Tensile properties were shown with metallurgical change in Fig. 1. Yield stress decreased gradually to 500°C and
decreased abruptly above 600°C irrespective of metallurgical change. Elongation decreased to 400°C, was the
minimum at 400°C, and increased above 400°C. Yield stress was the highest for 91B of two step heat treatment and
changed little with welding. Elongation was the lowest for 91B of two step heat treatment.