I don't really see the point of a physical copy. It's vulnerable and a hassle to store. You can store the same information properly encrypted on multiple micro SD cards. No one will ever know what's on there and they're much smaller. Just make sure you have plenty of them as they're not very durable.
Steel is pretty resilient, typical house fires don't reach the temperatures high enough to melt steel (~1400 deg. C). I'd be a little concerned with relying on only one type of medium as a BTC wallet backup, especially one with questionable data permanence.