Maraging steels are 18% nickel martensites strengthened not by carbon but by the precipitation of nickel-molybdenum and nickel-titanium intermetallics during a low-temperature ageing treatment — the name is a contraction of martensitic and ageing. Carbon is held below 0.03%, so the alloys harden right through without a quench, with no carburisation or decarburisation and almost no distortion. The grade number is the nominal aged yield strength in ksi: alloy 200 at 1380 MPa, alloy 250 at 1710 MPa, alloy 300 at 1972 MPa and alloy 350 at 2317 MPa, which places the top grade among the strongest commercially available steels of any kind. Strength is bought with ductility — reduction of area falls from 53% on alloy 250 to 28% on alloy 350 — so grade selection matters. Exotic Alloy manufactures all four as bolts, stud bolts, heavy hex nuts and custom CNC fasteners, machined soft and aged to final strength.
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These alloys contain no chromium whatsoever. Strength comes from intermetallic precipitation in an iron-nickel martensite, not from a passive film, so in damp air or any aqueous service a maraging fastener corrodes much like a low-alloy steel. General corrosion resistance is better than a common tool steel and the surface rusts evenly rather than pitting deeply, but cadmium, zinc, nickel or dry-film coating is required for exposed service — passivation is not an option because there is nothing to passivate. Because every grade here is a high-strength steel, electroplated fasteners must be given a hydrogen-relief bake after plating per ASTM B850 or AMS 2759/9. If you need the strength and corrosion resistance, ask us about the precipitation-hardening stainless grades instead.
The whole appeal of maraging steel to a fastener manufacturer is that you machine it soft and harden it without moving it. Material arrives solution annealed at 30–35 HRC, where it cuts about as readily as 4340 at the same hardness, so Exotic Alloy completes all turning, milling and thread rolling in that condition. Ageing at roughly 480°C then develops the full strength with a uniform, predictable linear contraction of only 0.05–0.10% — no quench, no distortion, no section-size effect and, because the alloys are essentially carbon-free, no protective atmosphere and no decarburised skin. The contraction is simply allowed for in the machined size.
The grade number is the nominal aged yield strength in ksi. Cobalt and titanium rise with strength; ductility falls.
| Grade | UNS | AMS Spec | Nominal Co / Mo / Ti | Aged Yield (Min) | Aged Hardness | Reduction of Area |
|---|---|---|---|---|---|---|
| Maraging 200 | K92810 | AMS 6520 | 8.5% / 3.3% / 0.2% | 1380 MPa (200 ksi) | 44–48 HRC | Highest toughness |
| Maraging 250 | K92890 | AMS 6512 | 7.5% / 4.8% / 0.4% | 1710 MPa (248 ksi) | 48–52 HRC | 53% min |
| Maraging 300 | K93120 | AMS 6514 | 9.0% / 4.8% / 0.6% | 1972 MPa (286 ksi) | 50–55 HRC | 46% min |
| Maraging 350 | K93160 | AMS 6515 | 12.0% / 4.8% / 1.4% | 2317 MPa (336 ksi) | 55–60 HRC | 28% min |
MIL-S-46850D previously covered all four grades. It was cancelled on 1 July 2024 and superseded by the corresponding SAE AMS specifications — confirm at order stage which document your drawing calls up.
We are committed to delivering zero-defect maraging steel fasteners. All products undergo rigorous testing including PMI (Positive Material Identification), post-age hardness and tensile verification, hydrogen-relief baking after plating, dimensional inspection, and material traceability with EN 10204 3.1 certification.
Exotic Alloy exports maraging steel fasteners to aerospace, defence, motorsport and precision tooling clients worldwide. Our dedicated logistics team ensures secure export packaging and timely deliveries by sea and air freight with full customs documentation support.