When 304 and 316 stainless aren’t strong enough — but you still need corrosion resistance — engineers reach for 17-4 PH. This precipitation-hardening stainless steel delivers the strength of a heat-treated tool steel (up to 1,310 MPa tensile) combined with the corrosion resistance of austenitic stainless. 17-4 PH stainless steel (UNS S17400) is a chromium-nickel-copper precipitation-hardening alloy prized for its high strength, hardness, and corrosion resistance, used in demanding industries such as aerospace, medical, energy, and precision machining.
But 17-4 PH is more complicated to specify than 304 or 316. The heat treatment condition you choose — H900, H1025, H1075, or H1150 — dramatically changes the properties. Choose wrong and you either pay for strength you don’t need, or you get a part that cracks in service from stress corrosion. This guide covers what 17-4 PH actually is, the heat treatment conditions, and how to choose.
Quick summary — 17-4 PH is a martensitic precipitation-hardening stainless steel. Specify it when you need strength > 800 MPa with corrosion resistance. Choose H900 for max strength (1,310 MPa, lower toughness), H1025/H1075 for balanced strength + toughness, H1150 for impact resistance and stress corrosion cracking resistance.
What 17-4 PH Actually Is
17-4 PH (also called 630, UNS S17400, AISI 630) is a martensitic precipitation-hardening stainless steel containing chromium, nickel, and copper. The “17-4” refers to its nominal composition: ~17% chromium, ~4% nickel. The “PH” stands for precipitation hardening — the strengthening mechanism.
Chemical composition (ASTM A564)
| Element | Range | Role |
|---|---|---|
| Chromium (Cr) | 15.0 - 17.5% | Corrosion resistance, martensite |
| Nickel (Ni) | 3.0 - 5.0% | Toughness, austenite stabilizer |
| Copper (Cu) | 3.0 - 5.0% | Forms precipitates (the strengthening mechanism) |
| Manganese (Mn) | 1.0% max | Deoxidizer |
| Niobium + Tantalum | 0.15 - 0.45% | Carbide stabilizer |
| Carbon (C) | 0.07% max | Hardness contribution |
The copper is what makes 17-4 PH special. 17-4 PH SS contains chromium, nickel, and copper, and heat treatment forms copper-rich precipitates within the microstructure that stop dislocation movements, dramatically increasing strength.
How precipitation hardening works
- Solution anneal (Condition A) — material is heated to ~1040°C, then rapidly cooled. Copper atoms are dispersed uniformly throughout the matrix. Material is relatively soft (~30 HRC) and machinable.
- Aging (H-condition heat treatment) — material is reheated to a lower temperature (482-621°C) and held. Copper-rich precipitates form throughout the structure, blocking dislocation movement.
- Result — strength and hardness dramatically increase. The specific properties depend on the aging temperature.
This two-step process is what lets you machine in the soft state, then harden after machining — a huge manufacturing advantage over through-hardened tool steels.
Heat Treatment Conditions Explained
The “H” number = the aging temperature in Fahrenheit. Lower H number = higher strength.
H900 — Maximum strength
H900 condition: precipitation hardened at approximately 482°C (900°F) for 4 hours, air cooled. Produces the highest strength and hardness, typically around 44 HRC. Suitable for applications requiring maximum strength and hardness.
| Property | Value |
|---|---|
| Yield strength | 1,070 MPa min (155 ksi) |
| Tensile strength | 1,170-1,310 MPa (170-190 ksi) |
| Elongation | 8% min |
| Hardness | 38-44 HRC |
| Use for | Precision gears, valve actuators, max-strength applications |
Trade-off: H900 has the lowest toughness and is the most susceptible to stress corrosion cracking (SCC) in chloride environments.
H1025 — Balanced strength + toughness
| Property | Value |
|---|---|
| Yield strength | 1,000 MPa min (145 ksi) |
| Tensile strength | 1,070 MPa min (155 ksi) |
| Elongation | 12% min |
| Hardness | 33-39 HRC |
| Use for | Aerospace structural parts, oil & gas, balanced strength |
H1075 — Higher toughness
| Property | Value |
|---|---|
| Yield strength | 860 MPa min (125 ksi) |
| Tensile strength | 1,000 MPa min (145 ksi) |
| Elongation | 13% min |
| Hardness | 32-38 HRC |
| Use for | High-stress, impact-resistant aerospace |
H1150 — Max toughness + SCC resistance
H1150 condition: precipitation hardened at approximately 621°C (1150°F). Offers good toughness and corrosion resistance, with hardness typically 27-35 HRC. Used in applications requiring moderate strength combined with good toughness and corrosion resistance.
| Property | Value |
|---|---|
| Yield strength | 790 MPa min (115 ksi) |
| Tensile strength | 965 MPa min (140 ksi) |
| Elongation | 16% min |
| Hardness | 27-35 HRC |
| Use for | Marine, chloride environments, impact loading |
H1150M / H1150D — Multi-step aging
For applications requiring maximum SCC resistance (offshore, chloride-rich environments), the H1150 process is repeated. Double aging produces coarser precipitates and improves SCC resistance further.
