Factors Affecting the Impact Toughness of Ultra Low Carbon Steel Weld Metal

摘要

The fundamental factors affecting the impact toughness of four gas metal arcwelds (GMAW) made on HSLA-100 base plate using a newly developed steel weld wire were studied. The weld metal analysis included chemistry, mechanical testing (hardness, CVN/FATT), as well as optical, scanning and transmission electron microscopy. Studies of inclusion composition using energy dispersive x-ray (EDX), and electron energy loss spectroscopy (EELS) in the transmission electron microscope were also performed. It was found that increasing oxygen content of the weld metal (due to increased oxygen in the shielding gas) led to increased non-metallic inclusion size and volume fraction; which in turn, led to both decreasing strength and toughness. The strength was lowered because increasing oxygen in the shielding gas led to increased 'consumption' of strengthening alloys such as carbon, manganese and silicon. The toughness was compromised by the increasing size and number of oxide inclusions as these provide sites for void formation and subsequent fracture.