Marval 18 is a French (Aubert & Duval) commercial designation for an 18% nickel maraging steel. Its composition - roughly 18% nickel, 8.5% cobalt, 5% molybdenum, 0.5% titanium, and a very low carbon content - places it squarely within the standard 18Ni(250) maraging grade family, the same composition class as the maraging-C250 material already covered elsewhere in this reference library. Like other maraging steels, its strength does not come from carbon and quench hardening the way conventional tool and alloy steels work; instead, the alloy is solution-annealed to a soft, easily machined martensitic condition, then aged at a relatively low temperature (typically around 480-500°C) to precipitate intermetallic compounds - primarily Ni3Mo and related phases - that raise tensile strength dramatically, into the 1700 N/mm² (250 ksi) class, without significant dimensional distortion.

That sequence - machine soft, then age to full strength - is what makes maraging steels attractive for precision aerospace and tooling components: rocket motor cases, landing gear parts, high-strength fasteners, and injection mold tooling that needs to hold tight tolerances through the hardening cycle. Marval 18 should be machined in the solution-annealed (pre-aged) condition wherever possible, exactly as with the maraging-C series grades.

In the solution-annealed (unaged) condition, Marval 18 machines similarly to a medium-strength alloy steel - noticeably easier than its final aged hardness would suggest, which is the entire point of the maraging process. Chip formation is generally manageable and the material does not work-harden as aggressively as an austenitic stainless, but its cobalt and molybdenum content still promote tool wear faster than a plain low-alloy steel of similar hardness, and its low carbon, nickel-rich matrix tends to produce long, stringy chips that need active chip control.

The critical rule with any maraging steel is sequencing: rough and finish machine in the soft, solution-annealed state whenever the process allows it, because cutting forces and tool wear both increase sharply once the part has been aged to its full 1700 N/mm² strength class. If material must be removed after aging, expect behavior closer to a hardened tool steel, with reduced speeds, more conservative feeds, and a harder carbide grade. Sharp, positive cutting edges and adequate coolant help control built-up edge and heat in either condition.