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The steel sector emits 25% of global industrial greenhouse gases, and the U.S. is the world’s second-largest steel consumer. In this article, we determine how CO2emissions attributable to U.S. steel consumption can be cut by 70% by 2050. We vary four key steel cycle parameters (U.S. steel stocks per capita, recycling rate, product lifespan, and manufacturing yield) in a dynamic material flow analysis to determine a range of values for annual steel demand and the scrap available for recycling. We combine these data with steelmaking technology and trade scenarios to calculate potential U.S. steel sector emissions in each year to 2050. Only 20% of the pathways we modeled for the U.S. steel sector achieved the emissions target. Emissions in 2050 are most sensitive to the CO2released per kilogram of steel produced and the steel stocks per capita. Deployment of emerging low carbon steelmaking technology alone is insufficient to achieve the emissions cut; conversely, reducing stocks per capita from the current ∼11 tons/capita toward levels in the U.K. and France, ∼8 tons/capita, would enable the emissions cut to be achieved under a range of foreseeable steelmaking technology scenarios and steel cycle parameters. If action to reduce per capita steel stocks is delayed by more than five years, then it is likely infeasible for the U.S. steel sector to stay within its 2050 CO2budget because of the increased demand for emissions-intensive steel made from iron ore.