Steel grade C45 (also known as ​1.0503​ or ​CK45​) is a very common ​unalloyed medium carbon steel​ widely used for mechanical and structural components. Unlike Q460D (which is high-strength alloy steel), C45 gets its properties primarily from its carbon content and heat treatment rather than significant alloying elements.

Here's a breakdown of its key characteristics:

​Naming & Standards:​

​C45:​ Indicates ​Carbon​ steel with approximately ​0.45% Carbon​ content.

​Standards:​ EN 10083-2, ISO 683/18, DIN 17200, JIS S45C, AISI 1045 (a very close equivalent).

​Chemical Composition (Typical %, DIN EN 10083-2):​

​Carbon (C):​ ​0.42% - 0.50%​ (Medium carbon - key to its strength and hardenability).

​Manganese (Mn):​ ​0.50% - 0.80%​ (Enhances hardenability and strength).

​Silicon (Si):​ ​0.10% - 0.40%​ (Primarily a deoxidizer, provides some strength).

​Phosphorus (P):​ ≤ ​0.045%​ (Impurity, kept low).

​Sulfur (S):​ ≤ ​0.045%​ (Impurity, typically increased slightly in 'free-cutting' variants like C45R for better machinability).

​Other Alloys:​ Minimal amounts of Cr (≤0.40%), Ni (≤0.40%), Mo (≤0.10%), Cu (≤0.40%), primarily incidental impurities.

​Mechanical Properties (As-Delivered Condition - Usually Normalized or Hot Rolled):​

​Yield Strength (Rp0.2):​ ​≥ 355 MPa​ (35 ksi)

​Tensile Strength (Rm):​ ​590 - 740 MPa​ (86 - 107 ksi)

​Elongation (A):​ ​≥ 17%​ (Good ductility in 'softer' state).

​Hardness (Brinell):​ ​170 - 210 HB​ (Typical for normalized/hot rolled condition).

​Key Features:​

​Heat Treatable:​ C45 is primarily valued for its ability to be heat treated (especially ​quenching and tempering​) to significantly increase strength and surface hardness.

Typical Hardness after Quenching & Tempering: ​~20 HRC - 40 HRC​ (Varies greatly with section size, quench method, and tempering temperature).

Surface Hardening: Also suitable for processes like ​induction hardening​ or ​flame hardening​ to create a very hard, wear-resistant surface layer (up to ​55 HRC+​) while maintaining a tough core.

​Good Machinability:​ In its softer (normalized/hot rolled) condition, C45 has fairly good machinability relative to higher carbon or alloy steels, though better than tool steels.

​Weldability:​ ​Fair to Moderate.​ Requires preheating (150-250°C) and controlled cooling for thicker sections. Higher carbon content increases risk of hardening and cracking in the Heat Affected Zone (HAZ). Post-Weld Heat Treatment (PWHT) is often recommended for critical components. Significantly less weldable than Q460D.

​Strength:​ Moderate strength as-delivered. Can achieve high strength through appropriate heat treatment, though lower than Q460D.

​Toughness:​ Good toughness in the normalized or tempered condition. Not inherently designed for low-temperature impact toughness like Q460D (No impact energy guarantee at -20°C).

​Cost:​ Generally lower cost than alloy steels like Q460D due to simpler chemistry.

​Heat Treatment Options:​

​Annealing / Normalizing:​ Performed after hot forming to refine grain structure and soften for machining.

​Quenching & Tempering (Q+T):​ The primary treatment to achieve high strength/toughness balance. Quenched in oil or water (depending on section size, water quench increases risk of cracking), then tempered.

​Surface Hardening:​ Induction/Flame hardening selectively hardens the surface.

​Stress Relieving:​ To remove machining stresses.

​Typical Applications:​ (Often used after final heat treatment)

Shafts, axles, spindles.

Gears (especially after surface hardening).

Bolts, studs, non-critical fasteners.

Crankshafts, connecting rods (for less demanding applications).

Machinery parts requiring moderate strength and good machinability (e.g., levers, pins, brackets).

Agricultural machinery components.

Rails for sliding applications.

Hand tools.

​In Summary:​

C45 is a ​workhorse medium carbon steel​, prized for its ​good machinability in the supplied state and its excellent response to heat treatment (especially quenching & tempering and surface hardening)​. Its properties stem mainly from its ​~0.45% carbon content​. It offers a good balance of strength, toughness, machinability, and cost for countless general engineering applications, but lacks the inherent high strength and guaranteed low-temperature toughness of alloy steels like Q460D.