Abstract
Solidification cracking susceptibility of carbon steels was evaluated by the transverse-Varestraint test to reveal the fundamental effect of solute elements in the steel such as carbon, silicon, manganese, phosphorus and sulfur. Fracture surface of a pear-shaped bead cracking occurred in a weld metal of the carbon steel by GMAW exhibited the characteristic features of solidification cracking. The smallest solidification brittle temperature range was a chemical composition obtained by a flux cored wire, followed in order of SS400 and SM400. According to the EPMA results, a manganese sulfide was observed in weld metals of the pear-shaped bead cracking and Varestraint test weld metal.
Numerical simulation considering FA mode solidification and the solidification segregation in carbon steels was carried out in order to clarify the effect of solute elements on solidification cracking. The solidification analysis suggested that carbon steels used in this study were solidified as fully delta ferrite until the solidification rate of 95%. The solid-liquid coexistence temperature range calculated by solidification analysis indicated similar tendency to the BTR evaluated by the transverse-Varestraint test. Then, the influence of solute element was virtually simulated by using the numerical simulation. It could be concluded that the solidification cracking susceptibility of carbon steels was attributed to the carbon amount at the terminal stage in solidification.
