Corrosion and erosion of steel is a serious materials engineering problem affecting all sorts of industries. Experimentally characterizing or theoretically modeling the complex surface and bulk solid state chemistry involved is nontrivial. By necessity, one must resort to approximate quantum mechanics techniques; here we employ first-principles Kohn-Sham density functional theory to explore a subset of chemical reactions involved in steel degradation. We focus on known chemical contaminants, CO and H2S, which are thought to lead to carburization, sulfidation, and hydrogen embrittlement of steel. We first examine their adsorption and dissociation on iron surfaces (as a model for steel). We then evaluate the incorporation of carbon and hydrogen into iron. Then we consider whether any sort of pretreatment, such as alloying the surface and near surface layers of steel, might inhibit these damaging surface reactions and subsequent impurity diffusion. Lastly, we suggest a possible multilayer protective coating design for steel.