven žarenjem na 800°C) te utjecaj porasta omjera ferit/austenit (dobiven žarenjem na temperaturi od 1100 do 1300°C) na otpornost prema abrazijskom i erozijskom trošenju, otpornost brazdanju te otpornost trošenju izazvanom kavitacijskom erozijom. Ispitan je i utjecaj erozije na otpornost rupičastoj koroziji kod svih uzoraka. Utvrđeno je da mikrostrukturne promjene nastale u metalu zavara i zoni utjecaja topline imaju veliki utjecaj na otpornost prema trošenju ispitanih slučajeva te da povećanje volumnog udjela sigma faze u mikrostrukturi značajno povećava utjecaj erozije na smanjenje otpornosti rupičastoj koroziji.In this work, duplex steels are described, along with their classification, most common application and properties, while particular attention is paid to welding of duplex steels and weldment microstructure. Several cases of wearing which can happen as a result of duplex steel application are described, as well as appearance and progression of pitting corrosion. In experimental part of the work, qualitative and quantitative analysis of the sample microstructure was performed. The sample was cut out from the rolled steel plate of 1.4462 grade and heat treated in order to obtain the microstructure which would, as much as possible match the actual weldment microstructure, which was analyzed as well. Increase of volume portion of the sigma-phase (obtained by annealing at 800°C) was investigated, as well as how increase of the ferrite/austenite ratio (obtained by annealing at the temperature from 1100 to 1300°C) influences resistance to abrasive and erosion wear, resistance to grooving and resistance to wearing caused by cavitation erosion. Influence of erosion on resistance to pitting corrosion was investigated for all samples. It was found that microstructural changes which appeared in the weld metal and in the heat affected zone significantly influence resistance to wearing in the investigated cases, as well as that increase of volume portion of the sigma-phase in microstructure significantly increases influence of erosion on decreasing of resistance to pitting corrosio