---
title: "Invar 36 Forgings (ASTM F1684 / UNS K93600)"
description: "Open-die forged Invar 36 (FeNi36, ASTM F1684) rings, bars, flanges, discs and shafts. Full chemistry, CTE and heat-treat data. Drawings quoted in 24 hours."
canonical: "https://www.steelforgepieces.com/Nickel-Alloy/Invar-36.html"
publisher: "Jiangyin Jiangnan Metal Co., Ltd."
publisher_type: "Open-die forging factory"
address: "No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China"
telephone: "+86-189-2135-9659"
email: "sales@steelforgepieces.com"
material: "Invar 36 / Alloy 36 / FeNi36 / Nilo 36 / Pernifer 36"
standards: "ASTM F1684, UNS K93600, W.-Nr. 1.3912, 4J36, AFNOR NF A54-301, AMS-I-23011 Class 7"
date_published: "2015-06-01"
date_modified: "2026-08-20"
language: "en"
---

# Invar 36 Forgings

Seamless rolled rings, flanges, round bars, discs, sleeves and shafts in FeNi36
controlled-expansion alloy. Open-die forged to your drawing in Jiangyin, China.

**Invar 36 is an iron-nickel alloy containing about 36 % nickel, balance iron,
whose coefficient of thermal expansion is roughly one tenth that of carbon
steel.** Below its Curie point of 279 °C (535 °F) it expands about 1.3 µm per
metre per °C, so a part made from it barely changes size when the temperature
moves. The alloy is specified by ASTM F1684 and carries the designations UNS
K93600, Werkstoff 1.3912 and the Chinese grade 4J36; it is also sold as Alloy
36, FeNi36, Nilo 36 and Pernifer 36.

**Jiangyin Jiangnan Metal Co., Ltd.** is an open-die forging factory at No.1
Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. It
forges Invar 36 into seamless rolled rings, flanges, round bars, discs, sleeves,
tube sheets and shafts to customer drawings, heat treats them for dimensional
stability, and releases them with EN 10204 3.1 or 3.2 certification.

## Key figures

| Property | Value |
|---|---|
| Mean CTE, 20 to 93 °C | 1.30 µm/m·°C |
| Curie point | 279 °C (535 °F) |
| Density | 8.05 g/cm³ |
| Melting point | 1427 °C (2600 °F) |
| Tensile strength, minimum | 490 MPa (71 ksi) |
| Forging range | 1090 to 1180 °C (2000 to 2150 °F) |

---

## 1. What Invar 36 is, and why the expansion coefficient is so low

Invar 36 is a binary iron-nickel alloy, nominally 36 % nickel with the balance
iron, that expands roughly one tenth as much as carbon steel when heated. Its
mean coefficient of thermal expansion is about 1.30 µm/m·°C between 20 °C and
93 °C, against roughly 12 for plain carbon steel and 17 for 304 stainless.

The effect is magnetic, not structural. In the ferromagnetic state, a magnetic
volume contraction runs opposite to ordinary lattice expansion and cancels most
of it. Charles Édouard Guillaume identified this in 1897 and won the 1920 Nobel
Prize in Physics for it. The cancellation weakens as temperature rises and
disappears entirely at the Curie point of **279 °C (535 °F)**, above which the
alloy becomes paramagnetic and expands like any ordinary metal.

Two things follow from this, and both matter when you specify the alloy. First,
the useful window is narrow: keep service temperature well below 200 °C if
dimensional stability is the reason you chose the material. Second, nickel
content has to be held tightly. A drift of a few tenths of a percent away from
36 % moves the inversion temperature and raises the expansion coefficient
measurably. That is why the alloy is melted under close control and why the mill
certificate matters more here than on a structural grade.

