Material number 1.2379: 1.2379
1.2379 is the European material number (Werkstoffnummer, EN 10027-2) for 1.2379, cold-work tool steel, 12 % Cr ledeburitic specified in EN ISO 4957.
What 1.2379 means
EN 10027-2 material numbers have the form 1.XXYY: the leading 1 is steel; the next two digits give the steel group (23 → Cr-Mo-V cold-work tool steels); the last two digits are a sequential number within that group. The number is unique to one composition and survives name changes, which is why 1.2379 has stayed constant while the symbolic name moved from X155CrVMo12-1 to 1.2379.
1.2379 at a glance
1.2379 (X153CrMoV12) is the ledeburitic 12 % chromium cold-work steel known everywhere as D2. With 1.5 % carbon and 12 % chromium it solidifies with a network of hard chromium carbides (M₇C₃) that, after hardening to 58–62 HRC, give the best wear resistance of any conventional tool steel below the powder-metallurgy grades. Molybdenum and vanadium refine the carbides and allow air or vacuum hardening with minimal distortion — the reason 1.2379 is the default steel for blanking and punching dies, shear blades and forming rolls.
Its weaknesses are the ones that come with coarse carbides: moderate toughness, difficult grinding, and heavy machining allowances in the annealed state (≤ 255 HB but abrasive). Tempering at 500–530 °C gives secondary hardening and allows PVD coating (TiN, TiCN) without losing hardness; the low-temperature temper (180–220 °C) gives maximum hardness for short-run tools.
AISI D2, JIS SKD11, GB Cr12Mo1V1 and BS BD2 are the same steel; Böhler K110, Uddeholm Sverker 21 and Buderus Cryodur 2379 are proprietary versions. The powder-metallurgy alternatives (1.2380 / Vanadis 4E, K390) are cross-referenced as functional upgrades.
Full data sheet for 1.2379 → · Equivalent grades →