ROOT CRACKING AND MAXIMUM HARDNESS IN HIGH-STRENGTH STEEL WELDS.

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 degree 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 H//m//a//x, depending on the intensity of restraint. The correlation between log Hc and Hmax was found to be far poorer than that between log Hc and Pcm, Ito and Bessyo carbon equivalent, which is adequate for low carbon content steels. An analysis by the cracking parameter P//H//A, proposed by the author considering local accumulation of hydrogen at the site of crack initiation, revealed that log H//c vs. H//m//a//x relation is severely affected by the C% of test Steels, thus a wide scatter in Hc values. For the same value of H//m//a//x, a lower carbon content is more favorable against root cracking. The estimation agrees well with the JIS-y test result. The critical values of H//m//a//x for crack-free welding without preheating, have been P//H//A-estimated depending on H//D values. As an application, the P//H// A-estimated critical values of H//m//a//x agree satisfactorily with the Harasawa-Hart's observed values in the H-type self-restrained root cracking tests.