Also need to be sure the discs/belts are actually made/spec'd for steel-grinding capability. Sellers of belts, for example, distinguish between 'sanding belts' for wood & other soft materials, versus 'grinding belts' made with abrasives & binders designed for hard metals. The difference being, the abrasives intended for wood will be less expensive, less sharp or even round/blocky in shape and not as tough. Abrasives made for steel should be tougher & sharper, if not also harder. Big variations in aluminum oxide abrasives, for example, some of which will be intended for wood & softer materials, versus the higher-end stuff made for grinding hard metals.
So, if the tools don't have the right belts or discs, it may not matter which machine (grinder or sander) is used.