​45 steel (also known as 45# steel or S45C)​ is a medium-carbon structural steel (carbon content: ​0.42–0.50%​) widely used in mechanical manufacturing due to its balanced strength, toughness, machinability, and cost-effectiveness.

Its applications span multiple industries, leveraging its adaptability to heat treatment (e.g., quenching, tempering, surface hardening). Below are its primary uses:

​1. Machinery Components​

45 steel is ideal for parts requiring ​moderate strength and wear resistance​, especially after heat treatment:

​Shafts and Axles​: Driveshafts, camshafts, and transmission shafts (after quenching + tempering, hardness: HRC 42–46) .

​Gears and Sprockets​: Gear teeth benefit from surface hardening to enhance durability .

​Bolts and Fasteners​: High-strength bolts for machinery, benefiting from its yield strength (≥355 MPa) and tensile strength (≥600 MPa) .

​Connecting Rods and Pins​: Used in engines and linkages due to fatigue resistance under cyclic loads .

​2. Automotive Parts​

Its balance of strength and formability makes it suitable for automotive structures:

​Chassis Components​: Crossbeams, brackets, and frames (using hot-rolled plates, thickness: 0.5–80 mm) .

​Steering and Suspension Parts​: Steering knuckles and torsion bars .

​3. Tooling and Molds​

Though not high-alloy tool steel, 45 steel serves in low-cost tooling:

​Mold Bases and Inserts​: Templates, guide pillars, and ejector pins (after surface hardening to HRC 48–52) .

​Repair Welding​: Used with(e.g., CMC-E45) to fix surface wear .

​4. Construction and Heavy Equipment​

​Structural Supports​: Crane booms, excavator arms, and hydraulic cylinders .

​Mining Equipment​: Drill rig components and conveyor parts .

​Critical Considerations​​

​Heat Treatment Dependency​​:

Quenching + tempering optimizes (tensile strength: 760–895 MPa) .

Thin sections (8–12 mm) prone to cracking during water quenching; oil cooling recommended .

​Limitations​​:

​Low Hardenability​​: Unsuitable for large-section parts (thickness >80 mm) .

​Welding Challenges​​: Requires preheating (150–200°C) and post-weld stress relief .

​Cost Efficiency​​: Lower cost than alloy steels (e.g., 40Cr), but inferior corrosion resistance .

​Comparison with Similar Steels​​

​Conclusion​​

45 steel’s versatility makes it a cornerstone material for ​medium-stress mechanical parts​​ across automotive, machinery, and tooling sectors. Its value lies in the cost-effective enhancement of properties via heat treatment, though designers must account for its limits and welding constraints.