Modification of high-alloyed filler metals for welding medium manganese steels

Abstract The energy transition and the goal of making Germany climate-neutral by 2045 have increased the demand for hydrogen as an energy carrier. Within this framework, the transportation and storage of hydrogen in liquid form at extreme low temperatures (> -196 °C) within welded steel containers need to be realized. In Europe, steels with a high nickel content like X8Ni9 are frequently used, but these steels are difficult to weld due to the magnetic remanence and have to undergo expensive post-weld heat treatments. In other regions of the world, the usage of medium manganese steels is more common. In this work, the focus is on the use of medium-manganese austenitic steels, which represent a more cost-effective, easier weldable, and readily available alternative to high-nickel steels. But in prior studies, it was shown that the strength of the weld metal using commonly available high-alloyed filler materials is not sufficient to meet the strength of the base material. To achieve this, this paper focuses on a slight alloy modification of the filler material to increase the strength of the weld metal. The toughness already matches the requirements of the industry. Overall, it is necessary to increase the strength of the material while ensuring adequate toughness. To modify the chemical composition of the weld metal, welding experiments with coating welding wires (using physical vapor deposition (PVD)) have been carried out. These coatings on the filler material can improve the mechanical properties, like strength and ductility of the weld metal. Furthermore, they can reduce the risk of cracking and other welding defects. For this study, the modification of the filler material was done by adding some amounts (< 1%) of Ni, TiN, Nb, and Ti. The medium-manganese austenite X2CrMnNiN17-7–5 (1.4371) is used as the base material. The steel under consideration is distinguished by elevated concentrations of manganese and nickel. These elements confer upon the steel distinctive mechanical properties, including elevated toughness at low temperatures and excellent weldability. A specific filler material, G 20 16 3 Mn N L, is used in the form of a wire with a diameter of 1.2 mm. The mechanical properties of the welded joint should correspond to those of the base material. It will be shown that due to the modification of the alloy composition of the filler material, the toughness and hardness of the weld metal can be influenced. It will be shown that the hardness, as an indicator of strength, can be increased by approximately 20HV compared to the weld metal of the unmodified filler wire. Especially, the addition of TiN could increase the hardness of the weld metal while keeping the toughness of the weld metal. Overall, the study will demonstrate that modifying the chemical composition of the filler material can be used to enhance the mechanical properties of the weld metal, thereby approaching the level of the base materials.