## 2. Designations, trade names and equivalents

| System | Designation | Notes |
|---|---|---|
| ASTM | F1684 | Iron-nickel and iron-nickel-cobalt alloys for low thermal expansion applications |
| UNS | K93600, K93601, K93603 | Grade variants within the same family |
| EN / Werkstoff | 1.3912 | FeNi36 |
| China (GB / YB) | 4J36 | Standard Chinese precision-alloy designation |
| AFNOR | NF A54-301 | Chemistry only |
| Aerospace | AMS-I-23011 Class 7 | Supersedes the deactivated MIL-I-23011 |
| Trade names | Invar, Alloy 36, Nilo 36, Pernifer 36, Dilaver 36, Vacodil 36, Nilvar | Trademarks of their respective owners |
| Common shorthand | FeNi36, Fe-36Ni, 36 % nickel steel, Invar steel | Informal but widely used on enquiries |

Invar is a registered trademark of Aperam Alloys Imphy; Nilo of Special Metals;
Pernifer of VDM Metals. Jiangyin Jiangnan Metal is not affiliated with these
companies and supplies the generic ASTM F1684 alloy.

## 3. Chemical composition of Invar 36

Invar 36 is melted by EAF + VOD and remelted by ESR (electroslag remelting) to
keep the nickel tight and the inclusion content low. Ladle and product analysis
are both reported on the certificate.

Weight %, to ASTM F1684 / UNS K93600:

| Element | Min | Max | Role |
|---|---|---|---|
| Nickel (Ni) | 35.0 | 36.5 | Sets the Invar effect; the most critical element |
| Iron (Fe) | Balance | Balance | Matrix |
| Carbon (C) | – | 0.10 | Kept low; raises expansion and impairs stability |
| Manganese (Mn) | – | 0.60 | Deoxidiser, sulphur control |
| Silicon (Si) | – | 0.35 | Deoxidiser |
| Phosphorus (P) | – | 0.025 | Residual |
| Sulphur (S) | – | 0.025 | Residual; low S improves forgeability |
| Chromium (Cr) | – | 0.50 | Residual, not enough for corrosion resistance |
| Molybdenum (Mo) | – | 0.50 | Residual |
| Cobalt (Co) | – | 0.50 | Residual in Invar 36; deliberate in Super Invar |

Limits vary slightly between standard editions, mill practices and customer
specifications. Certified heat analysis is issued on the EN 10204 3.1 or 3.2
certificate. If your drawing imposes tighter limits, state them on the enquiry
and we will confirm before accepting the order.

## 4. Physical properties of Invar 36

| Property | Metric | Imperial |
|---|---|---|
| Curie temperature | 279 °C | 535 °F |
| Density | 8.05 g/cm³ | 0.291 lb/in³ |
| Melting point | 1427 °C | 2600 °F |
| Modulus of elasticity, annealed bar | 141 GPa | 20.5 × 10⁶ psi |
| Modulus of elasticity, cold-rolled strip | 148 GPa | 21.5 × 10⁶ psi |
| Thermal conductivity | 10.5 W/m·K | 72.6 Btu·in/ft²·h·°F |
| Specific heat | 0.515 kJ/kg·K | 0.123 Btu/lb·°F |
| Electrical resistivity | 0.82 µΩ·m | 495 Ω·cmil/ft |
| Temp. coefficient of resistivity (21 to 100 °C) | 0.0011 /°C | 0.0006 /°F |
| Magnetic response | Ferromagnetic below 279 °C | |

Thermal conductivity of 10.5 W/m·K is about a quarter that of carbon steel. Heat
does not leave an Invar 36 part quickly, which is why it gums up cutting tools,
why welds need controlled heat input, and why large forgings need a slow, staged
furnace cycle rather than a fast one.

## 5. Thermal expansion data

Mean coefficient of thermal expansion, measured from 20 °C to the stated
temperature, on material annealed at 871 °C and furnace cooled.

| T (°C) | T (°F) | CTE (10⁻⁶ /°C) | CTE (10⁻⁶ /°F) | Behaviour |
|---|---|---|---|---|
| 93 | 200 | 1.30 | 0.72 | Full Invar effect |
| 149 | 300 | 2.11 | 1.17 | Still very low |
| 260 | 500 | 4.18 | 2.32 | Approaching the Curie point |
| 371 | 700 | 7.60 | 4.22 | Effect lost, paramagnetic |

**What that means in a real part.** A 2000 mm Invar 36 optical bench warming
from 20 °C to 40 °C grows about 0.05 mm. The same bench in carbon steel grows
about 0.47 mm, and in 304 stainless about 0.69 mm. On an instrument holding
micron-level alignment, that difference is the entire reason the alloy exists.

