Maraging steel

Composition and microstructure

Maraging steels contain very low carbon and relatively high nickel content; other deliberate additions (Co, Mo, Ti, Al) promote the formation of nanoscale intermetallic precipitates during ageing. The as‑quenched structure is a soft, ductile martensite with few carbides. Controlled ageing converts this matrix into a precipitation‑strengthened martensite, with finely dispersed intermetallic particles that raise strength while preserving toughness and fracture resistance.

Heat treatment and mechanical properties

Typical processing includes solution annealing to produce a homogeneous austenite, rapid cooling to room temperature to form a low‑carbon martensite and subsequent ageing at moderate temperatures for a specified time to precipitate strengthening phases. The resulting condition combines very high tensile and yield strengths with good toughness, predictable dimensional stability and often superior fatigue behavior compared with many conventional high‑strength steels. Low carbon content reduces the tendency to quench cracking and improves weldability.

Manufacturing, welding and additive techniques

Maraging steels are amenable to conventional forming and machining when soft (solution‑annealed) and then strengthened by ageing after final machining or fabrication. Welding is generally easier than for high‑carbon martensitic steels because of the low carbon level, but the weld and heat‑affected zone can alter local precipitation and may require post‑weld heat treatment or re‑ageing. In recent years maraging alloys have been used successfully with laser‑based additive manufacturing; parts are frequently aged after printing to achieve final properties.

Corrosion, surface treatment and joining

Most maraging steels are not stainless and have only moderate corrosion resistance unless specifically alloyed or surface treated. Protective coatings, platings or passivation processes are commonly applied when corrosion resistance is required. Their combination of high strength and good toughness makes joining by welding, brazing or mechanical fastening feasible, but careful control of thermal cycles and post‑heat treatment is important to retain designed properties.

Grades, history and naming

Common commercial grades are often identified by nominal nickel content and legacy strength numbers (for example, names such as 18Ni‑300 appear in literature and product data). Maraging steels were developed in the mid‑20th century as an alternative route to very high strength without heavy reliance on carbon hardening; their development opened new possibilities for precision, high‑performance components.

Applications

Because of their unusual combination of strength, toughness and dimensional stability, maraging steels are used in aerospace and rocketry, high‑performance tooling and dies, shafts and fittings, precision machine components, and some demanding sporting and racing applications. They are also chosen where predictable ageing behavior and tight tolerances are required, including parts produced by additive manufacturing followed by post‑processing.

Advantages and limitations

• Advantages: very high achievable strength with retained toughness, good dimensional stability, improved weldability relative to high‑carbon martensitic steels, tunable properties by composition and heat treatment.
• Limitations: higher material cost because of nickel and cobalt content, moderate corrosion resistance unless treated, and a requirement for precise thermal processing to obtain intended performance.