C45 steel (1.0503): properties, composition, equivalents
C45 (1.0503) is the 0.45 % carbon steel of EN 10083-2: 305 MPa yield normalized, 490–800 MPa tensile Q&T up to 16 mm. Composition, heat treatment, hardness, 1045/S45C/45# equivalents.
What is C45?
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.
C45 chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | 0.42 – 0.5 | |
| Si | ≤ 0.4 | |
| Mn | 0.5 – 0.8 | |
| P | ≤ 0.045 | C45E (1.1191): P ≤ 0.030, S ≤ 0.035; C45R (1.1201): S 0.020–0.040 for machinability |
| S | ≤ 0.045 | |
| Cr | ≤ 0.4 | Cr + Mo + Ni ≤ 0.63 % |
| Mo | ≤ 0.1 | |
| Ni | ≤ 0.4 |
EN 10083-2:2006 Table 3. C45 is the base quality; C45E is the fine-grain, low-P version (former Ck45); C45R has controlled sulphur.
C45 mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| +N normalized, ≤ 16 mm | 340 (49.3) | ≥ 620 (≥ 89.9) | 14 | ≤ 207 HB (+A) |
| +N normalized, 16–100 mm | 305 (44.2) | ≥ 580 (≥ 84.1) | 16 | — |
| +N normalized, 100–250 mm | 275 (39.9) | ≥ 560 (≥ 81.2) | 16 | — |
| +QT quenched & tempered, ≤ 16 mm | 490 (71.1) | 700–850 (101.5–123.3) | 14 | ≈ 210–250 HB |
| +QT, 16–40 mm | 430 (62.4) | 650–800 (94.3–116.0) | 16 | — |
| +QT, 40–100 mm | 370 (53.7) | 630–780 (91.4–113.1) | 17 | — |
EN 10083-2 Tables 5 and 6. Q&T values apply to the ruling section given; C45 has low hardenability, so through-hardening is only achieved below ~20 mm.
Impact toughness
C45 requires a minimum Charpy V-notch energy of 25 J at 20 °C (+QT, ≤ 16 mm, longitudinal, C45E only). Plain C45 has no impact requirement; C45E guarantees 25 J at room temperature in the Q&T condition.
C45 equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| 1045 | AISI / SAE | Identical | AISI/SAE 1045 (UNS G10450): C 0.43–0.50, Mn 0.60–0.90 — same carbon window; C45 additionally caps Cr/Mo/Ni. Interchangeable in practice. |
| 45 | GOST (Russia/CIS) | Identical | GOST 1050 Steel 45: C 0.42–0.50, Mn 0.50–0.80, Si 0.17–0.37. |
| S45C | JIS (Japan) | Identical | JIS G4051 S45C: C 0.42–0.48, Mn 0.60–0.90; matches C45 within rounding. |
| 080M46 | BS (superseded British) | Near | BS 970 080M46: C 0.42–0.50, Mn 0.60–1.00 — slightly wider Mn. |
| C45E | EN (European) | Near | Same grade with P ≤ 0.030 and guaranteed impact; order C45E when toughness or fine grain matters. |
| 42CrMo4 | EN (European) | Functional | Alloyed alternative with far higher hardenability for the same part geometry above 25 mm. |
Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for C45 →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| Ck45 | DIN 17200 (withdrawn 1987) | Ck45 = today's C45E (1.1191). Still the most-used name in German-speaking workshops. |
| C45 (1.0503) | DIN 17200 | Base quality, number unchanged. |
| 080M46 | BS 970 (withdrawn) | |
| XC45 / XC48 | NF A 35-552 | |
| C45 / C46 | UNI 7845 |
Product forms and tolerance standards
Product forms: round, square and flat bar (hot-rolled, peeled, cold-drawn), plate and wide flat, forgings, seamless tube (EN 10297), wire rod.
Dimensional tolerances: hot-rolled round bar: EN 10060; bright bar: EN 10278 (h9–h11); plate: EN 10029.
