AISI 4340 ESR (UNS G43400)
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4340 ESR (AMS 6414, 36CrNiMo4, 1.6511)
4340 ESR is a high-strength, low-alloy steel refined through the Electro-Slag Remelting (ESR) process to improve cleanliness, toughness, and fatigue resistance. It contains nickel, chromium, and molybdenum for excellent strength, hardenability, and impact resistance even in large cross sections. The ESR variant is preferred in aerospace, tooling, and high-performance components demanding superior internal soundness and mechanical reliability.
Chemical Composition:
| Element | Content (%) |
|---|---|
| Carbon (C) | 0.38 – 0.43 |
| Manganese (Mn) | 0.60 – 0.80 |
| Silicon (Si) | 0.15 – 0.30 |
| Chromium (Cr) | 0.70 – 0.90 |
| Nickel (Ni) | 1.65 – 2.00 |
| Molybdenum (Mo) | 0.20 – 0.30 |
| Phosphorus (P) | ≤ 0.025 |
| Sulfur (S) | ≤ 0.015 |
| Iron (Fe) | Balance |
Mechanical Properties:- (Quenched & Tempered Condition)
| Property | Value (typical) |
|---|---|
| Tensile Strength | 1080 – 1580 MPa |
| Yield Strength (0.2%) | 980 – 1400 MPa |
| Elongation (50 mm) | 10 – 18% |
| Reduction in Area | 40 – 55% |
| Impact Strength (Charpy V) | > 35 J @ -40°C |
| Hardness (Rockwell C) | 32 – 45 HRC |
Physical Properties:
| Property | Value |
|---|---|
| Density | 7.85 g/cm³ |
| Modulus of Elasticity | ~205 GPa |
| Thermal Conductivity | ~44.5 W/m·K |
| Specific Heat Capacity | ~475 J/kg·K |
| Melting Point | ~1425 – 1460 °C |
| Thermal Expansion | ~12.3 µm/m·°C (20–100°C) |
| Electrical Resistivity | ~230 nΩ·m |
Heat Treatment:
- Normalizing: 850 – 900°C (air cool)
- Hardening: Austenitize at 830 – 870°C → oil quench
- Tempering: 450 – 650°C depending on strength/toughness requirements
- Stress Relieving: 600 – 650°C after machining or welding
Applications:
- Aircraft landing gears
- Power transmission shafts
- High-strength fasteners
- High-load structural aerospace components
- Die and mold bases
- Performance racing and motorsport parts
Corrosion Resistance
Low corrosion resistance
Requires surface treatment or protective coatings in humid or marine environments
Primarily used in environments where mechanical performance takes precedence over corrosion