spore: profile
id: stainless-440c
spore_version: 0.2
family: stainless-martensitic
name: Stainless steel 440C
abbreviation: 440C (UNS S44004)
role: high-carbon martensitic stainless steel for bearings and valve parts
category: metals
type: steels-and-stainless
summary: 440C is the highest-carbon 400-series stainless steel, a martensitic iron alloy with 0.95 to 1.20 percent carbon and 16 to 18 percent chromium. Heat-treated, it reaches about HRC 60, the highest hardness of any stainless steel in these sources, and its hardness depends on the temper. It is used mainly for ball and roller bearings and valve parts.
best_for: Bearings and valve parts that must be hard and wear-resistant in the hardened and tempered condition (Carpenter, Aalco, Rolled Alloys)
weakest_at: Corrosion resistance in the annealed state or after tempering above about 800 F (427 C), and service above about 400 C (NASA 2018 maximum use temperature)
identity:
  formula: Fe balance, 0.95 to 1.20 C, 16.0 to 18.0 Cr, 0.75 max Mo (Rolled Alloys and Carpenter; EN 10088-3 gives 0.40 to 0.80 Mo), 1.00 max Mn, 1.00 max Si, 0.04 max P, 0.03 max S (wt%)
  source: rolled-440c
  where: Chemical composition table, Min and Max columns (Rolled Alloys bulletin 1142); EN 10088-3 Mo range from the Aalco datasheet
  designations:
    - system: UNS
      code: S44004
      source: rolled-440c
      where: 'Specifications line (UNS: S44004); also UNS #S44004 on the Carpenter page'
    - system: EN
      code: '1.4125'
      source: rolled-440c
      where: 'Specifications line (W. Nr./EN: 1.4125); also 1.4125 in the Aalco datasheet title'
    - system: JIS
      code: SUS440C
      source: patent-jp6207408
      where: 'Background text: SUS440C (C: specified in JIS G4303 as martensitic stainless steel)'
    - system: JIS
      code: G4303
      source: patent-jp6207408
      where: Same background sentence; JIS G4303 cited as the standard for martensitic grades
    - system: ASTM
      code: A 276
      source: rolled-440c
      where: 'Specifications line (ASTM: A 276); printed as ASTM A276 on the Carpenter page and in the Aircraft Materials specification list'
    - system: AMS
      code: '5630'
      source: rolled-440c
      where: 'Specifications line (AMS: 5630, 5880)'
    - system: AMS
      code: '5880'
      source: rolled-440c
      where: 'Specifications line (AMS: 5630, 5880)'
    - system: AISI
      code: 440C
      source: aircraft-materials-440c
      where: Title line (Alloy 440C / AISI 440C / AMS 5630)
tags:
  environments: []
  stresses: []
  applications:
    - mechanisms
    - propulsion-and-tanks
properties:
  - benchmark: density
    value: 0.275
    unit: lb/in3
    scope: material
    conditions:
      temperature: not stated
      heat_treatment: not stated
    method: 'Physical properties table as printed (Density: 0.275 lb/in3); the bulletin gives no SI value'
    status: ground
    source: rolled-440c
    where: Physical Properties table (Density row)
  - benchmark: density
    value: 7.65
    unit: g/cm3
    scope: material
    conditions:
      standard: EN 10088-3:2005 bar
      temperature: not stated
      heat_treatment: not stated
    method: Physical properties table as printed (Density 7.65 g/cm3)
    status: ground
    source: aalco-440c-bar
    where: Physical Properties table (Density row)
  - benchmark: density
    value: 7.7
    unit: g/cc
    scope: material
    conditions:
      temperature: not stated
      heat_treatment: not stated on the slide
    method: NASA Glenn 2018 comparison table, 440C column, printed as 7.7 g/cc
    status: ground
    source: nasa-2018-ntrs
    where: Technical Properties Comparison table, first table (Density row)
  - benchmark: elastic_modulus
    value: 200
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
      heat_treatment: not stated
    method: Physical properties table as printed (Modulus of Elasticity 200 GPa)
    status: ground
    source: aalco-440c-bar
    where: Physical Properties table (Modulus of Elasticity row)
  - benchmark: elastic_modulus
    value: 200
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
      heat_treatment: not printed on the datasheet
    method: UPMET datasheet, Physical Properties table, printed as 200 GPa
    status: ground
    source: upmet-440c
    where: Physical Properties table (Elastic Modulus row)
  - benchmark: elastic_modulus
    value: 200
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
      heat_treatment: not stated on the slide
