FENI36 Open-Die Forgings Invar 36 · Alloy 36 · UNS K93600 · W.Nr. 1.3912 · ASTM F1684

Below the Curie point, magnetostrictive contraction in FENI36 offsets most of the ordinary thermal expansion. A one metre FENI36 bar grows about 1.2 micrometres per degree Celsius. The same bar in 304 stainless steel grows about 17 micrometres, fourteen times more. This is why FENI36 is specified for metrology frames, laser benches, LNG membrane tanks and composite cure tooling.

Jiangyin Jiangnan Metal Co., Ltd. melts FENI36 by the EAF + VOD + ESR route: electric arc furnace, vacuum oxygen decarburisation, then electroslag remelting. This keeps gas content and inclusion levels low before forging. Nickel is held to a tight band because the low-expansion behaviour is sensitive to it. Drift away from 36 % moves the inversion temperature and reduces dimensional stability across the working range.

FENI36 is a single-phase austenitic alloy. It is strong, tough and ductile, it cannot be hardened by heat treatment, and its strength is set by the amount of cold work retained. Tensile strength runs from about 85,000 psi in the annealed condition to 120,000 psi and above in the hard condition.

FENI36 appears on drawings under many names. All of the designations below refer to the same nominal 36 % nickel-iron controlled-expansion alloy, and Jiangyin Jiangnan Metal Co., Ltd. forges to any of them on request.

Every FENI36 part listed below is produced to customer drawing or dimensional specification. Send a drawing, a sketch, or the finished dimensions and the required standard, and Jiangyin Jiangnan Metal Co., Ltd. will quote piece price, tooling and lead time.

Single-piece weight range: 10 kg to 8,000 kg. Rough-machined, fully machined and heat-treated conditions are all available, as is stress-relief treatment for parts that must hold dimension after machining.

Melting route

FENI36 for forging is melted by EAF + VOD and then electroslag remelted. ESR refines the solidification structure and lowers sulfur and non-metallic inclusion content. This matters for FENI36 because inclusion clusters act as ultrasonic reflectors in the thick sections typical of ring and tube-sheet forgings.

Open-die forging

Ingots are cogged and upset under hydraulic press to break down the as-cast structure and reach a forging reduction ratio suitable for the section size. Rings are then radial-axial rolled so that grain flow follows the circumference instead of being cut through by machining. This is why a rolled ring performs better than a ring cut from plate.

Heat treatment and stability

FENI36 cannot be hardened by any thermal treatment. Expansion behaviour does respond to thermal history. Rapid cooling lowers the expansion rate, slow cooling raises it, and cold work lowers it further. Parts intended for high-precision service are given a stabilising treatment after rough machining so that residual stress does not relax into dimensional drift in service.

Non-destructive examination

FENI36 forgings are ultrasonically examined to EN 10228-3, SEP 1921 or ASTM A388 as specified on the order. Dye penetrant, magnetic particle, hardness survey, dimensional report and mechanical testing are available on request.

Certification

Material certificates are issued to EN 10204 3.1. EN 10204 3.2 with third-party witness and endorsement is available where the end user, notified body or class society requires it.

Machining and welding notes

FENI36 machines like an austenitic stainless steel. It is tough and gummy, so it needs sharp carbide or high-speed-steel edges, positive rake, rigid setups and generous coolant. It welds readily by GTAW and GMAW using a matching filler such as CF36. A free-machining variant containing a controlled selenium addition exists where chip control on long production runs is critical.

FENI36 has the lowest expansion of the iron-nickel family, but it is not always the correct choice. Nickel content sets both the expansion coefficient and the Curie point, so raising nickel buys temperature range at the cost of dimensional stability.