Comprehensive Comparison：1045 vs C45 vs S45C

The following is a comprehensive comparative analysis of 1045, C45 and S45C steels, covering key aspects such as chemical composition, mechanical properties, application areas, heat treatment characteristics and standard differences:

1.Chemical Composition Comparison

Note: The carbon content of the three is similar, but the silicon content range of S45C is stricter, and the phosphorus and sulfur impurities are more strictly controlled (close to high-quality carbon steel).

2.Comprehensive Performance Comparison

Mechanical Properties Comparison (normalized or QT)

Note: The actual performance is significantly affected by the heat treatment process. S45C may show higher comprehensive strength after quenching and tempering.

Comparison of hardenability depth (end quench test)

Conclusion:
– S45C has a higher upper limit of manganese content (0.9%) and stricter impurity control, and its hardenability is significantly better than the other two, making it suitable for larger cross-section parts (such as hydraulic piston rods, mold mandrels).
– 1045 and C45 are more suitable for small shafts or parts that do not need to be fully hardened (such as bolts, washers).

Dynamic performance comparison: fatigue & impact toughness

Fatigue strength (rotating bending test)

Impact toughness (Charpy V-notch, room temperature)

• Quenched and tempered (tempered at 500°C):
  – 1045: 40–50 J
  – C45: 45–55 J
  – S45C: 50–60 J
• Reason: S45C has lower phosphorus and sulfur content (P≤0.030%, S≤0.035%), reducing the tendency of grain boundary embrittlement.

Performance in extreme environments

• Low temperature toughness (-40°C)
  – The impact value of S45C can still be maintained at 30–40 J, while 1045 and C45 may drop to 20–30 J, which is suitable for mechanical parts in cold regions.
• Corrosion resistance
  – All three require surface protection (such as galvanizing, painting), but S45C has a more uniform surface and better coating adhesion.

3.Comparison of Differences In Heat Treatment Processes

Hardenability:
– S45C has slightly better hardenability than 1045 and C45, and is suitable for slightly larger cross-section parts (such as diameter <50mm).
– C45 and 1045 are usually used for small and medium-sized parts (diameter <30mm).

Typical Process:

• Quenching temperature: 840–860°C (oil quenching or water quenching).
• Tempering temperature: 500–600°C (adjusted according to hardness requirements).
• Tempering brittleness range control
  All three need to avoid the 250–400°C tempering brittleness zone, but S45C has better impurity control and is less sensitive to brittleness during rapid cooling.
• Recommended tempering process:
  – High toughness requirement: tempering 600°C, hardness HRC 22–26
  – High strength requirement: tempering 450°C, hardness HRC 35–40

Suitability of surface hardening process

• High frequency quenching
  – S45C has a uniform carbon content, better hardening layer depth consistency (1.5-3mm), and surface hardness HRC 55-60.
  – 1045 and C45 may have uneven hardening layers due to local composition fluctuations.
• Carburizing (only for low carbon steel, not applicable here): All three are not recommended, and low carbon steel such as 1020 steel or S15C steel should be used instead.

4.Comparison of Metallographic Characteristics

• Commonalities of 1045/C45/S45C:
  All three are medium carbon steels, with ferrite + pearlite in the annealed state, and tempered troostite (high toughness) or tempered troostite (higher strength) after quenching + tempering.
• Differences:
  – S45C: Due to the lower silicon content (0.15-0.35%), the pearlite interlamellar spacing is finer, the martensite structure is more uniform after quenching, and the tempering stability is slightly better.
  – C45: The European standard has a lower control on the manganese content (0.5-0.8%), which may slightly affect the hardening depth.
  – 1045: The North American standard allows a slightly higher sulfur content (≤0.05%), which may form more sulfide inclusions and reduce the lateral impact toughness.
• Grain size effect
  – S45C usually requires finer grain size (ASTM 5-8), while 1045 and C45 may be ASTM 4-7. Fine grains can improve strength and fatigue life.

5. Processing & Welding Performance

• Machinability:
  – All three are free-cutting steels, but S45C has a lower sulfur content and its machinability is slightly inferior to 1045.
• Weldability:
  – Medium carbon steel has average weldability and needs to be preheated (150–300°C) and the cooling rate controlled to avoid cracks.
  – S45C has a slightly better weldability than 1045 and C45 due to stricter impurity control.

6. Application Fields

• 1045:
  – General mechanical parts such as shafts, gears, connecting rods, bolts, etc. (North American market).
• C45:
  – Transmission parts, hydraulic cylinders, tool chucks, etc. in the European machinery manufacturing industry.
• S45C:
  – High-precision parts in the Japanese and Asian markets, such as mold inserts, precision gears, and automotive steering parts.

7. In-depth Analysis of Industry Application Cases

• Automobile manufacturing industry
  – S45C: used for Japanese automobile steering knuckles and gearbox gear shafts, because of its high fatigue strength and adaptability to high-frequency vibration environments.
  – C45: European automakers prefer to use it for engine crankshafts (with surface quenching) because of the cost advantages of the local supply chain.
  – 1045: North American truck chassis connecting rods, focusing on cost and small cross-sectional dimensions.
• Molds and tools
  – S45C: Japanese precision mold inserts (such as injection mold guide pins), achieved HRC 48–52 through vacuum quenching, deformation <0.05mm.
  – C45: European tooling fixtures, milling after quenching and tempering, balancing strength and machinability.

8. Standard Interchange & Substitution

• International similar grades:
  – China GB 45 steel ≈ S45C ≈ C45 ≈ 1045.
  – Germany 1.0503 (C45) and S45C are interchangeable, but attention should be paid to the difference in heat treatment.
• Key differences:
  – S45C has stricter control over impurity elements (P, S) and is suitable for high reliability scenarios.
  – 1045 has lower cost and a more mature North American supply chain.

9.Summary & Selection Recommendations

• Determine the function of the part
  – High dynamic load/fatigue life → S45C
  – Static structural parts/cost priority → 1045 or C45
• Cross-sectional size
  – Diameter > 40mm → S45C (hardenability advantage)
  – Diameter < 25mm → 1045/C45
• Supply chain region
  – North America → 1045; Europe → C45; Asia → S45C

Through the above comparison, we can accurately match material properties according to specific application scenarios, regional supply and performance requirements. If you have further detailed requirements, please feel free to discuss with us.

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