C45: Steel Technical Specifications

01C45 Steel: Fundamental Characteristics and Properties

C45 (material number 1.0503) is a non-alloy quality steel for quenching and tempering covered by EN ISO 683-1:2018 (formerly 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 favourable balance of strength, machinability and cost. In the quenched and tempered condition (+QT) it develops a tensile strength ranging, depending on diameter, between 630 and 850 MPa; in the normalised condition (+N) it exhibits 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), whereas the material lends itself well 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 loads. For higher strength or hardenability requirements, alloy quenched and tempered steels such as 42CrMo4 or 39NiCrMo3 are used.

Reference standard: EN ISO 683-1:2018, which consolidated the former EN 10083-1 (general delivery conditions) and EN 10083-2 (non-alloy quality steels for quenching and tempering), covering composition, properties and delivery conditions; ISO 683-1 is the corresponding international reference. For cold-drawn, peeled and bright products, EN ISO 683-7:2024 (formerly EN 10277) applies; inspection certificates follow EN 10204. The EN designation C45 is the primary one; the equivalents AISI/SAE 1045, JIS S45C and former GOST 45 are indicative.

For formats, available diameters and quotes, see the dedicated C45 product page.

02Chemical Composition of C45 Steel

The chemical composition of C45 is defined by EN ISO 683-1:2018 (formerly EN 10083-2) on the basis of the cast analysis. As it is a non-alloy steel, chromium, molybdenum and nickel are permitted only as residual elements within limits that preserve its classification.

Carbon (0.42-0.50%) governs hardenability and the hardness achievable after hardening. Silicon (≤ 0.40%) acts as a deoxidizer and contributes to solid solution strengthening. Manganese (0.50-0.80%) increases hardenability, promotes a homogeneous martensite and binds residual sulphur as manganese sulphides, mitigating its hot-shortness effect. Phosphorus and sulphur are each limited to 0.045% to contain brittleness.

03Mechanical Properties of C45 Steel

3.1General Overview

Mechanical properties depend on the delivery condition and the reference diameter: the standard values always refer to a defined test section, because the limited hardenability causes the properties to decline as the section increases.

3.2Properties in the Normalised Condition (+N)

In the normalised condition, Rm is expressed as a minimum value (not as a range). The ferritic-pearlitic structure ensures homogeneity and good machinability, ideal for semi-finished products to be quenched and tempered or for applications with moderate mechanical requirements.

3.3Properties in the Quenched and Tempered Condition (+QT)

EN ISO 683-1:2018 (formerly EN 10083-2) defines the +QT properties of C45 up to a reference diameter of 100 mm. Beyond this, through-hardening is not guaranteed and the characteristics must be agreed between manufacturer and customer. Quenching and tempering produces a tempered martensite that optimises the strength-toughness ratio for components subject to moderate-to-high dynamic loads.

3.4Hardness

04C45 Hardenability 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 is achievable only on small-diameter sections; as the section 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 carbon content of 0.45% 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 at the nominal value, rising as residual elements increase. Since CEV is well above 0.45, welding requires preheating and specific precautions. The actual cast value must be derived from the analysis on the certificate (MTC, EN 10204).

05Physical Characteristics of C45 Steel

The following values are indicative literature data (not normative) and vary with temperature and metallurgical condition; they serve as a reference for thermal and dimensional calculations.

C45 does not have a sharp melting temperature but a solidification range typical of carbon steels (onset of melting approximately 1420-1460 °C, to be confirmed with a steelmaker source for critical calculations).

06Heat Treatments of C45 Steel

6.1Quenching and Tempering: the Q+T Cycle

This is the primary treatment for C45. Hardening involves austenitising at 820-860 °C and rapid cooling (water for the lower end of the range, oil for the upper end, depending on section and cracking risk). Tempering at 550-660 °C governs the strength-toughness trade-off: higher temperatures favour ductility and toughness, lower ones strength.

For other steels in the same family, see the quenched and tempered steels page.

