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Lesson 01·Foundations
Why surface treating exists
Why tool surfaces and tool interiors need to be different things, and why every shop runs into the hardness-toughness tradeoff.
4 min readLesson 1 of 10
Step 2 of 4Hardness and toughness move in opposite directions
In steel, hardness and toughness are coupled. Push hardness up and toughness goes down. Always. A through-hardened tool at the top of its hardness band has very little reserve against impact. A tool tempered back for toughness gives up wear resistance. There is no single hardness that wins both jobs.
Quick check
A new tool designer pushes their heat treater to deliver D2 at 64 HRC instead of the shop's usual 60-61 HRC, on the reasoning that "harder is better." Why is that a bad bet on stamping work?