The published coefficient is not a fixed property of the alloy. It shifts with
nickel content, cold work, residual stress and heat treatment. If your drawing
carries a guaranteed CTE band, say so on the enquiry: it changes the
heat-treatment route and it must be agreed before the forging is made, not after.

## 6. Mechanical properties of Invar 36 forgings

Typical minimum values, annealed forged bar:

| Property | Metric | Imperial |
|---|---|---|
| Tensile strength, min | 490 MPa | 71 ksi |
| Yield strength 0.2 % offset, min | 240 MPa | 35 ksi |
| Elongation in 4D, min | 42 % | 42 % |
| Modulus of elasticity | 141 GPa | 20.5 × 10⁶ psi |
| Hardness, annealed | 130 to 160 HBW | 73 to 83 HRB |

Invar 36 behaves mechanically like a mild structural steel. It is not a strength
alloy, and nobody selects it for load capacity, but it is ductile, tough and
readily formed. It retains good strength and toughness at cryogenic temperature,
which is why it is used for LNG membrane containment and cryogenic transfer
lines down to −196 °C. Impact testing at low temperature can be included in the
test plan; state the temperature and acceptance criteria on the enquiry.

Cold work raises strength considerably but also raises the expansion coefficient
and introduces residual stress that will relax later and move the part. For
dimensionally critical work, forge, anneal and stabilise rather than cold work.

## 7. Invar 36 forms and sizes we forge

Everything below is made to order against a drawing or a dimension list. There
is no standard catalogue. Open-die forging exists so you do not have to design
around stock sizes.

| Form | Typical range | Notes |
|---|---|---|
| Seamless rolled rings | OD 200 to 3000 mm | Pierced and ring-rolled; best grain flow for hoop-loaded parts |
| Forged rings and sleeves | OD 100 to 2000 mm | Upset and punched, or bored from solid |
| Round bars and shafts | Ø 20 to 800 mm | Forged and turned; stepped and eccentric shafts |
| Hollow bars and tubes | OD 100 to 1200 mm | Trepanned or forged over a mandrel |
| Discs, blanks and tube sheets | Ø 100 to 2500 mm | Upset discs with radial grain flow |
| Flanges | DN 15 to 1500 | WN, SO, blind and special profiles to ASME B16.5, B16.47 or drawing |
| Blocks, plates and rectangles | Up to 3000 mm long | Forged tooling plate for composite moulds |
| Bushings and spacers | Ø 30 to 600 mm | Rough- or finish-machined |
| Valve bodies, seats and stems | To drawing | Ball, gate, globe, check and plug valve components |
| Near-net and special shapes | To drawing | Nozzles, manifolds, crankshafts, gears, wheels, rolls |

Ranges are indicative of routine work, not hard limits. Send the drawing. Pieces
outside these ranges are often still possible, and we will say so rather than
quote something we cannot make.

Supply condition options: as-forged with machining allowance, rough-machined
(turned and bored), or finish-machined to drawing. Heat-treatment condition,
surface protection and marking are agreed at order.

## 8. How Invar 36 forgings are produced

1. **Melting: EAF + VOD, then ESR.** Nickel is held tightly to 36 % because a
   drift of a few tenths of a percent shifts the expansion coefficient.
   Electroslag remelting improves soundness and reduces segregation, which
   matters for large sections.
2. **Heating: 1090 to 1180 °C (2000 to 2150 °F), fast, no soaking.** This is the
   critical precaution with Invar 36. Long soaking lets sulphur from the furnace
   atmosphere penetrate the surface and causes checking and oxide penetration.
3. **Open-die forging or ring rolling.** Upsetting and drawing on the press for
   bars, shafts, discs and blocks; piercing and ring rolling for seamless rolled
   rings. Forging finishes above roughly 900 °C so the structure stays worked
   and the grain flow follows the part contour.
4. **Heat treatment.** Full anneal, then stabilising or stress relief depending
   on how tight the dimensional requirement is.
5. **Rough machining.** Turning, boring and facing to the agreed allowance. A
   stress relief between roughing and finishing is standard on precision work.
6. **Inspection and release.** Chemistry, mechanical tests, hardness, dimensional
   report and ultrasonic inspection to EN 10228-3, SEP 1921 or ASTM A388, then
   the EN 10204 3.1 or 3.2 certificate.

