The highest-strength stainless routinely specified — 17-4 combines 1310 MPa UTS (H900 condition) with corrosion resistance comparable to 304. Precipitation hardening after machining allows complex features to be cut in softer "Condition A" and then age-hardened to final strength with minimal distortion. The workhorse alloy for aerospace, nuclear, and high-performance industrial shafting.
Double the yield strength of 316L with similar corrosion envelope — ideal where heavy-section carbon steel would be used otherwise.
Precipitation aging at 480–620 °C causes <0.1% dimensional change, unlike carburizing or nitriding which can distort parts.
H900 condition reaches 40 HRC — sufficient for many valve, shaft, and seat applications without secondary case-hardening.
| Element | Content |
|---|---|
| Iron | Balance |
| Chromium | 15.0–17.5% |
| Nickel | 3.0–5.0% |
| Copper | 3.0–5.0% |
| Niobium + Tantalum | 0.15–0.45% |
| Carbon (max) | 0.07% |
Composition per ASTM A564. Specific mill test reports (MTR) available on request for production orders.
H900 (max strength, lower toughness), H1025 (balanced), H1150 (max toughness, lower strength) — the call-out must appear on the drawing.
Solution-annealed "Condition A" is soft (~30 HRC) and machines 2× faster than H900. Age-harden after machining whenever tolerance permits.
Below ~-30 °C toughness drops sharply. Use 316L or duplex for cryogenic applications.
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