Step 5 of 5
75%
Surface treatment sequencing: nitride, PVD, polish, in what order
The build order that takes an H13 forge die from rough block to coated, polished, ready-to-run, and why getting any step out of sequence is a failure mode rather than a slow ramp to nominal life.
Step 5 of 5Where stress relief belongs in the sequence
Stress relief at step 3 is the cycle most shops skip. Rough machining leaves residual tensile stress 50-200 µm deep on milled surfaces. Heat treat at step 5 relieves some of that stress through austenitizing, but the dimensional movement happens during the quench, when the unevenly distributed residual stress drives unpredictable distortion. A 2-4 hour cycle at 650°C between rough and semi-finish drops the residual stress without affecting downstream metallurgy. The cycle prevents the "we cannot finish-grind this back to size after HT" call that ends with a re-EDM and a thinner cavity floor.
A second stress relief between EDM and nitride is the same cycle for the same reason. EDM leaves residual tensile stress in the recast layer and below it. Nitriding inherits that stress state. A short relief cycle at 565°C for 2 hours after EDM stabilizes the cavity dimensions before the nitride run.
Quick check
A shop runs the build with no stress relief between rough and semi-finish machining. The part finishes machining on dimension, goes to heat treat, and comes back with 0.15 mm of warp on the parting line. Where did the warp come from?