Material number 1.0503: C45
1.0503 is the European material number (Werkstoffnummer, EN 10027-2) for C45, medium-carbon steel for quenching and tempering specified in EN 10083-2.
What 1.0503 means
EN 10027-2 material numbers have the form 1.XXYY: the leading 1 is steel; the next two digits give the steel group (05 → steels 0.25–0.55 % C or Rm 500–700 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 1.0503 has stayed constant while the symbolic name moved from Ck45 to C45.
C45 at a glance
C45 is the medium-carbon steel everybody has in the rack: 0.42–0.50 % carbon, no deliberate alloying, Werkstoff number 1.0503, specified in EN 10083-2 for quenching and tempering. Supplied normalized it gives 305–340 MPa yield and ~600 MPa tensile; quenched in water and tempered it reaches 490 MPa yield and 700–850 MPa tensile in sections up to 16 mm, and it can be induction- or flame-hardened to 55–58 HRC on the surface.
The catch is hardenability: with no Cr or Mo, C45 through-hardens only in thin sections (roughly 15–20 mm in water). Above that the core stays pearlitic and designers move to 42CrMo4. That trade-off — cheap, machinable, surface-hardenable, but shallow — defines where C45 is used: shafts, pins, gears with induction-hardened teeth, keys, bolts and machine parts of moderate size.
C45E (1.1191, the old Ck45) is the same chemistry with lower phosphorus and a guaranteed impact value; C45R (1.1201) adds controlled sulphur for machining. Internationally C45 is identical to AISI 1045, JIS S45C and GB/GOST 45.
Full data sheet for C45 → · Equivalent grades →