Fe‐Based Filler Material Forming Austenite‐Covered Packet Lath Martensite for Gas Tungsten Arc Welding of 9% Ni Steel

Abstract

Fe‐based filler material with a composition of Fe–20Ni–5Co–2.5Mn–0.2C is developed for welding 9% Ni steel. To ensure high weldability through compositional similarity, the composition of the Fe‐based filler material is designed based on that of 9% Ni steel. The filler material has elements such as Ni, Mn, Co, and C to enhance its compatibility with the 9% Ni steel. The Fe‐based filler material is designed to control the martensite formation temperature, resulting in the appearance of the martensite–austenite dual phase during rapid cooling. The weld joint shows a distinct microstructure characterized by the presence of austenite‐covered packet lath martensite. The mechanical properties of the weld joint are investigated via Vickers harness and tensile tests at 25 and −163 °C. In comparison to 9% Ni steel, the weld joint prepared using the Fe‐based filler material exhibits yield and tensile strengths that are ≈5.5% higher. Additionally, the tensile fracture of the specimen occurs exclusively within the base metal, without any involvement of the weld metal or heat‐affected zone. Further, the fracture surface is observed. In the findings of this study, the applicability of the Fe‐based filler material for welding 9% Ni steel is demonstrated.