Medium Carbon Steel is a category of plain carbon steels containing approximately 0.30% to 0.60% carbon. This range delivers a balanced combination of strength, hardness, ductility, and toughness, positioning these grades between low carbon (mild) steel and high carbon steel.
Medium carbon steel grades are extensively used for load-bearing, wear-resistant, and mechanically stressed components where heat treatment is required to tailor mechanical properties.
Typical Chemical Composition
| Element | Typical Range (%) |
|---|---|
| Carbon (C) | 0.30 – 0.60 |
| Manganese (Mn) | 0.60 – 1.65 |
| Silicon (Si) | ≤ 0.40 |
| Sulphur (S) | ≤ 0.050 |
| Phosphorus (P) | ≤ 0.050 |
| Iron (Fe) | Balance |
Microstructure & Metallurgical Behavior
• Ferrite + pearlite in annealed or normalized condition
• Martensite and tempered martensite after quenching and tempering
Metallurgical Significance
• Higher pearlite content increases strength and wear resistance
• Heat treatment enables controlled martensitic transformation
• Tempering restores toughness and reduces brittleness
Key Characteristics
Higher Strength & Hardness
• Increased carbon enhances tensile strength and surface hardness
• Suitable for shafts, gears, axles, and machine components
Moderate Ductility & Toughness
• Adequate elongation and impact resistance
• Performs well under cyclic loading and mechanical shock
Heat Treatable
• Quenching increases hardness and strength
• Tempering improves toughness and fatigue resistance
• Normalizing refines grain structure
Good Machinability (Annealed)
• Easy machining after annealing
• Machinability decreases after hardening
Refining & Processing Properties
Heat Treatment Refinement
• Annealing: Improves machinability and stress relief
• Normalizing: Enhances uniformity and mechanical reliability
• Quenching & tempering: Produces high-strength, wear-resistant steel
Grain Structure Control
• Normalizing refines grain size
• Fine grains improve fatigue resistance
Surface Hardening Compatibility
• Induction hardening for gears, shafts, and axles
• Carburizing for wear-resistant surfaces with tough cores
Typical Mechanical Properties
| Property | Typical Range |
|---|---|
| Tensile Strength | 550 – 900 MPa |
| Yield Strength | 300 – 650 MPa |
| Hardness (HB) | 170 – 280 (annealed) |
| Hardness (HRC) | Up to 55 (hardened & tempered) |
| Elongation | 10 – 20% |
| Impact Toughness | Moderate to good (tempered) |
| Density | ~7.85 g/cm³ |
Common Medium Carbon Steel Grades
AISI / SAE Grades
• AISI 1040 – Good strength–toughness balance (shafts, bolts, couplings)
• AISI 1045 – Excellent heat treat response (gears, axles, crankshafts)
• AISI 1050 / 1055 – Higher hardness and wear resistance (springs, blades)
European & British Grades
• EN8 (080M40 / C45) – Equivalent to AISI 1045 (shafts, studs, hydraulic rods)
• EN9 (070M55) – Higher carbon grade (springs, hammers, wear parts)
Available Forms
✔ Hot rolled sheets & plates
✔ Cold rolled sheets
✔ Bars (round, square, flat, hex)
✔ Forged blocks & billets
✔ Shafts & precision bars
✔ Pipes & tubes (limited usage)
Applications
Automotive & Mechanical: Crankshafts, axles, gears, connecting rods
Industrial Machinery: Press tools, spindles, couplings, fasteners
Construction: Load-bearing machine components, connectors
Tools & Hardware: Hammers, wrenches, agricultural tools, blades
Advantages
✔ Higher strength than mild steel
✔ Heat treatable for customized performance
✔ Good wear resistance
✔ Cost-effective and widely available
✔ Suitable for dynamic and load-bearing parts
Limitations
⚠ Lower weldability than low carbon steel (preheating recommended)
⚠ Reduced ductility compared to mild steel
⚠ Controlled heat treatment required
Why Choose Medium Carbon Steel
Medium carbon steel grades are selected when strength, durability, and wear resistance are essential without the extreme brittleness of high carbon steel. Their adaptability through heat treatment makes them core materials for automotive, machinery, forging, and industrial manufacturing sectors.