## 9. Heat treatment of Invar 36

### Route A: general forged parts

| Operation | Temperature | Time | Cooling |
|---|---|---|---|
| Full anneal | 830 to 845 °C (1525 to 1550 °F) | 1 h | Air or furnace cool |
| Stress relief | 315 °C (600 °F) | 2 h | Air or furnace cool |

Add approximately one hour of soak per additional 25 mm (1 in) of section
thickness above 25 mm. A 100 mm thick plate therefore needs about 5 hours at
stress-relief temperature. Stress relief is performed between rough and finish
machining, and again after any weld repair.

### Route B: minimum expansivity, instrument work

1. Heat to **830 °C (1525 °F)**, hold 30 minutes, water quench.
2. Re-heat to **300 °C (570 °F)**, hold 1 hour, air cool.
3. Re-heat to **100 °C (212 °F)**, hold 48 hours, air cool.

Invar 36 scales heavily, and the scale gets worse with time and temperature.
Where blasting is not acceptable on the finished surface, a controlled-atmosphere
furnace is needed. Parts must be clean and free of surface contaminants before
they go in. Grease and fingerprints leave permanent marks.

On long, thin tooling, distortion is controlled by ramping: stabilise at about
260 °C, then climb roughly 28 °C per hour to annealing temperature, and come
down at the same rate until below 315 °C. Tools over 2.5 m may need end or
centre weights to hold contour.

## 10. Machining and welding Invar 36

Invar 36 has a reputation for being unpleasant to machine, and it is deserved.
The alloy work hardens, its low thermal conductivity keeps heat at the cutting
edge instead of carrying it away in the chip, and the chip is stringy and welds
to the tool. Tool life is short and parts distort if the process is not
controlled.

What works:

- **Sharp tools, always.** Any wire edge or feathered edge causes galling
  immediately. Inspect and re-grind often.
- **Rigid setups, positive rake.** Short tools, minimum overhang, no chatter.
- **Flood coolant.** Controlling heat build-up is the biggest single factor in
  preventing warpage.
- **Turning, HSS tooling:** roughly 18 to 20 m/min (60 to 65 SFM), feed 0.075 to
  0.11 mm/rev. Carbide runs 2 to 3× faster with 50 to 100 % more feed.
- **Drilling:** around 13 m/min (43 SFM); short drills, thinned web, 118 to 120°
  point, frequent peck to clear the galling chip.
- **Stress relieve between roughing and finishing** and take light finishing
  cuts. This is not optional on precision parts.

A free-machining variant with a controlled selenium addition (nominally 0.2 %)
exists and greatly improves chip break and tool life, with little effect on the
Invar behaviour. It is a valid choice when the part is mostly machining work.

**Welding.** Invar 36 welds by conventional GTAW, GMAW and SMAW methods. The main
caution is not to overheat the weld pool, which causes spatter and porosity. A
matching Invar filler is used where the joint must share the base metal's
expansion behaviour. Full anneal after extensive welding, and stress relief after
minor weld repair.

