Abstract
The microstructure and properties of welds of duplex stainless steels are affected by cooling rate, so it is important to control welding heat input, and welding is performed in accordance with the recommended welding heat input range. In recent years, the demand for thick plates has been increasing, and there is a need to improve the efficiency of thick plate welding (high heat input). However, the range of welding heat input for welding thick plates has not been studied. The purpose of this study was to examine whether high heat input welding is possible for duplex stainless steels, and to propose a new welding heat input range that contributes to higher efficiency in welding thick plates. No sigma phase precipitation or hot cracking was confirmed in the weld metal and HAZ of 20 mm-thick duplex stainless steel (SUS329J3L) welded with heat inputs of 5 kJ/mm and 7 kJ/mm, which exceed the recommended heat input range, and good mechanical properties and pitting corrosion resistance were confirmed. Based on the TTT diagram, we examined the conditions under which sigma phase does not precipitate in SUS329J3L. As a result, the effective heat input is 3 kJ/mm, which is the upper limit of the recommended heat input range, when the plate thickness is about 10 mm. However, as the plate thickness exceeds 10 mm, the effective heat input at which sigma phase does not precipitate increases with increasing plate thickness, and the upper limit of the weldable heat input range becomes considerably larger, and good properties of welds were obtained even at a heat input of 7 kJ/mm in this study. Therefore, the upper limit of heat input to obtain sound welds in duplex stainless steel should be determined by the plate thickness, which will allow high heat input welding for welding thick plates and improve the efficiency of welding.
