Mechanical Properties
The mechanical properties of S45C depend on its heat treatment state-hot-rolled (as-delivered) and quenched & tempered (Q&T) are the two most common states, with significant differences in strength and ductility. All properties below comply with JIS G4051 and are tested via standard methods (tensile tests per JIS Z2241, impact tests per JIS Z2242).
2.1 Hot-Rolled State (As-Delivered)
Hot-rolled S45C is cooled naturally after rolling, with a ferrite-pearlite microstructure. It is suitable for low-load components or pre-processing (e.g., machining before heat treatment) due to its moderate strength and good machinability.
| Mechanical Property | Test Standard | Typical Value (Hot-Rolled) | Minimum Requirement (JIS G4051) |
|---|---|---|---|
| Yield Strength (YS) | JIS Z2241 | 280–350 MPa | ≥275 MPa |
| Tensile Strength (TS) | JIS Z2241 | 570–650 MPa | ≥530 MPa |
| Elongation (A) | JIS Z2241 | 15–20% | ≥16% (for diameter ≤100mm) |
| Reduction of Area (Z) | JIS Z2241 | 40–45% | ≥40% (for diameter ≤100mm) |
| Brinell Hardness (HB) | JIS Z2243 | 160–200 HB | ≤210 HB (no minimum requirement) |
| Charpy Impact Toughness (V-notch) | JIS Z2242 | 20–30 J (20℃) | No mandatory requirement (typical for hot-rolled state) |
2.2 Quenched & Tempered State (Q&T)
Most S45C components undergo quenching and tempering to optimize strength and toughness. The standard Q&T process is: quench at 820–860℃ (water/oil cooling) + temper at 500–650℃ (air cooling). This transforms the microstructure to tempered sorbite, balancing high strength and ductility.
| Mechanical Property | Test Standard | Typical Value (Q&T: 840℃ Quench + 600℃ Temper) | Application Significance |
|---|---|---|---|
| Yield Strength (YS) | JIS Z2241 | 400–480 MPa | Ensures resistance to plastic deformation under load (e.g., shafts bearing torque). |
| Tensile Strength (TS) | JIS Z2241 | 650–750 MPa | Provides sufficient load-bearing capacity for high-stress components (e.g., gears). |
| Elongation (A) | JIS Z2241 | 18–22% | Maintains ductility to avoid brittle fracture during impact (e.g., connecting rods in engines). |
| Reduction of Area (Z) | JIS Z2241 | 45–55% | Indicates good plastic deformation ability, critical for components requiring forging or bending. |
| Brinell Hardness (HB) | JIS Z2243 | 190–230 HB | Matches machinability and wear resistance-hard enough to resist wear (e.g., gear teeth) but not too hard to machine. |
| Charpy Impact Toughness (V-notch) | JIS Z2242 | 35–45 J (20℃) | Ensures toughness in dynamic load scenarios (e.g., mechanical transmission systems). |
Note: Adjusting the tempering temperature changes properties-lower tempering (400–500℃) increases hardness (240–280 HB) and strength but reduces toughness; higher tempering (650–700℃) improves toughness but lowers strength.