Eighteen percent nickel marage steel can be used to fabricate welded airframe structure. The weldability is excellent and the heat treatment is simple. The mechanical properties of marage steel sheet is presented at ambient and elevated temperatures. TIG welded properties are also determined. The adaptation of this alloy for use in a tubular truss weldment is discussed. The tensile, notch tensile, and compressive yield strengths are very good, but the fatigue strength is low compared to a weldable low alloy steel. Marage steel can be used to advantage for high strength, short life applications such as experimental aircraft structure.