Nickel Alloy M25S ST+A
Precip hard
UNS N24025 · ASTM A494 M25S
ST+A = solution treated (~870 °C, quenched) and aged
Full solution treat plus age for the highest and most uniform hardness in heavy or segregated sections.
Values for the ST+A condition
Other M25S tempers and conditions
M25S is listed in 3 conditions; see the grade overview at M25S.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | As-cast condition; softer and slightly less brittle, used where the 300 HB minimum is not contractually required. | 415 | 620 | 2.5 | 25 HRC | 2.4 % IACS |
HTDefault Age hardened | Standard supply condition for wear parts: aged to meet the ASTM A494 minimum 300 HB with maximum galling resistance. | 550 | 760 | 1.5 | 34 HRC | 2.3 % IACS |
ST+AThis page Solution treated (~870 °C, quenched) and aged | Full solution treat plus age for the highest and most uniform hardness in heavy or segregated sections. | 590 | 790 | 1 | 35 HRC | 2.2 % IACS |
What is M25S ST+A?
M25S ST+A is M25S in the ST+A condition — full solution treat plus age for the highest and most uniform hardness in heavy or segregated sections. M25S ST+A has a yield strength of 590 MPa (85.6 ksi) and a tensile strength of 790 MPa (115 ksi) — stronger than 81% of nickel alloy grades. Elongation at break is 1% and the elastic modulus is 172 GPa (24.9 Msi). M25S ST+A has a density of 8.36 g/cm³ (0.302 lb/in³), heavier than 54% of nickel alloy grades. It melts at 1,010°C (1,850 °F). HT is the default condition FabDigit quotes; ST+A is available on request or by drawing note.
Advantages
- Low embodied carbon — 11 kg CO₂/kg, better than 85% of nickel alloy grades
- Conducts heat well — 17.5 W/m·K (10.1 BTU/hr·ft·°F), better than 84% of nickel alloy grades
- High electrical conductivity — 2.2 % IACS, better than 83% of nickel alloy grades
- High strength — 590 MPa (85.6 ksi), better than 81% of nickel alloy grades
Limitations
- Low fracture toughness — 22 MPa·√m (20 ksi·√in), worse than 99% of nickel alloy grades
- Limited formability — 2/100, worse than 99% of nickel alloy grades
- Limited ductility — 1%, worse than 98% of nickel alloy grades
- Difficult to weld — 10/100, worse than 94% of nickel alloy grades
- Difficult to machine — 10/100, worse than 93% of nickel alloy grades
M25S ST+A properties
Typical room-temperature values for M25S ST+A; 22 are specific to this condition. Other listed values are M25S reference data and may not represent this condition. Bars are the position among nickel alloy grades.
Physical3
M25S ST+A has a density of 8.36 g/cm³ (0.302 lb/in³), heavier than 54% of nickel alloy grades. It melts at 1,010°C (1,850 °F).
Mechanical16
M25S ST+A has a yield strength of 590 MPa (85.6 ksi) and a tensile strength of 790 MPa (115 ksi) — stronger than 81% of nickel alloy grades. Elongation at break is 1% and the elastic modulus is 172 GPa (24.9 Msi).
Thermal4
M25S ST+A is rated for continuous service to 450°C (842 °F). It conducts heat at 17.5 W/m·K (10.1 BTU/hr·ft·°F), better than 84% of nickel alloy grades. Thermal expansion is 13 µm/m·K (7.22 µin/in·°F).
Electrical3
M25S ST+A conducts electricity at 2.2 % IACS, better than 83% of nickel alloy grades.
Chemical & Environmental3
Corrosion resistance is very good (75/100), worse than 63% of nickel alloy grades.
Sustainability4
Producing a kilogram of M25S ST+A takes about 130 MJ of energy and emits 11 kg of CO₂ — less than 87% of nickel alloy grades. Typical recycled content is 40%.
Manufacturability8
M25S ST+A's machinability is not recommended (10/100, worse than 93% of nickel alloy grades); weldability not recommended (10/100); formability not recommended (2/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with M25S ST+A
Is M25S easy to machine?
Hard and abrasive — use rigid setups, carbide or CBN tooling, low speed with heavy positive feed; finish grinding is often preferred on wear surfaces.
Can M25S be welded?
Poor weldability: high Si promotes hot cracking; limit to minor defect repair with Ni-Cu (ERNiCu-7) filler, preheat and post-weld age, or braze instead.
Can M25S be formed, bent or molded?
Sand or investment casting only; good fluidity from the silicon, but feed heavy sections well as the alloy has low hot ductility.
What surface finishes work on M25S?
Not anodizable; typically supplied ground/lapped or passivated — the alloy is used bare and self-protecting in seawater.
M25S chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Cu | 27 – 33 | 30 |
| Siprovides age hardening and galling resistance | 3.5 – 4.5 | 4 |
| Fe | ≤ 3.5 | 1.5 |
| Mn | ≤ 1.5 | 0.8 |
| C | ≤ 0.25 | 0.15 |
| S | ≤ 0.03 | 0.01 |
| NiNi + Co, remainder | ≥ 60 (balance) | — |
M25S ST+A — frequently asked
What is M25S ST+A used for?
M25S ST+A is typically used for valve trim, pump casings and marine hardware castings. In short: hardest cast Ni-Cu grade; galling-resistant valve trim alloy; low ductility, grind-finished.
What is the yield strength of M25S ST+A?
M25S ST+A has a typical yield strength of 590 MPa (85.6 ksi) and a tensile strength of 790 MPa (115 ksi) — stronger than 81% of nickel alloy grades. Strength varies by condition: see the 3 listed tempers.
Is M25S ST+A easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 93% of nickel alloy grades). Hard and abrasive — use rigid setups, carbide or CBN tooling, low speed with heavy positive feed; finish grinding is often preferred on wear surfaces.
Can M25S ST+A be welded?
Not readily — weldability is rated not recommended (10/100). Poor weldability: high Si promotes hot cracking; limit to minor defect repair with Ni-Cu (ERNiCu-7) filler, preheat and post-weld age, or braze instead.
What surface finishes work on M25S ST+A?
Not anodizable; typically supplied ground/lapped or passivated — the alloy is used bare and self-protecting in seawater.
Can M25S ST+A be formed, bent or molded?
Sand or investment casting only; good fluidity from the silicon, but feed heavy sections well as the alloy has low hot ductility.
What is the maximum service temperature of M25S ST+A?
M25S ST+A is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between M25S-HT and M25S-AC?
HT is the default condition — standard supply condition for wear parts: aged to meet the ASTM A494 minimum 300 HB with maximum galling resistance. AC: as-cast condition; softer and slightly less brittle, used where the 300 HB minimum is not contractually required. Yield strength is 550 MPa in HT versus 415 MPa in AC.
Sources
- ASTM A494/A494M — Castings, Nickel and Nickel Alloy — ASTM International (2023)
- ASM Handbook Vol.2 — Properties and Selection: Nonferrous Alloys — ASM International (1990)
- ASM Handbook Vol.15 — Casting — ASM International (2008)
- Monel/Ni-Cu casting alloy data (S-Monel type) — Special Metals / Nickel Institute (2020)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.