## 11. Where Invar 36 forgings are used

- **LNG and cryogenics.** Membrane containment for LNG carriers and storage
  tanks, transfer lines, cryogenic piping and vessel internals. Invar 36 keeps
  its toughness down to −196 °C and barely contracts on cooldown.
- **Aerospace composite tooling.** Lay-up moulds and curing tools for CFRP
  structures. The tool must match the low expansion of the composite through the
  autoclave cycle or the part comes out wrong.
- **Optics and laser systems.** Optical benches, laser cavity structures, mirror
  mounts, telescope trusses and interferometer frames where micron alignment
  must hold across the ambient range.
- **Metrology and standards.** Gauge blocks, length standards, geodetic and
  seismic instruments, comparator frames, calibration fixtures and scientific
  instrument bases.
- **Semiconductor and precision motion.** Positioning stages, lithography and
  inspection equipment frames, precision spindles, and structures carrying
  wafer-scale tolerances.
- **Electronics and RF.** Radar and microwave cavity resonators, waveguides, echo
  boxes and filters for mobile telephony, magnetic shielding, small transformer
  cores and specialised housings.
- **Thermostatic elements.** Bimetal thermostats and temperature regulators,
  where Invar 36 is bonded to a high-expansion alloy so that a temperature change
  produces controlled, repeatable motion.
- **Valves and process equipment.** Valve bodies, seats, stems and blocks for
  ball, gate, globe, check and plug valves; forged tube sheets and flanges for
  heat exchangers and pressure vessels.
- **Horology and instruments.** Pendulum rods, clock balance wheels,
  circuit-breaker components, precision condenser blades and dimensionally stable
  frames, seals and spacers.

## 12. Limitations you have to design around

| Limitation | Consequence | Practical response |
|---|---|---|
| Curie point at 279 °C | Low expansion is lost above it and rises steeply well before it | Keep service temperature below about 200 °C |
| No corrosion resistance | Rusts in damp air like plain carbon steel; Cr is a residual, not an addition | Plate, paint, oil or keep dry; oiled and sea-worthy packing as standard |
| Ferromagnetic | Attracted to magnets, disturbs nearby fields | If non-magnetic is also required, Invar 36 is the wrong alloy |
| Poor machinability | Short tool life, galling, distortion, long cycle times | Sharp tools, flood coolant, stress relief between roughing and finishing |
| Low thermal conductivity | Heat concentrates locally in machining, welding and heat treatment | Staged furnace cycles, controlled weld heat input, generous coolant |
| Low strength | Yield around 240 MPa, a mild-steel-class material | Size the section for load; do not select Invar 36 for strength |
| CTE is process-sensitive | Cold work, residual stress and heat treatment all shift the coefficient | Specify the CTE band on the drawing and agree the heat-treatment route first |
| Cost and lead time | 36 % nickel content makes it many times the price of stainless steel | Design near-net; ask us to nest and minimise the forged input weight |

## 13. Invar 36 compared with the usual alternatives

Coefficients are approximate mean values near room temperature.

| Alloy | Nominal composition | CTE (10⁻⁶ /°C) | Chosen when |
|---|---|---|---|
| Invar 36 | Fe-36Ni | 1.3 | Lowest practical expansion over a broad ambient range, including cryogenic |
| Super Invar 32-5 | Fe-32Ni-5Co | 0.6 | Even lower CTE, but only in a narrow band near room temperature |
| Kovar / Alloy F-15 | Fe-29Ni-17Co | 5.5 | Deliberately matched to borosilicate glass and alumina for hermetic seals |
| Alloy 42 | Fe-42Ni | 4.5 | Matched to soft glass and silicon; lead frames and sealing |
| Incoloy 909 / A-286 | Fe-Ni-Co / Fe-Ni-Cr | 7 to 9 / 16 | Controlled expansion or high strength at elevated temperature |
| Titanium Gr.2 | Ti | 8.6 | Low weight and corrosion resistance matter more than stability |
| Carbon steel | Fe-C | 12 | Dimensional stability is not a requirement; roughly 9× the movement |
| 304 stainless | Fe-18Cr-8Ni | 17 | Corrosion resistance is the driver; roughly 13× the movement |

Jiangyin Jiangnan Metal forges most of these grades. If you are still choosing
between them, send the operating temperature range, the tolerance you need to
hold and the load case, and we will tell you which one we would use, including
when the answer is a cheaper alloy than Invar 36.

