The steel frame of the EDC is made of 420HC, I think. It's highly rust resistant, but I suppose if you leave it outside in rain for a few days, it can develop some oxidation like any other knife. It gets hazy hot and humid during the summer where I live now, so if I'm out running and working up a sweat, I rub the entire knife with some Tuf-Cloth. I haven't seen one speck of rust yet.