Solidification Cracking Mechanism of Carbon Steel Weld Metal

It is well known that the solidification cracking susceptibility of carbon steel weld metal increases with increasing Sulfur (S) and Phosphorus (P) contents. However, solidification cracking was detected in the weld metal of low/medium carbon (C) steels welded by low-carbon welding wire, even in low S/P content steels, after changing the welding parameters. To clarify the mechanism of solidification cracking of the weld metal for low S/P, low/medium carbon steels welded by low-C welding wire, the effect of travel speed on solidification cracking susceptibility was studied, and the S and/or P compounds formed on the solidification cracks were identified by energy-dispersive x-ray spectroscopy (EDS) and Auger electron spectroscopy (AES). The solidification cracking susceptibility of the weld metal increased with increasing travel speed. The C content of the weld metal also increased with the increasing travel speed, but the S/P contents did not change at any of the studied travel speeds. The S compounds were detected on the solidification cracks. It was concluded that the S content in the remaining liquid phase in the solid-liquid region increases with increasing travel speed due to the increasing amount of the austenite phase formed during the peritectic reaction. In this way, the solidification cracking susceptibility of carbon steel increased with increasing travel speed.