17-4PH
Full Analysis of 17-4PH Alloy Materials (Martensite Precipitation Hardened Stainless Steel)
I. Standard system
17-4PH is mainly implemented in accordance with ASTM A564/A564M standard (specifying forgings, bars, etc.), with associated extended standards:
- Aerospace field: ASTM A693 (Grade 630, such as AMS 5604B aerospace bars);
- International grade: UNS S17400 (Unified Numbering System of the United States, a global universal identifier);
- Corresponding grades in various countries:
- China: New grade 05Cr17Ni4Cu4Nb, old grade 0Cr17Ni4Cu4Nb;
- Japan: SUS630 (JIS G4303);
- Germany: 1.4542 (DIN EN 10088).
II. Analysis of Names and Codes
- Meaning of “17-4PH”:
- “17” represents that the content of chromium (Cr) is about 17%, and “4” represents that the content of nickel (Ni) is about 4% (actual Ni content is 3.0 – 5.0%, taking a typical value);
- “PH” is the abbreviation of Precipitation Hardening, emphasizing that high strength is achieved by precipitating strengthening phases (such as ε-Cu, NbC) through aging treatment.
III. Chemical composition (mass fraction%, ASTM standard)
17-4PH adopts the design of “Cr-Ni-Cu-Nb Quaternary Synergy”, with precise elements:
| Element | Content Range | Core Function |
|---|---|---|
| C | ≤0.07 | Strictly control carbide precipitation, optimize workability and corrosion resistance |
| Cr | 15.0 – 17.5 | Form a Cr₂O₃ passivation film, provide basic corrosion resistance |
| Ni | 3.0 – 5.0 | Stabilize martensitic structure, improve toughness and corrosion resistance |
| Cu | 3.0 – 5.0 | Precipitate ε-Cu nano strengthening phases (5 – 20 nm) during aging, significantly increase strength (verified by research at University of Science and Technology Beijing) |
| Nb | 0.15 – 0.45 | Refine grains, inhibit intergranular corrosion, precipitate NbC to assist in strengthening |
| Mn | ≤1.00 | Improve toughness and workability |
| Si | ≤1.00 | Assist in deoxidation, optimize casting performance |
| P/S | ≤0.040/≤0.030 | Strictly control impurities, reduce the risk of embrittlement/heat cracking |
IV. Mechanical properties (heat treatment state)
17-4PH can flexibly adjust strength through aging temperature (core advantage), and its typical properties are as follows:
| Condition | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (HB) | Application Focus |
|---|---|---|---|---|---|
| Solution Annealed | ≥620 | ≥310 | ≥20 | ≤363 (≤38 HRC) | Forming and processing (such as machining, welding) |
| Aged at 480°C | ≥1310 | ≥1180 | ≥10 | ≥375 (≥40 HRC) | High-stress scenarios (such as landing gears) |
| Aged at 550°C | ≥1060 | ≥1000 | ≥12 | ≥331 (≥35 HRC) | Balance of strength and toughness (such as valves) |
| Aged at 580°C | ≥1000 | ≥865 | ≥13 | ≥302 (≥31 HRC) | Corrosion resistance priority (such as marine equipment) |
| Aged at 620°C | ≥930 | ≥725 | ≥16 | ≥277 (≥28 HRC) | Best plasticity (such as precision components) |
- Physical Properties: Density 7.80 g/cm³, non-magnetic (the martensitic matrix still remains non-magnetic, distinguishing it from traditional martensitic stainless steel).
V. Heat Treatment Requirements (Two Steps of Solution and Aging)
- Solution Treatment (Basic Preparation):
- Temperature: 1020 – 1060°C (hold for 1 – 2 hours);
- Cooling: Rapid water cooling (to obtain martensitic structure and lay a structural foundation for age strengthening);
- Function: Dissolve carbides, homogenize composition, and restore plasticity and workability.
- Aging Treatment (Strength Regulation):
After solution treatment, strengthening phases are precipitated through air – cooling aging, and temperature determines the performance tendency:
| Aging Process | Temperature Range | Core Microscopic Changes |
|---|---|---|
| Aging at 480°C | 470 – 490°C | A large amount of ε-Cu precipitates, maximizing strength |
| Aging at 550°C | 540 – 560°C | Synergistic strengthening of ε-Cu + NbC, toughness improved |
| Aging at 580°C | 570 – 590°C | Precipitates coarsen, corrosion resistance optimized |
| Aging at 620°C | 610 – 630°C | Precipitates further coarsen, plasticity best |
VI. Main application fields (high strength+corrosion resistance scene)
17-4PH, with “customized strength + better corrosion resistance than ordinary martensite”, covers the following fields:
- High-end Equipment:
- Aerospace: Turbine blades, landing gears (aged at 480°C, high strength and impact resistance);
- Nuclear power: Nuclear waste storage barrels (aged at 580°C, radiation-resistant + corrosion-resistant).
- Industrial Machinery:
- Valves, shafts, fasteners (aged at 480 – 550°C, high strength and wear resistance);
- Automobile/chemical industry: Precision components (aged at 550°C, balance of strength and toughness).
- Corrosive Environments:
- Offshore platforms: Helicopter decks, mooring systems (aged at 580°C, seawater-resistant + salt spray-resistant);
- Food processing: Pickling tanks, sterile equipment (aged at 620°C, organic acid-resistant + hygienic compliance).
- Petroleum Field:
- Logging/drilling tools (H900 system, i.e., aged at 480°C, high strength and wear resistance);
- Completion components (H1100 system, aged at higher temperatures, corrosion resistance priority).
Key Summary
- Core Advantages: Strength covers 620 – 1310 MPa (flexible control), corrosion resistance is close to 304 stainless steel (in atmospheric and dilute acid environments), and excellent hot and cold workability (easy to form in solution annealed state).
- Limitations: Long-term service temperature ≤ 300°C (precipitates coarsen at high temperatures, resulting in strength reduction), and nickel-based alloys (such as Hastelloy) need to be used instead in concentrated hydrochloric acid/hydrofluoric acid environments.
17-4PH is a “benchmark for corrosion-resistant steel with customized strength”. It breaks through the performance boundaries of traditional stainless steel through the precipitation hardening mechanism and becomes a core material in high-end fields such as aviation, nuclear power, and marine.