Steel Super Invar STAB
Heat-treated state
UNS K93601 · ASTM F1684 · GB 4J32
STAB = stabilized
Choose for metrology and optical structures where long-term dimensional drift and lowest CTE scatter matter; applied after rough machining.
Values for the STAB condition
Other Super Invar tempers and conditions
Super Invar is listed in 5 conditions; see the grade overview at Super Invar.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault Annealed | Standard stocked condition for plate, bar and forgings that will be machined and then stabilized. | 300 | 500 | 35 | 150 HB | 2.2 % IACS |
STABThis page Stabilized | Choose for metrology and optical structures where long-term dimensional drift and lowest CTE scatter matter; applied after rough machining. | 310 | 500 | 33 | 155 HB | 2.2 % IACS |
Hot rolled | Economical heavy plate and forging stock; always anneal and stabilize before precision use. | 340 | 530 | 28 | 165 HB | 2.2 % IACS |
Cold drawn | Higher strength and better straightness/tolerance for small bar and wire; expect higher residual stress, so stabilize before final machining of precision parts. | 570 | 680 | 12 | 18 HRC | 2.2 % IACS |
Cold Rolled Hard | For springy shims, diaphragms and thin strip where stiffness/strength is needed and low-expansion tolerance is looser. | 650 | 750 | 5 | 23 HRC | 2.1 % IACS |
What is Super Invar STAB?
Super Invar STAB is Super Invar heat treated to STAB — choose for metrology and optical structures where long-term dimensional drift and lowest CTE scatter matter; applied after rough machining. Super Invar STAB has a yield strength of 310 MPa (45 ksi) and a tensile strength of 500 MPa (72.5 ksi) — weaker than 83% of steel grades. Elongation at break is 33% and the elastic modulus is 145 GPa (21 Msi). Super Invar STAB has a density of 8.15 g/cm³ (0.294 lb/in³), heavier than 97% of steel grades. It melts at 1,425°C (2,597 °F). ANN is the default condition FabDigit quotes; STAB is available on request or by drawing note.
Advantages
- Ductile — tolerates forming and impact — 33%, better than 96% of steel grades
- Good corrosion resistance — 28/100, better than 94% of steel grades
- Forms and bends easily — 72/100, better than 88% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Poor heat conductor — 10.5 W/m·K (6.07 BTU/hr·ft·°F), worse than 100% of steel grades
- Limited service temperature — 150°C (302 °F), worse than 99% of steel grades
- Low stiffness — 145 GPa (21 Msi), worse than 98% of steel grades
- Low electrical conductivity — 2.2 % IACS, worse than 98% of steel grades
- High embodied carbon — 5.5 kg CO₂/kg, worse than 97% of steel grades
Super Invar STAB properties
Typical room-temperature values for Super Invar STAB; 22 are specific to this condition. Other listed values are Super Invar reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
Super Invar STAB has a density of 8.15 g/cm³ (0.294 lb/in³), heavier than 97% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
Super Invar STAB has a yield strength of 310 MPa (45 ksi) and a tensile strength of 500 MPa (72.5 ksi) — weaker than 83% of steel grades. Elongation at break is 33% and the elastic modulus is 145 GPa (21 Msi).
Thermal5
Super Invar STAB is rated for continuous service to 150°C (302 °F). It conducts heat at 10.5 W/m·K (6.07 BTU/hr·ft·°F), worse than 100% of steel grades. Thermal expansion is 0.35 µm/m·K (0.194 µin/in·°F).
Electrical3
Super Invar STAB conducts electricity at 2.2 % IACS, worse than 98% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (28/100), better than 94% of steel grades.
Sustainability4
Producing a kilogram of Super Invar STAB takes about 75 MJ of energy and emits 5.5 kg of CO₂ — more than 97% of steel grades. Typical recycled content is 25%.
Manufacturability7
Super Invar STAB's machinability is poor (30/100, worse than 89% of steel grades); weldability very good (70/100); formability very good (72/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Super Invar STAB
Is Super Invar easy to machine?
Gummy and work-hardening: use sharp positive-rake carbide, heavy rigid setups, 25–60 m/min, generous flood coolant, and rough-machine → stabilize → finish-machine to hold micron tolerances.
Can Super Invar be welded?
GTAW/EBW with matching Fe-32Ni-5Co filler on clean, oil-free surfaces; avoid Ni-free steel fillers as they raise local CTE, and re-stabilize after welding.
Can Super Invar be formed, bent or molded?
Austenitic and ductile in the annealed state — deep drawing, spinning and bending are straightforward; interstage anneal at 830–870 °C after heavy reductions.
What surface finishes work on Super Invar?
Takes a good lapped/optical polish but rusts readily, so protect with electroless nickel, chromium plate, black oxide or paint; no anodizing (ferrous).
Super Invar chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| NiNi+Co balance sets the Invar minimum | 31 – 33 | 32 |
| Co | 4 – 6 | 5 |
| Clow C for dimensional stability | ≤ 0.05 | 0.02 |
| Mn | ≤ 0.6 | 0.35 |
| Si | ≤ 0.3 | 0.15 |
| Crresidual | ≤ 0.25 | — |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
Super Invar STAB — frequently asked
What is Super Invar STAB used for?
Super Invar STAB is typically used for optical bench and telescope mirrors mounts, laser gyroscope structures, high-precision length standards and aerospace metrology fixtures. In short: lowest CTE Invar variant; narrow useful temperature band; optical and metrology grade.
What is the yield strength of Super Invar STAB?
Super Invar STAB has a typical yield strength of 310 MPa (45 ksi) and a tensile strength of 500 MPa (72.5 ksi) — weaker than 83% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is Super Invar STAB easy to machine?
Not especially — machinability is rated poor (30/100, worse than 89% of steel grades). Gummy and work-hardening: use sharp positive-rake carbide, heavy rigid setups, 25–60 m/min, generous flood coolant, and rough-machine → stabilize → finish-machine to hold micron tolerances.
Can Super Invar STAB be welded?
Yes — weldability is rated very good (70/100). GTAW/EBW with matching Fe-32Ni-5Co filler on clean, oil-free surfaces; avoid Ni-free steel fillers as they raise local CTE, and re-stabilize after welding.
What surface finishes work on Super Invar STAB?
Takes a good lapped/optical polish but rusts readily, so protect with electroless nickel, chromium plate, black oxide or paint; no anodizing (ferrous).
Can Super Invar STAB be formed, bent or molded?
Austenitic and ductile in the annealed state — deep drawing, spinning and bending are straightforward; interstage anneal at 830–870 °C after heavy reductions.
What is the maximum service temperature of Super Invar STAB?
Super Invar STAB is rated for continuous use to about 150°C (302 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Super Invar-ANN and Super Invar CR-H?
ANN is the default condition — standard stocked condition for plate, bar and forgings that will be machined and then stabilized. CR-H: for springy shims, diaphragms and thin strip where stiffness/strength is needed and low-expansion tolerance is looser. Yield strength is 300 MPa in ANN versus 650 MPa in CR-H.
Sources
- ASTM F1684 — Standard Specification for Iron-Nickel and Iron-Nickel-Cobalt Alloys for Low Thermal Expansion Applications — ASTM International (2021)
- Super-Invar 32-5 Controlled Expansion Alloy — Carpenter Technology (2020)
- ASM Handbook Vol.2 — Properties of Low-Expansion Fe-Ni and Fe-Ni-Co Alloys — ASM International (1990)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.