9419560 Schlesinger The thermodynamics of bismuth and lead in liquid and solid iron-carbon solutions are investigated using an adapted isopiestic technique. The use of bismuth in place of lead in free-machining steels and the removal of lead from free-machining steel scrap will benefit from a better understanding of lead and bismuth distribution between the phases (liquid, solid, and vapor) in steelmaking operations. This research improves on the results of previous investigations of the iron-lead and iron-bismuth alloy systems. It includes the effects of added carbon content on the chemical potential of bismuth and lead in liquid alloys and delta iron ferrite. The focus is on determining the interaction coefficients needed for modeling liquid iron-carbon-(bismuth, lead) solutions as a function of temperature and composition. %%% This research produces thermodynamic data needed for reliable estimates of the disposition of bismuth and lead in steelmaking systems. It advances the level of high temperature thermodynamic research performed in the U.S. ***