Often we find ourselves scrounging metal for projects. If you are making anything you want to hold an edge you need something with some carbon in it. For decades the quick test was to grind on it and look at the spark pattern to determine what kind of metal it is. In the September 1959 issues of Popular Mechanics has one of the best write-ups I’ve seen and it even has some good color pictures.
Learning the properties of various types of iron will really help you in any projects you work on. Low carbon steel will not harden like high carbon steel, but it is tougher and will not crack as easily. This is why blacksmiths of times past would weld in a piece of high carbon steel for the edge of an axe. The high carbon steel would harden and hold an edge while the lower carbon steel in the back would hold up to the stresses on the eye and pole of the axe.
The best way to learn this is to grind know types of metal and learn the spark pattern. If you can’t do that then the article linked to above gives you a good starting point.