No, it is not safe to put stainless steel in a microwave. Microwaving stainless steel can cause sparks and potentially damage both the microwave and the metal. Stainless steel is a good conductor of electricity, and when microwaved, it can create an electric current that leads to arcing, which is the production of sparks.
Arcing can damage the interior of the microwave, including the magnetron, which is the component responsible for generating the microwave radiation. This can result in the microwave malfunctioning or even becoming a fire hazard.
To avoid any potential risks and damage, it's essential to only use microwave-safe containers and utensils. Stick to materials like microwave-safe glass, ceramic, or microwave-safe plastics that are explicitly labeled for microwave use. Always follow the manufacturer's guidelines and safety recommendations for both your microwave and the containers you use in it to ensure safe and efficient microwave cooking.