I’ve read a number of books on heat treating steel, but how do I know if it really is working with my lawn mower blades?
I field tested some small pieces off of one blade and here is the proof.
The steel on the top picture was annealed (softened) on one end and heat treated on the other end. To anneal, I heated the metal to cherry red and let it cool slowly at room temperature. To harden the other side, I heated it to cherry red until a magnet will no longer stick to the steel (around 1500 degrees) and then dunked it in vegetable oil.
When put in a vice and bent with a crescent wrench, the heat treated side snapped like a pretzel. This is good, as it means that the heating and rapid cooling in oil is producing the proper effect on this steel. The other side of the metal bent like taffy after it was annealed and bent with the crescent wrench.
The second picture shows a whole piece of steel that was heat treated, but then “normalized” in an oven at 400 degrees for two hours. The metal turned a straw color which indicates it will retain a 58 Rockwell hardness or so. Once bent in the vise w/ the crescent wrench, it went about 45 degrees before it snapped.
I normalize my blades after heat treating them in this same manner, so this proves to me that they should be very durable and hold an edge. The proof is in the pudding, or steel in this case.