17-4 vs 15-5 PH is a close comparison between two precipitation hardening martensitic stainless steels. Both combine high strength with moderate corrosion resistance, both are hardened by a single low-temperature aging treatment, and both are widely used in aerospace, oil and gas, valves and pumps. 17-4 PH is the more common and less expensive grade. 15-5 PH was developed as a lower-ferrite variant with better transverse toughness, which matters in larger sections and critical aerospace parts.
17-4 PH vs 15-5 PH: Comparison Table
Values are typical for bar in the H1025 condition unless noted. Cost is a relative per-part index including material, where one 17-4 part at quantity 1 equals 100.
| Factor | 17-4 PH (UNS S17400) | 15-5 PH (UNS S15500) |
|---|---|---|
| Relative cost, qty 1 | 100 | 110 to 130 |
| Relative cost, qty 10 | 42 | 48 to 58 |
| Relative cost, qty 100 | 20 | 24 to 30 |
| Relative cost, qty 1,000 | 12 | 15 to 19 |
| Nominal chemistry | About 17% Cr, 4% Ni, 4% Cu | About 15% Cr, 5% Ni, 3.5% Cu |
| Tensile strength, H1025 | About 155 ksi | About 155 ksi |
| Transverse toughness | Good | Better, due to low delta ferrite |
| Typical machined tolerance | ±0.0005 to ±0.002 in | ±0.0005 to ±0.002 in |
| Surface finish | Ra 16 to 63 µin | Ra 16 to 63 µin |
| Corrosion resistance | Similar to 304 in many environments | Similar to 17-4 |
| Common specifications | AMS 5643, ASTM A564 | AMS 5659 (remelted), ASTM A564 |
| Availability and lead time | Widely stocked | Less common, some sizes on longer lead |
| Typical use case | Valve stems, pump shafts, fittings, tooling, general high-strength parts | Aerospace fittings, large-section structural parts, critical components |
Heat Treat Conditions
Both alloys are supplied in Condition A (solution annealed) and aged to a range of conditions. H900 gives the highest strength and hardness, about 40 to 44 HRC, with lower toughness. H1025 and H1075 balance strength and toughness. H1150 and H1150M give the lowest hardness, the highest toughness and improved resistance to stress corrosion cracking. Many oil and gas specifications require double-aged H1150D for sour service. Aging causes a small, predictable dimensional change, commonly cited around 0.0004 to 0.0006 in per inch of contraction for H900, which matters on tight features.
When 17-4 PH Wins
- General high-strength stainless parts. Shafts, stems, fittings and hardware where cost and availability matter.
- Short lead times. Wide stock availability in round bar and plate.
- Smaller cross sections. Where transverse properties are not critical.
When 15-5 PH Wins
- Aerospace structural parts. Many drawings call for 15-5 PH to AMS 5659, which is consumable electrode remelted for cleanliness.
- Large sections. More uniform properties through the thickness and in the transverse direction.
- Toughness-critical service. Low delta ferrite improves impact and fracture toughness.
Common Mistakes
- Leaving the condition off the drawing. "17-4" is incomplete without H900, H1025, H1150 or similar.
- Substituting 17-4 for 15-5 without engineering approval on aerospace work. They are not interchangeable to the specification.
- Finish machining tight features in Condition A and then aging without allowing for dimensional change.
- Specifying H900 for parts that need toughness or stress corrosion resistance. Higher aging temperatures are often the better tradeoff.
Machining Strategy
Parts can be machined in Condition A and then aged, or machined in an already-aged condition such as H1025 or H1150. Machining in an aged condition avoids distortion from aging, while machining in Condition A is faster on heavy stock removal. A common approach is to rough in Condition A, age, then finish critical features.
How This Applies at Wexmar
Wexmar machines 17-4 PH and 15-5 PH on our lathes, horizontal machining centers and Swiss-type machines. Heat treatment is done by qualified outside processors that we manage, and we sequence machining around aging to hold tight features. Material certs, heat-lot traceability, CMM reports and FAI in AS9102 format are available. See materials, inspection and quality, and the guide on 303 vs 304 vs 316.
Getting a Quote
Include the specification and final condition on the drawing. You can upload a drawing for an instant estimate, reviewed by a human estimator, or call (315) 400-2654.