Abstract Electron beam welding parameters have been shown to influence heat-affected zone (HAZ) microfissuring behavior in cast Inconel 718 (Inconel is a trademark of INCO Alloys). Travel speed was shown to be the most significant factor in influencing HAZ cracking behavior by modifying the thermal gradient(s) and subsequently the stress state in the HAZ. This has been shown previously to be related to a change in weld pool geometry and to the effect of speed on heat flow in the weld zone. Microfissuring in the HAZ was observed to occur intergranularly in areas containing Laves phase. Liquation of the Laves phase and subsequent wetting of the grain boundary is believed to be but one element of the complex interactions occuring in the HAZ during the weld thermal cycle.