spore: profile
id: invar-36
spore_version: 0.2
family: nickel-alloys
name: Invar 36
abbreviation: FeNi36
role: low-expansion structural alloy
category: metals
type: nickel-superalloys
summary: >
  Invar 36 is an iron-nickel alloy with 36 % nickel whose thermal expansion nearly cancels near room temperature:
  1.3 ppm/K from room temperature to 93 °C, against roughly 11 to 15 ppm/K for ordinary steel. That is why it is used
  for the structures that hold optical elements at a fixed spacing in telescopes and instruments. It is a soft metal
  (276 MPa yield in the annealed condition), loses corrosion resistance in humid air, and drifts dimensionally
  unless it is stress-relieved before final machining.
best_for: "Holding a dimension across temperature changes: 1.3 ppm/K near room temperature, and 1.8 ppm/K between -240 and -18 °C"
weakest_at: "Humid air, where Matthey says its corrosion resistance falls; and dimensional drift from cold work unless it is heat-treated before final machining"
identity:
  formula: "Fe-36Ni (FeNi36, 64FeNi): iron with 36.00 wt% nickel nominal (range 35.0-37.0), manganese 0.35 (maximum 0.60), silicon 0.20 (maximum 0.40), carbon 0.02 (maximum 0.15), iron balance; UNS K93600, K93601 and K93603"
  crystal_system: face-centred cubic
  source: matthey-feni36
  where: "Chemical composition table (Fe balance, Ni 35.0-37.0, Si <= 0.40, Mn <= 0.60, C <= 0.15); the nominal 36.00 / 0.35 / 0.20 / 0.02 values are Carpenter's type analysis; UNS numbers are printed by Carpenter (K93601, K93603), Nicofe (K93603) and Matthey (approximately K93600); the
    face-centred-cubic lattice is stated in Matthey's Technische Hauptmerkmale"
tags:
  environments: [deep-space]
  stresses: [extreme-cold, thermal-cycling, vibration]
  applications: [optics-and-cameras, electronics-and-chips, cryogenic-fuel]
properties:
  - benchmark: density
    value: 8.05
    unit: g/cm3
    scope: material
    conditions: {form: "wrought bar and strip", temperature: "not stated"}
    method: Value printed in a supplier datasheet
    status: ground
    source: nicofe-invar36
    where: PHYSICAL PROPERTIES table, row Density
  - benchmark: density
    value: 8.13
    unit: g/cm3
    scope: material
    conditions: {form: "cold-rolled strip and foil", temperature: "not stated", note: "higher than the 8.05 printed by Nicofe and by Carpenter; not reconciled in the sources"}
    method: Value printed in a producer datasheet
    status: ground
    source: matthey-feni36
    where: Physikalische Eigenschaften, row Dichte (spezifisches Gewicht)
  - benchmark: cte
    value: 1.3
    unit: ppm/K
    scope: material
    conditions: {temperature_range: "21 to 93 °C (70 to 200 °F)", unit_in_source: "1.30 x 10^-6 cm/cm/°C in the metric column; 0.72 x 10^-6 in/in/°F in the English column"}
    method: Mean coefficient of thermal expansion from the manufacturer's table; the metric column was copied and the English column is kept in unit_in_source
    status: ground
    source: carpenter-invar36
    where: Physical properties, row MEAN COEFFICIENT OF THERMAL EXPANSION, 200 °F (93 °C) line
  - benchmark: cte
    value: 2.11
    unit: ppm/K
    scope: material
    conditions: {temperature_range: "21 to 149 °C (70 to 300 °F)", unit_in_source: "2.11 x 10^-6 cm/cm/°C; 1.17 x 10^-6 in/in/°F"}
    method: Mean coefficient of thermal expansion from the manufacturer's table
    status: ground
    source: carpenter-invar36
    where: Physical properties, row MEAN COEFFICIENT OF THERMAL EXPANSION, 300 °F (149 °C) line
  - benchmark: cte
    value: 4.18
    unit: ppm/K
    scope: material
    conditions: {temperature_range: "21 to 260 °C (70 to 500 °F)", unit_in_source: "4.18 x 10^-6 cm/cm/°C; 2.32 x 10^-6 in/in/°F"}
    method: Mean coefficient of thermal expansion from the manufacturer's table
    status: ground