6.2Normalising and Annealing

Normalising (840-880 °C, air) refines the grain and homogenises 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 ease chip removal.

6.3Surface Hardening and Welding

Induction or flame surface hardening brings the surface to 55-60 HRC over a tough core, for localized wear (splined shafts, pinions, contact surfaces). Weldability is limited: preheating (approximately 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.

07C45 Compared: 42CrMo4 and 39NiCrMo3

When the hardenability or strength of C45 is not sufficient (large sections, high loads, severe fatigue), the choice shifts to alloy quenched and tempered steels. For +QT properties, the following comparison uses the common size class > 40-100 mm.

Related technical datasheets: 42CrMo4 and 39NiCrMo3.

08Industrial Applications of C45 Steel

8.1Automotive and Power Transmission

Drive shafts, camshafts, axles, connecting rods and gears: after quenching and tempering the material provides 630-800 MPa Rm in the most common working sections; on gears, surface hardening (55-60 HRC) combines surface hardness with core toughness.

8.2Industrial Machinery and Equipment

This is the main field of use: shafts, pins, hubs and components for lathes, milling machines, presses and CNC machine tools, as well as press columns, die shoes and extrusion shafts, where both strength and machinability are decisive.

8.3Construction and Structural Steelwork

Connecting elements, tie rods and components requiring higher strength than mild steels; for welded joints the weldability precautions apply. Also used for dies and tooling where wear resistance (with surface hardening) and core toughness are required.

09Delivery Conditions of C45

10International Equivalents (Indicative)

11Frequently Asked Questions about C45 Steel

11.1What is the difference between C45, C45E and C45R?

Sulphur 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 sulphur (S ≤ 0.035%), for greater homogeneity and toughness. C45R (1.1201) has sulphur controlled within a range (≈ 0.020-0.040%) to optimise machinability.

11.2Can C45 steel be welded?

Weldability is limited by the carbon content (CEV ≈ 0.56). It 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.

11.3What are the optimal heat treatments for C45?

Quenching and tempering (hardening at 820-860 °C + tempering at 550-660 °C) is the reference treatment for mechanical properties. Where localized wear resistance is required, induction surface hardening brings the surface to 55-60 HRC while keeping the core tough.

11.4Up to what diameter can C45 be through-hardened?

Due to its limited hardenability, EN ISO 683-1:2018 (formerly EN 10083-2) specifies properties in the quenched and tempered condition only up to 100 mm; beyond this, through-hardening is not guaranteed and the characteristics must be agreed. For large sections, alloy steels (42CrMo4, 39NiCrMo3) are used instead.

11.5How does C45 perform under fatigue and wear?

After quenching and tempering it offers good fatigue strength under moderate stresses; surface hardening improves wear resistance on contact surfaces (pinions, splined shafts). For high fatigue loads or large sections, alloy steels are preferred.

11.6What are the international equivalents of C45?

C45 / 1.0503 (EN ISO 683-1:2018 (formerly EN 10083-2)) corresponds approximately 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.

11.7Is C45 suitable for precision components?

Yes, with some care: for tight tolerances, start from quenched and tempered material and carry out finishing operations after heat treatment to manage distortion. Good machinability facilitates high-quality finishing.

12Siderticino's C45 Steel Offering

Siderticino supplies C45 steel - including the C45E and C45R variants - compliant with EN ISO 683-1:2018 (formerly EN 10083-2) and EN ISO 683-7:2024 (formerly EN 10277), with full traceability and EN 10204 documentation (type 2.1 declaration and, on request, type 3.1 inspection certificate), in the delivery conditions most suitable for the application (+N, +QT, +A, +S, +C, +SH). The price depends on the delivery condition, surface finish, treatments and dimensions: to receive a quotation, please specify the surface finish, heat-treatment condition, profile, cut-to-size dimensions and any treatments.

Go to the C45 product page for formats and diameters, request a quote or use the steel bar weight calculator tool.