For corrosion resistant steel (CRES/"stainless") I've had good luck with one of the commercial oven cleaners. One available here called "EZ-Off" works at low(er) temperature, and it's just a spray on and let linger, rinse off. It helps to stick the stuff in a warm (140F/60C) oven for a few hours. A slight bit of minor scrubbing on stubborn spots may be needed, preferably with a CRES "scouring pad."

For cast iron that's really crusty, I usually just stick it in the oven and run the oven "self-cleaning" cycle. (Ours is a "pyrolitic clean" kind, the "catalytic" kind might not work as well.) If you can get 500F/260 C the cast iron will come out like fresh-cast. (Smoke is usually minor, but you might want to ventilate some.) You will, obviously, want to re-season the cast iron; but if you wipe it with a little cooking oil and leave it in the bottom of the oven, with a fresh oil-wipe before each cycle, and use to oven for normal baking a few times it should be suitably prepared for the next trip to the wild places.

Note the above note (somewhere back up there) re alumin(i)um melting point though. Don't try the "oven" method with Al pots.

John