A Study on the Weldability of INCOLOY 825 Alloys and STS316L Alloys

Bellows are widely used as parts in industrial machinery such as ships, valves, automotive, semiconductor equipment, flow and pressure sensors, and even in aircraft. Due to the recent depletion of conventional fossil fuels, natural liquified petroleum is increasingly demanded as an alternative energy, which in turn increases the demand for bellows on LNG ships. As the material used the bellows of LNG ships, the STS316L and INCOLOY 825 alloy, resistant to low-temperature embrittlement and corrosion, are used. STS316L is low-carbon stainless steel with a carbon content of less than 0.03%, preventing intergranular corrosion by welding work and maintaining its toughness and strength at a low temperature. In addition, Ni-Fe-Cr-based INCOLOY 825 alloy, containing Mo, Cu and Ti, is an alloy material resistant to general local corrosion in various atmospheres. INCOLOY 825 alloy is widely used for the creation of chemical processing equipment and in pollution-treatment facilities, oil and gas reduction equipment, acid manufacturing plants, pickling plants, nuclear fuel reprocessing and radioactive waste treatment facilities as well as in the bellows of LNG ships. Furthermore this material maintains good mechanical properties across a wide range of temperatures from ultra-low temperatures up to temperature approaching 500 °C. In this study, to assess its quality as a LNG ship bellows material, the STS316L and INCOLOY 825 alloy, used at an ultra-low temperature, the optimal welding conditions were established and its formability was analyzed by conducting an Erichsen test.