18Ni300

18Ni300 is a precipitation-hardening maraging steel grade recognized for its combination of very high strength and toughness. The name indicates roughly 18 percent nickel content and a designation associated with the high-strength level achieved after aging.

Composition and microstructure are dominated by nickel, with small additions of elements such as cobalt, molybdenum, titanium, and aluminum to enable age hardening. The carbon content is kept very low to promote good weldability, toughness, and dimensional stability. The aging process produces intermetallic precipitates (notably Ni3Ti and Ni3Mo) that impart peak strength without compromising toughness.

Heat treatment typically involves a solution heat treatment around 800–860°C to dissolve precipitates, followed by quenching or air cooling. The material is then aged at approximately 480–500°C for several hours to precipitate strengthening phases. This aging yields very high strength, commonly described as around 300 ksi (approximately 2 GPa) in tensile strength after peak aging, with excellent toughness and good dimensional stability.

Properties of 18Ni300 include high strength, good fatigue resistance, and relatively good machinability compared with other high-strength steels. Its low carbon content contributes to good weldability, though post-weld aging is often required to regain full properties after welding.

Applications are concentrated in aerospace tooling, forming dies, molds, and other components requiring high strength and toughness, such as rocket motor casings, gears, and high-performance fasteners. It remains a favored choice where a combination of high strength, toughness, and precision is essential.