    method: NASA Glenn 2018 comparison table, printed as 200 GPa (Young's Modulus row)
    status: ground
    source: nasa-2018-ntrs
    where: Technical Properties Comparison table (Young's Modulus row)
  - benchmark: elastic_modulus
    value: 30.4
    unit: psi x 10^6
    scope: material
    conditions:
      temperature: 70 F
      heat_treatment: not stated
      basis: dynamic modulus, as printed
    method: Physical properties table, Modulus of Elasticity, Dynamic, printed as 30.4 psi x 10^6 at 70 F; dynamic, not the static value
    status: ground
    source: rolled-440c
    where: Physical Properties table (Modulus of Elasticity, Dynamic row)
  - benchmark: poissons_ratio
    value: 0.3
    unit: '-'
    scope: material
    conditions:
      heat_treatment: not stated on the slide
    method: NASA Glenn 2018 comparison table, printed as 0.3 for 440C
    status: ground
    source: nasa-2018-ntrs
    where: Technical Properties Comparison table (Poisson's ratio row)
  - benchmark: thermal_conductivity
    value: 24.2
    unit: W/m.K
    scope: material
    conditions:
      temperature: not stated
    method: Physical properties table as printed (Thermal Conductivity 24.2 W/m.K)
    status: ground
    source: aalco-440c-bar
    where: Physical Properties table (Thermal Conductivity row)
  - benchmark: thermal_conductivity
    value: 24
    unit: W/m-°K
    scope: material
    conditions:
      temperature: not stated
      heat_treatment: not stated on the slide
    method: NASA Glenn 2018 comparison table, printed as 24 W/m-°K for 440C
    status: ground
    source: nasa-2018-ntrs
    where: Technical Properties Comparison table (Thermal conductivity row)
  - benchmark: thermal_conductivity
    value: 13.2
    unit: Btu·ft/ft2·hr·°F
    scope: material
    conditions:
      temperature: 70 F
      heat_treatment: not stated
    method: Physical properties table at 70 F, printed as 13.2 Btu ft/ft2 hr F (unit printed with bullets)
    status: ground
    source: rolled-440c
    where: Physical Properties table (Thermal Conductivity row, temperature column 70)
  - benchmark: cte
    value: 10.1
    unit: 10-6/K
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: x10^-6 /K
    method: Physical properties table as printed (Thermal Expansion 10.1 x10^-6 /K); same unit written in short form
    status: ground
    source: aalco-440c-bar
    where: Physical Properties table (Thermal Expansion row)
  - benchmark: cte
    value: 10
    unit: 10-6/°C
    scope: material
    conditions:
      temperature: not stated
      heat_treatment: not stated on the slide
    method: NASA Glenn 2018 comparison table, printed as 10x10^-6/°C for 440C
    status: ground
    source: nasa-2018-ntrs
    where: Technical Properties Comparison table (Thermal expansion row)
  - benchmark: cte
    value: 5.6
    unit: in/in°F x 10^-6
    scope: material
    conditions:
      temperature: 70 F to the indicated temperature (table column at 70 F)
      heat_treatment: not stated
    method: 'Physical properties table, coefficient marked with footnote: 70 F to indicated temperature; printed in inches per inch per F'
    status: ground
    source: rolled-440c
    where: Physical Properties table (Coefficient of Thermal Expansion row and footnote)
  - benchmark: melting_point
    value: 2500
    value_high: 2700
    bound: range
    unit: °F
    scope: material
    conditions:
      temperature: melting range as printed
      heat_treatment: not stated
    method: Physical properties table as printed (Melting Range 2500 - 2700 F)
    status: ground
    source: rolled-440c
    where: Physical Properties table (Melting Range row)
  - benchmark: electrical_resistivity
    value: 0.6
    unit: 10-6 ohm.m
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: x10^-6 Ω.m
    method: Physical properties table as printed (Electrical Resistivity 0.6 x10^-6 Ω.m)
    status: ground
    source: aalco-440c-bar
    where: Physical Properties table (Electrical Resistivity row)
  - benchmark: electrical_resistivity
    value: 0.6
    unit: 10-6 ohm.m
    scope: material
    conditions:
      temperature: not stated
      heat_treatment: not stated on the slide
      basis: approximate, printed with a tilde
    method: NASA Glenn 2018 comparison table, first table, printed as ~0.60x10^-6 Ω-m for 440C
    status: ground
    note: The second 440C table on the same slide prints about 36 x10^-6 Ω-cm, which conflicts; the first table is used.
