Welding Tips and Tricks

Hey folks,

I had some general questions about steel that I have noticed and was curious about.

I have been practicing and doing some little projects on hot and cold rolled mild steel. One of the things I have noticed is that when I get metal stock/scrap that isn't rusty yet, and I don't grind it and leave it as is, it remains rust free. However when I grind material shiny, or get my finger oils on it from handling material barehanded it will start to rust where I have ground or touched the material.

I was curious does the scale on hot rolled act as a barrier between the metal and the oxygen that is trying to make it react/oxidize and keep it rust free. For something like cold rolled, the mill scale is supposed to be gone right? Cold rolled I notice acts the same way. Is there a film on the steel that keeps it oxidation free. Finally when you touch material barehanded why does it start to rust. Is oils from our skin breaking up the coating on the materials and allowing oxidation to happen?

This is more of a general question about material processing at a mill.

Your suspicions are correct. The mill scale does help ward off rust, but it is not permanent or fool proof. Grind it clean, and the base metal will rust/flash rust under normal conditions.

Thanks for the response and new vocabulary for me. I'll keep that in mind when getting new stock. Flash rust was something I was noticing, as well as my rusty finger and hand prints in the middle of my cold rolled sheets.