17-4 PH (UNS S17400) is the most widely used high-strength precipitation-hardening stainless steel, renowned for its unique combination of properties.
What does “17-4 PH” stand for?
- “17”: Approximate Chrome content (17%).
- “4”: Approximate Nickel content (4%).
- “PH”: Durcissement par précipitation, the heat treatment process that gives it high strength.
17-4 PH Stainless Steel Characteristics
- Haute résistance: Through aging heat treatment, tensile strength can reach 1000-1380 MPa, comparable to Class 12.9 alloy steel.
- Good Corrosion Resistance: Superior to most martensitic stainless steels, approaching the level of 304; resistant to atmosphere, water, seawater atmosphere, and various chemical media.
- Excellent Machinability: Easy to perform complex cutting operations in the solution-annealed condition (Condition A).
- Precipitation Hardening Mechanism: Strengthened by the precipitation of copper-rich phases through simple low-temperature aging (480-620°C), rather than traditional quenching.
- Soudabilité: Good, but requires re-solution treatment and aging after welding to restore properties.
- Magnétique: Becomes magnetic after aging.
17-4 PH Stainless Steel Equivalent Designations
| Country/System | Common Designation | Standard Example |
| USA | 17-4 PH, UNS S17400 | ASTM A564 Type 630 |
| International | X5CrNiCuNb16-4 | ISO 683-13 |
| Europe/Germany | 1.4542 | EN 10088-3 |
| Japon | SUS 630 | JIS G4303 |
| Chine | 05Cr17Ni4Cu4Nb | GB/T 20878 |
| France | Z6CNU17-04 | AFNOR NF |
| Royaume-Uni | 630S17 | BS |
17-4 PH Stainless Steel Chemical Composition
| Élément | Content Range (wt%) | Rôle |
| Chrome | 15.0 – 17.5 | Provides the foundation for stainless steel corrosion resistance |
| Nickel | 3.0 – 5.0 | Stabilizes microstructure, enhances toughness and corrosion resistance |
| Cuivre | 3.0 – 5.0 | Most critical element, precipitates during aging to form strengthening phases |
| Niobium+Tantalum | 0.15 – 0.45 | Forms carbonitrides, refines grain, aids strengthening |
| Carbone | ≤ 0.07 | Maintains low carbon to improve weldability and machinability |
| Manganèse | ≤ 1,00 | Deoxidizer, stabilizes austenite |
| Silicium | ≤ 1,00 | Deoxidizer |
| Phosphore | ≤ 0,04 | Impurity, lower is better |
| Soufre | ≤ 0,03 | Impurity, lower is better |
| Fer | Équilibre | Base metal |
17-4 PH Stainless Steel Heat Treatment Conditions & Mechanical Properties
Properties are entirely determined by the heat treatment condition. The condition code is part of the material designation.
| Condition | Traitement thermique | Résistance à la traction (MPa) | Limite d'élasticité (MPa) | Allongement (%) | Hardness (HRC) | Caractéristiques |
| UN | Recuit en solution | ~1000 | ~800 | ~10 | ≤ 38 | Soft condition, for machining only |
| H900 | Aged at 480°C | ~1310 | ~1170 | ~10 | 40-48 | Maximum strength, lower toughness |
| H1025 | Aged at 550°C | ~1170 | ~1070 | ~12 | 38-44 | Haute résistance |
| H1075 | Aged at 580°C | ~1100 | ~1000 | ~12 | 36-42 | Balanced |
| H1100 | Aged at 595°C | ~1060 | ~1000 | ~13 | 34-40 | Usage général |
| H1150 | Aged at 620°C | ~1000 | ~860 | ~14 | 30-36 | Most common, best overall performance |
H1150 is the most commonly used condition, achieving the optimal balance of strength, toughness, and corrosion resistance.
Primary Application Areas
- Aérospatial: Landing gear, engine components, fasteners
- Energy & Petrochemical: Pump shafts, valve stems, offshore platform components
- Food & Medical: Surgical instruments, food processing screws (requires certification)
- Military & High-End Manufacturing: Firearm components, precision molds, high-performance fasteners
- Industrie générale: Shafts, gears, bolts requiring high strength + corrosion resistance
Common FAQs of 17-4 PH Stainless Steel
You MUST specify the heat treatment condition (e.g., H1150, H900). The properties of 17-4 PH are entirely defined by its final aging treatment. Ordering just "17-4 PH" is incomplete and can lead to receiving material with incorrect strength or hardness.
- H900: Aged at 900°F (482°C). Offers the highest strength and hardness (~1310 MPa, HRC 42-48) but has lower toughness and is more susceptible to stress corrosion cracking. Use for maximum strength in non-corrosive or mildly corrosive environments.
- H1150: Aged at 1150°F (620°C). Offers the best overall combination of strength (~1000 MPa, HRC 30-36), toughness, ductility, and résistance à la corrosion. This is the most widely used and recommended condition for general applications.
Rule of Thumb: When in doubt, choose H1150 for its balanced performance.
17-4 PH (especially in the H1150 condition) has good corrosion resistance, generally better than most martensitic steels (like 410/440) but slightly lower than 304 austenitic stainless steel in many environments. It performs well in atmospheric, fresh water, and seawater splash conditions but is not recommended for continuous immersion in seawater or strong acids.
Yes, it has good weldability. However, the heat-affected zone (HAZ) will be in an annealed, softened state after welding. For critical applications, the part must be re-solution treated and re-aged (re-heat-treated) after welding to restore uniform strength and corrosion resistance across the entire component.
Yes, 17-4 PH is magnetic, especially in its hardened conditions (H900, H1150). Its microstructure is martensitic.
The key advantage is corrosion resistance without plating/coating.
- 17-4 PH: High strength + inherent corrosion resistance. Can be used "bare" in many environments.
- Alloy Steel (4140): High strength but will rust rapidly unless protected by plating, painting, or other coatings.
- Coût: It is significantly more expensive than standard carbon/alloy steels and common austenitic stainless steels (304/316).
- Not for Severe Corrosion: It is not suitable for highly reducing acids (e.g., hydrochloric, sulfuric) or severe chloride environments where higher alloys (e.g., Hastelloy, duplex stainless) are needed.
- Heat Treatment Sensitivity: Performance is 100% dependent on correct and uniform heat treatment.
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