Found this in the April MTU Alumnus magazine:Microwave Magic
As gee-whiz as it is, Hwang’s innovation is not just a high-end parlor trick. The microwave energy reduces the iron oxide to iron, and the electric arc furnace smelts the iron into steel, all in one device.
It’s not intended to be a technology that can be used on Mars (Hwang sees it as a technology that can revitalize the American steelmaking industry), but I wonder if it could be. Granted, one is unlikely to find a supply of coal on Mars, but the planet has plentiful carbon, some of which could be obtained as a byproduct of oxygen production from atmospheric carbon dioxide (unless the coal is only required to provide carbon monoxide to reduce the iron oxide, in which case carbon monoxide byproducts from other ISRU reactions could be used).