Invar 36 Machining Services

Also known as FeNi36 · UNS K93600 · EN 1.3912

Invar 36 machining is ordered when a part must not move as temperature changes: FeNi36 expands about 1.2 µm/m·°C at 20–100 °C. DEK mills, turns, EDMs and grinds it to ±0.005 mm on request, with heat-treat cycles that keep dimensions stable.

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Metal machined bracket with cutouts on blue background

UNS K93600
EN 1.3912 (Ni36)
ASTM F1684
AMS-I-23011 Class 7
JIS Ni 36

1.2–1.5

CTE µm/m·°C
450–550 MPa

Tensile Strength
240–280 MPa

Yield Strength
8.05 g/cm³

Density

Invar 36 Machining Capabilities and Tolerances

Tolerances, finishes and part sizes DEK holds on Invar 36, inspected on CMM at 20 ± 0.5 °C after a 4-hour soak.

Milled & turned
±0.025 mm
±0.005 mm on request
Swiss-turned features
±0.003 mm
1 mm to 250 mm dia.
5-axis mold surfaces
±0.01 mm
profile
Bores
H6/H7
standard fits
Ground flatness
0.003 mm
over 300 mm
Surface finish
Ra 0.8–1.6 µm
as-machined
Ground finish
Ra 0.2–0.4 µm
precision grinding
Prototype lead time
3–5 days
plus heat-treat cycles

Invar 36 Properties and Equivalent Designations

Annealed Invar 36 data: below its Curie temperature (about 230 °C) the CTE is near zero, then rises steeply above 200 °C.

Mechanical Properties

Tensile strength 450–550 MPa
Yield strength 240–280 MPa
Hardness, annealed 130–170 HB
Hardness, cold worked up to 250 HB
Machinability ~35–40% (1212 = 100%)

Physical & Thermal

CTE, 20–100 °C 1.2–1.5 µm/m·°C
CTE limit, ASTM F1684 ≤1.6
CTE, 20–200 °C 2.0–2.5
Curie temperature about 230 °C
Density 8.05 g/cm³
Thermal conductivity 10.5 W/m·K

Chemical Composition

Ni 35–37%
Mn ≤0.6%
Si ≤0.35%
C ≤0.10% (0.05% typical)
Fe balance

Designations & Stock

UNS K93600
EN 1.3912 (Ni36)
DIN / JIS Ni36 / Ni 36
Round bar 6–250 mm
Plate 6–100 mm

Why Fe-Ni36 Machining Is Gummy

How Invar 36 behaves on the shop floor: stringy chips, work hardening, trapped heat and slow stress relaxation.

Fe-Ni36 machining behaves like a soft austenitic stainless: the chip is long and stringy and welds to the edge if speed or feed drifts low. We run sharp, positive-rake, polished carbide with feeds high enough that the tool cuts rather than plows.

With 10.5 W/m·K, heat stays at the cut, so flood coolant is standard. Machining stresses relax over weeks unless removed by the stress-relief sequence run through heat treatment.

Every finishing pass takes at least 0.1 mm to stay under the work-hardened skin.
Tools are changed on schedule; thread milling rather than tapping above M6.
Wire EDM cuts flexures and thin slots that would deflect under a cutter.
Critical features finish on precision grinding.

Cutting Speed
40–80 m/min
Positive-rake polished carbide
Machinability
~35–40%
1212 steel = 100%
Work Hardening
150 to 250+ HB
Thin skin, rubbing tool
Min. Finish Pass
0.1 mm
Stays below hardened skin
Stress Drift
10–30 µm
300 mm part, if not relieved

Optical, Metrology and Tooling Applications

Invar 36 parts machined where a few micrometers of thermal drift would break the function.

Optical Mounts

Mirror mounts, laser resonator frames, lens cells and interferometer bases; 5-axis machining cuts contoured mirror mounts.
Metrology Fixtures

CMM artifacts, gauge fixtures and length standards, built on a CTE of about 1.2 µm/m·°C at 20–100 °C.
Semiconductor Parts

Wafer stage components and reticle holders for semiconductor equipment where thermal stability sets positioning accuracy.
Composite Layup Molds

Layup molds, mandrels and satellite optical benches; Invar's CTE matches cured carbon-epoxy after a 180 °C autoclave cure.

