Steel 18Ni(400) Overaged
Precip hard
also T-400, C-400
Deliberate overage when a little more toughness/ductility is worth trading ~10 % of strength.
Values for the Overaged 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 |
|---|---|---|---|---|---|---|
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 |
OveragedThis page 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) Overaged?
18Ni(400) Overaged is 18Ni(400) in the Overaged condition — deliberate overage when a little more toughness/ductility is worth trading ~10 % of strength. 18Ni(400) Overaged has a yield strength of 2,350 MPa (341 ksi) and a tensile strength of 2,450 MPa (355 ksi) — stronger than 100% of steel grades. Elongation at break is 8% and the elastic modulus is 200 GPa (29 Msi). 18Ni(400) Overaged 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; Overaged is available on request or by drawing note.
Advantages
- High strength — 2,350 MPa (341 ksi), better than 100% of steel grades
- Polishes to a fine finish — 80/100, better than 97% of steel grades
- Good corrosion resistance — 25/100, better than 92% of steel grades
Limitations
- Limited formability — 7/100, worse than 98% of steel grades
- High embodied carbon — 6.5 kg CO₂/kg, worse than 98% of steel grades
- Poor heat conductor — 19 W/m·K (11 BTU/hr·ft·°F), worse than 97% of steel grades
- Low electrical conductivity — 2.7 % IACS, worse than 96% of steel grades
- Limited ductility — 8%, worse than 95% of steel grades
18Ni(400) Overaged properties
Typical room-temperature values for 18Ni(400) Overaged; 22 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) Overaged 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) Overaged has a yield strength of 2,350 MPa (341 ksi) and a tensile strength of 2,450 MPa (355 ksi) — stronger than 100% of steel grades. Elongation at break is 8% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
18Ni(400) Overaged is rated for continuous service to 425°C (797 °F). It conducts heat at 19 W/m·K (11 BTU/hr·ft·°F), worse than 97% of steel grades. Thermal expansion is 10.1 µm/m·K (5.61 µin/in·°F).
Electrical3
18Ni(400) Overaged conducts electricity at 2.7 % IACS, worse than 96% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (25/100), better than 92% of steel grades.
Sustainability4
Producing a kilogram of 18Ni(400) Overaged 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) Overaged's machinability is poor (22/100, worse than 95% of steel grades); weldability very good (70/100); formability not recommended (7/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 18Ni(400) Overaged
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) Overaged — frequently asked
What is 18Ni(400) Overaged used for?
18Ni(400) Overaged 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) Overaged?
18Ni(400) Overaged has a typical yield strength of 2,350 MPa (341 ksi) and a tensile strength of 2,450 MPa (355 ksi) — stronger than 100% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is 18Ni(400) Overaged easy to machine?
Not especially — machinability is rated poor (22/100, worse than 95% 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) Overaged be welded?
Yes — weldability is rated very good (70/100). 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) Overaged?
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) Overaged 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) Overaged?
18Ni(400) Overaged is rated for continuous use to about 425°C (797 °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.