Durimphy is a French trade name for an 18% nickel maraging steel, DIN designation X2NiCoMoTi18-9-5 (WNr 1.6358). It sits in the same maraging family already documented on this site under Maraging C300 and related C/T-series pages, and shares essentially the same 18Ni-9Co-5Mo-Ti chemistry and two-step processing logic: solution annealing produces a soft, low-carbon nickel martensite, and a subsequent aging treatment precipitates fine intermetallic compounds that develop the alloy's full strength. Despite appearing in this library's cobalt-superalloy-heavy batch, Durimphy is a maraging steel, not a cobalt-base superalloy - the cobalt content here is a strengthening addition within an iron-nickel martensite, not the base metal.

Solution-annealed and aged, Durimphy reaches roughly 2,000 N/mm2 (about 290 ksi) tensile strength, matching the performance class of the 18Ni-300 (C300) maraging grade. That combination of very high strength with good fracture toughness, dimensional stability through heat treatment, and good weldability is what makes this alloy family a standard choice for aerospace structural components, high-performance tooling, and precision die and mold work.

Durimphy follows the same split-personality machinability as the rest of the maraging family, and this is an important distinction from the cast cobalt superalloys elsewhere in this reference: in the solution-annealed (unaged) condition - typically in the low-to-mid 30s HRC - the low-carbon nickel martensite machines reasonably well with standard carbide tooling, comparable to a moderately hard alloy steel. Nearly all rough and semi-finish machining is done in this condition, before the part is aged to develop its full strength.

Once aged, Durimphy climbs to roughly the same hardness class as Maraging C300 - on the order of 54-56 HRC - and machining becomes considerably more demanding. Cutting forces and tool wear increase sharply, and post-aging work is generally limited to grinding, EDM, or very light precision cuts rather than significant stock removal. Because the strengthening mechanism is fine intermetallic precipitation rather than a coarse carbide network (unlike the cobalt superalloys machined elsewhere in this library), aged Durimphy is less abrasive than an equally hard tool steel, but the combination of high hardness and high toughness still narrows the practical machining window considerably. The speeds below reflect the solution-annealed condition, which is how this material is normally machined before final aging.