    source: carpenter-invar36
    where: Physical properties, row MEAN COEFFICIENT OF THERMAL EXPANSION, 500 °F (260 °C) line
  - benchmark: cte
    value: 1.18
    unit: ppm/°C
    scope: material
    conditions: {temperature_range: "30 to 100 °C", unit_in_source: "1.18 (ppm/°C)"}
    method: Value printed in the supplier's linear-expansion table
    status: ground
    source: nicofe-invar36
    where: LINEAR COEFFICIENT OF PHYSICAL THERMAL EXPANSION table, 30-100 °C line
  - benchmark: cte
    value: 4.92
    unit: ppm/°C
    scope: material
    conditions: {temperature_range: "30 to 300 °C", unit_in_source: "4.92 (ppm/°C)"}
    method: Value printed in the supplier's linear-expansion table
    status: ground
    source: nicofe-invar36
    where: LINEAR COEFFICIENT OF PHYSICAL THERMAL EXPANSION table, 30-300 °C line
  - benchmark: cte
    value: 1.8
    unit: ppm/°C
    scope: material
    conditions: {temperature_range: "-240 to -18 °C", unit_in_source: "1.8 (10^-6/ºC)", note: "the only cryogenic entry read; no value below -240 °C"}
    method: Value printed in the producer's physical-properties table
    status: ground
    source: matthey-feni36
    where: Physikalische Eigenschaften, row Wärme-Ausdehnungskoeffizient lin.
  - benchmark: melting_point
    value: 1427
    unit: °C
    scope: material
    conditions: {basis: "melting range, printed as 2600 °F (1427 °C); not a single melting point"}
    method: Value printed in the manufacturer's physical-properties table
    status: ground
    source: carpenter-invar36
    where: Physical properties, row MELTING RANGE
  - benchmark: curie_temperature
    value: 279
    unit: °C
    scope: material
    conditions: {printed_as: "535 °F / 279 °C"}
    method: Value printed in the manufacturer's physical-properties table
    status: ground
    source: carpenter-invar36
    where: Physical properties, row CURIE TEMPERATURE
  - benchmark: specific_heat
    value: 515
    unit: J/(kg·K)
    scope: material
    conditions: {temperature: "20 °C"}
    method: Value printed in the producer's physical-properties table
    status: ground
    source: matthey-feni36
    where: Physikalische Eigenschaften, row Spezifische Wärme bei 20°C
  - benchmark: thermal_conductivity
    value: 72.85
    unit: Btu·in/(hr·ft²·°F)
    scope: material
    conditions: {temperature: "not stated", unit_in_source: "72.85 Btu-in/hr/ft2/°F, equal to about 10.5 W/(m·K)"}
    method: Value printed in the manufacturer's physical-properties table; the importer converts the printed unit
    status: ground
    source: carpenter-invar36
    where: Physical properties, row THERMAL CONDUCTIVITY
  - benchmark: thermal_conductivity
    value: 10.5
    unit: W/(m·K)
    scope: material
    conditions: {temperature: "20 °C", note: "matches Carpenter's 72.85 Btu-in/hr/ft2/°F after conversion to about 10.5 W/(m·K)"}
    method: Value printed in the producer's physical-properties table
    status: ground
    source: matthey-feni36
    where: Physikalische Eigenschaften, row Wärmeleitfähigkeit bei 20°C
  - benchmark: elastic_modulus
    value: 140
    unit: GPa
    scope: material
    conditions: {form: "cold-rolled strip and foil", unit_in_source: "140 kN/mm2"}
    method: Value printed in the producer's physical-properties table
    status: ground
    source: matthey-feni36
    where: Physikalische Eigenschaften, row Elastizitätsmodul, E
  - benchmark: elastic_modulus
    value: 141
    unit: GPa
    scope: material
    conditions: {form: "not stated", unit_in_source: "141 kMPa, which is 141 GPa"}
    method: Value printed in the supplier's physical-properties table
    status: ground
    source: nicofe-invar36
    where: PHYSICAL PROPERTIES table, row Modulus of elasticity (Mechanical Properties block)
  - benchmark: yield_strength
    value: 40
    unit: ksi
    scope: material
