Characterization of Duplex Stainless Steel after Welding and Annealing

Dupleks nehrđajući čelici se nazivaju još i austenitno-feritni nehrđajući čelici te svoje ime duguju miješanoj strukturi austenita i ferita pri sobnoj temperaturi. Osnova dupleks nehrđajućih čelika je Fe-Cr-Ni-N sustav, a glavne faze su austenit (γ) i ferit (α). Glavna prednost dupleks nehrđajućih čelika je dobra korozijska otpornost. Oni uglavnom sadrže viši sadržaj kroma te niži sadržaj nikla, a često sadrže i molibden radi povećanja otpornosti na koroziju. U ovom radu provedena je mikrostrukturna analiza i ispitivanje mikrotvrdoće zavarenog dupleks nehrđajućeg čelika X2CrNiMoN22-5-3. Uzorci su zavareni tako da je korijen zavara zavaren TIG postupkom, a za popunu zavara korišten je REL postupak zavarivanja. Analiza mikrostrukture i mikrotvrdoće je provedena prije i nakon žarenja (850 °C/60min/zrak). Uzorci su nakon žarenja metalografski pripremljeni. Optička mikroskopija i pretražna elektronska mikroskopija s energetsko disperzijskom spektrometrijom su korištene za mikrostrukturnu karakterizaciju. Prije žarenja mikrostruktura se sastojala od ferita i austenita, a nakon žarenja je utvrđena prisutnost sigma faze u zoni taljenja. Mikrotvrdoća uzoraka prije i nakon žarenja mjerena je metodom po Vickersu. Nakon žarenja zamijećen je najveći porast mikrotvrdoće u zoni taljenja (s 294,9 HV1 na 357,0 HV1).Duplex stainless steelsalso called austenitic-ferritic stainless steels, owe their name to the mixed austenite and ferrite structure at room temperature. Basis of duplex stainless steels is Fe-Cr-Ni-N system, whereas austenite (γ) and ferrite (α) are main phases. Main adventage of duplex stainless steel is very good corrosion resistance. They usually contain higher content of chromium, lower content of nickel and often contain molybdenum to increase corrosion resistance. In this paper microstructure analysis and microhardness testing was carried out on welded duplex stainless steel X2CrNiMoN22-5-3. Samples were welded so that the root of weld was welded with TIG process, and for filling REL process was used. Analysis of microstructure and microhardness was conducted before and after annealing (850 °C/ 60 min/ air). Afterannealing,the samples were metallographically prepared. Optical microscopy and scanning electron microscopy with energy dispersion spectrometer were used for microstructural charaterization. Before annealing microstructure was consisted of ferrite and austenite, and after annealing presence of sigma phase was determined in melting zone.Microhardness of samples before and after heat treatment was measured by Vickers method. After annealing it is noticed the highest increase in microhardness in melting zone (from 294,9 HV1 to 357,0 HV1)