| Traditional research approaches to solidification cracking and hydrogen cracking phenomenon in weld metal have been completely unrelated. Nevertheless, there is some speculation in the literature that the two types of cracking are related. The present study adopted a new approach to relating both types of cracking problems to the solidification behavior of steels. Differential Thermal Analysis (DTA) was utilized to study the solidification behavior of a series of HSLA steels. Fullscale varestraint testing was used to investigate the hot cracking tendencies of these steels with the objective of applying a hot cracking theory developed for austenitic stainless steels based upon their solidification behavior. Also a modified varestraint testing techniques were used to study the effect of hydrogen on hot cracking susceptibility and the possibility of hot cracks acting as hydrogen crack initiation sites. Energy Dispersive Spectroscopy (EDS) was carried out on the surfaces of both types of cracks to determine the presence of segregants. From this investigation, it was concluded that the hot cracking theory for austenitic stainless steels can be extended to ferritic steels. In the ferritic steels studied, true dual phase solidification mode was most resistant to solidification cracking. The presence of hydrogen increased hot cracking susceptibility in the varestraint test. Hot Crack Induced (HCI) hydrogen cracks were observed to have propagated from the preformed hot cracks in the modified varestraint test. The HCI hydrogen cracks were verified by comparing the nature of their fracture surface with that of a weld metal hydrogen crack occurring in a gas metal arc weld. The same pattern of segregation was observed on the solidification and hydrogen crack surfaces. This indicated a strong possibility that hydrogen cracking also occurred along solidification grain boundaries, a situation which infers that the hydrogen crack was a continuation of the hot crack. |