    conditions: {form: "annealed bar and strip", basis: "typical value, not a guaranteed minimum"}
    method: Value printed in the manufacturer's typical-mechanical-properties table
    status: ground
    source: carpenter-invar36
    where: Typical mechanical properties, row Annealed bars and strip, YIELD STRENGTH column
  - benchmark: yield_strength
    value: 276
    unit: MPa
    scope: material
    conditions: {form: "not stated", basis: "typical value"}
    method: Value printed in the supplier's physical-properties table
    status: ground
    source: nicofe-invar36
    where: MECHANICAL PROPERTIES block, row Yield strength
  - benchmark: ultimate_tensile_strength
    value: 65
    unit: ksi
    scope: material
    conditions: {form: "annealed bar and strip", basis: "typical value, not a guaranteed minimum"}
    method: Value printed in the manufacturer's typical-mechanical-properties table
    status: ground
    source: carpenter-invar36
    where: Typical mechanical properties, row Annealed bars and strip, TENSILE STRENGTH column
  - benchmark: ultimate_tensile_strength
    value: 518
    unit: MPa
    scope: material
    conditions: {form: "not stated", basis: "typical value"}
    method: Value printed in the supplier's physical-properties table
    status: ground
    source: nicofe-invar36
    where: MECHANICAL PROPERTIES block, row Tensile strength
  - benchmark: elongation
    value: 35
    unit: "%"
    scope: material
    conditions: {form: "annealed bar and strip", gauge: "2 in (50.8 mm)"}
    method: Value printed in the manufacturer's typical-mechanical-properties table
    status: ground
    source: carpenter-invar36
    where: Typical mechanical properties, row Annealed bars and strip, ELONGATION column
  - benchmark: electrical_resistivity
    value: 84
    unit: µΩ·cm
    scope: material
    conditions: {temperature: "not stated"}
    method: Value printed in the supplier's physical-properties table
    status: ground
    source: nicofe-invar36
    where: PHYSICAL PROPERTIES table, row Electrical resistivity
  - benchmark: electrical_resistivity
    value: 75
    unit: µΩ·cm
    scope: material
    conditions: {temperature: "not stated", note: "Matthey prints 75; Nicofe prints 84"}
    method: Value printed in the producer's physical-properties table
    status: ground
    source: matthey-feni36
    where: Physikalische Eigenschaften, row Spezifischer elektrischer Widerstand
corrosion:
  - environment: "Dry indoor air; humid air and condensation"
    headline: "Invar 36 holds up in dry air but its corrosion resistance drops as humidity rises."
    effect: >
      Matthey states that FeNi36 has good corrosion resistance in a dry atmosphere at room temperature, but that the
      resistance decreases in humid environments. Carpenter rates humidity resistance as "Good" on a four-level
      comparative scale and warns that the rating is for comparison only; Carpenter lists chromium, cadmium and nickel
      plating and zinc coating among the usual methods for the alloy.
    rating: low
    conditions: {form: "wrought bar, strip and foil", coating: "none in the datasheets; the alloy is plated for service in humid air"}
    source: matthey-feni36
    where: Technische Hauptmerkmale, sentence on corrosion resistance ("in trockener Atmosphäre ... gute Korrosionsbeständigkeit ... nimmt jedoch in feuchten Umgebungen ab"); see also carpenter-invar36, Corrosion resistance section
  - environment: "Forging furnace atmosphere containing sulfur"
    headline: "Long furnace soaks can pit the surface during forging."
    effect: >
      Carpenter warns that soaking Invar 36 in a forging furnace can produce a checked surface through absorption of
      sulfur from the furnace atmosphere or oxide penetration, and recommends heating quickly at 2000 to 2150 °F
      (1100 to 1180 °C).
