Quick Answer
17-4 PH is a precipitation-hardening stainless steel that combines corrosion resistance close to 304 with strength up to three times higher. The cast version is designated CB7Cu-1 (ASTM A747). After a simple aging treatment it reaches tensile strengths from roughly 930 to over 1,300 MPa depending on condition. Buyers pick it for pump shafts and impellers, valve internals, aerospace brackets and food machinery parts that would deform or wear too fast in CF8/CF8M.
Composition (Cast CB7Cu-1)
| Element | Typical range |
|---|---|
| Chromium | 15.5–17.7% |
| Nickel | 3.6–4.6% |
| Copper | 2.5–3.2% |
| Niobium (Cb) | 0.15–0.35% |
| Carbon | ≤ 0.07% |
Copper is the active ingredient: during aging, copper-rich precipitates form throughout the martensitic matrix and block dislocation movement — that is the “precipitation hardening”.
Heat Treatment Conditions and Strength
| Condition | Aging temperature | Typical tensile | Character |
|---|---|---|---|
| H900 | 482°C | ~1,310 MPa | Maximum strength and hardness (~40 HRC) |
| H1025 | 552°C | ~1,070 MPa | Balanced strength and toughness |
| H1075 | 579°C | ~1,000 MPa | Better toughness, common default |
| H1150 | 621°C | ~930 MPa | Best ductility and stress-corrosion resistance |
The buyer must state the condition on the drawing. “17-4 PH” alone is incomplete — H900 and H1150 behave like different materials in service. If the part sees chlorides under sustained stress, the overaged conditions (H1100/H1150) resist stress-corrosion cracking far better than H900.
When 17-4 PH Beats the Usual Suspects
- vs CF8M (cast 316): three to five times the yield strength; slightly lower chloride resistance. Choose 17-4 when parts wear, gall or flex — impeller vanes, wear rings, shaft sleeves.
- vs CA15 / 410 martensitic: similar strength class but 17-4 corrodes far less and machines in the solution-treated state before aging — a real cost saver.
- vs alloy steel + plating: no coating to chip. Corrosion resistance is through-thickness.
Casting and Machining Workflow
The practical production route most buyers want: investment cast → solution treat → rough machine → age to final condition → finish machine. Machining before aging is dramatically easier (about 30 HRC vs 40+ HRC after H900). Parts with tight tolerances need the aging distortion (small, but real) accounted for — we handle this sequencing routinely in our lost wax casting plus CNC machining line, delivering finished parts rather than raw castings.
Typical Applications
- Pump impellers, wear rings and shafts in water and mildly corrosive service
- Valve stems, balls and seats requiring hardness plus corrosion resistance
- Food processing machine parts under high mechanical load
- Aerospace and defense brackets and structural fittings
FAQ
Is 17-4 PH magnetic?
Yes. Its matrix is martensitic, so it is strongly magnetic — unlike CF8/CF8M austenitic castings.
Can 17-4 PH castings be welded?
Yes, with matching filler and proper pre/post treatment, but weld zones lose aged strength until re-aged. Design welds into low-stress areas or plan a re-aging cycle.
What corrosion environments should 17-4 avoid?
Hot concentrated chlorides and reducing acids. For those, austenitic (CF8M), duplex (CD4MCu) or nickel grades (CN7M) are the right family.
Does 17-4 PH need special casting equipment?
No exotic equipment, but tight foundry process control on chemistry and the two-step heat treatment. Ask the foundry to document both on the certificate.