M50NiL is a variant of M50, a specialized, high performance steel often used in the aerospace sector. Both of these materials perform admirably in critical, high-speed, elevated temperature applications where grades like 52100 or 440C may fall short.
But how do you choose between M50NiL and M50? In this article, Sullivan partner consultant and owner of Bearing Consultants LLC, John Normandin, helps us explain the different uses and benefits of these two steels. Read on to learn what to consider when choosing M50NiL or M50.
Carburizable M50NiL vs. Through-Hardened M50
M50NiL (AMS 6278) is a low-carbon, high-nickel variant of M50 (AMS 6491, AMS 6490). Both grades are premium alloy steels with a high degree of cleanliness and excellent resistance to multi-axial stresses and softening at high service temperatures.
While M50 and M50NiL are common to aerospace applications (and may be useful in high-speed motorsports), their main distinction lies in their hardening methods: M50 is a through-hardened steel, whereas M50NiL is carburizable.
“The advantage of carburization is you get a hard surface plus a ductile core, which is like the supporting structure. In very high-speed applications that’s really critical,” says John.
| M50 Chemical Composition | ||||||||||||
| C | Mn | Si | P | S | CR | Ni | Mo | Cu | V | Co | W | |
| min. | 0.11 | 0.15 | 0.1 | -- | -- | 4 | 3.2 | 4 | -- | 1.13 | -- | -- |
| max. | 0.15 | 0.35 | 0.25 | 0.015 | 0.01 | 4.25 | 3.6 | 4.5 | 0.1 | 1.33 | 0.25 | 0.15 |
| M50NiL Chemical Composition | ||||||||||||
| C | Cr | Si | Ni | V | W | Mn | Mo | S | P | Co | Cu | |
| min. | 0.8 | 4 | -- | -- | 0.9 | -- | 0.15 | 4 | -- | -- | -- | -- |
| max. | 0.85 | 4.25 | 0.25 | 0.15 | 1.1 | 0.25 | 0.35 | 4.5 | 0.008 | 0.015 | 0.25 | 0.1 |
A through-hardened M50 component has a uniform hardness throughout, whereas carburizing M50NiL gives it a hard surface layer with a softer core. This makes it good for components with complex cross-sections with stress risers or applications where preventing crack propagation is crucial, like in jet engines. Both M50 and its NiL variant perform well in high-heat environments.
Aerospace Applications & Considerations for M50NiL vs. M50
In demanding environments, critical components face complex challenges. Designers carefully evaluate materials to satisfy performance, reliability, and safety requirements. M50 and M50NiL may be good candidates for pushing performance boundaries.
As John puts it, “Engineers in aerospace design to operating conditions, temperature, and environment. They have a whole system built up and it’s got to last so many cycles or so many flights. Materials must work to that life goal.”
Elevated Temperature Environments
While 52100 is a versatile steel with high hardness and abrasion resistance, it begins to lose hardness at temperatures around 350°F (176°C). M50 steel and M50NiL perform well in aerospace applications up to 600oF (316oC) for components such as bearings, gears, etc.
Extending Fatigue Life
Both M50 (when used in demanding aerospace applications) and M50NiL are produced using a VIM-VAR remelting process. This ensures a high level of cleanliness, extending fatigue life compared to conventional bearing steels (like 52100 or 440C). M50 and M50NiL are worth considering if fatigue resistance is a priority.
Preventing Crack Propagation
An advantage of carburizing M50NiL, as with any carburizing steel, is increased ductility. When a crack initiates in a through-hardened steel like M50, it continues into a component’s core. For carburized M50NiL, when a crack begins on the hard surface, the metal’s ductile core can prevent it from continuing deeper.
Corrosion Resistance Requirements
It’s worth noting that M50 and M50NiL, like 52100, are not corrosion-resistant steels. They are excellent for components in gear boxes, compressors, or other enclosed or encapsulated systems. Premium grades like XD15NW are recommended when high hardness, fatigue resistance, and corrosion resistance are paramount. And, look to XD16N if your application is in an elevated-temperature environment.
Get Personalized Recommendations for Choosing M50NiL or M50
Sullivan Steels stocks specialty steels, including M50, M50NiL, as well as corrosion-resistant XD15NW and XD16N. If your requirements include high fatigue strength at elevated temperatures, our experts on staff can guide you through the process of choosing a grade to match your application. Start a Live Chat or contact us to get started!