    source: nasa-2018-ntrs
    where: Technical Properties Comparison table, first table (Electrical resistivity row)
  - benchmark: max_service_temp
    value: 400
    unit: °C
    scope: material
    conditions:
      basis: maximum use temperature, printed as about 400 C (approximate)
      heat_treatment: not stated on the slide
    method: NASA Glenn 2018 comparison table, Maximum use temp row, printed as ~400 °C for 440C
    status: ground
    note: Printed with a tilde (about 400 C); the slide does not give the basis or the temper.
    source: nasa-2018-ntrs
    where: Technical Properties Comparison table (Maximum use temp row)
  - benchmark: fracture_toughness
    value: 22
    unit: MPa/√m
    scope: material
    conditions:
      heat_treatment: not stated on the slide
    method: NASA Glenn 2018 comparison table, printed as 22 MPa/√m for 440C (Fracture toughness row); benchmark name is not in property-canon.yaml
    status: ground
    source: nasa-2018-ntrs
    where: Technical Properties Comparison table (Fracture toughness row)
  - benchmark: hardness
    label: Rockwell C after a one-hour temper at 300 F
    value: 60
    unit: HRC
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered one hour at 300 F
      specimen: 1 in round
    method: Typical Hardness table, Rockwell C row, as printed
    status: ground
    source: rolled-440c
    where: Typical Hardness table (300 F column)
  - benchmark: hardness
    label: Rockwell C after a one-hour temper at 400 F
    value: 59
    unit: HRC
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered one hour at 400 F
      specimen: 1 in round
    method: Typical Hardness table, Rockwell C row, as printed
    status: ground
    source: rolled-440c
    where: Typical Hardness table (400 F column)
  - benchmark: hardness
    label: Rockwell C after a one-hour temper at 500 F
    value: 57
    unit: HRC
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered one hour at 500 F
      specimen: 1 in round
    method: Typical Hardness table, Rockwell C row, as printed
    status: ground
    source: rolled-440c
    where: Typical Hardness table (500 F column)
  - benchmark: hardness
    label: Rockwell C after a one-hour temper at 600 F
    value: 56
    unit: HRC
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered one hour at 600 F
      specimen: 1 in round
    method: Typical Hardness table, Rockwell C row, as printed
    status: ground
    source: rolled-440c
    where: Typical Hardness table (600 F column)
  - benchmark: hardness
    label: Rockwell C after a one-hour temper at 700 F
    value: 56
    unit: HRC
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered one hour at 700 F
      specimen: 1 in round
    method: Typical Hardness table, Rockwell C row, as printed
    status: ground
    source: rolled-440c
    where: Typical Hardness table (700 F column)
  - benchmark: hardness
    label: Rockwell C after a one-hour temper at 800 F
    value: 56
    unit: HRC
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered one hour at 800 F
      specimen: 1 in round
    method: Typical Hardness table, Rockwell C row, as printed
    status: ground
    source: rolled-440c
    where: Typical Hardness table (800 F column)
  - benchmark: hardness
    label: Annealed hardness (approximate)
    value: 223
    unit: HB
    scope: material
    conditions:
      heat_treatment: 'annealed: heat to 1550 to 1600 F, slow cool in the furnace'
    method: Annealing paragraph, printed as Brinell hardness should be approximately 223
    status: ground
    note: Approximate value, as printed.
