I was just given 3 Large circular saw blades, from a local shop. The are carbide tipped, but of interest is the center material? I have no idea what it is made of? A magnet does stick to it. It seem to be tough, but not real hard? I have cut them into strips with a cut off wheel. They were 20" in dia. and .130 thick. one is thicker @ .230"

I will experiment with hardening, and temp. before making any blades.
Any suggestions?

Go to bladeforums.com and ask. I don't know about yours but many blades are made from L-6 a very fine knife steel.

Never assume that a saw blade is L6 ,most of them aren't !! Since the tips are carbide they'll use the lowest grade they can for the blade. It's much easier to get a proper piece of steel , without the guess work .
This is the standard answer that I and others give on Bladeforums !!

when you are just starting out you use what ever you can get your hands on? why mess up a Good piece of metal when you can mess up a Free piece of metal? I wonder if our fore fathers would have thrown away a Free piece of metal?

If you can get an earlier saw blade with teeth cut from the blade itself rather than a carbide tipped type you should have a better chance of getting a usable blade from the steel.

Von Gruff.

IF the blades still are usable, I think I would find them a home and use the money to buy steel with a pedigree you can trace.

If the are not serviciable, then what the heck one has to mess up some steel to practice, it might as well be free steel.