1. C45 Steel: Fundamental Characteristics and Properties
C45 (material number 1.0503) is a non-alloy quality quenched and tempered steel standardized by EN 10083-2, with a nominal carbon content of 0.45%. It is one of the most widely used medium-carbon steels in European mechanical engineering, thanks to its favorable balance of strength, machinability and cost. In the quenched and tempered condition (+QT) it achieves a tensile strength ranging, depending on diameter, between 630 and 850 MPa; in the normalized condition (+N) it shows a homogeneous ferritic-pearlitic structure and good machinability. Its hardenability is limited: through-hardening is effective only on small and medium sections (the standard specifies +QT properties up to 100 mm), while the material is well suited to induction or flame surface hardening (55-60 HRC).
Typical applications include shafts, pins, gears, connecting rods, hubs, tools and components subject to moderate static and dynamic stresses. For higher strength or hardenability requirements, alloy quenched and tempered steels such as 42CrMo4 or 39NiCrMo3 are used instead.
Reference standards: EN 10083-2 (non-alloy quenched and tempered steels) for composition and properties, together with EN 10083-1 for general delivery conditions; ISO 683-1 is the corresponding international reference; for cold-drawn, peeled and bright products EN 10277 applies; inspection certificates follow EN 10204. The EN designation C45 is the primary one; the AISI/SAE 1045, JIS S45C and former GOST 45 equivalences are indicative.
For formats, available diameters and quotations, see the dedicated C45 product page.
2. Chemical Composition of C45 Steel
The chemical composition of C45 is defined by EN 10083-2 based on cast (ladle) analysis. Since it is a non-alloy steel, chromium, molybdenum and nickel are permitted only as residual elements within limits that preserve its classification.
| C | Si | Mn | P max | S max | Cr max | Mo max | Ni max | Cr+Mo+Ni max |
|---|---|---|---|---|---|---|---|---|
| 0.42-0.50 | ≤ 0.40 | 0.50-0.80 | 0.045 | 0.045 | 0.40 | 0.10 | 0.40 | 0.63 |
Carbon (0.42-0.50%) governs the hardenability and hardness achievable after quenching. Silicon (≤ 0.40%) acts as a deoxidizer and contributes to strengthening through solid solution. Manganese (0.50-0.80%) increases hardenability, promotes a homogeneous martensite and binds residual sulfur as manganese sulfides, reducing its hot-embrittling effect. Phosphorus and sulfur are each limited to 0.045% to contain brittleness.
3. Mechanical Properties of C45 Steel
3.1. General Overview
Mechanical properties depend on the delivery condition and the reference diameter: standard values always refer to a defined test section, since the limited hardenability causes properties to decrease as the section size increases.
3.2. Properties in the Normalized Condition (+N)
| Diameter d [mm] | Rp0.2 min [MPa] | Rm min [MPa] | A min [%] |
|---|---|---|---|
| ≤ 16 | 340 | 620 | 14 |
| > 16-100 | 305 | 580 | 16 |
| > 100-250 | 275 | 560 | 16 |
In the normalized condition, Rm is expressed as a minimum value (not as a range). The ferritic-pearlitic structure ensures homogeneity and good machinability, making it ideal for semi-finished products to be quenched and tempered or for applications with moderate mechanical requirements.
3.3. Properties in the Quenched and Tempered Condition (+QT)
| Diameter d [mm] | Rp0.2 min [MPa] | Rm [MPa] | A min [%] | Z min [%] |
|---|---|---|---|---|
| ≤ 16 | 490 | 700-850 | 14 | 35 |
| > 16-40 | 430 | 650-800 | 16 | 40 |
| > 40-100 | 370 | 630-780 | 17 | 45 |
| > 100 | Not specified by the standard – subject to agreement (limited hardenability) | |||
EN 10083-2 defines the +QT properties of C45 up to a reference diameter of 100 mm. Beyond that, through-hardening is not guaranteed and the characteristics must be agreed between manufacturer and customer. Quenching and tempering produce a tempered martensite that optimizes the strength-toughness ratio for components subject to moderate to high dynamic stresses.