    source: rolled-440c
    where: Annealing paragraph
  - benchmark: hardness
    label: Brinell hardness at the 600 F temper
    value: 580
    unit: HB
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered 600 F
      test_temperature: not printed
    method: Typical Mechanical Properties table, Brinell Hardness column, as printed
    status: ground
    source: aircraft-materials-440c
    where: Typical Mechanical Properties table (Alloy 440C row, Brinell Hardness)
  - benchmark: hardness
    label: As heat treated, before any tempering
    value: 60
    unit: HRC
    scope: material
    conditions:
      heat_treatment: heat treated to HRC 60 per the HPOTP bearing procedure, not tempered in this row
      specimen: AISI 440C rods 7.9 mm diameter
    method: 'Tempering section, text: as-heat-treated material (HRC 60)'
    status: ground
    source: nasa-1984-ntrs
    where: Tempering Behavior and Hot Hardness section (Specimens; Figure 14 text)
  - benchmark: hardness
    label: After tempering at 540 C for 10 to 945 s, from HRC 60
    value: 57
    value_high: 58
    bound: range
    unit: HRC
    scope: material
    conditions:
      heat_treatment: from HRC 60, tempered at 540 C (1000 F) for 10 to 945 s
      temperature: 540 C (1000 F)
      time: 10, 105 and 945 s
    method: Short-term tempering results, printed as reduced the hardness from the initial value of HRC 60 to HRC 57-58
    status: ground
    source: nasa-1984-ntrs
    where: Short-Term Tempering Behavior, Results
  - benchmark: hardness
    label: After tempering at 650 C for 105 s, from HRC 60
    value: 50.5
    unit: HRC
    scope: material
    conditions:
      heat_treatment: from HRC 60, tempered at 650 C (1200 F) for 105 s
      temperature: 650 C (1200 F)
      time: 105 s
    method: Results text, printed as the hardness was reduced to HRC 50.5 at 105 seconds
    status: ground
    source: nasa-1984-ntrs
    where: Short-Term Tempering Behavior, Results (text after Figure 12)
  - benchmark: hardness
    label: After tempering at 650 C for 420 s, from HRC 60
    value: 46.5
    unit: HRC
    scope: material
    conditions:
      heat_treatment: from HRC 60, tempered at 650 C (1200 F) for 420 s
      temperature: 650 C (1200 F)
      time: 420 s
    method: Results text, printed as the hardness was reduced to HRC 46.5 at 420 seconds
    status: ground
    source: nasa-1984-ntrs
    where: Short-Term Tempering Behavior, Results (text after Figure 12)
  - benchmark: hardness
    label: After tempering at 760 C for 10 s, from HRC 60
    value: 44
    unit: HRC
    scope: material
    conditions:
      heat_treatment: from HRC 60, tempered at 760 C (1400 F) for 10 s
      temperature: 760 C (1400 F)
      time: 10 s
    method: Results text, printed as the hardness was reduced to HRC 44 in 10 seconds at 760 C
    status: ground
    source: nasa-1984-ntrs
    where: Short-Term Tempering Behavior, Results (text after Figure 12)
  - benchmark: hardness
    label: After tempering at 760 C for 105 s, from HRC 60
    value: 40
    unit: HRC
    scope: material
    conditions:
      heat_treatment: from HRC 60, tempered at 760 C (1400 F) for 105 s
      temperature: 760 C (1400 F)
      time: 105 s
    method: Results text, printed as HRC 40 in 105 seconds at 760 C
    status: ground
    note: The Figure 14 caption prints HRC 58 for 760 C at 105 s; the text value of HRC 40 is used.