    rating: moderate
    conditions: {process: "forging", atmosphere: "furnace gases"}
    source: carpenter-invar36
    where: Workability, Forging paragraph
risks:
  hazards:
    - text: >
        Nickel is the hazard in this alloy. Of 4,778 company reports aggregated by PubChem from the ECHA C&L inventory,
        99.9 % classify nickel as a skin sensitiser (H317, may cause an allergic skin reaction) and the signal word is
        Danger; some notifications also carry carcinogenicity category 2 and respiratory sensitisation category 1.
        Solid Invar releases little nickel, but grinding and cutting dust does.
      ghs: [H317]
      source: pubchem-nickel
      where: Safety and Hazards, GHS Classification (CID 935), ECHA C&L notifications summary and hazard statements
    - text: >
        Iron is the balance of the alloy. PubChem's aggregation of 6,013 company reports says 74.1 % of them find iron
        does not meet the GHS hazard criteria, while 15.5 % classify it as a flammable solid (H228). Fine iron powder
        can ignite and reacts with moisture to give hydrogen, so machining fines are the concern, not solid Invar.
      ghs: [H228]
      source: pubchem-iron
      where: Safety and Hazards, GHS Classification (CID 23925), ECHA C&L notifications summary and hazard statements
  failure_risks:
    - mode: "Dimensional drift after machining"
      trigger: "Cold work left in the part by machining, forming or drawing"
      consequence: "Carpenter says cold-work stresses cause very slight changes in dimensional stability with time and temperature, detectable only with sensitive instruments; for a telescope spacer that is enough to move focus."
      severity: moderate
      source: carpenter-invar36
      where: Heat treatment, Heat treatment for optimal dimensional stability
    - mode: "Rust and staining in humid storage"
      trigger: "Condensation, washing or humid air without plating"
      consequence: "Matthey says corrosion resistance falls in humid environments; Carpenter rates humidity resistance only as Good on a comparative scale."
      severity: low
      source: matthey-feni36
      where: Technische Hauptmerkmale, corrosion sentence
    - mode: "Change of length in a magnetic field"
      trigger: "Exposure to a magnetic field while the part is in service"
      consequence: "Wikipedia states that Invar's dimensional stability depends on a balance between two magnetic structures, that magnetic fields disturb it, and that the alloy has a propensity to creep."
      severity: moderate
      source: wikipedia-invar
      where: Properties section, paragraph on magnetic structure and dimensional stability
  handling:
    - text: >
        For best dimensional stability, heat to 1500 °F (815 °C), hold 30 minutes per inch of thickness, water quench,
        reheat to 600 °F (315 °C) for one hour, then air cool; Carpenter also ages 24 to 48 hours at 200 °F (93 °C)
        where temporal stability is needed. Do this before final machining.
      source: carpenter-invar36
      where: Heat treatment, Heat treatment for optimal dimensional stability
    - text: "Forge at 2000 to 2150 °F (1100 to 1180 °C), heat quickly and avoid long soaking, which can check the surface through sulfur pickup."
      source: carpenter-invar36
      where: Workability, Forging
    - text: "Grinding and cutting dust contains nickel, a skin sensitiser (H317); use dust extraction and gloves, and keep iron fines away from ignition sources."
      source: pubchem-nickel
      where: Safety and Hazards, GHS Classification (CID 935); see also pubchem-iron
uses:
  - application: optics-and-cameras
    device: "Metering structures that hold the spacing between optical elements in a space telescope"
    example: >
      A 1972 JPL/Itek study for an outer-planets television camera used Invar 36 for all structures that control the
      spacing between optical elements where athermalisation was required. The report pairs Invar 36 rods with shorter
      aluminium paths, whose expansions work in opposite directions, and says Super-Invar was rejected because its
      expansion was less stable over long periods.
