This is what it looks like when I heat treat a blade. Heat treatment refers to the process where softer steel is hardened so that it stands up to use as a knife blade.
To heat treat steel, I heat it up beyond “cherry red” to glowing red. For 1095 steel (as this blade is), this occurs at a temperature above 1335° F.
At this point in the heat treat, the steel looses is magnetic properties. This is called the Austenite phase. The steel actually changes crystal structure at this point. This is all part of the hardening process of the blade.
Once the blade is heated to austenite temperatures, it’s important to quench the blade so that the steel cools rapidly. This is what hardens the blade.
After the blade has cooled sufficiently, then you must “temper” the blade to slightly lower the hardness so that the steel is not too brittle and prone to chipping, cracking or breaking. Tempering is accomplished basically baking them in an oven at a much lower temperature then the heat treat temperature. I double temper all of my blades which leaves them between 62-63 RC on the Rockwell hardness scale.
The golden straw color you see in the picture below is the sign of a proper heat treat. Different colors in the steel tell different stories about the steel and how well it was heat treated and tempered. This golden straw color is ideal.
You can see a slight scratch at the end of my thumb. This is where I tested the hardness with a hardness test file. I started with the 60RC file and it didn’t even leave a mark on the surface, which means the blade is harder than 60 RC. Then I tried the next file up which was the 65 RC file. It barely left a scratch on the surface. This means the final hardness should be around 62-63.
Then finally I start cleaning the blade and sanding it down which brings it closer to what it will look like finished.