With correct heat-treatment, the utilization and final hardness are over 63HRC, which is harder than glass. Hardening is done in a vacuum or with inert gas at 850° C. Holding time is 5 minutes. The cooling rate is the same as it is with hardening using oil. To transform the remaining amounts of austenite, a cooling at 90° C or annealing at 140° C can be performed. Afterward, an annealing process at 150° C should follow to activate annealing of the remaining unannealed martensite (the untransformed austenite remaining from deep cooling or first-annealing).
- Etch in Fe3Cl or a 30% solution of warm sulfuric acid, then polish.