Nickel Maraging 300

Aging Procedure

Age at 900°F (482°C) for 3–6 hours (typically 3 hours minimum for standard sections; larger cross-sections should be aged for longer periods), followed by air cooling. This precipitation hardening treatment produces minimum tensile strength of ~290 ksi (2000 MPa), minimum yield strength of ~270 ksi (1862 MPa), and hardness of 52–54 HRC. For die casting tooling requiring overaged structure for thermal stability, aging at 980–1000°F (527–538°C) for 6 hours may be used.

Annealing Procedure

Anneal at 1500°F (816°C) for 1 hour per inch of cross-section thickness (minimum 1 hour), then air cool. For die casting applications, annealing at 1500–1525°F for 1 hour per inch of thickness after rough machining is typical. This restores the soft martensitic microstructure with a maximum hardness of 30–35 HRC.

Applications

Maraging 300 is used in high-strength structural applications requiring exceptional strength, toughness, and minimal distortion. Primary applications include: aerospace primary structures (landing gear beams, drag struts, side stays), missile and rocket motor casings, space launch vehicle structural rings and inter-stage adapters, aircraft and spacecraft main frames and wing spars, transmission shafts, torsion springs, driveshafts, load cells, gas centrifuge rotors for uranium enrichment, munitions, precision tooling and die casting dies, injection mold cores and inserts, precision punches, and autosport components.

Cold Workability

Due to its low carbon content and martensitic yet ductile annealed microstructure, Maraging 300 can be cold-rolled up to approximately 90% without cracking. Cold working in the annealed state is readily accomplished by conventional methods.

Corrosion Resistance

Maraging 300 is moderately corrosion-resistant as a non-stainless alloy. It exhibits resistance to stress corrosion cracking and hydrogen embrittlement, which enhances performance in harsh environments. Corrosion resistance can be improved by cadmium plating or phosphating. The alloy is not recommended for aggressive corrosive environments without protective surface treatment.

Forgeability

Maraging 300 can be forged using procedures similar to those for austenitic stainless steel Type 304. The alloy has good hot workability. Customized forgings are a standard product form for this alloy.

Formability

Maraging 300 can be readily formed by conventional methods in the annealed condition due to its good ductility (elongation ~16%, reduction of area ~70% when annealed). Due to its low carbon content, it can be cold-rolled up to 90% without cracking. Forming should be performed in the solution annealed condition prior to aging.

Heat Treatability

Maraging 300 cannot be hardened by conventional quench-and-temper heat treatment; hardening is achieved exclusively through the aging (precipitation hardening) process. No protective atmosphere is required during annealing or aging due to the essentially carbon-free composition.

Hot Workability

Maraging 300 can be hot worked using procedures similar to those for austenitic stainless steel (e.g., Type 304). Hot working should be conducted within appropriate temperature ranges. Age hardening begins when the alloy is exposed to elevated temperatures for extended times, so hot working schedules must be controlled accordingly.

Machinability

In the solution annealed condition (30–35 HRC), machinability of Maraging 300 is comparable to steels such as 4340 at equivalent hardness. Conventional machining is readily accomplished. After aging to full hardness, machining becomes significantly more demanding; rigid equipment, very sharp carbide tools, and an abundance of coolant are essential. The preferred practice is to machine components to near-final dimensions in the annealed state and then age, leveraging the negligible dimensional change during the aging treatment.

Other Comments

Maraging 300 is also known as VASCOMAX® C300, Maraging C300, Type 300, and Vdimor 300. DIN equivalent designations are Werkstoff Nr. 1.6358 and 1.6354. The alloy is a member of the 18Ni maraging steel family along with Maraging 200, 250, and 350 grades. Higher grades contain more cobalt and titanium. MIL-S-46850 was cancelled effective July 1, 2024, and each grade is now governed by separate SAE AMS specifications. The production, import, and export of maraging steels is closely monitored internationally due to suitability for gas centrifuges used in uranium enrichment. The material may also be surface-hardened by nitriding.

Other Physical Properties

Maraging 300 exhibits exceptional dimensional stability during both annealing and aging, with predictable uniform shrinkage of approximately 0.05% on all dimensions during the aging treatment. This near-zero distortion characteristic eliminates the need for post-heat-treatment machining and is a significant advantage over conventional high-strength steels. The alloy retains its strength up to approximately 840°F (450°C) and maintains good notch impact resistance down to -58°F (-50°C).

Principle Design Features

Maraging 300 (also known as VASCOMAX® C300, UNS K93120) is an ultra-high-strength, essentially carbon-free, 18% nickel, cobalt-strengthened maraging steel. It derives its strength not from carbon but from precipitation of intermetallic compounds (Ni3Mo, Ni3Ti, etc.) during a simple low-temperature aging treatment. The alloy is produced by double vacuum melting — Vacuum Induction Melting (VIM) followed by Vacuum Arc Remelting (VAR) — to provide low impurity levels and consistent properties. It is supplied in the solution annealed condition (maximum 35 HRC), enabling finish machining prior to final aging. A key advantage is near-zero distortion during aging: the uniform contraction of approximately 0.05% allows components to be machined to precise final tolerances before hardening. The alloy achieves a minimum tensile strength of ~290 ksi (2000 MPa) and yield strength of ~270 ksi (1862 MPa) after aging at 900°F (482°C).

Weldability

Maraging 300 has excellent weldability. It can be welded in both the annealed and aged conditions without preheating, using conventional welding methods (TIG, MIG, electron beam). Post-weld aging at 900°F (482°C) for a minimum of 3–6 hours, followed by air cooling, is required to restore full strength in the heat-affected zone. Because the alloy is essentially carbon-free, a protective atmosphere is not required during annealing or aging.