That looks like very heavy stamped steel. Those are wonderful too. Expensive, no?

Yes, they will rust if you use anything acidic in them and don't clean/oil right away. I'll sometimes make a stew in my dutch oven when I want to cook outside on the campfire, (hmmm, that gives me an idea!)but I always empty the stew into some other container and clean and oil my dutch oven as soon as the cooking is finished. I've made the mistake of not doing that too many times (because I'm very lazy at heart, especially after I've eaten) and then had to spend way too much time getting it back in top shape.

I almost had a guy talked into giving me a set of pans similar to yours that was sitting in the back of his trailer with a bunch of other junk on its way to the dump. They were filthy and a bit abused. But as usual I ended up talking too much and told the guy how he could make them usable again. At least they didn't get thrown away!