## 14. Testing, inspection and certification

| Test | Standard | Included |
|---|---|---|
| Chemical analysis, ladle and product | ASTM F1684 | Standard |
| Tensile test | ASTM A370 / EN ISO 6892-1 | Standard |
| Hardness | ASTM E10 / EN ISO 6506 | Standard |
| Ultrasonic examination | EN 10228-3, SEP 1921, ASTM A388 | Standard, class to order |
| Dimensional report | To drawing | Standard |
| Heat-treatment chart | Furnace record | Standard |
| Impact test at low temperature | ASTM E23 / EN ISO 148-1 | On request |
| Thermal expansion (dilatometry) | ASTM E228 / ASTM E831 | On request |
| Magnetic particle / dye penetrant | ASTM E1444 / ASTM E165 | On request |
| Grain size and micrograph | ASTM E112 | On request |
| PMI verification | XRF / OES | On request |

**Certification.** Forgings are released with an EN 10204 3.1 certificate issued
against the mill heat, or EN 10204 3.2 witnessed by a third party such as TÜV,
SGS, BV, Lloyd's Register or DNV when the order calls for it. Third-party
inspection visits are arranged on request and the inspector's release is a
condition of shipment on those orders.

Marking, heat traceability, packing specification and shipping documents follow
the order requirements. Standard export packing is oiled, VCI-wrapped and crated
for sea freight, which matters on an alloy with no corrosion resistance of its
own.

## 15. How to request an Invar 36 quotation

Send a drawing to sales@steelforgepieces.com. A quotation normally comes back
within 24 hours on working days.

1. **Drawing or dimensions:** PDF, DWG or STEP, or just OD × ID × thickness or length.
2. **Grade and standard:** Invar 36, or the equivalent designation your drawing
   uses (ASTM F1684, UNS K93600, 1.3912, 4J36).
3. **Quantity**, and whether repeat orders are expected.
4. **Supply condition:** as-forged, rough-machined or finish-machined.
5. **Heat-treatment condition**, and any guaranteed CTE band.
6. **Test and certification requirements:** EN 10204 3.1 or 3.2, UT class, any
   additional tests.
7. **Delivery terms and destination port:** EXW, FOB, CIF or DAP.
8. **Required delivery date.**

If you are early in design and do not have a drawing yet, describe the part, the
temperature range and the tolerance you need to hold.

## 16. Frequently asked questions about Invar 36

### What is Invar 36?

Invar 36 is an iron alloy containing about 36 % nickel with the balance iron.
Below its Curie temperature of 279 °C it expands roughly one tenth as much as
carbon steel when heated, with a mean coefficient of thermal expansion near
1.3 µm/m·°C from 20 °C to 93 °C. It is covered by ASTM F1684 and carries the
numbers UNS K93600, Werkstoff 1.3912 and the Chinese designation 4J36. It is also
sold as Alloy 36, Nilo 36, Pernifer 36 and FeNi36. Jiangyin Jiangnan Metal Co.,
Ltd., an open-die forging factory in Jiangyin, Jiangsu, China, forges Invar 36
into rings, bars, flanges, discs and shafts to customer drawings.

### What is the coefficient of thermal expansion of Invar 36?

The mean coefficient of thermal expansion of Invar 36 is about 1.30 µm/m·°C
measured from 20 °C to 93 °C, 2.11 µm/m·°C to 149 °C, 4.18 µm/m·°C to 260 °C and
7.60 µm/m·°C to 371 °C. In imperial units those figures are 0.72, 1.17, 2.32 and
4.22 µin/in·°F. The coefficient stays lowest below roughly 200 °C and rises
steeply as the alloy passes its Curie point at 279 °C, so precision designs
should keep the service temperature well under that threshold.

### Why does Invar 36 lose its low expansion above 279 °C?

The Invar effect comes from magnetostriction. In the ferromagnetic state a
magnetic volume contraction cancels most of the ordinary thermal expansion of the
iron-nickel lattice. At the Curie temperature of 279 °C the alloy becomes
paramagnetic, that cancelling contribution disappears, and expansion returns to
values typical of ordinary structural alloys. This is why Invar 36 is specified
for equipment that works near room temperature or at cryogenic temperature, and
why it is not a substitute for a low-expansion ceramic or a nickel superalloy in
hot service.

