Concrete cutting blades

[RWGearhart]

A friend of mine uses concrete cutting saw blades in his job. He cut some knife blades out of one. When he couldn't drill holes in the handle, he annealed it in the forge. Now he can't get it to harden again. He has quenched in vegetable oil and water without getting hard enough to beat the file. I don't know how color/temp when quenching.
Anyone have any ideas?

 

[BlackAnvil]

The annealing process might have changed the microstructure of the steel, which could make it tougher to re-harden. You might want to try cooling it down more slowly during quenching, or think about using a double-quench technique to get the hardness you’re aiming for.

 

[FireAndFury]

Concrete cutting blades typically have abrasive carbide particles in them rather than hardenable steel, as they're meant to wear away rather than harden. If you find that it's steel, heat it until it’s non-magnetic, about 1500°F. Keep it at that temp for a short time then quench it right away in oil. After tempering at 400°F, you can check the hardness with a file.

 

[RWGearhart]

The annealing process might have changed the microstructure of the steel, which could make it tougher to re-harden. You might want to try cooling it down more slowly during quenching, or think about using a double-quench technique to get the hardness you’re aiming for.

I'm still novice, can you expand on your answer a bit to explain how?