Current research on using biochar as foaming agents in electric arc furnace (EAF) steelmaking is limited to pyrolysis biochar treated with nitrogen. Therefore, this study used pyrolysis corn stalk biochar treated with nitrogen (PN) as a reference, the physical and chemical properties, the ability to reduce iron oxide, and the reaction mechanism of pyrolysis corn stalk biochar treated with superheated steam (PSS) and hydrothermal corn stalk biochar (HC) were investigated. HC contains a large number of hydrogen-containing functional groups, which can release large amounts of H2 during the reduction of iron oxide, while PSS has a higher fixed carbon content and produces higher amounts of CO and CO2 gas. Dividing the thermogravimetric results into three reduction stages, the results show that the large amount of volatile fraction contained in HC contributes to Stage 1 and that the gasification reaction ability of PSS is stronger than that of PN. The results of the kinetic analysis showed that the best reaction mechanism for the three reduction stages of the three biochars was the Jander diffusion equation. This work provides theoretical guidance for the use of PSS and HC as foaming agents in EAF steelmaking.