15-7PH is a chromium-nickel-molybdenum-aluminium semi-austenitic precipitation-hardening (PH) stainless steel. This datasheet presents the material within the American (ASTM / ASME / AMS / UNS) standard system.
With about 15% chromium, 7% nickel, 2.5% molybdenum and 1% aluminium, PH 15-7Mo is essentially the 17-7PH composition with about 2% molybdenum substituted for chromium, giving higher room- and elevated-temperature strength and improved corrosion resistance. It is supplied in the soft austenitic (Condition A) state, formed, then transformed to martensite and precipitation-hardened by a multi-step heat treatment that precipitates an aluminium-rich phase. It distorts little on hardening and is particularly useful where high strength must be retained at elevated temperature.
Typical applications include aerospace structural components, springs, diaphragms, retaining rings and high-strength corrosion-resistant hardware operating at elevated temperature.
Typical values, RH950 condition.
| Property | Value | Unit |
|---|---|---|
| Density | 7.80 | g/cm³ |
| Melting range | 1400–1440 | °C |
| Elastic modulus | 200 | GPa |
| Coefficient of thermal expansion (20–100 °C) | 11.0 | µm/m·°C |
| Thermal conductivity (20 °C) | 15.5 | W/m·K |
| Specific heat (20 °C) | 460 | J/kg·K |
| Structure | Semi-austenitic (precipitation-hardening) | — |
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Iron | Fe | Balance | — | Base element |
| Chromium | Cr | 14.0 | 16.0 | Corrosion resistance |
| Nickel | Ni | 6.50 | 7.75 | Austenite stability |
| Molybdenum | Mo | 2.0 | 3.0 | Strength; pitting resistance |
| Aluminium | Al | 0.75 | 1.50 | Precipitation-hardening phase (Ni-Al) |
| Manganese | Mn | — | 1.00 | Deoxidiser |
| Silicon | Si | — | 1.00 | Deoxidiser |
| Carbon | C | — | 0.09 | Strength |
| Phosphorus | P | — | 0.040 | Residual impurity |
| Sulphur | S | — | 0.030 | Residual impurity |
Typical values by heat-treatment condition, per ASTM A564 / AMS 5520 for UNS S15700.
| Condition | Tensile strength | 0.2% Yield | Hardness |
|---|---|---|---|
| TH1050 | ≥1210 MPa (175 ksi) | ≥1100 MPa (160 ksi) | ~40 HRC |
| RH950 | ≥1450 MPa (210 ksi) | ≥1310 MPa (190 ksi) | ~44 HRC |
| CH900 (cold-rolled + aged) | ≥1690 MPa (245 ksi) | ≥1620 MPa (235 ksi) | ~46 HRC |
| Condition A (annealed) | ~895 MPa (130 ksi) | ~380 MPa (55 ksi) | ~B88 HRB |
Confirm against the mill test report. Elongation typically ≥2–6% in hardened conditions, higher in Condition A.
| Environment | Performance | Notes |
|---|---|---|
| Atmospheric / general | Good | Better than 17-7PH (molybdenum addition) |
| Mild acids | Moderate | At low concentrations |
| Chloride pitting | Moderate | Improved by molybdenum vs 17-7PH |
| Oxidation | Good | Retains strength at elevated temperature |
| Seawater | Limited | Not recommended for prolonged exposure |
The molybdenum addition gives better corrosion resistance and higher strength than 17-7PH; resistance remains below the austenitic stainless steels.
A semi-austenitic precipitation-hardening alloy; supplied in Condition A (soft, austenitic) and hardened by a multi-step transformation-plus-ageing sequence.
Solution Treatment (Condition A) Supplied solution-treated (~1065 °C) in the soft austenitic condition for forming.
Transformation and Precipitation Hardening TH1050: austenite-conditioning at ~760 °C, cool to transform to martensite, then age at ~565 °C. RH950: condition at ~955 °C, sub-zero cool (~−73 °C) to transform, then age at ~510 °C for higher strength. CH900: cold-roll to martensite then age at ~480 °C for maximum strength. Air cool after ageing.
Weldable by common fusion and resistance methods; matching filler is used. Heat treatment after welding develops full properties.
| Welding Process | Applicability | Filler / Consumable |
|---|---|---|
| GTAW / TIG | Good | Matching 15-7-type filler |
| GMAW / MIG | Good | Matching filler |
| Resistance / spot | Good | — |
Weld in Condition A; heat-treat after welding to develop strength.
Machining Guidelines
| Parameter | Recommendation |
|---|---|
| Preferred condition | Condition A for best formability and machinability |
| Work hardening | High rate; positive feeds, rigid setup |
| Coolant | Ample flood coolant |
Forming Processes
| Process | Notes |
|---|---|
| Cold forming | Excellent in Condition A (formable semi-austenitic PH) |
| Hot forming | ~1150–950 °C; solution treat + age afterward |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Aerospace | Structural parts, skins, fittings | High strength at elevated temperature |
| Spring / fastener | Springs, washers, clips | Spring properties + fatigue resistance |
| Instrumentation | Diaphragms, bellows | Formability + fatigue resistance |
| General industrial | High-strength formed components | Strength + minimal distortion |
| Product Form | ASTM Standard | ASME / AMS |
|---|---|---|
| Plate, sheet and strip | ASTM A693 grade 632 | ASME SA-693 / AMS 5520 |
| Bar and wire | ASTM A564 grade 632 | ASME SA-564 / AMS 5657 |
| Wire (spring) | ASTM A313 (632) | — |
| Welding consumables | Matching 15-7-type filler | — |
Chromium-nickel-molybdenum-aluminium semi-austenitic precipitation-hardening stainless steel. UNS S15700.
| Grade | Cr % | Ni % | Mo % | Al % | Best Used For |
|---|---|---|---|---|---|
| 15-7PH | 14–16 | 6.5–7.75 | 2.0–3.0 | 0.75–1.5 | Semi-austenitic PH; high strength at temperature |
| 17-7PH | 16–18 | 6.5–7.75 | — | 0.75–1.5 | Semi-austenitic PH; springs, formability |
| AM-350 | 16–17 | 4–5 | 2.5–3.25 | — | Semi-austenitic PH; high strength |
| AM-355 | 15–16 | 4–5 | 2.5–3.25 | — | Semi-austenitic PH; highest strength |
| 17-4PH | 15–17.5 | 3–5 | — | — | Martensitic PH; general high strength |




