Invar 36/Nilo 36/UNS K93600 & K93601/W. Nr. 1.3912/Alloy 36 bar

Invar 36 bar, also known as Nilo 36, Alloy 36, and designated as UNS K93600 (normal grade) and K93601 (free-machining grade), with material number W.Nr. 1.3912, is a nickel-iron alloy famous for its extremely low coefficient of thermal expansion (CTE) at and around room temperature. This bar stock form is a fundamental material for machining components where dimensional stability under varying temperatures is critical, such as in precision instruments, optical systems, scientific devices, and aerospace frameworks.

Introduction to Invar 36 (Alloy 36)

Invar 36 is the original and most widely used “low expansion” alloy. Its unique property arises from a specific nickel content (approximately 36%) which counteracts the normal thermal expansion of iron, resulting in a minimal dimensional change over a defined temperature range (typically -50°C to 100°C). The bar stock is essential for manufacturing precision parts like laser cavity frames, geodetic survey tapes, clock pendulums, molds for composite curing, and components in cryogenic equipment.

Chemical Composition of Invar 36 Bar

The near-zero expansion characteristic of Invar 36 bar is achieved through precise control of its nickel-iron balance. Supplied by Shanghai NC Metal Materials Co., Ltd., the bar stock adheres to specifications that guarantee its predictable thermal behavior.

Mechanical and Thermal Properties of Invar 36 Bar

The value of Invar 36 bar lies in its thermal stability, not high strength. Its mechanical properties are sufficient for structural applications in stable environments.

Standard Specifications, Bar Forms, and Available Sizes

Shanghai NC Metal Materials Co., Ltd. supplies Invar 36 bar in various forms tailored for precision engineering applications.

Primary Applications of Invar 36 Bar Stock

Machined components from Invar 36 bar are indispensable in applications demanding dimensional invariance: Aerospace & Satellites: Structural frames, waveguide supports, and optical benches for satellites and space telescopes where temperature cycling is severe. Precision Instrumentation: Frames for laser systems, interferometers, seismographs, and precision gauge blocks. Molding & Tooling: Molds for aerospace composite part curing (e.g., carbon fiber), where dimensional stability ensures part accuracy. Cryogenic Engineering: Components for LNG equipment and scientific cryostats. Telecommunications: Precision parts in microwave and radio frequency systems. Geodetic Survey: Length standards and tapes used for high-precision land measurement.

Machining and Fabrication of Invar 36 Bar

Standard Invar 36 (UNS K93600) has fair machinability, similar to low-carbon steel, but it is gummy and can work-harden. For improved machinability, the free-machining grade (UNS K93601) with added sulfur is available. Recommendations for machining include: using sharp, positive-rake carbide tools; moderate speeds and feeds; and ample coolant to prevent work hardening and clear chips. Stress relieving after rough machining and before finishing is highly recommended to minimize distortion and lock in dimensional stability, as residual stresses can affect the low expansion property.

Heat Treatment and Stability

Invar 36 is typically supplied in the annealed condition to ensure optimal dimensional stability. The recommended annealing cycle is heating to 830-850°C (1525-1560°F) in a protective atmosphere, holding, and furnace cooling to below 300°C (570°F), then air cooling. This relieves stresses and homogenizes the structure. For the highest stability, a stabilization heat treatment (aging) at 95-150°C (200-300°F) for an extended period may be performed after final machining to relieve micro-stresses and ensure the component’s dimensions are stable in service.

Welding and Joining

Invar 36 can be welded using Gas Tungsten Arc Welding (GTAW/TIG) and Gas Metal Arc Welding (GMAW/MIG) with matching filler metal (e.g., ERNiCrFe-7 or dedicated Invar filler). However, welding introduces significant localized heat and stress, which can distort the component and alter the low-expansion properties in the heat-affected zone (HAZ). Therefore, welding is generally avoided for precision components. If welding is necessary, a full post-weld anneal and re-stabilization heat treatment are required, which is often impractical. Mechanical fastening or adhesive bonding are preferred joining methods.

Reference Pricing and Key Purchasing Factors

The price of Invar 36 bar from Shanghai NC Metal Materials Co., Ltd. is driven by its high nickel content, specialized processing for stability, and its niche application market.