Z2NKDT18-10-5 is a maraging steel — its strength has nothing to do with carbon content and everything to do with a two-step transformation. Cooling from solution-annealing temperature produces a soft, low-carbon nickel martensite (with carbon held below roughly 0.03%, this "martensite" is nothing like the hard, brittle martensite in a conventional tool steel). A subsequent aging treatment at a moderate temperature then precipitates fine intermetallic compounds — built around the alloy's cobalt, molybdenum, and titanium content — through that soft matrix, and that precipitation is what develops the steel's full strength.

With roughly 18% nickel, 9-10% cobalt, and about 5% molybdenum plus a small titanium addition, 1.2709 sits in the same high-strength maraging family as grades like 18Ni-300, and it is prized in mold and die work for the same reasons that family is used in aerospace: very high strength combined with genuine fracture toughness, excellent dimensional stability through heat treatment (there's little of the distortion risk that comes with quench-hardening a conventional tool steel), and good weldability. That combination makes it a mainstay for injection mold cavities and cores, die-casting dies for light metals, and cold-extrusion tooling, where a mold needs to hold tight dimensional tolerance through hardening and then run for a long service life under repeated thermal and mechanical cycling.

Like every maraging grade, 1.2709 has two very different personalities depending on which side of the aging treatment you're cutting it on. In the solution-annealed (unaged) condition — typically in the low-to-mid 30s HRC — the low-carbon nickel martensite machines comparably to a moderately hard alloy steel. Because the strengthening precipitates haven't formed yet, there's no carbide network to fight, and standard carbide tooling handles roughing and semi-finish work without much drama. This is the condition in which the overwhelming majority of material removal takes place, since molds and dies are almost always machined close to final form before the aging cycle.

After aging, hardness climbs into the 50-54 HRC range and cutting forces increase substantially, but because the strengthening mechanism is fine intermetallic precipitation rather than a coarse, abrasive carbide network, aged maraging steel is noticeably less punishing on tooling than a conventional tool steel hardened to the same HRC. Even so, post-aging machining is typically limited to light finishing, EDM, or grinding rather than significant stock removal — the cutting parameters below apply to the solution-annealed condition in which this material is normally machined.