Side-by-side comparison
| Condition | Aging Temp | Yield (MPa) | Tensile (MPa) | Elongation | Hardness (HRC) |
|---|---|---|---|---|---|
| Condition A (solution annealed) | — | 760 | 1,030 | 4 | 36 max |
| H900 | 482°C | 1,070 | 1,170-1,310 | 8 | 38-44 |
| H925 | 496°C | 1,000 | 1,140 | 10 | 36-42 |
| H1025 | 552°C | 1,000 | 1,070 | 12 | 33-39 |
| H1075 | 580°C | 860 | 1,000 | 13 | 32-38 |
| H1150 | 621°C | 790 | 965 | 16 | 27-35 |
| H1150M | 621°C ×2 | 760 | 930 | 18 | 25-32 |
How 17-4 PH Compares to Other Stainless Steels
| Grade | Yield (MPa) | Corrosion | Cost | Best Use |
|---|---|---|---|---|
| 304 | 215 | Good | $$ | General use, food contact |
| 316L | 170 | Excellent | $$$ | Marine, chemical, medical |
| 17-4 PH H1025 | 1,000 | Good | $$$$ | Strong + corrosion resistant |
| 17-4 PH H900 | 1,070 | Moderate | $$$$ | Max strength applications |
| AISI 4140 (alloy steel) | 655 | Poor | $$ | High-strength, non-corrosive env |
| Duplex 2205 | 450 | Excellent | $$$$ | Marine + moderate strength |
The 17-4 PH advantage: it’s the only stainless steel that delivers 1,000+ MPa yield strength while maintaining decent corrosion resistance. 304/316 cap out around 200 MPa. Alloy steels like 4140 can match the strength but corrode aggressively.
For comparison with other stainless, see our 304 vs 316 guide and carbon vs stainless steel comparison.
Typical Applications
| Industry | Application | Typical Condition |
|---|---|---|
| Aerospace | Landing gear, structural fittings, fasteners | H1025 |
| Oil & gas | Valve stems, pump shafts, downhole tools | H1075 / H1150 |
| Marine | Pump shafts, propeller hardware | H1150 / H1150M |
| Medical | Surgical instruments, orthopedic implants | H1100 / H1150 |
| Defense | Gun parts, missile components | H900 |
| Nuclear | Pressure vessel components, valves | H1100 / H1150 |
| Food processing | High-stress mixer shafts, pump impellers | H1075 / H1150 |
| Chemical processing | Aggressive media pumps, valve trim | H1150 |
Stress Corrosion Cracking — The Critical Warning
This is where 17-4 PH specification gets dangerous. In warm chloride environments, 17-4PH in the H900 condition can be prone to SCC. However, this risk drops significantly when the material is aged at higher temperatures. For any application exposed to tensile stress in a marine or other chloride-rich setting, aging at H1025 or above is strongly advised. The H1150 condition delivers the greatest resistance to SCC.
Specification rules to avoid SCC failure:
- Marine / coastal: Specify H1150 minimum
- Chemical plant chloride exposure: H1150 or H1150M
- Offshore oil & gas: H1150 + post-aging stress relief
- Indoor / dry environments: H900 to H1075 are fine
The temptation is to spec H900 for the highest strength. Don’t — unless your environment is truly chloride-free and stress levels are well below yield. The failure mode is sudden brittle fracture, not gradual corrosion.
Manufacturing Considerations
Machining
Machine in Condition A (solution annealed). The material is moderately machinable in this state (similar to 304). After machining, heat treat to the required H condition.
Machining in hardened state is possible but slow, hard on tooling, and produces poor surface finish. Always machine first, harden after.
Welding
17-4 PH is weldable but requires careful procedure:
- Pre-weld: Material should be in solution-annealed condition
- Filler: Match parent material (e.g., AMS 5826)
- Post-weld: Re-solution anneal + age to restore properties
The weld zone won’t have the same strength as parent material without post-weld heat treatment. For more on stainless welding, see our TIG vs MIG guide.
Forming
17-4PH has limited cold forming properties. Cold forming can only be undertaken on plates in the fully annealed condition. For complex formed parts, design for hot forming or machine from billet.
Surface treatment
- Passivation: Required after machining/grinding per ASTM A380 to restore corrosion resistance
- Plating: Not typically needed (inherent corrosion resistance is good)
- Coating: Powder coat or paint compatible for cosmetic applications
Specification Best Practices
A complete 17-4 PH specification includes:
- Grade and standard: 17-4 PH per ASTM A564 (or AMS 5643/5604 for aerospace)
- Heat treatment condition: H900 / H1025 / H1075 / H1150 (or H1150M for severe SCC)
- Form: Bar, plate, sheet, forging
- Surface condition: Pickled, ground, polished
- Inspection: Mill test certificate (EN 10204 3.1 minimum)
- For aerospace/medical: Trace element limits, specific NDT requirements
- Passivation: Per ASTM A380 / A967 after final machining
How DRAmetal Handles 17-4 PH
DRAmetal reviews 17-4 PH work as a project-defined route. The RFQ must state the material specification and condition, approved material source, required mill record, machining state, heat-treatment specification and source, passivation, NDT, dimensional inspection and final evidence package.
DRAmetal holds ISO 9001, AS9100D and ISO 13485 quality-system certifications; certification details are available on request for supplier qualification. These do not establish heat-treatment or NDT approval for a particular process or part. Customer approval, qualified external processes and independent testing must be defined before quotation where the contract requires them. For our stainless steel material scope, see the material page. For a drawing review, submit your specifications; the initial response target is within 24 working hours.
Bottom Line
17-4 PH stainless steel is the engineering material when you need both high strength (800-1,300 MPa) and corrosion resistance — a combination no austenitic stainless can match. But the right specification is everything. Choose H900 for max strength but in non-chloride environments. Choose H1025/H1075 for the strength-toughness sweet spot. Choose H1150 for impact, chloride exposure, and SCC resistance.
The main specification risks are selecting a heat-treatment condition without considering the environment, omitting post-weld condition controls or leaving surface treatment undefined. For drawing-defined components, compare custom sheet-metal bracket manufacturing with the laser-cutting service, then confirm the exact alloy condition, process sequence, outsourced heat treatment and buyer-owned environmental validation before quotation.
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