Steel 18Ni(400)-SA (Solution annealed)
Heat-treated state
also T-400, C-400
The soft as-supplied mill condition — machine, form and weld here, then age.
Values for the SA condition
Other 18Ni(400) tempers and conditions
18Ni(400) is listed in 5 conditions; see the grade overview at 18Ni(400).
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
SAThis page Solution annealed | The soft as-supplied mill condition — machine, form and weld here, then age. | 900 | 1,170 | 12 | 33 HRC | — |
Cold drawn | Cold-drawn small bar and wire for close tolerance and finish before customer ageing. | 1,250 | 1,400 | 6 | 40 HRC | 2.4 % IACS |
aged 510–540 °C for improved toughness | Deliberate overage when a little more toughness/ductility is worth trading ~10 % of strength. | 2,350 | 2,450 | 8 | 54 HRC | 2.7 % IACS |
AgedDefault Solution annealed + aged 480 °C, 3–6 h, air cool | Standard full-strength condition (~400 ksi); pick for maximum strength-to-weight with minimal heat-treat distortion. | 2,680 | 2,760 | 6 | 58 HRC | — |
Cold worked (ausformed/marformed) then aged 480 °C | Wire, strip and thin sections where cold reduction before ageing pushes strength above the standard aged level, at the cost of ductility. | 2,850 | 2,950 | 3 | 60 HRC | 2.6 % IACS |
What is 18Ni(400)-SA?
18Ni(400)-SA is 18Ni(400) heat treated to SA — the soft as-supplied mill condition — machine, form and weld here, then age. 18Ni(400)-SA has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 90% of steel grades. Elongation at break is 12% and the elastic modulus is 200 GPa (29 Msi). 18Ni(400)-SA has a density of 8.1 g/cm³ (0.293 lb/in³), heavier than 97% of steel grades. It melts at 1,400°C (2,552 °F). Aged is the default condition FabDigit quotes; SA is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 80/100, better than 97% of steel grades
- Good corrosion resistance — 25/100, better than 92% of steel grades
- High strength — 900 MPa (131 ksi), better than 90% of steel grades
- Readily welded — 75/100, better than 76% of steel grades
Limitations
- Poor heat conductor — 18 W/m·K (10.4 BTU/hr·ft·°F), worse than 98% of steel grades
- High embodied carbon — 6.5 kg CO₂/kg, worse than 98% of steel grades
- Low electrical conductivity — 2.6 % IACS, worse than 97% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
- Difficult to machine — 40/100, worse than 77% of steel grades
18Ni(400)-SA properties
Typical room-temperature values for 18Ni(400)-SA; 13 are specific to this condition. Other listed values are 18Ni(400) reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
18Ni(400)-SA has a density of 8.1 g/cm³ (0.293 lb/in³), heavier than 97% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical15
18Ni(400)-SA has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 90% of steel grades. Elongation at break is 12% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
18Ni(400)-SA is rated for continuous service to 400°C (752 °F). It conducts heat at 18 W/m·K (10.4 BTU/hr·ft·°F), worse than 98% of steel grades. Thermal expansion is 10.1 µm/m·K (5.61 µin/in·°F).
Electrical3
18Ni(400)-SA conducts electricity at 2.6 % IACS, worse than 97% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (25/100), better than 92% of steel grades.
Sustainability4
Producing a kilogram of 18Ni(400)-SA takes about 90 MJ of energy and emits 6.5 kg of CO₂ — more than 98% of steel grades. Typical recycled content is 20%.
Manufacturability7
18Ni(400)-SA's machinability is fair (40/100, worse than 77% of steel grades); weldability very good (75/100); formability fair (50/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 18Ni(400)-SA
Is 18Ni(400) easy to machine?
Do all roughing in the solution-annealed state (rates similar to 4340 at 33 HRC, ~45 % of 1212); aged material needs rigid setups, ceramic/CBN or coated carbide, low feeds and generous coolant, and grinding is often preferred for finishing.
Can 18Ni(400) be welded?
Excellent for its strength class — GTAW/EBW/laser with matching filler, no preheat, low heat input, clean surfaces; re-age at 480 °C after welding to restore joint strength, and never weld in the aged condition without re-solutioning if maximum toughness is needed.
