300M Round Bar (UNS K44200)
300M Round Bar is a high-strength, vacuum-melted low-alloy steel derived from AISI 4340 with silicon added for improved strength and fatigue resistance. It is renowned for its exceptional toughness, very high tensile strength, and superior fatigue performance, making it a preferred material for aerospace and high-stress structural applications. Typically supplied in VAR (Vacuum Arc Remelted) condition, 300M ensures superior cleanliness and reliability.
Key Features
- Ultra-high-strength low-alloy steel
- Vacuum melted (VAR) for superior cleanliness
- Excellent fracture toughness and fatigue resistance
- Outstanding response to quenching and tempering
- Proven performance under extreme stress and cyclic loading
Equivalent Grades
| Grade | Relationship |
|---|---|
| AISI 4340 | Base chemistry |
| EN 40NiCrMo7 | Closest |
| BS 970 708M40 | Comparable |
Sizes
- Diameter: 12 mm to 400 mm
- Length: Fixed or cut-to-length
- Precision tolerances available on request
300M Chemical Composition
| Element | Percentage (%) |
|---|---|
| Carbon (C) | 0.38 – 0.46 |
| Silicon (Si) | 1.45 – 1.80 |
| Nickel (Ni) | 1.65 – 2.00 |
| Chromium (Cr) | 0.70 – 0.95 |
| Molybdenum (Mo) | 0.30 – 0.45 |
| Manganese (Mn) | 0.65 – 0.90 |
| Vanadium (V) | ≤ 0.10 |
| Iron (Fe) | Balance |
300M Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | 1860 – 1960 MPa |
| Yield Strength | 1650 – 1720 MPa |
| Elongation | 8 – 12% |
| Reduction of Area | ≥ 35% |
| Hardness | 52 – 55 HRC |
UNS K44200 Physical Properties
| Property | Value |
|---|---|
| Density | 7.83 g/cm³ |
| Melting Point | ~1425°C |
| Modulus of Elasticity | 205 GPa |
| Thermal Conductivity | ~42 W/m·K |
| Coefficient of Thermal Expansion | ~11.5 × 10⁻⁶ /°C |
Types of 300M Round Bar
- VAR Round Bar
- Hot Rolled Round Bar
- Forged Round Bar
- Peeled Round Bar
- Turned & Polished Round Bar
- Quenched & Tempered Round Bar
Applications
- Aircraft landing gear components
- Aerospace structural parts
- High-strength fasteners
- Shafts, axles, and critical load-bearing components
- Defense and motorsport applications
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