Stainless Steel 17-4PH
Executive Summary
Section titled “Executive Summary”17-4PH stainless steel (UNS S17400, AISI 630) is a precipitation‑hardenable martensitic alloy that combines high mechanical strength, elevated hardness and good corrosion resistance. Its composition, with approximately 17 % chromium, 4 % nickel and 4 % copper, allows tensile strengths above 1 300 MPa to be achieved through heat treatment. It is widely used in the aerospace, marine, chemical, medical and oil industries, where components require excellent mechanical behavior up to temperatures close to 300 °C and corrosion resistance comparable to that of some austenitic stainless steels. Its martensitic structure gives it magnetic properties.
Chemical Composition
Section titled “Chemical Composition”The chemical composition of 17-4PH steel is given in the following table. Iron constitutes the balance.
| Element | Content (%) |
|---|---|
| Chromium (Cr) | 15.0 – 17.5 |
| Nickel (Ni) | 3.0 – 5.0 |
| Copper (Cu) | 3.0 – 5.0 |
| Manganese (Mn) | ≤ 1.0 |
| Silicon (Si) | ≤ 1.0 |
| Niobium + Tantalum (Nb+Ta) | 0.15 – 0.45 |
| Carbon (C) | ≤ 0.07 |
| Phosphorus (P) | ≤ 0.04 |
| Sulfur (S) | ≤ 0.03 |
| Iron (Fe) | Balance |
Physical Properties
Section titled “Physical Properties”The physical properties of 17-4PH in the annealed condition are:
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.75 g/cm³ | 0.280 lb/in³ |
| Modulus of elasticity (tension) | 190 – 210 GPa | 27 557 – 30 458 ksi |
| Shear modulus | 77.4 GPa | 11 200 ksi |
| Poisson’s ratio | 0.27 – 0.30 | 0.27 – 0.30 |
| Magnetic structure | Ferromagnetic (martensitic) | Ferromagnetic |
Mechanical Properties
Section titled “Mechanical Properties”The mechanical properties depend on the heat treatment condition. Condition A (annealed) has a hardness of 352 HB (36 HRC, 349 HV). After aging, the strength and hardness can vary significantly, as shown in the following table of typical values for conditions designated according to aging temperature.
| Condition | Tensile Strength (MPa / ksi) | Yield Strength (MPa / ksi) | Elongation in 4D (%) | Hardness Rockwell C (HRC) |
|---|---|---|---|---|
| H900 | 1 310 / 190 | 1 170 / 170 | 10 | 44 |
| H925 | 1 240 / 180 | 1 070 / 155 | 10 | 42 |
| H1025 | 1 170 / 170 | 1 000 / 145 | 12 | 39 |
| H1075 | 1 100 / 160 | 930 / 135 | 13 | 37 |
| H1150 | 1 000 / 145 | 830 / 120 | 15 | 34 |
| H1150M | 970 / 141 | 790 / 115 | 17 | 32 |
The values of elastic modulus, shear modulus and Poisson’s ratio are those given in the physical properties and remain practically constant in all states.
Thermal Properties
Section titled “Thermal Properties”| Property | SI Value | Imperial Value |
|---|---|---|
| Coefficient of thermal expansion (21 – 93 °C) | 10.8 µm/m·°C | 6.00 µin/in·°F |
| Thermal conductivity (H900 at 149 °C) | 17.9 W/m·K | 124 BTU·in/hr·ft²·°F |
| Thermal conductivity (H900 at 482 °C) | 22.6 W/m·K | 156.8 BTU·in/hr·ft²·°F |
| Specific heat (typical) | 460 J/kg·K | 0.11 BTU/lb·°F |
Equivalent Designations
Section titled “Equivalent Designations”17-4PH steel is known under multiple designations in different norms and standards. The following table lists the most common ones.
| Standard | Designation |
|---|---|
| AISI | 630 |
| UNS | S17400 |
| ASTM A564 | 630 |
| ASTM A693 | 630 |
| ASTM A705 | 630 |
| AMS 5643 | 17-4PH |
| AMS 5604 | 17-4PH |
| MIL | MIL‑S‑81591 / MIL‑C‑24111 |
| SAE | J467 (17-4PH) |
| ASME | SA564 / SA705 |
Heat Treatments
Section titled “Heat Treatments”The heat treatment of 17-4PH comprises two main stages: solution treatment and aging.
