Chemical Composition
The chemical composition of S45C is strictly regulated by JIS G4051 to ensure consistent mechanical performance. All element contents are given as mass percentages (%) and are critical to determining the steel's hardenability, strength, and ductility.
| Element | Symbol | Content Range (JIS G4051) | Role & Impact |
|---|---|---|---|
| Carbon | C | 0.42–0.50% | Core strengthener: Carbon forms carbides (Fe₃C) in the steel matrix, directly increasing hardness and tensile strength. A content of 0.42–0.50% balances strength and machinability-too little carbon (＜0.42%) reduces quenching hardenability, while excess carbon (＞0.50%) causes brittleness and poor weldability. |
| Manganese | Mn | 0.60–0.90% | Toughness & hardenability enhancer: Manganese dissolves in the iron matrix to refine grain structure, improving tensile strength and impact toughness. It also offsets the brittling effect of sulfur by forming MnS (less harmful than FeS), preventing "hot shortness" (fracture during hot rolling/forging). |
| Silicon | Si | 0.17–0.37% | Solid solution strengthener: Silicon forms a solid solution with iron, boosting yield strength and elastic modulus without significantly reducing ductility. It also aids in deoxidation during steelmaking, reducing internal defects like porosity. |
| Phosphorus | P | ≤0.030% | Harmful impurity: Phosphorus segregates at grain boundaries, causing "cold brittleness"-the steel becomes brittle at low temperatures (＜0℃), increasing the risk of fracture under impact. JIS G4051 strictly limits P to ≤0.030% to minimize this risk. |
| Sulfur | S | ≤0.035% | Harmful impurity: Sulfur reacts with iron to form FeS, which has a low melting point and weakens grain boundaries. This causes "hot brittleness"-the steel cracks easily during high-temperature processing (e.g., forging, welding). The ≤0.035% limit ensures processability. |
| Copper | Cu | ≤0.25% (max) | Trace element: Copper is often present as a residual element from raw materials. A small amount (≤0.25%) slightly improves atmospheric corrosion resistance but has minimal impact on main mechanical properties. Excess Cu (＞0.25%) can reduce toughness, so it is strictly controlled. |
Note: For high-quality S45C (e.g., for precision shafts), additional trace elements like chromium (Cr ≤0.20%) or nickel (Ni ≤0.20%) may be present in minimal amounts to further refine grain structure, but these are not mandatory per JIS G4051.