C45/ 1.0503 / 1045

C45 is the benchmark unalloyed quenched-and-tempered steel: free of alloying elements it stays economical, while its medium carbon content responds clearly to quenching. Hardenability is limited compared to alloy steels — in large sections only the zone near the surface hardens; where full-section strength is needed, 42CrMo4 is the better choice. Naming causes frequent confusion: CK45 is the old DIN 17200 designation; its current successor is C45E (1.1191) with tighter phosphorus and sulphur limits, while C45R (1.1201) is the resulphurized machining variant. Mechanical values are identical for all three. Typical heat treatment: quenching from 820–860 °C (water/polymer) and tempering at 550–660 °C; delivery conditions are +A (annealed, ≤ 207 HB), +N (normalized) or +QT. Flame or induction hardening achieves 54–58 HRC at the surface — the classic solution for ways, pins and shaft journals. Weldability is moderate: thin sections weld without issues, thick sections call for 150–250 °C preheat. Aktif Çelik supplies C45 as hot rolled round, square and flat bars and as bright bars in h9/h11 tolerance, with EN 10204 3.1 certification.