Can 18Ni(400) be formed, bent or molded?
Form, bend and draw only in the annealed condition; ageing is a simple 480 °C air treatment with ~0.05–0.1 % linear shrinkage and negligible distortion, so parts can be finish-machined close to size before ageing.
What surface finishes work on 18Ni(400)?
Not corrosion resistant — phosphate, dry-film lube, cadmium/nickel plate with mandatory hydrogen bake-out, or PVD/electroless nickel; avoid acid pickling and shot-peen or stress-relieve carefully at this strength to limit hydrogen and notch effects.
18Ni(400) 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 |
|---|---|---|
| Ccarbon-free martensite; kept as low as vacuum melting allows | ≤ 0.01 | 0.01 |
| Ni400-grade chemistry runs lower Ni than the 200/250/300 grades despite the '18Ni' family name | 12 – 13.5 | 13 |
| Co | 14.5 – 15.5 | 15 |
| Momain precipitation hardener at this strength level | 9.5 – 10.5 | 10 |
| Ti | 0.15 – 0.3 | 0.2 |
| Al | 0.05 – 0.15 | 0.1 |
| Si | ≤ 0.1 | 0.05 |
| Mn | ≤ 0.1 | 0.05 |
| P | ≤ 0.01 | — |
| S | ≤ 0.01 | — |
| Febalance; VIM + VAR double vacuum melted | balance | — |
18Ni(400)-SA — frequently asked
What is 18Ni(400)-SA used for?
18Ni(400)-SA is typically used for high-performance rocket motor cases, ultra-high-strength shafts, specialized ordnance components and aerospace fasteners. In short: strongest maraging steel grade; 400 ksi class UTS; minimal ageing distortion.
What is the yield strength of 18Ni(400)-SA?
18Ni(400)-SA has a typical yield strength of 900 MPa (131 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 90% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is 18Ni(400)-SA easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Do all roughing in the solution-annealed state (rates similar to 4340 at 33 HRC, ~45 % of 1212); aged material needs rigid setups, ceramic/CBN or coated carbide, low feeds and generous coolant, and grinding is often preferred for finishing.
Can 18Ni(400)-SA be welded?
Yes — weldability is rated very good (75/100). Excellent for its strength class — GTAW/EBW/laser with matching filler, no preheat, low heat input, clean surfaces; re-age at 480 °C after welding to restore joint strength, and never weld in the aged condition without re-solutioning if maximum toughness is needed.
What surface finishes work on 18Ni(400)-SA?
Not corrosion resistant — phosphate, dry-film lube, cadmium/nickel plate with mandatory hydrogen bake-out, or PVD/electroless nickel; avoid acid pickling and shot-peen or stress-relieve carefully at this strength to limit hydrogen and notch effects.
Can 18Ni(400)-SA be formed, bent or molded?
Form, bend and draw only in the annealed condition; ageing is a simple 480 °C air treatment with ~0.05–0.1 % linear shrinkage and negligible distortion, so parts can be finish-machined close to size before ageing.
What is the maximum service temperature of 18Ni(400)-SA?
18Ni(400)-SA is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 18Ni(400) Aged and 18Ni(400)-SA?
Aged is the default condition — standard full-strength condition (~400 ksi); pick for maximum strength-to-weight with minimal heat-treat distortion. SA: the soft as-supplied mill condition — machine, form and weld here, then age. Yield strength is 2,680 MPa in Aged versus 900 MPa in SA.
Sources
- ASM Handbook Vol. 1: Properties and Selection: Irons, Steels, and High-Performance Alloys — Maraging Steels — ASM International (1990)
- ASM Specialty Handbook: Carbon and Alloy Steels — ASM International (1996)
- Metals Handbook Desk Edition — Ultrahigh-Strength Steels — ASM International (1998)
- ASTM A538/A538M — Pressure Vessel Plates, Alloy Steel, Precipitation Hardening (Maraging), 18Ni family — ASTM (2015)
- VascoMax / maraging steel grade data (C-series and T-series) — Carpenter Technology (Latrobe/Teledyne Vasco heritage) (2020)
- MatWeb — 18Ni(400) maraging steel, aged — MatWeb LLC (2024)
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.