Precipitation-Hardening Stainless Steel
Precipitation-hardening stainless steels carry 12–17 % chromium and 4–8 % nickel with a few percent of copper, aluminum or molybdenum that precipitate as fine particles during a single low-temperature age, so the part is machined soft and hardened afterwards with almost no distortion. 17-4 PH in the H900 condition yields about 1,170 MPa at 40–44 HRC with corrosion resistance close to 304 — roughly three times the strength of 316 — and the group as a whole spans 1,000–1,650 MPa yield.
Popular PH stainless grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| 17-4 PH | 760 | 1,030 | 7.78 | Fair | Very good | The default; shafts, fittings and molds to 1,170 MPa |
| 15-5 PH | 795 | 1,030 | 7.8 | Fair | Very good | Ferrite-free 17-4 for aerospace and thick sections |
| 13-8 PH | 827 | 1,000 | 7.76 | Poor | Good | Highest toughness and SCC resistance; landing gear |
| 17-7 PH | 276 | 896 | 7.81 | Poor | Good | Formable sheet aged to spring strength; washers |
| 15-7 Mo | 415 | 950 | 7.8 | Fair | Fair | Semi-austenitic sheet with more strength to 480 °C |
| Custom 450 | 1,205 | 1,310 | 7.75 | Poor | Good | Easier-machining 17-4; usable unaged at 800 MPa |
| Custom 465 | 795 | 1,000 | 7.78 | Fair | Good | Strongest PH stainless; about 1,650 MPa yield |
Choose PH stainless for
Pump and compressor shafts, valve stems and gates, aerospace fittings, actuator and landing-gear components, high-strength fasteners, gears, firearm parts, surgical instruments and plastic-mold cores — parts that need 1,000 MPa or more yield strength plus real corrosion resistance, machined to size in the soft condition and aged afterwards.
Look elsewhere when
Hardness rather than strength is the goal (440C at 58–60 HRC, or 420 for blades), the part runs above about 315 °C for long periods where 17-4 PH over-ages (A286 or Inconel 718), it sits in seawater or hot chlorides (2205 or 2507 — PH grades pit like 304 and crack under stress in chlorides), or strength is not needed and 304 or 316L will do without the aging step. For sheet parts that must be formed and then be hard, full-hard 301 is the simpler answer.
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PH stainless by application
- Shafts, stems and fittings
- 17-4 PH in H1025 or H1075 for the balance of strength and toughness, H1150 or H1150-M where impact or hydrogen sulfide is involved; 15-5 PH when the drawing is aerospace or the section is thick.
- Aerospace structure and fasteners
- 13-8 PH for pins, flap tracks and landing-gear parts; Custom 465 for the highest-strength fasteners and shafts; 15-5 PH H1025 for fittings and brackets.
- Springs, washers and diaphragms
- 17-7 PH in condition C aged to CH900 for flat springs and Belleville washers; RH950 for formed parts that must reach 1,400 MPa; 15-7 Mo when the spring runs hotter, to about 480 °C.
- Instruments and mold cores
- 17-4 PH H900 for surgical instruments, dental tools and plastic-mold cores at 40–44 HRC where 420 would rust; Custom 465 for the thinnest, stiffest instrument shafts.
Working with PH stainless
- Machining
- Machine in condition A (about 33 HRC) or, for the best tool life and finish, in H1150; 17-4 PH cuts about like 304 with shorter chips and less work hardening. Age after machining — H900 shrinks about 0.05 % and H1150 about 0.1 %, so tight bores are held to the aged size or finish-ground afterwards. Aged H900 stock can still be turned and milled with carbide, slowly.
- Heat treatment
- Solution-anneal at 1,040 °C (condition A), then a single age: H900 is 482 °C for 1 h (1,170 MPa yield, 40–44 HRC), H1025 is 552 °C for 4 h, H1150 is 621 °C for 4 h (about 860 MPa yield, 33 HRC max) and H1150-M double-ages for maximum toughness. 17-7 PH needs the two-step TH1050 or RH950 cycle, the latter with a hold at −73 °C. Aging is done in air with no quench, which is why distortion stays low.