    source: ntrs-19720025731
    where: Section 3.4.1, paragraphs on structural materials and the athermalisation scheme (pages 3-19 and 3-20)
  - application: electronics-and-chips
    device: "Semiconductor components, optical and laser benches, precision instruments"
    example: >
      Carpenter lists semiconductor components, optical and laser systems, temperature-regulator components and
      electronic devices as applications; Nicofe lists optoelectronics, optical and laser benches, electronics,
      scientific instruments and precision tooling.
    source: carpenter-invar36
    where: Applications list, first page; see also nicofe-invar36, Applications
  - application: cryogenic-fuel
    device: "Containers for liquefied natural gas and cryogenic energy storage"
    example: "Matthey lists containers for LNG tankers and cryogenic energy storage among the applications of FeNi36."
    source: matthey-feni36
    where: Technische Hauptmerkmale, applications sentence
supply:
  - subject: "Nickel (the alloying element that sets the expansion)"
    producers:
      - {country: Indonesia, share_percent: 66.7, year: 2025}
      - {country: Philippines, share_percent: 6.9, year: 2025}
      - {country: Russia, share_percent: 5.1, year: 2025}
      - {country: Canada, share_percent: 3.6, year: 2025}
      - {country: "New Caledonia", share_percent: 3.6, year: 2025}
      - {country: China, share_percent: 3.1, year: 2025}
    critical_lists:
      - {list: "U.S. critical minerals list (nickel is described as a critical mineral in the USGS Mineral Commodity Summaries 2026 nickel chapter, in the discussion of Executive Order 14285)", listed: true}
    recycling: >
      USGS reports that nickel recovered from scrap accounted for approximately 60 % of apparent U.S. consumption in
      2025, mostly as nickel in stainless-steel scrap.
    substitutes:
      - "USGS: low-nickel, duplex or ultrahigh-chromium stainless steels substitute for austenitic grades in construction; nickel-free specialty steels substitute in power generation and petrochemicals; titanium alloys substitute in corrosive environments."
    source: usgs-nickel-2026
    where: >
      World Mine Production and Reserves table, 2025 estimate column (3,900,000 t world total; shares computed from
      that table by dividing each country's figure by the total); Recycling paragraph
  - subject: "Iron (the balance of the alloy)"
    producers:
      - {country: Australia, share_percent: 37.7, year: 2025}
      - {country: Brazil, share_percent: 16.2, year: 2025}
      - {country: India, share_percent: 11.9, year: 2025}
      - {country: China, share_percent: 11.2, year: 2025}
      - {country: Russia, share_percent: 3.3, year: 2025}
    recycling: "USGS: none for iron ore; iron and steel scrap is covered in a separate chapter."
    source: usgs-iron-2026
    where: >
      World Mine Production and Reserves table, 2025 estimate, usable-ore columns (2,600,000 thousand tons world
      total; shares computed from that table); Recycling line
documents:
  - {title: "Carpenter Technology Invar 36 data sheet (v 07-25)", type: datasheet, url: "https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/Invar%2036.pdf", year: 2025}
  - {title: "Nicofe Invar 36 controlled expansion alloys datasheet v2", type: datasheet, url: "https://www.nicofe.com/wp-content/uploads/2025/12/IAW3078-Nicofe-INVAR-36-A4-datasheet-v2.pdf", year: 2025}
  - {title: "Lamineries Matthey FeNi36 (Invar) datasheet", type: datasheet, url: "https://www.matthey.ch/fileadmin/user_upload/downloads/fichetechnique/DE/FeNi36-Invar_v22D.pdf"}
  - {title: "Itek/JPL, Outer Planets Mission Television Subsystem Optics Study, final report, 28 July 1972 (NASA NTRS 19720025731)", type: report, url: "https://ntrs.nasa.gov/api/citations/19720025731/downloads/19720025731.pdf", year: 1972}
  - {title: "USGS Mineral Commodity Summaries 2026: Nickel", type: report, url: "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.pdf", year: 2026}
  - {title: "USGS Mineral Commodity Summaries 2026: Iron ore", type: report, url: "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-iron-ore.pdf", year: 2026}
  - {title: "PubChem: Nickel (CID 935)", type: database, url: "https://pubchem.ncbi.nlm.nih.gov/compound/935", year: 2026}
  - {title: "PubChem: Iron (CID 23925)", type: database, url: "https://pubchem.ncbi.nlm.nih.gov/compound/23925", year: 2026}
  - {title: "Wikipedia: Invar (history and magnetic explanation only)", type: database, url: "https://en.wikipedia.org/wiki/Invar", year: 2026}
gaps:
  - "No quantitative corrosion rate, pitting potential or salt-spray result was read; the corrosion section rests on two qualitative datasheet statements. The ScienceDirect paper on cerium in Fe-36Ni corrosion (S2238785424011049) could not be opened from this machine."