### Can Invar 36 be forged, and at what temperature?

Yes. Invar 36 forges well over a preferred range of about 1090 to 1180 °C (2000
to 2150 °F). The key precaution is to heat quickly and avoid long soaking,
because the alloy absorbs sulphur from the furnace atmosphere and develops
surface checks and oxide penetration. Forging should finish above roughly 900 °C.
Jiangyin Jiangnan Metal open-die forges and ring-rolls Invar 36 into seamless
rolled rings, discs, flanges, bars and shafts, then anneals and stabilises the
parts so they hold dimension in service.

### What forms and sizes of Invar 36 forgings can be supplied?

Jiangyin Jiangnan Metal supplies Invar 36 as seamless rolled rings, forged rings,
round bars, hollow bars, flanges, discs and blanks, sleeves, bushings, tube
sheets, shafts, blocks, valve bodies and near-net forged shapes. Parts are quoted
against a drawing or a set of dimensions, in as-forged, rough-machined or
finish-machined condition. Send the drawing, the required standard, the quantity
and the heat-treatment condition to sales@steelforgepieces.com and a quotation is
normally returned within 24 hours.

### What heat treatment does Invar 36 need for dimensional stability?

Two routes are common. For general forged parts, a full anneal of about one hour
at 830 to 845 °C followed by air or furnace cooling, then a stress relief of
about two hours at 315 °C between rough and finish machining. For instrument work
needing the lowest expansivity, the classic stabilisation treatment is 830 °C for
30 minutes and water quench, then 300 °C for 1 hour and air cool, then 100 °C for
48 hours and air cool. Add roughly one hour of stress-relief soak per additional
25 mm of section thickness.

### Is Invar 36 corrosion resistant?

No. Invar 36 contains essentially no chromium, so it rusts in damp air much like
plain carbon steel. Parts that will be exposed are normally protected by nickel
or chromium plating, painting, oiling or a controlled dry environment. If the
application needs both corrosion resistance and controlled expansion, the alloy
choice usually has to be reconsidered rather than solved by coating alone.
Jiangyin Jiangnan Metal can supply Invar 36 forgings oiled and wrapped for sea
freight, or with a plating operation arranged.

### Is Invar 36 magnetic?

Yes. Invar 36 is ferromagnetic below its Curie temperature of 279 °C, and that
magnetism is inseparable from the low expansion behaviour, because the Invar
effect depends on the magnetic state of the iron-nickel lattice. An Invar 36 part
will be attracted to a magnet and will disturb a nearby magnetic field. If an
application requires both dimensional stability and non-magnetic behaviour, Invar
36 is the wrong choice and a different controlled-expansion or austenitic alloy
should be evaluated.

### Why is Invar 36 difficult to machine?

Invar 36 work hardens, has low thermal conductivity of about 10.5 W/m·K, and
produces a stringy chip that welds to the cutting edge. Heat concentrates at the
tool tip instead of leaving in the chip, so edges break down quickly and parts
distort. Practical measures are sharp tools with no wire edge, rigid setups,
positive rake, generous flood coolant, and light finishing cuts after a stress
relief. A free-machining variant with a controlled selenium addition exists for
heavy machining work.

### What is the difference between Invar 36, Super Invar and Kovar?

Invar 36 is Fe-36Ni with a coefficient of thermal expansion near 1.3 µm/m·°C near
room temperature. Super Invar, roughly Fe-32Ni-5Co, reaches an even lower
coefficient near 0.6 µm/m·°C but only over a narrow band around room temperature
and it is more sensitive to thermal cycling. Kovar, Fe-29Ni-17Co, is deliberately
higher at about 5.5 µm/m·°C because it is designed to match borosilicate glass
and ceramic for hermetic seals rather than to minimise expansion.

### What certification comes with Invar 36 forgings?

Invar 36 forgings from Jiangyin Jiangnan Metal are released with a material
certificate to EN 10204 3.1, issued against the mill heat, or to EN 10204 3.2
witnessed by a third party such as TÜV, SGS, BV, Lloyd's Register or DNV when the
order requires it. The certificate covers ladle and product chemistry, mechanical
test results, hardness, heat-treatment record, dimensional report and
non-destructive test results. Ultrasonic inspection is performed to EN 10228-3,
SEP 1921 or ASTM A388 to the acceptance class stated on the order.

