You're correct on many points. But I had to chime in when I read statements like "Inferior metal will have a lower melting/softening point than higher grade metal", "... lose the surface hardness...", and "... degradation of the structure...". I couldn't let this misinformation go unanswered, which I am uniquely qualified to catch.

What bothers me is that, way too often, I read discussions on rotors and warping, and invariably someone will chime in and blame the "metallurgy" of a rotor and/or its chinese origin in the same breath. Metallurgy is a mystery to most people, including many engineers, and it's all too easy to make such a blanket statement blaming the "metallurgy", because it's easy to do and few people are familiar with metallurgy. Nor have any posters done any forensic metallurgical study to develop any experience on this matter. I'm all to familiar with metallurgy. It's no mystery to me, especially rotor material, which is the most forgiving to produce. Today, one poster on another site even blamed rotor corrosion on "bad metallurgy".

If rotors are warped, it is more likely that they aren't true, too thin, overtorqued, or overheated, rather than the "metallurgy" or simply being of chinese origin. The first five answers to the OP were the best.