  - "The sources disagree on density (8.05 in Nicofe and Carpenter against 8.13 in Matthey), Curie temperature (279 °C in Carpenter and Nicofe against 230 °C in Matthey) and melting point (1427 °C in Carpenter and Nicofe against 1450 °C in Matthey). Both density values are entered; the Curie and melting disagreements are noted here rather than entered twice."
  - "The UNS number is printed three ways: K93600 (Matthey, approximately), K93601 and K93603 (Carpenter) and K93603 (Nicofe). All three are recorded in the identity formula."
  - "No vacuum outgassing, radiation, atomic-oxygen or thermal-vacuum data for Invar 36 were read. The only space source is the 1972 JPL optics study, which is a design report, not a test."
  - "NIST publishes cryogenic curve fits for Invar (4 to 300 K) but they are coefficients, not printed values; they were not reduced to numbers here, so the only cryogenic CTE entered is Matthey's -240 to -18 °C entry."
  - "The taxonomy has no controlled-expansion-alloy type, so this profile is filed under nickel-superalloys, the nearest bucket; Invar is not a superalloy."
  - "Hardness (70 HRB annealed, Carpenter) is not in property-canon.yaml and was left out rather than inventing a benchmark name."
  - "No cost or lead-time data were read."
sources:
  carpenter-invar36:
    title: "Carpenter Technology: Invar 36 data sheet (v 07-25)"
    id: "Carpenter Technology data sheet, Invar 36, v 07-25"
    url: "https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/Invar%2036.pdf"
    year: 2025
    kind: datasheet
    license: "Manufacturer datasheet, cited not reproduced"
  nicofe-invar36:
    title: "Nicofe: Invar 36 controlled expansion alloys datasheet v2"
    id: "Nicofe datasheet IAW3078 v2"
    url: "https://www.nicofe.com/wp-content/uploads/2025/12/IAW3078-Nicofe-INVAR-36-A4-datasheet-v2.pdf"
    year: 2025
    kind: datasheet
    license: "Supplier datasheet, cited not reproduced"
  matthey-feni36:
    title: "Lamineries Matthey: Invar FeNi36 datasheet"
    id: "Lamineries MATTHEY, FeNi36-Invar, v22D"
    url: "https://www.matthey.ch/fileadmin/user_upload/downloads/fichetechnique/DE/FeNi36-Invar_v22D.pdf"
    kind: datasheet
    license: "Producer datasheet, cited not reproduced"
  ntrs-19720025731:
    title: "Outer Planets Mission Television Subsystem Optics Study, final report, 28 July 1972"
    id: "NASA NTRS 19720025731 (Itek 72-9320-1, for JPL)"
    url: "https://ntrs.nasa.gov/api/citations/19720025731/downloads/19720025731.pdf"
    year: 1972
    kind: report
    license: "NASA NTRS public document"
  usgs-nickel-2026:
    title: "Mineral Commodity Summaries 2026: Nickel"
    id: "USGS MCS 2026, nickel"
    url: "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.pdf"
    year: 2026
    kind: report
    license: "USGS public domain"
  usgs-iron-2026:
    title: "Mineral Commodity Summaries 2026: Iron ore"
    id: "USGS MCS 2026, iron ore"
    url: "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-iron-ore.pdf"
    year: 2026
    kind: report
    license: "USGS public domain"
  pubchem-nickel:
    title: "PubChem: Nickel (CID 935), Safety and Hazards"
    id: "PubChem CID 935"
    url: "https://pubchem.ncbi.nlm.nih.gov/compound/935"
    year: 2026
    kind: database
    license: "PubChem, U.S. National Library of Medicine"
  pubchem-iron:
    title: "PubChem: Iron (CID 23925), Safety and Hazards"
    id: "PubChem CID 23925"
    url: "https://pubchem.ncbi.nlm.nih.gov/compound/23925"
    year: 2026
    kind: database
