85# Carbon Steel: Medium-Carbon Structural Steel for Mechanical Components & General Engineering
85# carbon steel (equivalent to AISI 1085, UNS G10850, or DIN C85) is a medium-carbon, non-alloy structural steel renowned for its balanced combination of strength, hardness, and machinability. With a nominal carbon content of 0.85%, this grade delivers high tensile strength (up to 800 MPa after heat treatment) while retaining moderate ductility for cold-forming operations. It is widely utilized in applications requiring wear resistance, such as shafts, gears, springs, and hand tools. This article explores its chemical composition, mechanical properties, heat treatment processes, and industrial applications.
1. Chemical Composition (GB/T 699-2015 & ASTM A29 Standards)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | 0.82 – 0.90% | Primary hardening element; increases tensile strength and wear resistance via martensite formation |
| Manganese (Mn) | 0.50 – 0.80% | Enhances hardenability; combines with sulfur to improve machinability (MnS inclusions) |
| Silicon (Si) | 0.15 – 0.35% | Deoxidizer; improves strength without significant ductility loss |
| Phosphorus (P) | ≤ 0.035% | Impurity; minimized to prevent cold brittleness and reduce crack sensitivity |
| Sulfur (S) | ≤ 0.035% | Improves machinability but controlled to avoid hot shortness |
| Chromium (Cr) | ≤ 0.25% | Residual element; slight improvement in hardenability if present |
| Nickel (Ni) | ≤ 0.30% | Residual element; minimal impact on properties at low concentrations |
| Copper (Cu) | ≤ 0.25% | Residual element; can improve atmospheric corrosion resistance if ≥ 0.20% |
2. Mechanical Properties (As-Rolled vs. Heat-Treated)
| Condition | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (HB) | Impact Toughness (J) |
|---|---|---|---|---|---|
| Hot-Rolled (Normalized) | 550 – 700 | 300 – 400 | ≥ 12 | 170 – 210 | ≥ 20 |
| Annealed (780-820°C) | ≤ 650 | ≤ 380 | ≥ 18 | ≤ 197 | ≥ 30 |
| Quenched & Tempered (820°C oil quench, 500°C temper) | 800 – 1000 | 500 – 700 | ≥ 9 | 200 – 250 | ≥ 25 |
3. Heat Treatment Processes
- Normalizing (880-920°C): Heating followed by air cooling to refine grain structure, improve machinability, and prepare for subsequent hardening. Typical hardness: 180-220 HB.
- Annealing (780-820°C): Slow furnace cooling to reduce hardness (≤ 197 HB) for cold-forming operations like bending or drawing. Produces a pearlitic-ferritic microstructure.
- Quenching (800-840°C, Oil/Water): Rapid cooling to form martensite, achieving maximum hardness (60-65 HRC). Water quenching risks cracking; oil is preferred for complex shapes.
- Tempering (150-650°C): Post-quench heating to reduce brittleness and adjust hardness:
- 150-250°C: Retains high hardness (55-60 HRC) for cutting tools.
- 350-500°C: Balanced strength/toughness (40-50 HRC) for springs and shafts.
- 500-650°C: Maximizes toughness (25-35 HRC) for structural components.
- Surface Hardening (Induction/Carburizing): Localized hardening (e.g., gear teeth) via high-frequency induction or carburizing (0.8-1.2% case carbon) to 58-62 HRC.
4. Key Applications by Industry
Automotive & Transportation
Axle shafts, transmission gears, clutch components, and suspension springs — heat-treated to 45-55 HRC for fatigue resistance under cyclic loads.
Machinery & Equipment
Spindles, arbors, die holders, and conveyor rollers — normalized or quenched/tempered to 200-250 HB for wear resistance in industrial environments.
Hand Tools & Hardware
Hammers, chisels, wrenches, and punches — oil-quenched to 55-60 HRC with tempered edges to balance hardness and impact resistance.
Construction & Infrastructure
High-strength bolts (Grade 8.8), anchor rods, and railway clips — tempered to 250-300 HB for tensile strength and corrosion resistance (with coating).
5. Comparison with Similar Carbon Steel Grades
| Grade | Carbon (%) | Key Properties | Typical Applications |
|---|---|---|---|
| 85# (C85) | 0.82-0.90 | High strength post-heat treatment; good wear resistance; moderate machinability | Gears, shafts, springs, hand tools |
| 1045 (C45) | 0.42-0.50 | Lower hardness (max 55 HRC) but better toughness; easier to weld | Machine parts, forged components, hydraulic rods |
| 1060 (C60) | 0.55-0.65 | Higher ductility than 85#; suitable for cold heading | Fasteners, agricultural equipment, low-stress springs |
| 1095 (C95) | 0.90-1.03 | Maximum hardness (65 HRC) but brittle; poor weldability | Knives, blades, high-wear industrial parts |
6. Machining & Fabrication Guidelines
- Machining: Best performed in the annealed or normalized state (hardness ≤ 220 HB). Use high-speed steel (HSS) or carbide tools with sulfurized cutting oils. Typical speeds:
- Turning: 20-30 m/min (HSS), 80-120 m/min (carbide)
- Drilling: 15-25 m/min (HSS)
- Milling: 18-28 m/min (HSS)
- Welding: Limited weldability due to high carbon. Preheat to 150-200°C and post-weld stress-relieve at 600-650°C. Use low-hydrogen electrodes (E7018). Avoid in critical load-bearing welds.
- Cold Forming: Only feasible in annealed condition (≤ 197 HB). Bend radii ≥ 2× material thickness to prevent cracking.
- Surface Treatment: Phosphate coating or black oxide (for corrosion resistance) followed by oil dip. For decorative parts, nickel/chrome plating after hardening.
7. Request a Carbon Steel Quote
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