As long as your stainless steel container has the etching "DISHWASHER, MICROWAVE, AND OVEN SAFE," you're free to use it in any of those machines. Please remove the lid before heating. Please note - if your container is dented or bent, DO NOT use it in the microwave.
If your stainless steel container does not indicate that it is "DISHWASHER, MICROWAVE, AND OVEN SAFE," please transfer them to a dish before heating in the microwave and remove the lid before heating in the oven.
