S45C is a medium-carbon steel widely used for machinery structures. Its mechanical properties vary significantly depending on the heat treatment, making it a critical consideration for engineers. This guide explains the strength, hardness, and toughness data under annealed, normalized, and quenched & tempered states to help you optimize part design and machining processes.
Mechanical Properties of S45C by Heat Treatment
1. Annealed State (Softened)
In the annealed state, S45C is relatively soft and easy to machine, making it ideal for blanks or parts requiring subsequent heat treatment.
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Tensile Strength: Approx. 550–600 MPa
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Brinell Hardness: Approx. HB 160–220
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Elongation: 18–22%
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Features: Good impact toughness; excellent for turning and milling; lower preheating requirements for welding.
2. Normalized State
Normalizing improves grain uniformity and strength, suitable for parts requiring higher mechanical performance.
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Tensile Strength: Increased to 600–650 MPa
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Hardness: Approx. HB 190–240
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Elongation: 15–18%
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Features: Slightly lower impact toughness than annealing but maintains good machinability; ideal for shafts and gear blanks.
3. Quenched and Tempered (Q&T) State
Through quenching and tempering (through-hardening), S45C achieves the optimal balance of strength and toughness, making it the top choice for medium-load components.
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Tensile Strength: Approx. 650–800 MPa
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Hardness: HRC 28–38 (HB 280–340)
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Elongation: 12–16%
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Features: Best for drive shafts, gears, and connecting rods. Under proper conditions, induction hardening can reach a surface hardness of approx. HRC 55, while the core retains toughness.
Toughness, Fatigue Life, and Practical Considerations
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Fatigue Life: S45C in a Q&T state offers excellent fatigue resistance, specifically for cyclic loading parts.
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Toughness: Low Phosphorus (P) and Sulfur (S) content ensures superior toughness and prevents brittle fracture.
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Mass Effect: Due to hardenability limits, large-diameter parts may have lower core hardness. Engineers must account for the hardness gradient between the surface and the core during evaluation.
S45C Frequently Asked Questions (FAQ)
Q1: How should I estimate S45C Tensile and Yield Strength for design?
A: S45C strength varies by heat treatment. While annealed strength is around 550–600 MPa, the Quenched & Tempered state boosts this to 650–800 MPa with significantly higher yield strength. This makes it ideal for components subjected to high cyclic loads like gears and rods.
Q2: How is the machinability and chip removal of S45C?
A: S45C offers excellent machinability. The annealed state is softer, extending tool life during heavy roughing. For a better surface finish, the normalized state is recommended to prevent "sticky" chips. For precision parts, Double Steel suggests using cold-finished (bright) bars to skip external diameter roughing.
Q3: How do I ensure purchased S45C meets JIS G4051 standards?
A: Always request a Mill Test Report (MTR). Verify that Carbon (C) is within 0.42–0.48% and Manganese (Mn) is within 0.60–0.90%. For large cross-sections requiring deep hardening, consider upgrading to an alloy steel like SCM440 (4140).
Conclusion
S45C offers flexible mechanical properties that meet diverse engineering needs through proper heat treatment.
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