Key property values
C45 yield strength
Normalized (+N): ≥ 340 MPa ≤ 16 mm, ≥ 305 MPa 16–100 mm. Quenched and tempered (+QT): ≥ 490 MPa ≤ 16 mm, 430 MPa 16–40 mm, 370 MPa 40–100 mm.
C45 tensile strength
+N: ≥ 620 MPa (≤ 16 mm) / ≥ 580 MPa (16–100 mm). +QT: 700–850 MPa (≤ 16 mm), 650–800 MPa (16–40 mm), 630–780 MPa (40–100 mm).
C45 hardness
Soft-annealed (+A) max 207 HB; normalized ≈ 170–210 HB; Q&T ≈ 210–250 HB (core, ≤ 16 mm). Surface hardening by induction or flame reaches 55–58 HRC; through-hardened thin sections quenched in water reach 58–60 HRC before tempering.
Heat treatment temperatures
Normalize 840–880 °C air; soft anneal 650–700 °C; harden 820–860 °C water (or oil for thin, simple shapes); temper 550–660 °C for Q&T, 150–200 °C after surface hardening. Ac1 ≈ 725 °C, Ac3 ≈ 785 °C, Ms ≈ 340 °C.
Physical properties
Density 7.85 g/cm³, E = 210 GPa, thermal conductivity ≈ 45 W/m·K, expansion 11.5 × 10⁻⁶/K (20–100 °C).
Weldability
Weldability is limited: with CEV ≈ 0.55–0.65 % C45 hardens in the heat-affected zone and cracks without precautions. Preheat 200–300 °C, use low-hydrogen basic electrodes, and temper or stress-relieve at 550–650 °C after welding. Where possible weld in the normalized (not Q&T) condition and heat-treat afterwards. Avoid welding surface-hardened areas.
Machining, forming and heat treatment
Machinability index about 55–60 % (annealed/normalized) relative to 1212; C45R with 0.02–0.04 % S improves chip breaking. Machine before hardening wherever possible; Q&T at 250 HB is still machinable with carbide. Cold forming is limited to gentle bends in the annealed state; hot forming 1100–850 °C followed by normalizing. Induction and flame hardening are the main surface treatments; nitriding is possible but shallow.
Typical applications
- Shafts, axles and spindles up to ~60 mm diameter
- Gears and sprockets with induction-hardened teeth
- Pins, bolts (property class 8.8 after Q&T), studs and keys
- Hydraulic cylinder rods (chrome-plated C45E)
- Machine components, couplings, rollers, rams
- Hand tools, hammers and agricultural wear parts (flame-hardened)
C45 compared with related grades
Frequently asked questions
Is C45 the same as 1045?
Yes. C45 (EN 10083-2) and AISI/SAE 1045 have the same carbon window (0.42–0.50 %) and near-identical Mn; mills routinely dual-certify. C45E is the cleaner version (P ≤ 0.030 %, guaranteed impact).
What is the difference between C45 and C45E?
C45E (1.1191, formerly Ck45) has P ≤ 0.030 % and S ≤ 0.035 %, fine-grain practice and a guaranteed 25 J impact in the Q&T condition. C45 (1.0503) allows P and S up to 0.045 % and has no impact requirement.
How hard can C45 get?
Surface: 55–58 HRC after induction or flame hardening. Through-hardened: 58–60 HRC as-quenched in thin sections (≤ 15–20 mm water quench), falling quickly in thicker bars because hardenability is low. Typical Q&T core hardness is 210–250 HB.
Can C45 be welded?
Only with preheat (200–300 °C), low-hydrogen consumables and post-weld tempering. For welded assemblies designers usually choose S355J2 for the structure and C45 only for the machined part, joined mechanically.
What is C45 equivalent to in China and Japan?
GB/T 699 grade 45 (45#) and JIS G4051 S45C are both identical in composition.
Related grades
Verified against EN 10083-2:2006; EN 10083-2:2006 Tables 3, 5 and 6; EN 10083-1:2006 (delivery conditions). Last checked: September 2026.