Invar Alloy Product Introduction
Product Overview
Invar (UNS N09901, commonly known as Invar 36) is a nickel-iron (Ni-Fe) low-thermal-expansion alloy defined by its exceptional dimensional stability over a wide temperature range. Unlike high-temperature-focused Nimonic 263, corrosion-optimized Monel series, or medium-strength Incoloy alloys, Invar features a precise nickel content (35-37%)—a critical design that minimizes thermal expansion via a unique austenitic matrix interaction. Its coefficient of thermal expansion (CTE) is as low as 1.2×10⁻⁶/℃ (20-230℃), nearly 1/10 that of carbon steel, enabling it to maintain near-constant dimensions under temperature fluctuations. It retains moderate mechanical strength (tensile strength ≥480 MPa) and good ductility, making it the gold standard for precision components in aerospace, optics, and metrology—where “ultra-low thermal expansion + dimensional reliability” are irreplaceable.
International Grade Comparison
Standard System | Grade | Description |
ASTM (USA) | N09901 | UNS Unified Numbering System Grade (primary Invar grade) |
EN (EU) | NiFe36 | EN 10088-1 Standard Grade (low-expansion Ni-Fe alloy) |
JIS (Japan) | NW09901 | JIS G4902 Standard Grade (equivalent to Invar 36) |
DIN (Germany) | 1.9330 | DIN 17750 Standard Grade (classic Invar alloy) |
ISO (International) | NiFe36 | ISO 6363 Standard Grade (dimensional stability-optimized alloy) |
Physical Properties (Room Temperature & Low-Expansion Highlights)
Property Indicator | Typical Value (Room Temp) | Unit | Performance Advantage (Dimensional Stability) |
Tensile Strength | ≥480 | MPa | Retains ≥420 MPa strength at 200℃; sufficient for precision structural loads |
Yield Strength (0.2% Offset) | ≥275 | MPa | No significant yield degradation up to 230℃ |
Elongation (50mm Gauge Length) | ≥30 | % | High ductility enables precision forming (e.g., thin-walled tubes) |
Coefficient of Thermal Expansion (CTE) | 1.2×10⁻⁶ | /℃ (20-230℃) | 10x lower than carbon steel (13×10⁻⁶/℃); 5x lower than Incoloy 800 |
Density | 8.05 | g/cm³ | Lower than Ni-Cr-Co alloys (e.g., Nimonic 263: 8.35 g/cm³) |
Melting Point | 1430-1450 | ℃ | Stable liquidus/solidus; no phase transformation in service range |
Magnetic Property | Ferromagnetic | — | Typical magnetic permeability: 800 (at 500 Oe); suitable for magnetic precision components |
Chemical Composition (Mass Fraction, Key Elements for Low Expansion)
Chemical Symbol | Composition Range (%) | Role in Dimensional Stability |
Ni | 35.0-37.0 | Core element for low expansion; forms austenitic matrix to suppress thermal expansion |
Fe | Balance (≈63) | Matrix base; optimizes magnetic properties and cost-effectiveness |
C | ≤0.05 | Ultra-low content prevents carbide precipitation; avoids expansion coefficient variation |
Mn | ≤0.5 | Improves hot workability; reduces hot cracking during forging |
Si | ≤0.3 | Minimizes oxide inclusions; maintains uniform CTE across the material |
S/P | ≤0.015/≤0.02 | Ultra-low impurities to prevent localized expansion anomalies |
Cu | ≤0.2 | Trace addition to refine grain size; enhances dimensional consistency |
Product Characteristics
1.Exceptional Low Thermal Expansion: CTE of 1.2×10⁻⁶/℃ (20-230℃) ensures near-zero dimensional change under temperature fluctuations—critical for precision components where 0.01mm deviation would cause failure;
2.Superior Dimensional Stability: No phase transformation (remains austenitic) in service range (up to 300℃); avoids expansion spikes from phase changes (unlike ferritic low-expansion alloys);
3.Balanced Strength & Ductility: Tensile strength (≥480 MPa) meets structural requirements for precision parts (e.g., instrument frames), while 30% elongation enables complex forming (e.g., deep drawing);
4.Good Processability: Compatible with cold/hot working (rolling, forging, bending) and precision machining (CNC milling, grinding); surface finish Ra 0.8 μm for optical components;
5.Controlled Magnetic Properties: Ferromagnetic nature (permeability ≈800) suits magnetic precision devices (e.g., magnetic sensors) without compromising expansion performance.
Metallographic Structure
At room temperature, Invar features a single-phase face-centered cubic (FCC) austenitic matrix with uniform grain size (ASTM 5-8 grades). The 36% Ni content stabilizes the austenitic structure—this crystal structure exhibits minimal lattice expansion with temperature increases (the core mechanism of Invar’s low CTE). No ferritic or martensitic phases form in the service range (up to 300℃), eliminating dimensional jumps from phase transformations. Trace impurities (C, Si) are dissolved in the matrix, with no harmful precipitates to disrupt expansion uniformity.
Product Forms and Executive Standards
Product Form | Main International Executive Standards | Application Reference |
Plates/Sheets | ASTM B388, EN 10088-2 | Precision instrument bases, optical telescope frames |
Strips/Foils | ASTM B165, EN 10106 | Thin-walled satellite antenna components, semiconductor wafer carriers |
Bars/Rods | ASTM B389, EN 10269 | Metrology standards (length), gyroscope frames |
Tubes/Pipes | ASTM B608, EN 10216-5 | Aerospace fuel lines (dimensional stability in temperature cycling) |
Wires | ASTM B753, EN 10250-3 | Precision springs (dimensional stability), magnetic sensor coils |
