Material number 1.0401: C15
1.0401 is the European material number (Werkstoffnummer, EN 10027-2) for C15, unalloyed case-hardening steel specified in EN 10084.
What 1.0401 means
EN 10027-2 material numbers have the form 1.XXYY: the leading 1 is steel; the next two digits give the steel group (04 → steels 0.12–0.25 % C or Rm 400–500 MPa); 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 1.0401 has stayed constant while the symbolic name moved from Ck15 to C15.
C15 at a glance
C15 is the simplest case-hardening steel: 0.12–0.18 % carbon, no alloying, Werkstoff number 1.0401 for the base quality and 1.1141 for C15E (the old Ck15, with lower phosphorus and fine-grain practice) — both in EN 10084. Carburizing puts 0.7–0.9 % carbon into the surface, which quenches to 55–62 HRC over a soft, tough core of about 500–600 MPa. Hardenability is very low, so the hard case is thin and the part must be small: pins, bushes, small gears, rollers, levers and cold-headed fasteners.
C15 also serves outside case hardening as a general low-carbon engineering bar — the European version of AISI 1015/1018 — for machined parts, welded fittings and cold-drawn shafting where a bright, dimensionally accurate bar is needed and strength is not critical. Cold drawing raises its yield to around 450 MPa.
AISI 1015, JIS S15C and GB/GOST 15 are identical in composition; 1018 is the near match most US warehouses supply. For larger case-hardened parts the step up is 16MnCr5.
Full data sheet for C15 → · Equivalent grades →