Please keep in mind that heat treat starts with selection of the steel and includes all events to the finished blade.
After forging is nearly completed I give the blade three quenches from critical in room temperature oil for 35 seconds. Since I started this I have experienced no blade warp! These quenches promote blade uniformity.
Then two flash normalizing cycles followed by a full normalizing cycle to room temp. in still air, after cool into the freezer over night.
Then three tempering heats at 988 f, in my Paragon at room temp, heated to 988 in one hour, then held for 2 hours and allowed to cool in Paragon to room temp. Then in the freezer overnight for a total of thee cycles.
Hardening: Three cycles - with a torch to critical, then quenched in Texaco Type A heated to 165 f. the blade is allowed to cool to room temp. in the oil. One cycle a day, and into the home freezer over night.
Tempering: From room temp. into the Paragon - up to 388 in one hour, held at temp for two hours, then allowed to cool to room temp in the Paragon, then into the home freezer over night one cycle a day for three days.
-Why?
When forged properly, quality 5160 and 52100 are great steels.
The time between cycles costs us nothing and allows what happens to develop more completely. Let us consider some abstract thoughts - say 90 % of what happens during heat treat happens in the first cycle, then 90% of the remaining 10% happens in the second cycle and 90% of that still remaining 10 % happens in the third cycle, we have come to a point of diminishing returns. I have found that when seeking the best blade seek, that time is a significantly contributing factor.
The extended times and depth of the cycles have proven to enhance blade performance (as I measure it).
The cycles utilized in multiple quench result in no measurable retained austenite in the hardened part of our blades. There is also no measurable carbon loss.
For the beginner it is easy to over heat steel, or create a significant stress raiser into a blade. Those who claim we must temper immediately after quenching a blade probably do so due to lessons learned thanks to stress in the blade, either by virtue of the steel they chose or their methods. They temper quick to save a faulty blade.
I would much rather have a blade fail in my shop than in a client's hands.
