Cast iron melts at temperatures above 2200 °F and does not exhibit indications of deterioration until temperatures far beyond 700 °F, therefore any temperature that you can create in your house is safe for cast iron. Although cast iron will continue to heat up after being removed from the fire, it should be replaced when its color changes to dark brown or black.
The best way to test if your pan is still good is to add some oil and heat it up over medium-high heat. If it smokes slightly or smells like metal, then it's still good. A pan that has been sitting around the house for years may no longer produce smoke or smell, but still be usable. However, if it starts to make strange noises, such as clicking or rattling, then it's time for replacement.
There are several types of cast iron available on the market, so it's important to know the quality of the product you are buying. Since cast iron becomes toxic when burned, make sure that you don't leave it unattended when it's heating up. Also, don't use aluminum foil to wrap the handle or side panels of the pan because this will prevent the pan from conducting heat properly.
Finally, avoid pans with signs of damage such as dents or cracks, since these may contain hidden holes that allow water to enter the pan.
Your food has no idea where your burner is set, simply the temperature of the pan's surface. Because the stove shouldn't be able to reach that hot, the cast iron should be OK. Cast iron has a melting temperature of around 2100 degrees Fahrenheit. That means that if your pot isn't hotter than this temperature, then you're good to go.
The only thing you need to worry about is not burning yourself. If you don't have an oven to test your pots in, just stick a wooden spoon in the hot pot and pull it out quickly! The handle will still be warm enough to touch.
Also worth mentioning is that as long as the center of the pot isn't yet liquid, you can move onto the next step. So if some water gets into the pot during this process, that's fine too! Once the water starts boiling, you'll know when it's time to quit heating up your kitchen.
Finally, make sure that you don't leave any hot spots in your kitchen. These could become burners on their own if not checked regularly. A heat diffuser or fan would be advisable if there are areas where the heat is being trapped for a long period of time.
In conclusion, cast iron can get very hot on the stovetop, but as long as you don't let it get too hot, you should be safe.
Common Heat Treatment for Specific Cast-Iron Tempering is conducted for at least 4 hours at temperatures ranging from 205 °C (400 °F) to 260 °C (450 °F). This softens the martensite, alleviates part of the transformation stresses, and enhances strength and impact toughness by 50–80%. Martensitic stainless steel has greater hardness and corrosion resistance than regular carbon steel. It can be hardened further by heat treating, but the cost of doing so is prohibitively expensive for use on cooking utensils.
Cast iron can also be heat treated by heating it to a high temperature and then slowly cooling it down. This process creates a matrix of hard, brittle material called "white metal" around any remaining liquid inside the vessel. The white metal acts as an insulator, keeping the liquid cool while the rest of the pot heats up during next stage of the heat treatment. The advantage of this method is that it does not require access to specialized equipment. Disadvantage is that it takes longer than common heat treatment because the pot has to be reheated and cooled down several times before it is considered done.
Heating cast iron beyond its critical temperature causes all of the liquid to evaporate, leaving only solid iron behind. The pot is now said to be "coked". Coking removes most of the oil content from the iron, making it more suitable for baking goods like biscuits or cakes.