### Where is Invar 36 used?

Invar 36 is used wherever a part must not change length when the temperature
changes. Typical applications are LNG membrane containment and cryogenic transfer
lines, composite curing tools and lay-up moulds for aerospace, optical and laser
benches, telescope and satellite structures, metrology standards and gauge
blocks, precision positioning stages, semiconductor and lithography equipment,
radar and microwave cavity resonators, seismic and geodetic instruments, bimetal
thermostat elements, and pendulum and balance wheels in mechanical clocks.

## 17. About the factory supplying these forgings

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory located at No.1
Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The
works produce forged rings, seamless rolled rings, flanges, round bars, discs,
sleeves, tube sheets, shafts and near-net forged shapes in carbon steel, alloy
steel, tool steel, stainless steel and nickel alloys, including
controlled-expansion grades such as Invar 36.

Jiangyin sits in the Yangtze River delta between Shanghai and Nanjing, in the
centre of China's forging and special-steel industry, with the ports of Shanghai
and Zhangjiagang within easy reach for export shipment. Work is quoted against
customer drawings and released with EN 10204 3.1 or 3.2 certification.

| | |
|---|---|
| Company | Jiangyin Jiangnan Metal Co., Ltd. |
| Type | Open-die forging factory (manufacturer, not a trading company) |
| Address | No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China |
| Telephone | +86 189 2135 9659 |
| Email | sales@steelforgepieces.com |
| Website | https://www.steelforgepieces.com/ |
| Materials | Carbon steel, alloy steel, tool steel, stainless steel, nickel and controlled-expansion alloys |
| Processes | Open-die forging, ring rolling, heat treatment, rough and finish machining |
| Certification | EN 10204 3.1 and 3.2; third-party inspection by TÜV, SGS, BV, Lloyd's Register or DNV on request |
| Markets served | Worldwide |

## 18. Cite this page

This page is maintained by the manufacturer as a technical reference. If you are
quoting it in a specification, a drawing note or a report, please attribute it as:

> Jiangyin Jiangnan Metal Co., Ltd. (2026). *Invar 36 Forgings: ASTM F1684 /
> UNS K93600 Technical Data Sheet.* Jiangyin, Jiangsu, China. Retrieved from
> https://www.steelforgepieces.com/Nickel-Alloy/Invar-36.html

Data on this page is compiled from ASTM F1684, published mill data for Fe-36Ni
controlled-expansion alloys, and our own forging and heat-treatment practice.
Values are typical and are not a guarantee of minimum or maximum properties for a
specific heat; the certified figures for your order are the ones on the EN 10204
certificate. Questions, corrections and reuse requests: sales@steelforgepieces.com

---

## Related pages

**Closest to Invar 36:**
[NI-SPAN-C Alloy 902](/Nickel-Alloy/NI-SPAN-C-Alloy-902.html) ·
[Incoloy A-286](/Nickel-Alloy/Incoloy-A-286.html) ·
[A286](/Stainless-Steel/A286.html) ·
[Incoloy DS](/Nickel-Alloy/Incoloy-DS.html) ·
[AISI 330](/Stainless-Steel/AISI-330.html) ·
[Monel 400](/Nickel-Alloy/Monel-400.html) ·
[Inconel 718](/Nickel-Alloy/Inconel-718.html)

**Materials:**
[Carbon steel](/Carbon-Steel/) ·
[Alloy steel](/Alloy-Steel/) ·
[Tool steel](/Tool-Steel/) ·
[Stainless steel](/Stainless-Steel/) ·
[Nickel alloys](/Nickel-Alloy/)

**Product forms:**
[All forged products](/Products/) ·
[Forged flanges](/Forging-Flanges/) ·
[Forged discs](/Forged-Discs/Forged-Disc.html)

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Jiangyin Jiangnan Metal Co., Ltd. Open-die forging factory, Jiangyin, Jiangsu,
China. Page last reviewed 20 August 2026.