2515 is a historic low-carbon, high-nickel carburizing steel from the old SAE 25xx series, equivalent to Wnr. 1.5680 / DIN 12Ni19 (also seen as X12Ni5) / AFNOR Z18N5. Its defining feature is a large nickel addition — roughly 4.75-5.25% — with essentially no chromium or molybdenum, which was the standard approach before Cr-Ni-Mo grades became common: nickel alone was relied on to deliver core toughness and, notably, good low-temperature (cryogenic) impact resistance in the carburized and hardened part.

2515 is supplied and machined in the annealed or normalized condition, then carburized and case-hardened to produce a wear-resistant surface over a nickel-toughened core. It was historically specified for gears, pins, and shafts in equipment that had to retain toughness in cold service environments. Most new designs have moved to modern Cr-Ni-Mo case-hardening grades, but 2515 still appears on legacy drawings and in spare-parts work for older equipment.

In its annealed or normalized condition, 2515 is one of the softer and more machinable steels in this alloy family — low carbon and the absence of chromium or molybdenum carbides keep cutting forces modest and tool wear low. The high nickel content can introduce some gumminess and a tendency toward built-up edge at low cutting speeds, similar to other nickel-alloyed steels, but overall it cuts easily compared with the Cr-Mo and Cr-Ni-Mo grades in this family.

As a carburizing steel, 2515 is machined to final dimensions in the soft, annealed state before case hardening. All the cutting work — turning, milling, drilling, gear cutting — happens before the carburize-and-harden cycle; post-treatment work is limited to grinding the hardened case.

A sharp, positive-rake coated carbide edge run at adequate cutting speed avoids the built-up-edge tendency that nickel steels can show at low speeds. Chip control is generally good, and tool life is typically strong given the low alloy carbide content in this grade.