Engineering · Machining guide
How to machine 17-7PH stainless.
17-7PH is the semi-austenitic precipitation-hardening stainless used for springs, diaphragms, and thin high-strength sheet parts. Three different aging cycles (CH, RH, TH) produce different mechanical properties — and the right machining approach depends on which one is on the drawing. This is the toughest of the common stainless grades to machine.
01 · Conditions
CH, RH, TH.
17-7PH ships in Condition A (austenitic, soft, ~85 HRB) and is processed through one of three age-hardening cycles to reach final properties:
- Condition CH900: cold-rolled and aged. Sheet/strip, used for springs and diaphragms.
- Condition RH950: refrigeration treatment + aging. Higher strength than TH.
- Condition TH1050: thermal treatment + aging. Most-cited bar condition. ~190 ksi UTS.
Standard machining practice: machine in Condition A (the soft austenitic state), then heat-treat to the final condition. Don’t try to machine fully aged 17-7PH — work-hardening is severe and tool life poor.
02 · Cutting parameters — Condition A
Slow, sharp, no dwell.
| Operation | Tool | SFM | IPT / IPR |
|---|---|---|---|
| Roughing turn | Coated carbide | 150–225 | 0.008–0.014 IPR |
| Finishing turn | Coated carbide | 225–300 | 0.004–0.008 IPR |
| End mill (rough) | Solid carbide | 120–180 | 0.002–0.004 IPT |
| End mill (finish) | Solid carbide | 180–250 | 0.001–0.003 IPT |
| Drilling | HSS-Co | 40–70 | 0.002–0.005 IPR |
IPT (chip-load) values assume roughly ½–1″ end mills; scale down for smaller tools — see the chip-load chart.
03 · Practical notes
Same discipline as Inconel.
- Tooling: sub-micron-grain coated carbide with sharp positive-rake geometry. Honed edges (0.0004–0.0008″).
- No dwell: work-hardens worse than 304/316L. Stopping the spindle while engaged creates a hardened zone the next pass has to chew through.
- Coolant: water-soluble flood, EP additives helpful. Through-tool coolant improves yields significantly.
- Heat-treat distortion: CH900 cold-rolled material doesn’t need post-machining heat treat. TH1050 grows a net ≈0.4% (≈0.004 in/in: about +0.0045 in/in at the 1400 °F conditioning step, −0.0005 in/in at the 1050 °F age), so a 2″ dimension moves ~0.008″ — leave finish stock for tight-tolerance work.
- For sharp inside corners on aged material: wire EDM, same as 17-4PH. See our 5-axis wire EDMs.
- Common AMS: 5644 (bar & forgings), 5528 / 5529 (sheet & strip).
Keep exploring
Related tools & references
Mechanical properties, UNS, AMS specs, and machinability at a glance.
Convert these SFM and IPT figures into spindle RPM and feed rate.
Recommended chip load by tool diameter for stainless.
17-7PH density for part weight and stock estimates.
Compare 17-7PH against other precipitation-hardening stainless grades.
Need 17-7PH stainless parts machined?
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