Steel Super Invar-HR (Hot rolled)
Supply condition
UNS K93601 · ASTM F1684 · GB 4J32
Economical heavy plate and forging stock; always anneal and stabilize before precision use.
Values for the HR 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 |
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 |
HRThis page 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-HR?
Super Invar-HR is Super Invar supplied in the HR condition — economical heavy plate and forging stock; always anneal and stabilize before precision use. Super Invar-HR has a yield strength of 340 MPa (49.3 ksi) and a tensile strength of 530 MPa (76.9 ksi) — weaker than 76% of steel grades. Elongation at break is 28% and the elastic modulus is 145 GPa (21 Msi). Super Invar-HR 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; HR is available on request or by drawing note.
Advantages
- Good corrosion resistance — 26/100, better than 93% of steel grades
- Ductile — tolerates forming and impact — 28%, better than 89% of steel grades
- Forms and bends easily — 65/100, better than 81% 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-HR properties
Typical room-temperature values for Super Invar-HR; 23 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-HR 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-HR has a yield strength of 340 MPa (49.3 ksi) and a tensile strength of 530 MPa (76.9 ksi) — weaker than 76% of steel grades. Elongation at break is 28% and the elastic modulus is 145 GPa (21 Msi).
Thermal5
Super Invar-HR 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 0.8 µm/m·K (0.444 µin/in·°F).
Electrical3
Super Invar-HR conducts electricity at 2.2 % IACS, worse than 98% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (26/100), better than 93% of steel grades.
Sustainability4
Producing a kilogram of Super Invar-HR 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-HR's machinability is poor (30/100, worse than 89% of steel grades); weldability very good (70/100); formability good (65/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Super Invar-HR
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-HR — frequently asked
What is Super Invar-HR used for?
Super Invar-HR 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-HR?
Super Invar-HR has a typical yield strength of 340 MPa (49.3 ksi) and a tensile strength of 530 MPa (76.9 ksi) — weaker than 76% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is Super Invar-HR 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-HR 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-HR?
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-HR 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-HR?
Super Invar-HR 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.