XM-12 is a copper-bearing martensitic precipitation-hardening (PH) stainless steel. This datasheet presents the material within the American (ASTM / ASME / AMS / UNS) standard system.
With about 15% chromium, 5% nickel and 3% copper plus niobium, 15-5PH combines high strength and hardness with good corrosion resistance and excellent transverse toughness and ductility. It was designed as a more ductile variant of 17-4PH, with improved through-thickness (short-transverse) properties achieved by a controlled, low-ferrite microstructure. The alloy is martensitic in the annealed (solution-treated) condition and is strengthened by a single low-temperature ageing treatment that precipitates a copper-rich phase. A range of strength levels is obtained by choosing the ageing temperature (the H-condition).
Typical applications include aerospace structural and engine components, valve and pump parts, shafts, fasteners, gears, and nuclear and chemical-process hardware requiring high strength with moderate corrosion resistance.
| Property | Value | Unit |
|---|---|---|
| Density | 7.8 | g/cm³ |
| Melting range | 1400–1440 | °C |
| Elastic modulus | 196 | GPa |
| Coefficient of thermal expansion (20–100 °C) | 10.8 | µm/m·°C |
| Thermal conductivity (20 °C) | 17.8 | W/m·K |
| Specific heat (20 °C) | 420 | J/kg·K |
| Structure | Martensitic (precipitation-hardening) | — |
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Iron | Fe | Balance | — | Base element |
| Chromium | Cr | 14.0 | 15.5 | Corrosion resistance; martensite former |
| Nickel | Ni | 3.5 | 5.5 | Toughness; martensite stability |
| Copper | Cu | 2.5 | 4.5 | Precipitation-hardening phase |
| Niobium | Nb | 0.15 | 0.45 | Carbide stabiliser; grain refinement |
| Manganese | Mn | — | 1.00 | Deoxidiser |
| Silicon | Si | — | 1.00 | Deoxidiser |
| Carbon | C | — | 0.07 | Strength; martensite hardness |
| Phosphorus | P | — | 0.040 | Residual impurity |
| Sulphur | S | — | 0.030 | Residual impurity |
Typical values by ageing (H) condition, per ASTM A564 / AMS 5659 for UNS S15500.
| Condition | Tensile strength | 0.2% Yield | Hardness |
|---|---|---|---|
| H900 | ≥1310 MPa (190 ksi) | ≥1170 MPa (170 ksi) | ~44 HRC |
| H1025 | ≥1070 MPa (155 ksi) | ≥1000 MPa (145 ksi) | ~35 HRC |
| H1075 | ≥1000 MPa (145 ksi) | ≥860 MPa (125 ksi) | ~32 HRC |
| H1150 | ≥930 MPa (135 ksi) | ≥725 MPa (105 ksi) | ~28 HRC |
Confirm against the mill test report. Elongation typically ≥10–16% depending on condition.
| Environment | Performance | Notes |
|---|---|---|
| Atmospheric / general | Good | Superior to 400-series martensitic steels |
| Mild acids (acetic, nitric, dilute) | Good | At low concentrations |
| Chloride pitting | Moderate | Lower than austenitic grades |
| Stress-corrosion cracking | Improved at higher ageing | Over-aged (H1100–H1150) gives best SCC resistance |
| Seawater | Limited | Not recommended for prolonged exposure |
Corrosion resistance is roughly comparable to type 304 in many environments; resistance and SCC behaviour improve with higher (over-aged) ageing conditions.
A martensitic precipitation-hardening alloy; supplied in Condition A (solution-treated) and hardened by a single low-temperature ageing treatment.
Solution Treatment (Condition A) Approximately 1040 °C followed by cooling to room temperature to form a martensitic structure.
Precipitation Hardening (Ageing) A single low-temperature ageing treatment precipitates a copper-rich phase. The temperature sets the strength level: H900 (~480 °C) gives maximum strength; higher temperatures (H1025, H1075, H1100, H1150) progressively lower strength while increasing toughness and SCC resistance. No quench required after ageing; air cool.
Weldable by common fusion methods; matching filler (AWS A5.4 E630 / ER630) is used. A post-weld solution treatment and ageing restores full properties.
| Welding Process | Applicability | Filler / Consumable |
|---|---|---|
| GTAW / TIG | Good | AWS A5.9 ER630 |
| GMAW / MIG | Good | ER630 |
| SMAW / stick | Good | AWS A5.4 E630 electrode |
Weld in the solution-treated (Condition A) or over-aged condition; re-age after welding to restore strength.
Machining Guidelines
| Parameter | Recommendation |
|---|---|
| Preferred condition | Condition A or over-aged (H1150M) for best machinability |
| Tooling | Carbide tooling; rigid setup |
| Coolant | Ample flood coolant |
Forming Processes
| Process | Notes |
|---|---|
| Cold forming | Limited in hardened conditions; form in Condition A |
| Hot forming | ~1150–950 °C; solution treat + age afterward |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Aerospace | Structural fittings, engine parts, actuators | High strength + transverse toughness |
| Power generation | Steam/gas turbine blades, shafts | Strength + moderate corrosion resistance |
| Oil & gas | Valve and pump components, shafts | Strength + corrosion resistance |
| General industrial | Fasteners, gears, high-strength parts | Hardness + machinability |
| Product Form | ASTM Standard | ASME / AMS |
|---|---|---|
| Bar, wire and forgings | ASTM A564 grade XM-12 | ASME SA-564 / AMS 5659 |
| Plate, sheet and strip | ASTM A693 grade XM-12 | AMS 5862 |
| Forgings | ASTM A705 grade XM-12 | ASME SA-705 |
| Castings (equivalent) | ASTM A747 grade CB7Cu-2 | — |
| Welding consumables | AWS A5.4 E630 / A5.9 ER630 | — |
Copper-bearing martensitic precipitation-hardening stainless steel. UNS S15500.
| XM Grade | Type | Cr % | Ni % | Best Used For |
|---|---|---|---|---|
| XM-12 | Martensitic PH (Cu) | 14–15.5 | 3.5–5.5 | High-strength PH; transverse toughness |
| XM-13 | Martensitic PH | 11–12.5 | 10.5–11.5 | Ultra-high-strength PH (different type) |
| XM-16 | Martensitic PH | 11.5–13.5 | 4.5–5.5 | High-strength PH (Custom 455, different type) |
| XM-25 | Martensitic PH | 11.5–13 | 8–9 | High-strength PH (different type) |
| XM-27 | Ferritic | 25–27.5 | — | Corrosion-resistant ferritic (different type) |




