Scrap steel is everywhere, and very little of it has the right chemistry for making good knives.
But if all you want is to get some practice shaping steel with whatever tools you have laying around (with no intention of it ever being a useful knife), then scrap steel may serve some limited useful purpose. Some people swear by it, and will tell you that we "known steel" users are just being snobs.
And it's true... we are snobs. We don't like wasting our time on things that don't meet our needs or demands. We especially don't like wasting our time and resources shaping a piece of steel that has no real chance of being anything more than a knife-shaped object that can't hold an edge.
So if you have lots of time and resources to waste, scrap steel may be fine for you. At the very least you will have a chance to figure out what tools do and don't work well at shaping steel. Be prepared for the fact that most of the tools used for woodworking won't be useful.