1984 Volume 2 Issue 3 Pages 376-382
Effects of maximum hardness in the HAZ on root crack initiation in the JIS-y (oblique-Y groove) cracking test are discussed. The values of critical hydrogen concentration Hc at the location of root crack initiation at 100°C on the way of cooling, were calculated, assuming uniform diffusion of hydrogen through weld zone. The value of log Hc decreased linearly with an increase of Hmax, depending on the intensity of restraint. The correlation between llog Hc and Hmax was found to be far poorer than that between log He and Pcm, Ito and Bessyo carbon equivalent, which is adequate for low carbon content steels. An analysis by the cracking parameter PHA, proposed by the author considering local accumulation of hydrogen at the site of crack initiation, revealed that log Hc vs. Hmax relation is severely affected by the C% of test steels, thus a wide scatter in Hc values. For the same value of Hmax, a lower carbon content is more favourable against root cracking. The estimation agrees well with the JIS-y test result. The critical values of Hmax for crack-free welding without preheating, have been PHA-estimated depending on HD values. As an application, the PHA-estimated critical values of Hmax agree satisfactorily with the Harasawa-Hart's observed values in the H-type self-restrained root cracking tests.