C-20 beryllium copper (copper alloy C82500) blades are hardened in a heat treating oven. Props are held at 650 deg. F (+- 5 deg F) for 2.5 to 3 hrs. The time in the oven is not critical, but the temperature is to achieve the ultimate tensile & yield strength. The tensile strength should be 160,000 psi with a rockwell hardness of 45. These blades will not bend & cannot be repitched without annealing.