Maraging 350 Steel
18Ni maraging steel, the strongest of the family
Typical values for the temper in the title
Maraging 350 is the strongest grade in the 18Ni family: more cobalt (about 12%) and titanium (about 1.4%) than 300. After aging it reaches about 2360 MPa and about 58 HRC.
The cost is lower toughness and ductility (about 6% elongation). It is used where strength is the main requirement: small mechanism parts at extreme load, springs, tooling and dies.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | ≈2360 MPa (aged) | |
| Yield strength Rp0.2 | ≈2320 MPa (aged) | |
| Elongation A | ≈6% | |
| Modulus of elasticity E | 200 GPa | |
| Density ρ | 8.0 g/cm³ | |
| Hardness | ≈58 HRC (aged) | |
| Machinability | 65% (annealed, before aging) | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| Ni nickel | 18.0–19.0 | martensitic matrix |
| Co cobalt | 11.5–12.5 | age strengthening |
| Mo molybdenum | 4.6–5.2 | strengthening precipitates |
| Ti titanium | 1.3–1.6 | maximum strengthening |
| C carbon | max 0.03 | very low |
| Fe iron | balance |
Ranges per MIL-S-46850D. Properties per the SSA data sheet.
Conditions and heat treatment
Maraging steels are supplied annealed (relatively soft, about HRC 30–35), machined in that condition, and gain strength by a simple low-temperature aging, with very small dimensional change.
| Condition | Properties | When to choose it |
|---|---|---|
| Annealed | easy to machine | machining |
| Aged (about 480–510 °C) | about 2360 MPa, about 58 HRC | the finished part |
Applications
- Mechanism parts at extreme load
- High-strength springs
- Tooling and dies
- Missile parts
- Small pins and shafts
Fabrication
Aging
At about 480 °C for several hours, without quenching. The dimensional change is small and predictable, so finish machining can be done before aging.
Welding
Welds well for a steel of this strength (very low carbon). Age after welding.
Corrosion
Not stainless. Protect with a coating.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| Maraging 300 | 2050 / 2000 MPa | Excellent | Maraging 300: tougher · material page |
| Maraging 250 | ≈1750 MPa (aged) / ≈1710 MPa (aged) | Good — age after welding | Maraging 250: the toughest of the family · material page |
| 300M | 1930 / 1690 MPa | Very difficult | 300M: a high-strength QT steel, cheaper · material page |
Common mistakes
Using 350 in a part with sharp notches
Toughness is low, and the part is notch sensitive.
Choosing 350 where 300 is enough
Toughness drops and cost rises.
Leaving it unprotected
It rusts.
Equivalents, standards and supply
| Standards | AMS 6515 / MIL-S-46850 |
|---|---|
| Forms | bar · plate · forging |
| Producers | ATI (VascoMax) · Carpenter |
Learn more
Values are typical and for comparison only, and depend strongly on condition and diameter. For design, rely on the standard and on the mill certificate. Sources: SAE J403 and J404, ASTM A29, A322 and A519 (composition), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026