- Solution treatment (Condition A): Heating at 1 038 °C (1 900 °F) for 30 minutes, followed by rapid cooling to a temperature below 16 °C (60 °F) to ensure complete martensitic transformation.
- Aging (H conditions): Starting from condition A, the material is aged at the temperature indicated in its designation for controlled times:
- H900: 482 °C (900 °F) for 1 h, air cooling.
- H925, H1025, H1075, H1100, H1150: soak for 4 h at the corresponding temperature, air cooling.
- H1150M: double stage: 760 °C (1 400 °F) for 2 h, air cooling, followed by 620 °C (1 150 °F) for 4 h, air cooling. This overaging treatment significantly improves resistance to stress corrosion cracking.
Manufacturing and Processing
Section titled “Manufacturing and Processing”Machinability In the annealed condition (A), 17-4PH exhibits a machinability of 48 % relative to the reference steel AISI 1212 (100 %). It produces long, adhesive chips; therefore, solution treatment after machining is recommended if working in the H1150M state before final hardening.
Forming The material can be cold formed to a moderate degree. For severe deformations, working in the annealed condition is recommended.
Welding It can be welded satisfactorily by conventional fusion and resistance methods. Oxyacetylene welding is not recommended. Generally, filler metal of similar composition is used, and a post‑weld aging treatment is necessary to recover the mechanical properties in the affected zone.
Applications by Industry
Section titled “Applications by Industry”Thanks to its excellent combination of mechanical strength, hardness and corrosion resistance, 17-4PH is used in sectors where reliability is critical:
- Aerospace: Structural components, fasteners, shafts, brackets and landing gear parts.
- Marine: Propulsion shafts, propellers, valves and components exposed to salt spray.
- Oil and gas: Valves, pumps, downhole tool bodies and drilling equipment.
- Chemical: Pump casings, agitators and parts in contact with mildly corrosive media.
- Medical: Surgical instruments, prostheses and implantable devices due to its biocompatibility and sterilizability.
- Firearms: Gun parts requiring high strength and wear resistance.
Comparison with Similar Materials
Section titled “Comparison with Similar Materials”Compared to austenitic stainless steels such as 304, 17-4PH offers up to three times higher tensile strength and much higher hardness, although its corrosion resistance in very aggressive environments (e.g., stagnant seawater) is inferior, and it can suffer pitting corrosion. With respect to 15-5PH, the main difference lies in the microstructure and weldability; 17-4PH has a slightly higher carbon content, which favors the hardening response, while 15-5PH shows a lower tendency to cracking in thick weldments. Compared to traditional martensitic steels such as 410, 17-4PH retains much better corrosion resistance and can operate at higher temperatures without losing mechanical properties.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum tensile strength of 17-4PH?
Section titled “What is the maximum tensile strength of 17-4PH?”It reaches 1 310 MPa (190 ksi) in condition H900, and 1 300 MPa (190 ksi) as a typical reference value.
What Rockwell hardness can be obtained with the H900 treatment?
Section titled “What Rockwell hardness can be obtained with the H900 treatment?”A hardness of 44 HRC is achieved in the H900 (482 °C) aging condition.
What is the machinability of 17-4PH compared to a reference steel?
Section titled “What is the machinability of 17-4PH compared to a reference steel?”In the annealed state, its machinability is 48 % relative to AISI 1212 steel, which has 100 % relative machinability.
Up to what maximum temperature can 17-4PH work while maintaining its properties?
Section titled “Up to what maximum temperature can 17-4PH work while maintaining its properties?”The recommended maximum continuous service temperature is 300 °C (572 °F) to preserve strength and hardness.
Is 17-4PH stainless steel magnetic?
Section titled “Is 17-4PH stainless steel magnetic?”Yes, its martensitic structure makes it ferromagnetic, unlike austenitic steels such as 304.
Can 17-4PH be welded and what method is recommended?
Section titled “Can 17-4PH be welded and what method is recommended?”It is weldable by all common fusion and resistance methods (TIG, MIG, plasma), but oxyacetylene welding is not advised; post‑weld treatment is often required.
References
Section titled “References”- azom.com: https://www.azom.com/article.aspx?ArticleID=6778
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/machinability-metals-d_1450.html
- steelnumber.com: https://www.steelnumber.com/index.php