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Model No: Invar 36
Invar 36
Lork supplies Invar 36 bars in the 4mm–100mm range; sizes of 0.5–4mm and 100mm or larger are available via custom order. We also provide CNC machining services for Invar alloys, including precision-ground bars (h6/h7 tolerances) and cut-to-length processing.
Quantity :
Invar 36 Common Trade Names: Invar 36, Nilo 6, Pernifer 6
Invar 36 （UNS K93600） is a nickel-iron, low expansion alloy that contains 36% nickel and possesses a rate of thermal expansion approximately one-tenth that of carbon steel. Alloy 36 maintains nearly constant dimensions over the range of normal atmospheric temperatures, and has a low coefficient of expansion from cryogenic temperatures to about 500°F. This nickel iron alloy is tough, versatile and retains good strength at cryogenic temperatures.
The delivery condition of Invar bars directly determines the difficulty of machining and the final dimensional stability. While cold-drawn bars offer high strength and excellent dimensional accuracy, they also harbor significant internal stresses; if subsequent machining operations—such as turning or drilling—remove material, the resulting stress release can cause the part to deform. For high-precision applications, it is recommended to purchase annealed material and perform a stress-relief annealing treatment after machining.
"Condition Matching"in Invar 36 Bar Procurement
Scenario 1: Structural components for precision instruments (requiring extensive turning and milling)
- Recommended condition: Annealed round bar
- Reason: Low hardness (HB 130–180) makes turning, milling, and drilling easy. Stress-relief annealing (300–400°C) should be performed after machining to eliminate processing stresses and ensure dimensional stability.
⚠️ Note: If cold-drawn stock is machined directly, the release of stress after removing the surface layer may cause the part to warp or bend.
Scenario 2: Optical mounts / Laser equipment brackets (requiring extremely high dimensional precision)
- Recommended condition: Precision-ground rod (annealed + stress-relief annealed)
- Rationale: No dimensional drift is permissible after the assembly of such components. Suppliers should provide dimensional inspection reports confirming that stress-relief treatment has been performed.
Scenario 3: Cryogenic equipment (LNG, liquid nitrogen)
- Recommended condition: Annealed
- Reason: Invar 36 exhibits excellent toughness at cryogenic temperatures and does not undergo a ductile-to-brittle transition, making it a commonly used material in cryogenic engineering.
Scenario 4: Large-diameter bars (>100 mm) required
- Recommended condition: Hot-forged or hot-rolled
- Reason: Cold-drawn bars typically have a limited maximum diameter. Large diameters require forging or rolling; the material is likely supplied in a hot-worked condition, so the machining allowance for subsequent processing must be verified.
Chemical Composition:
The nickel content of Invar 36 must be precisely controlled at around 36%; a deviation of 0.5% causes the coefficient of thermal expansion to shift by an order of magnitude.
C | 0.15 max |
Mn | 0.6 max |
P | 0.006 max |
S | 0.004 max |
Si | 0.4 max |
Cr | 0.25 max |
Ni | 36.0 |
Co | 0.5 max |
Fe | balance |
Mechanical Properties:
Temperature | Yield Strength | Tensile Strength | Elongation | Reduction | |||
°C | °F | MPa | Psi | MPa | Psi | 2” % | % |
20 | 68 | 240 | 35.0 | 490 | 71.0 | 42 | 70 |
Heat treatment process
Type 1: Softening annealing
Temperature: 830–880°C; hold for 1–2 hours; water quench
Purpose: Eliminate work hardening and restore plasticity
Temperature: 830–880°C; hold for 1–2 hours; water quench
Purpose: Eliminate work hardening and restore plasticity
Type 1: Stress-relief annealing
Temperature: 300–400°C; hold for 1–2 hours; air cool
Purpose: To eliminate machining stresses and stabilize dimensio
Temperature: 300–400°C; hold for 1–2 hours; air cool
Purpose: To eliminate machining stresses and stabilize dimensio
⚠️ Crucial Reminder: If stress-relief annealing is skipped after turning, milling, and drilling, the part's dimensions will drift after sitting for a few days or undergoing temperature fluctuations. This is the most common pitfall when machining Invar 36 bar stock.
A note from Lork Group engineers: If you are purchasing Invar 36 bar stock for precision components, we recommend specifying"stress-relief annealing after machining"on your drawings. While many suppliers do not proactively mention this, it is a crucial step for ensuring dimensional stability. If you are unsure whether your machining process is optimal, feel free to send us your drawings and process details, and we can provide a technical assessment.