    license: "PubChem, U.S. National Library of Medicine"
  wikipedia-invar:
    title: "Wikipedia: Invar"
    id: "Wikipedia, Invar (revision read 2026-10-19)"
    url: "https://en.wikipedia.org/wiki/Invar"
    year: 2026
    kind: web
    license: "CC BY-SA 4.0 (cited, not reproduced)"
license: CC-BY-4.0
updated: "2026-10-19"
review:
  status: draft
  method: assistant
  checked_values: 22
  unreachable: 1
  caveats: 4
  note: >
    Values were read by an AI assistant on 2026-10-19 from the pages and PDFs named in each entry: the Carpenter,
    Nicofe and Matthey PDFs were downloaded and converted with pdftotext, the JPL report text was extracted from the
    NTRS PDF, and the two USGS chapters and the PubChem records came from their PDFs and REST API. Unreachable: the
    ScienceDirect paper on cerium in Fe-36Ni corrosion. Caveats: strengths are typical values of one manufacturer,
    density and Curie temperature differ between sources, the cryogenic CTE covers only -240 to -18 °C, and the
    space use comes from a 1972 design report rather than a test.
story:
  recipe:
    line: >
      Invar 36 is a single-phase face-centred-cubic iron-nickel alloy of about 36 wt% nickel and 64 wt% iron, with
      manganese at 0.35 wt% nominal (maximum 0.60), silicon at 0.20 (maximum 0.40) and carbon at 0.02 (maximum 0.15),
      as Carpenter prints it; Matthey widens the nickel range to 35.0-37.0 wt%. It is supplied as wrought bar, strip,
      plate and wire.
    parts:
      - {name: Iron, symbol: Fe, share_note: "balance (about 64 wt%)", atomic_weight: 55.84, role: "The magnetic host that makes the Invar effect possible: the alloy's expansion cancels because of the way its two magnetic states respond to heat.", source: pubchem-iron, where: "Molecular weight 55.84, PubChem CID 23925"}
      - {name: Nickel, symbol: Ni, share_percent: 36, share_high: 37, share_note: "wt%, nominal 36.00", atomic_weight: 58.693, role: "Sets the expansion minimum at about 36 wt%; away from that composition the alloy expands like ordinary steel.", source: matthey-feni36, where: "Chemical composition table, Ni 35.0-37.0; atomic weight 58.693, PubChem CID 935"}
  risk_groups:
    - title: For people
      level: 1
      verdict: "Nickel sensitiser, iron fines flammable"
      lead: "The alloy is mostly iron, but the nickel in it is the health hazard, and machining produces both nickel-bearing dust and fine iron."
      points:
        - {label: "Skin", line: "Nickel is classified H317 (may cause an allergic skin reaction) by 99.9 % of the company reports aggregated by PubChem, and some reports add carcinogenicity category 2 and respiratory sensitisation."}
        - {label: "Dust and fines", line: "Iron powder is a flammable solid (H228) in 15.5 % of reports; fine iron reacts with moisture to release hydrogen."}
    - title: In service
      level: 2
      verdict: "Stable only if stress-relieved"
      lead: "The low expansion is the point of the alloy, but cold work and humidity both work against it."
      points:
        - {label: "Dimensional drift", line: "Cold-work stresses change the length very slightly with time and temperature; Carpenter's stabilising heat treatment is the fix."}
        - {label: "Corrosion", line: "Corrosion resistance is good in dry air but falls in humid environments, so unprotected parts stain."}
    - title: In space
      level: 1
      verdict: "Design data only"
      lead: "The space record found here is a design study, not a flight qualification."
