Wrap-up
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Lesson 02·Foundations
Heat treating tool steel
Austenitize, quench, temper. What each step does and why skipping the second temper cracks parts in service.
5 min readLesson 2 of 10
Tying it together
What this means on the shop floor
- "As hard as possible" is the wrong spec. Every grade has a sweet spot for the application. Common industry hardness ranges (verify against your specific application and steel grade with your heat treater): stamping punches commonly 58-62 HRC, hot work dies often 44-52 HRC, cold heading tools sometimes 60-64 HRC. The reason isn't tradition — it's the toughness-hardness tradeoff. Too hard and the part chips. Too soft and it deforms.
- Get a hardness witness coupon from every heat treat batch. A coupon is a small scrap of the same steel processed alongside your tool. You can Rockwell-test the coupon without destroying anything. If the coupon reads wrong, your tool is wrong too.
- Pre-machining-allowance matters. Tool steel grows slightly during heat treat (typically 0.001-0.003 inch per inch in cross-section) and can warp. Don't finish-grind critical dimensions before heat treat unless your tolerance is generous.
Heat treatment by itself only takes you so far. For most production tooling, the heat-treated substrate is the foundation you build coatings or surface diffusion on top of. The next four lessons cover the additional treatments that sit on top of heat treatment.