Maraging 300 and Maraging 350 are the top two steps of the carbon-free age-hardening steels. In both, carbon is max 0.03%; the strength comes not from carbon but from the intermetallic precipitates formed during ageing at 480–510 °C.
The number in the grade name states the nominal tensile strength in ksi: 300 ksi and 350 ksi.
Cobalt and titanium up
According to our datasheets, nickel is at the same level in both grades: 18.0–19.0% in Maraging 300 and 18.5% (nominal) in Maraging 350. Molybdenum is similar as well (4.60–5.20% against 4.8% nominal).
The difference comes down to two elements. Cobalt rises from 8.00–9.50% to 12.0%. Titanium rises from 0.55–0.80% to 1.40% — roughly double.
Titanium is the direct source of the Ni₃Ti precipitates formed during ageing; the higher its content, the denser the precipitates and therefore the higher the strength. Cobalt lowers the solubility of molybdenum and so makes more Ni₃Mo precipitation possible — that is, it does not form precipitates itself but supports the formation of the others.
The result is visible in the figures on our datasheet: after ageing, Maraging 350 reaches 2415 MPa (350 ksi) tensile and 2275 MPa (330 ksi) yield strength, with a hardness of 55–60 HRC. The price is ductility: elongation is at 8% (4D).
Comparison in numbers
| PROPERTY | Maraging 300 | Maraging 350 |
|---|---|---|
| Nickel (Ni) | 18.0 – 19.0% | 18.5% (nominal) |
| Cobalt (Co) | 8.00 – 9.50% | 12.0% (nominal) |
| Molybdenum (Mo) | 4.60 – 5.20% | 4.8% (nominal) |
| Titanium (Ti) | 0.55 – 0.80% | 1.40% (nominal) |
| Aluminium (Al) | 0.05 – 0.15% | 0.05 – 0.15% |
| Carbon (C) | max 0.03% | max 0.03% |
| Manganese (Mn) | max 0.10% | — |
| Silicon (Si) | max 0.10% | — |
| Solution annealing | — | 820 – 860 °C |
| Ageing | — | 480 – 510 °C |
| Tensile strength Rm | — | 2415 MPa (350 ksi) |
| Yield strength Rp0.2 | — | 2275 MPa (330 ksi) |
| Hardness | — | 55 – 60 HRC |
| Elongation | — | 8% (4D) |
| Density | 8000 kg/m³ | — |
| UNS | K93120 | — |
| W.Nr (DIN/EN) | 1.6358 · 1.6354 | — |
| AMS | 6514 · 6521 | 6515 |
Values are taken from our product datasheets. Mechanical values are not given on our Maraging 300 datasheet, so those cells are left blank; certified values are shared at the order stage.
Which one, and when?
Maraging 300 is sufficient — aerospace fasteners, rocket motor casings, highly stressed shafts, forging and injection dies, actuator parts. The strength-to-toughness balance is at its best point in this class and it is easier to source. If the specification calls out AMS 6514 or AMS 6521, this is the grade being asked for.
Maraging 350 is required — parts where strength is the absolute priority and the section has to be reduced: racing and aerospace shafts, special die cores, high-performance fasteners. If the specification calls out AMS 6515, 300 is not an acceptable substitute.
Note: the fracture toughness of the 350 class is lower than that of 300. In parts where crack tolerance is critical, the gain in strength is not always the right trade-off.
The other members of the family
For the step below, see our Maraging 250 – 300 comparison; for a carbon-bearing alternative in the same strength class, our 300M – AerMet 100 article.
Technical datasheets
Maraging 300 — chemical composition, mechanical values, standard equivalents
Maraging 350 — chemical composition, mechanical values, standard equivalents
Both grades are supplied to order in round bar, flat bar, plate, sheet, pipe and forged forms. Contact us for a quotation.