      points:
        - {label: "What the report says", line: "The 1972 JPL study chose Invar 36 for metering structures and rejected Super-Invar for long-term instability of its expansion."}
        - {label: "What is missing", line: "No thermal-vacuum, outgassing or radiation test of Invar 36 was read."}
  why: >
    Invar 36 works because its thermal expansion nearly vanishes near room temperature: 1.3 ppm/K up to 93 °C, where
    ordinary steel would be about ten times higher. A structure made of it barely changes length when the temperature
    moves, which is what a telescope needs to keep its mirrors and detectors at a fixed spacing. The cost is a soft
    metal (276 MPa yield annealed), a sensitivity to humidity, and a length that drifts unless the part is stress-relieved
    before final machining.
  uses:
    - where: "Space telescope optics"
      line: "A 1972 JPL/Itek study used Invar 36 for every structure that set the spacing between optical elements, pairing Invar rods with shorter aluminium paths whose expansions oppose each other."
    - where: "Precision instruments and laser benches"
      line: "Carpenter lists semiconductor components, optical and laser systems and temperature-regulator parts; Nicofe lists optoelectronics, optical benches and precision tooling."
    - where: "Cryogenic vessels"
      line: "Matthey lists LNG tanker containers and cryogenic energy storage."
  can_do:
    - {label: "Expansion", benchmark: cte, line: "1.3 ppm/K to 93 °C, 2.11 to 149 °C and 4.18 to 260 °C (Carpenter); 1.18 over 30-100 °C (Nicofe); 1.8 between -240 and -18 °C (Matthey)."}
    - {label: "Stiffness", benchmark: elastic_modulus, line: "140 GPa (Matthey) and 141 GPa (Nicofe)."}
    - {label: "Strength", benchmark: yield_strength, line: "276 MPa yield and 518 MPa tensile (Nicofe); 40 ksi yield and 65 ksi tensile in the annealed condition (Carpenter)."}
    - {label: "Melting", benchmark: melting_point, line: "1427 °C melting range (Carpenter)."}
    - {label: "Conductivity", benchmark: thermal_conductivity, line: "10.5 W/(m·K) at 20 °C (Matthey), the same as Carpenter's 72.85 Btu-in/hr/ft2/°F."}
  compare: >
    Invar 36 is the reference low-expansion metal, and everything else in this comparison is judged against it. Its
    expansion of 1.3 ppm/K near room temperature is roughly a tenth that of carbon steel and far below aluminium, which
    is why optical structures mix the two: the aluminium moves, the Invar barely does, and the difference can be arranged
    to cancel. It pays for that with low strength (276 MPa yield), a density of 8.05 g/cm3, and a corrosion resistance
    that Matthey says falls in humid air.
  compare_rows:
    - {label: "Thermal expansion", benchmark: cte}
    - {label: "Stiffness", benchmark: elastic_modulus}
    - {label: "Strength", benchmark: yield_strength}
  handling:
    - "Stress-relieve before final machining: heat, water-quench, reheat and age, following the schedule in the handling notes."
    - "Forge quickly at temperature and do not soak, or the surface can check."
    - "Keep grinding dust and iron fines away from ignition sources, and protect skin from nickel-bearing dust."
  good_for:
    - "Holding optical spacing across temperature swings: 1.3 ppm/K near room temperature."
    - "Cryogenic instruments: 1.8 ppm/K between -240 and -18 °C."
    - "Precision instruments, laser benches and semiconductor components."
  watch_out:
    - "Humid air: corrosion resistance falls, and the datasheets offer no quantitative rate."
    - "Dimensional drift from cold work unless the part is stress-relieved before final machining."
    - "Magnetic fields disturb the dimensional stability, and the alloy can creep."
  verdict: >
    Invar 36 is the reference low-expansion metal: unmatched for holding a dimension near room temperature, but soft,
    rust-prone in humid air and only as stable as its heat treatment. Use it where the dimension matters more than the
    strength.