A Study on Characteristics of Duplex Stainless Steel (ASTM A240 UNS S31803) Weld Metals made with FCAW

Characteristics of duplex stainless steel(DSS) weld metals made with FCAW were evaluated in terms of microstructure, ferrite content, EDS and XRD analysis, hardness, tensile strength, impact toughness and pitting corrosion resistance. Three heat inputs of 7.6, 12.5, 18.0kJ/cm were employed to make joints of DSS with E2209T1-1/4 wire. Microstructure in root zone of weld metals showed primary austenite, secondary austenite and δ-ferrite, and the content of Cr, Mo in secondary austenite was lower than that in primary austenite. Microstructures in cap zone consisted of δ-ferrite and primary austenite. Acicular austenite in heat input 7.6kJ/cm was formed whereas allotriomorphic austenite in heat input 18.0kJ/cm was formed. FN (Ferrite Number) values by WRC-1992 diagram using Creq and Nieq was between 40 and 50. Hardness of weld metals was higher than that of base metal in all heat inputs. Hardness of weld metals in heat input 18.0kJ/cm was generally lower than that of HAZ. Impact absorbed energy of weld metals of heat input 18.0kJ/cm at 0°C and -40°C was the highest. In pitting corrosion test, the least amount of pitting corrosion occurred in heat input 12.5kJ/cm. Critical pitting corrosion temperature(CPT) in heat inputs of 7.6, 12.5kJ/cm was 25°C, and that in heat input of 18.0kJ/cm was 20°C because secondary austenite was largely formed in heat input of 18.0kJ/cm. Key words: Duplex stainless steel, FCAW, CPT, Secondary austenite, Pitting corrosion