Yes, it would have to be steel, because I beige other types of metal rats can chew through. They can also chew through cement, brick, any type or thickness of wood, plastic, chicken wire, drywall, and lead pipes, basically anything that isn't steel.
They can also jump 8 feet in the air, can tread water for 2 days and swim a quarter mile. They can fit through a space the diameter of a quarter, and can las longer without water then a camel. They will eat almost anything, veggies in the garden, and your livestock.
They will kill and eat chicks, and in desperation attack full grown chickens. I took all of this info from the article I linked in my first post.