Annealing – Annealing must be performed after hot working and before re-hardening. Heat at a rate not exceeding 400°F per hour to 1,575°F/1,675°F, and hold at temp. for one hour per inch of max thickness; 2 hours minimum. Cool slowly, not exceeding 50°F per hour to 1000°F. Continue to cool in ambient temp.
Hardening—Preheating: – In a controlled environment, preheat slow and thoroughly to 1,300°F/1,400°F, equalize, then raise to 1,800°F/1,850°F and hold for an hour per inch of greatest cross section of material. When maximum hardness is the primary requirement, quench in still air and temper immediately. Use a double preheat on complex tools.
Quenching – Air, pressurized gas, or warm oil. For pressurized gas quenching, a minimum rate of 50°F per minute to below 1000°F is required to obtain the optimum properties in the steel. For oil, quench until black, about 900°F, then cool in still air to 150°F/ 125°F.
Tempering – Temper immediately after quenching. Typical tempering range is 1,000°F/1,150°F. Hold at the tempering temp. for 1 hour per inch of thickness, but for 2 hours minimum, then air cool to ambient temp. Double tempering is required. To maximize toughness and tool performance, a third temper is often used as a stress relief after all finish work is completed.
Tempering Chart –
@ 400°F typical hardness Rockwell “C” 54.
@ 1,100°F typical hardness Rockwell “C” 46.
@ 1,200°F typical hardness Rockwell “C” 36.
* Above values are typical and are not guaranteed.