Weld metal impact toughness of electron beam welded 9% Ni steel

9% Ni steel was electron beam welded and the impact toughness of its weld m etal was investigated. The improvement of weld metal toughness was studied by an increase of Ni content in the weld metal and its mechanism was discus sed. The weld metal impact toughness was as low as 25-55 J at -196 degreesC . However, it increased remarkably by an increase of Ni and showed 118 J at the same temperature when Ni content was 16.6%. As Ni lowers the martensit e start temperature, martensite formed in weld metal with a high Ni content has more chance of auto-tempering because of its slow cooling rate at a lo w temperature range. Therefore, the improvement is believed to be due to th e formation of auto-tempered martensite and retained austenite during the c ooling cycle after welding (C) 2001 Kluwer Academic Publishers.