Using just those exact words, I would assume you meant a person had been employed in the steel industry for most of his or her life. Context would definitely help.

The others are correct,not enough info to understand the true meaning.Could be that a person was working in the steel industry for their entire life or a maybe like the Terminater...made of steel.

It sounds like a guarantee for steel cookware, garden tools etc.

Без контекста трудно дать правильный ответ, а предположения, что имеется в виду не имеют ценности.

When you pull phrases like this out of context, you make it hard for us to explain. I'm guessing this has to do with construction or kitchen pans. If stuff is made of steel it lasts a life-time. The phrase would appear to come from some stainless steel set advertisement. Please provide context next time.