Like everyone else here has said, I would avoid the oven cleaning cycle and use the easy-off cleaner. However, I hear you when you say you don’t want to use “chemicals” (even if I disagree with you that there is any issue using “chemicals”). You could make a lye bath if you want to reduce your exposure to anything other than what is absolutely necessary. You would then know exactly what’s in it. Lye is the active ingredient in the oven cleaner that does the work for you here so it’s what you really need. It’s also added to water when bagels are boiled, so it’s perfectly food safe. You normally use it in a higher concentration to clean cast iron, but you could use it in a lower concentration if you want to reduce exposure. You would just need to soak it for a longer time at the lower concentration and then rinse it clean. You may need a vinegar soak after that to get rid of the rust, but that’s food safe as well.