Invar 36 vs Kovar and Other Low-CTE Materials

Choose Invar 36 when the part itself must hold dimension; choose Kovar when it must match glass or alumina in a seal.

Criteria	This GradeInvar 36	Kovar	Super Invar
Nickel content	36% Ni	29% Ni	32% Ni
Cobalt content	–	17% Co	5% Co
CTE (µm/m·°C)	1.2–1.5	about 5–6	near 0.3
Chosen for	Dimensional hold	Glass-to-metal seals	Lowest CTE
Machinability	~35–40%	Slightly easier	–
Stress relief	Needed	Needed	–

CNC Machining + Finish for Invar 36

Invar has no chromium and rusts like plain steel, so DEK ships parts oiled or with a finish applied to the parts we machine.

Electroless nickel plated Available

The usual finish on machined Invar 36 parts, applied after machining to protect an alloy that rusts like plain steel.
Gold plated Available

Gold plating is offered on Invar 36 parts we machine, typically specified with the plating spec sent alongside the drawing.
Black oxided Available

Black oxide is applied to machined Invar 36 parts as one of the usual protective finishes for this chromium-free alloy.
Rust-preventive oil Available

Every Invar 36 part ships with rust-preventive oil, since the alloy has no chromium and corrodes like plain steel.

Request an Invar 36 Machining Quote

Send a STEP, IGES or PDF drawing with stability requirement, tolerances and plating spec. An engineer lays out the stress-relief sequence and prices it within 6 hours.

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Metal bracket with cutouts on reflective surface

Why DEK for Low Expansion Alloy Machining

20+ years of low expansion alloy machining in Invar, Kovar and Super Invar, with heat cycles, grinding and CMM inspection controlled in one workflow.

Why DEK for Invar Machining

DEK is ISO 9001:2015, ISO 13485 and AS9100D certified by TÜV. Every lot gets a spectrometer check, and parts are inspected on CMM at controlled temperature. Invar 36 is the base grade on our Invar machining page.

Stress-relief cycles are built into the process and the quote. Engineer-reviewed quotes return within 6 hours, with no MOQ and prototypes in 3–5 days plus heat-treat cycles, through our CNC machining services workflow.

When Invar 36 Is (and Isn't) the Right Choice

Choose Invar 36 when thermal drift of more than a few micrometers over a 10–20 °C swing would break the function: optical alignment, metrology references, and composite tooling cured at 180 °C, including frames up to about 1000 mm on CNC milling.

Do not choose it for service above 200 °C, where the CTE rises sharply toward the Curie point, for yield strength above 280 MPa, for corrosive environments without plating, or for large low-precision structures where its price is not justified.

Raw Stock

CNC Machined

Finished Parts
Raw Stock

CNC Machined

Finished Parts

Invar 36 Machining FAQ

Common questions from engineers specifying Invar 36 parts for stability.

Is Invar 36 difficult to machine?

It is gummy rather than hard. Machinability is about 35–40% of 1212 free-machining steel, similar to 316 stainless: long stringy chips, built-up edge and rapid work hardening under a rubbing tool. Sharp positive-rake carbide, moderate speeds, firm feeds and flood coolant give clean results.

Does Invar 36 need stress relief after machining?

Yes, for any part specified for dimensional stability. Rough machine, stress relieve at 315–370 °C, semi-finish, stabilize at 95–100 °C for 24–48 h, then finish. Otherwise machining stresses relax over weeks and shift dimensions by 10–30 µm on a 300 mm part.

What is the difference between Invar 36 and Kovar?

Invar 36 (36% Ni) has the lowest CTE, about 1.2–1.5 µm/m·°C, and is used when the part itself must stay dimensionally stable. Kovar (29% Ni, 17% Co) has a CTE of 5–6 µm/m·°C matched to borosilicate glass and alumina, and is used for glass-to-metal and ceramic-to-metal seals.

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