3.4. Hardness
| Condition | Hardness |
|---|---|
| Annealed +A (EN 10083-2) | ≤ 207 HBW |
| Treated for cold shearability +S (EN 10083-2) | ≤ 255 HBW |
| Quenched and tempered +QT (indicative, converted from Rm) | ≈ 185-250 HBW |
| Induction/flame surface hardening | 55-60 HRC |
4. Hardenability of C45 and Carbon Equivalent
The hardenability of C45 is intrinsically limited by the absence of alloying elements: standard C45 is not normally supplied with a guaranteed Jominy hardenability band (reserved for alloy grades in the +H version). In practice, through-hardening can only be achieved on small-diameter sections; as the section size increases, the core remains largely ferritic-pearlitic, which is why the standard specifies +QT properties only up to 100 mm. For surface hardening, on the other hand, the 0.45% carbon content is fully sufficient to reach 55-60 HRC.
For weldability purposes, the carbon equivalent CEV (IIW formula: C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15) is approximately ≈ 0.56 based on the nominal value, with increases as residual elements rise. Since CEV is well above 0.45, welding requires preheating and specific precautions. The actual cast value should be obtained from the analysis on the certificate (MTC, EN 10204).
5. Physical Characteristics of C45 Steel
The following values are indicative literature data (not standardized) and vary with temperature and metallurgical condition; they serve as a reference for thermal and dimensional calculations.
| Property | Indicative value |
|---|---|
| Density | ≈ 7.85 g/cm³ |
| Modulus of elasticity E | ≈ 210 GPa (20 °C); ≈ 205 GPa (100 °C); ≈ 185 GPa (300 °C) |
| Coefficient of linear expansion (20-100 °C) | ≈ 11-12 x10-6 K-1 |
| Thermal conductivity | ≈ 45-50 W/(m·K) |
| Specific heat | ≈ 460-490 J/(kg·K) |
C45 does not have a sharp melting point but a solidification range typical of carbon steels (melting onset indicatively 1420-1460 °C, to be confirmed from mill sources for critical calculations).
6. Heat Treatments of C45 Steel
| Treatment | Temperature and medium |
|---|---|
| Forging / hot rolling | 1100 → 850 °C |
| Normalizing (+N) | 840-880 °C, air cooling |
| Soft annealing (+A) | 680-710 °C, furnace cooling |
| Quenching (austenitizing) | 820-860 °C, water or oil cooling |
| Tempering | 550-660 °C, air cooling |
6.1. Quenching and Tempering
This is the primary treatment for C45. Quenching involves austenitizing at 820-860 °C and rapid cooling (water for the lower part of the range, oil for the upper part, depending on section size and cracking risk). Tempering at 550-660 °C controls the strength-toughness trade-off: higher temperatures favor ductility and toughness, lower temperatures favor strength.
For other steels in the same family, see the quenched and tempered steels page.
6.2. Normalizing and Annealing
Normalizing (840-880 °C, air) refines the grain and homogenizes the microstructure, either as a final condition for moderate requirements or as preparation for machining. Soft annealing (680-710 °C, furnace) lowers the hardness (≤ 207 HBW) to facilitate chip removal.
6.3. Surface Hardening and Welding
Induction or flame surface hardening brings the surface to 55-60 HRC over a tough core, for localized wear resistance (splined shafts, pinions, contact surfaces). Weldability is limited: preheating (indicatively 150-250 °C) and post-weld stress relieving at 550-660 °C are recommended to prevent hydrogen cracking. Where welding is frequent or critical, a lower-carbon steel (C25, C35) or a structural steel (S355) is preferable.
7. C45 Compared: 42CrMo4 and 39NiCrMo3
When the hardenability or strength of C45 is insufficient (large sections, high loads, severe fatigue), the choice shifts to alloy quenched and tempered steels. The following comparison uses, for the +QT properties, the common size class > 40-100 mm.
| Characteristic | C45 (1.0503) | 42CrMo4 (1.7225) | 39NiCrMo3 (1.6510) |
|---|---|---|---|
| Standard | EN 10083-2 | EN 10083-3 | EN 10083-3 |
| Type | non-alloy | Cr-Mo alloy | Ni-Cr-Mo alloy |
| C [%] | 0.42-0.50 | 0.38-0.45 | 0.35-0.43 |
| Main alloying elements | – | Cr 0.90-1.20; Mo 0.15-0.30 | Ni 0.70-1.00; Cr 0.60-1.00; Mo 0.15-0.25 |
| Rp0.2 min +QT [MPa] | 370 | 650 | 685 |
| Rm +QT [MPa] | 630-780 | 900-1100 | 880-1080 |
| Hardenability | limited | high | high |
| Through-hardening (indicative) | small sections | up to ≈ 60 mm (oil) | even large sections |
| Weldability | limited | limited (preheating) | poor (preheating; sensitive to temper embrittlement) |
| Typical applications | shafts, pins, moderately stressed gears | shafts, gears, high-strength fasteners | highly stressed components, large sections |
Related technical data sheets: 42CrMo4 and 39NiCrMo3.
