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Invar bar stock refers to semi-finished solid bars made from Invar 36 alloy, a nickel-iron material renowned for its exceptionally low coefficient of thermal expansion. These bars are supplied in various shapes—round, flat, square, and rectangular—and are commonly used in machining, fabrication, and thermal-stability-critical components. Invar bar stock is widely utilized in aerospace tooling, measuring equipment, electronic devices, cryogenic systems, and optical structures where dimensional consistency is essential across temperature fluctuations.
Chemical Composition of Invar 36 Bar Stock
The elemental makeup of Invar 36 ensures its thermal stability and magnetic characteristics:
| Element | Content (%) |
|---|---|
| Nickel (Ni) | 35.0 – 37.0 |
| Iron (Fe) | Balance |
| Carbon (C) | ≤ 0.05 |
| Silicon (Si) | ≤ 0.35 |
| Manganese (Mn) | ≤ 0.60 |
| Phosphorus (P) | ≤ 0.02 |
| Sulfur (S) | ≤ 0.02 |
Common Shapes and Dimensions
Invar bar stock comes in a range of geometries and sizes to meet varied industry needs:
| Bar Type | Size Range (mm) | Form |
|---|---|---|
| Round Bar | 2 – 300 diameter | Cold-drawn, Hot-rolled |
| Flat Bar | 3 – 100 thickness | Annealed, Ground |
| Square Bar | 5 – 100 side length | Precision cut |
| Rectangular Bar | Custom dimensions | Forged or hot-rolled |
Mechanical and Physical Properties
Invar bar stock delivers consistent strength and dimensional reliability over a wide range of environments:
| Property | Typical Value |
|---|---|
| Density | 8.1 g/cm³ |
| Thermal Expansion (20–100°C) | ~1.2 × 10⁻⁶ /°C |
| Tensile Strength | 485–620 MPa |
| Yield Strength | 240–450 MPa |
| Elongation | ~30% |
| Hardness | ~130 HB |
| Modulus of Elasticity | ~140 GPa |
Applications of Invar Bar Stock
Owing to its stability and machinability, Invar bar stock is used across various fields where temperature-sensitive performance is crucial:
| Industry | Use Case |
|---|---|
| Aerospace | Molds and fixtures for composite part production |
| Metrology | Length standards, calibration instruments |
| Electronics | Support frames, carriers |
| Optical Devices | Precision mounting frames |
| Cryogenic Engineering | Low-temperature structural supports |
Machining and Fabrication Guidelines
Invar bar stock can be fabricated using conventional processes, although special considerations are recommended to avoid stress and work hardening:
| Operation | Recommendation |
|---|---|
| Machining | Use carbide tooling, slow feed rates |
| Welding | Use Invar 36 filler; avoid heat buildup |
| Forming | Can be cold-worked or annealed if needed |
| Heat Treatment | Anneal at 830–950°C for stress relief |
Standards and Designations
Invar 36 bar stock conforms to international norms ensuring quality and consistency in critical use cases:
| Standard | Grade |
|---|---|
| UNS | K93600 |
| ASTM | B753, F1684 |
| AMS | 2241, I23011 |
| DIN | 1.3912 |
Supply Formats and Packaging
Suppliers provide Invar bar stock in lengths typically ranging from 1 to 6 meters, or cut to size per customer requirements. Each piece is packaged in rust-proof wrapping or wooden crates to protect during international transport. Certification for mechanical tests and chemical analysis is usually included with delivery.
Related Questions
What is Invar bar stock used for?
Invar bar stock is used to manufacture precision parts in aerospace, optics, electronics, and cryogenic systems where low thermal expansion is required.
Is Invar bar stock magnetic?
Yes, Invar bar stock is magnetic at room temperature due to its iron base structure, although it has lower magnetic permeability compared to pure iron.
Can Invar bar stock be machined?
Yes, Invar bar stock is machinable using standard tools, but due to its work-hardening tendency, slow speeds and sharp cutting tools are recommended.