Heat input control when welding 2205 duplex

The key to welding 2205 is maintaining roughly a 50:50 ferrite-austenite balance. Too much ferrite reduces toughness, while excessive heat input precipitates sigma phase. Guidelines: - Heat input is usually controlled between 0.5 and 2.5 kJ/mm. - Use 2209 filler (ER2209). Do not substitute 316L filler. - Keep interpass temperature at or below 150 degrees Celsius and cool if necessary. - Backing gas, argon or a nitrogen-hydrogen mix, must be used to prevent root oxidation. - Post-weld heat treatment is generally not required; if it is, control it strictly and verify phase balance. Metallographic sampling after welding is recommended to confirm the phase ratio.