8. Industrial Applications of C45 Steel
8.1. Automotive and Power Transmission
Drive shafts, camshafts, axles, connecting rods and gears: after quenching and tempering, the material offers 630-800 MPa of Rm in the most commonly used sections; on gears, surface hardening (55-60 HRC) combines surface hardness with core toughness.
8.2. Industrial Mechanics and Machinery
This is the main field of application: shafts, pins, hubs and components for lathes, milling machines, presses and CNC machine tools, as well as press columns, sub-dies and extrusion shafts, where both strength and machinability are decisive.
8.3. Construction and Structural Engineering
Connecting elements, tie rods and components requiring higher strength than mild steels; for welded joints, the precautions regarding weldability apply. Also used for dies and tooling where wear resistance (with surface hardening) and core toughness are required.
9. Delivery Conditions of C45
| Code | Condition |
|---|---|
| +N | Normalized |
| +QT | Quenched and tempered (quenching + tempering) |
| +A | Annealed (for machinability) |
| +S | Treated for cold shearability |
| +C | Cold-drawn |
| +SH | Peeled |
10. International Equivalents (Indicative)
| System | Designation |
|---|---|
| EN / Werkstoff | C45 / 1.0503 |
| ISO | 683-1 C45 |
| AISI / SAE (USA) | 1045 |
| JIS (Japan) | S45C |
| UNI (former, Italy) | C45 |
| GOST (former, Russia) | 45 |
11. Frequently Asked Questions about C45 Steel
11.1. What is the difference between C45, C45E and C45R?
The sulfur content and classification differ. C45 (1.0503) is a non-alloy quality steel with P and S ≤ 0.045%. C45E (1.1191) is a special steel with controlled low sulfur (S ≤ 0.035%), for greater homogeneity and toughness. C45R (1.1201) has sulfur controlled within a range (≈ 0.020-0.040%) to optimize machinability.
11.2. Can C45 steel be welded?
Weldability is limited by the carbon content (CEV ≈ 0.56). Welding is possible with preheating (≈ 150-250 °C) and post-weld stress relieving at 550-660 °C to prevent hydrogen cracking. For predominantly welded structures, low-carbon steels (C25, C35) or structural steels such as S355 are more suitable.
11.3. What are the optimal heat treatments for C45?
Quenching and tempering (quenching at 820-860 °C + tempering at 550-660 °C) is the reference treatment for mechanical properties. Where localized wear resistance is needed, induction surface hardening brings the surface to 55-60 HRC while keeping the core tough.
11.4. Up to what diameter can C45 be through-hardened?
Due to its limited hardenability, EN 10083-2 specifies quenched and tempered properties only up to 100 mm; beyond that, through-hardening is not guaranteed and the characteristics must be agreed upon. For larger sections, alloy steels (42CrMo4, 39NiCrMo3) are used instead.
11.5. How does C45 behave under fatigue and wear?
After quenching and tempering, it offers good fatigue resistance for moderate stresses; surface hardening improves wear resistance on contact surfaces (pinions, splined shafts). For high fatigue loads or large sections, alloy steels are preferred.
11.6. What are the international equivalents of C45?
C45 / 1.0503 (EN 10083-2) corresponds indicatively to AISI/SAE 1045, JIS S45C and former GOST 45. These are reference equivalents, not exact matches: composition and requirements must be verified against the standard and the certificate.
11.7. Is C45 suitable for precision components?
Yes, with care: for tight tolerances, start from quenched and tempered material and perform finishing operations after heat treatment, to manage distortion. Good machinability facilitates high-quality finishing.
12. Siderticino’s C45 Steel Offering
Siderticino supplies C45 steel – including the C45E and C45R variants – compliant with EN 10083-2 and EN 10277, with full traceability and inspection certification according to EN 10204 (type 2.1 and, on request, 3.1), in the delivery conditions most suitable for the application (+N, +QT, +A, +S, +C, +SH). Price depends on delivery condition, execution, treatments and dimensions: for a quote, please specify execution, heat treatment condition, profile, dimensions to size and any required treatments.
Go to the C45 product page for formats and diameters, request a quote or use the steel bar weight calculator tool.