1, it is not impossible to put metal utensils in the microwave oven. I used to put the metal fork on a plate and heat it in the microwave oven. By the time I thought of this problem, the heating work had been completed and nothing unusual had happened. As the fork is soaked in the soup, I can't judge whether the metal is abnormally heated. But on one occasion, I observed sparks from the fork. (I didn't see clearly whether it discharged with the furnace wall)

I once heated pizza or potatoes wrapped in aluminum foil in a microwave oven, and there was nothing unusual.

However, I used to heat something with an instant noodle bag with tin foil and watch it burn.

2. Metal objects will reflect microwaves (the four walls of the microwave oven are made of metal, so that the microwaves are constantly reflected in the cavity), which will lead to uneven heating of food (overheating in some places and insufficient heating in some places). If there are flammable substances, they may burn because of overheating in some places (I guess that's why I saw the instant noodle bag catch fire)

3. According to some professional data, microwave may make the metal objects in it carry too much charge and produce discharge (maybe this is the reason why I observed the fork strike fire).

According to the above statement, I think the metal in the furnace wall mainly plays the role of reflecting and shielding microwaves, so that the microwaves are constantly reflected inside the furnace wall and the objects in it are heated. However, the metal in the furnace may be: 1, and the food is unevenly heated due to reflection; 2, leading to a fire. So it is forbidden to put metal objects in the microwave oven.