Tim, there's a couple Youtubers Pete&Peter who have concluded that oxides are formed in high heat environments. Rust is not oxidation, but the decomposition of iron in the presence of moisture (either humidity or water) and air. Neither of those two substances (water or air) seem to contain oxygen. Oxygen is formed by air put through a heat process. Everything we've known as "oxidation" or corrosion or rust is in fact decomposition and hence why you've found rusted metal to be weakened. Metal oxides or heat-treated metals are hardened. I suggest you check out Peter&Pete on YouTube.