- Welding
- 17-4 PH and 15-5 PH weld well by TIG or MIG with matching ER630 filler and no preheat; weld in condition A or over-aged, then age (or re-solution-treat and age) so the joint matches the base metal. 17-7 PH welds readily in condition A. 13-8 PH and Custom 465 are welded solution-treated and given the full cycle afterwards.
- Finishing
- Passivate per ASTM A967 after final machining or aging. Corrosion resistance is best in H1150 and drops slightly toward H900, which is also the most sensitive to chloride stress cracking — one reason NACE MR0175 limits 17-4 PH in sour service to the double-aged H1150-D condition at 33 HRC. Black oxide, PVD and nitriding all work; aging scale is blasted or pickled off.
Other stainless steel series
Precipitation-Hardening Stainless Steel — frequently asked
What is PH stainless?
Precipitation-hardening stainless steels carry 12–17 % chromium and 4–8 % nickel with a few percent of copper, aluminum or molybdenum that precipitate as fine particles during a single low-temperature age, so the part is machined soft and hardened afterwards with almost no distortion. 17-4 PH in the H900 condition yields about 1,170 MPa at 40–44 HRC with corrosion resistance close to 304 — roughly three times the strength of 316 — and the group as a whole spans 1,000–1,650 MPa yield.
Which grade of PH stainless should I use?
17-4 PH is the workhorse: pump shafts, valve stems, gears, fittings and mold components, aged anywhere from H900 (strongest) to H1150 (toughest). 15-5 PH is the same alloy remelted to remove delta ferrite, with better transverse toughness — the aerospace and thick-forging choice. 13-8 PH (also listed as PH 13-8 Mo) is the premium grade: about 1,410 MPa yield in H950 with the best toughness and stress-corrosion resistance, for landing gear and high-strength pins. 17-7 PH and 15-7 Mo are the semi-austenitic sheet grades — formable as delivered, then aged (TH1050, RH950 or cold-rolled CH900) to 1,000–1,500 MPa for springs, washers and diaphragms. Custom 450 gives 17-4 strength with easier machining and is usable unaged at about 800 MPa yield; Custom 465 is the strongest, about 1,650 MPa yield in H950, for aerospace fasteners and medical instruments. 1.4980 is the EN designation of A286, the austenitic PH grade for bolts at 650 °C.
Which grade of PH stainless is the strongest?
S46910 has the highest yield strength in the series at 2,000 MPa; Alloy 465 follows at 1,586 MPa. Values are for each grade's default condition.
Which grade of PH stainless is easiest to machine?
S46800 (machinability good, 55/100), then 1.4594 (45/100).
Is PH stainless heat-treatable?
Yes. These grades gain their strength from heat treatment; the conditions and their properties are listed on each grade page.
17-4 PH or 15-5 PH?
They are the same 15–17 % Cr, 4–5 % Ni, 3–5 % Cu alloy with the same H-conditions, strengths and hardness. 15-5 PH is vacuum-remelted and balanced to be free of delta ferrite, which gives it better transverse ductility and toughness in thick bar and forgings — the reason aerospace drawings and AMS 5659 call for it. 17-4 PH is more common in bar and plate and a little cheaper; for round parts under about 75 mm the two behave alike.
Which H condition should I specify for 17-4 PH?
H900 (482 °C, 1 h) gives the most strength — about 1,170 MPa yield at 40–44 HRC — but the lowest toughness and the least resistance to chloride stress cracking. H1025 and H1075 are the usual compromise for shafts and fittings (about 1,000 MPa yield, 35–38 HRC). H1150 (about 860 MPa yield, 33 HRC max) and the softer H1150-M are specified for impact toughness, cryogenic service and sour gas. A drawing that says only "17-4 PH" has not specified the strength.