Maraging 250 and Maraging 300 belong to a family that is completely different from conventional steels. In both, carbon is at max 0.03% — that is, they do not take their strength from carbon. The structure forms as a soft martensite containing 17–19% nickel; hardness is gained later, during the ageing treatment carried out at around 480 °C, through the fine precipitates formed by molybdenum and titanium.
The practical consequence is this: the material machines easily in the annealed condition, the part is aged after it has been finished, and dimensional change during that stage stays very low. There is no quench cracking risk. That is why these grades are preferred for tooling, shafts, aircraft fasteners and rocket casings.
What makes the difference: cobalt and titanium
The nickel and molybdenum contents of the two grades are almost identical. The difference comes down to two elements: cobalt rises from 7.0–8.5% to 8.0–9.5%, and titanium from 0.3–0.5% to 0.55–0.80%. Titanium is the main source of the precipitates formed during ageing; the higher its content, the higher the strength obtained. Cobalt supports the precipitation behaviour of molybdenum.
The number in the grade name states the nominal yield strength in ksi. Accordingly, our datasheet gives the yield strength of Maraging 250 after ageing as min 1724 MPa (250 ksi).
Comparison in numbers
| PROPERTY | Maraging 250 | Maraging 300 |
|---|---|---|
| Carbon (C) | max 0.03% | max 0.03% |
| Nickel (Ni) | 17.0 – 19.0% | 18.0 – 19.0% |
| Cobalt (Co) | 7.0 – 8.5% | 8.00 – 9.50% |
| Molybdenum (Mo) | 4.6 – 5.2% | 4.60 – 5.20% |
| Titanium (Ti) | 0.3 – 0.5% | 0.55 – 0.80% |
| Aluminium (Al) | 0.05 – 0.15% | 0.05 – 0.15% |
| Tensile strength Rm | min 1758 MPa (255 ksi) | — |
| Yield strength Rp0.2 | min 1724 MPa (250 ksi) | — |
| Elongation (4D) | min 6% | — |
| Hardness | ≥ 48 HRC | — |
| Density | — | 8000 kg/m³ |
| UNS | K92890 | K93120 |
| W.Nr (DIN/EN) | 1.6359 | 1.6358 · 1.6354 |
| AMS | 6512 | 6514 · 6521 |
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 for the required heat treatment condition are shared at the order stage.
Which one, and when?
Maraging 250 is sufficient — injection and forging dies, die cores, medium-duty actuator shafts, tooling parts where dimensional stability is critical. If the specification calls out AMS 6512, this is the grade being asked for.
Maraging 300 is required — aerospace fasteners, rocket motor casings and highly stressed shafts where a higher strength class is wanted. If the specification calls out AMS 6514 or AMS 6521, 250 is not an acceptable substitute.
The top of the family
For higher strength there is Maraging 350. If you are looking for a carbon-bearing alternative in the same strength class, AerMet 100 and 300M come into play; our comparison of those two is here.
Technical datasheets
Maraging 250 — chemical composition, mechanical values, standard equivalents
Maraging 300 — 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.