Abstract
The critical hydrogen content of steels and the critical temperature for hydrogen attack were evaluated by using the Nelson chart and various data on hydrogen content. The critical contents of hydrogen were 0.6ppm for carbon steel and 2.4-4.3ppm for 2%Cr-1/2%Mo steel. The critical temperatures were 494K for carbon steel and 670K for 2%Cr-1/2%Mo steel. The relation between the critical hydrogen content of steel and the critical temperature for hydrogen attack was discussed tentatively.