    source: nasa-1984-ntrs
    where: Short-Term Tempering Behavior, Results (text after Figure 12)
  - benchmark: hardness
    label: Hot hardness at 540 C, used HPOTP race
    value: 30
    bound: upper
    unit: HRC
    scope: material
    conditions:
      temperature: 540 C (1000 F)
      specimen: cut from a used HPOTP bearing race that measured HRC 50 at room temperature
      test: hot-hardness apparatus; diamond pyramid hardness numbers converted in the text
    method: Hot-Hardness Measurements section, printed as less than DPHN 300 (HRC 30) at 540 C (1000 F)
    status: ground
    source: nasa-1984-ntrs
    where: Hot-Hardness Measurements section (Figure 15 discussion)
  - benchmark: hardness
    label: Hardness range as compared by NASA Glenn
    value: 58
    value_high: 62
    bound: range
    unit: HRC
    scope: material
    conditions:
      heat_treatment: not stated on the slide
    method: NASA Glenn 2018 comparison table, Hardness row, printed as 58 to 62 HRC for 440C
    status: ground
    source: nasa-2018-ntrs
    where: Technical Properties Comparison table (Hardness row, 440C column)
  - benchmark: ultimate_tensile_strength
    value: 1965
    unit: MPa
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered 600 F
      test_temperature: not printed
    method: Typical Mechanical Properties table, Ultimate Tensile Strength column (MPa), as printed
    status: ground
    source: aircraft-materials-440c
    where: Typical Mechanical Properties table (Alloy 440C row, Ultimate Tensile Strength column)
  - benchmark: ultimate_tensile_strength
    value: 285
    unit: ksi
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered 600 F
      temperature: 70 F
    method: Representative Tensile Properties table, Ultimate Tensile Strength row, printed as 285 ksi
    status: ground
    source: rolled-440c
    where: Mechanical Properties table (Representative Tensile Properties, Ultimate Tensile Strength row)
  - benchmark: yield_strength
    value: 1896
    unit: MPa
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered 600 F
      test_temperature: not printed
      basis: 0.2 percent offset yield, as printed
    method: Typical Mechanical Properties table, Yield Strength 0.2% (MPa) column, as printed
    status: ground
    source: aircraft-materials-440c
    where: Typical Mechanical Properties table (Yield Strength column)
  - benchmark: yield_strength
    value: 275
    unit: ksi
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered 600 F
      temperature: 70 F
      basis: 0.2 percent offset yield, as printed
    method: Representative Tensile Properties table, 0.2% Yield Strength row, printed as 275 ksi
    status: ground
    source: rolled-440c
    where: Mechanical Properties table (0.2% Yield Strength row)
  - benchmark: elongation
    value: 2
    unit: '%'
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered 600 F
      gauge: 2 in, as printed in the Elongation column
    method: Typical Mechanical Properties table, Elongation column, as printed
    status: ground
    source: aircraft-materials-440c
    where: Typical Mechanical Properties table (Elongation column)
  - benchmark: elongation
    value: 2
    unit: '%'
    scope: material
    conditions:
      heat_treatment: hardened 1900 F, oil quench, tempered 600 F
      temperature: 70 F
    method: Representative Tensile Properties table, Elongation row, printed as 2 %
    status: ground
    source: rolled-440c
    where: Mechanical Properties table (Elongation row)
corrosion:
  - environment: Atmosphere, fresh water, foods, alkalies and mild acids
    headline: Good general resistance, best when hardened, tempered and passivated.
    effect: 'Aalco: good resistance to the atmosphere, fresh water, foods, alkalies and mild acids, with the best resistance in the hardened, tempered and passivated condition. A smooth polished surface also helps.'
    rating: low
    conditions:
      best_case: hardened, tempered and passivated, polished
    source: aalco-440c-bar
    where: Corrosion Resistance section
  - environment: Compared with the common austenitic grades
    headline: Lower corrosion resistance than the common austenitic grades.
    effect: 'Aalco: corrosion resistance is lower than the common austenitic grades, and the useful temperature range is limited by loss of ductility below zero and loss of strength by over-tempering at elevated temperatures.'
    rating: moderate
    source: aalco-440c-bar
    where: Martensitic stainless steels paragraph
  - environment: Many environments, compared with 304
    headline: About the same as 304 in many environments.
    effect: 'Aalco: the corrosion resistance of 440C approximates that of 304 in many environments.'
    rating: low
    source: aalco-440c-bar
    where: Corrosion Resistance section
  - environment: Annealed condition, or hardened and tempered above about 800 F (427 C)
    headline: Corrosion resistance is reduced when annealed or tempered above 800 F.
    effect: 'Carpenter: 440C is not usually recommended for elevated temperature applications, since corrosion resistance is reduced when used in the annealed condition or hardened and tempered above about 800 F (427 C).'
    rating: moderate
    conditions:
      temperature: above about 800 F (427 C) temper, or annealed
    source: carpenter-440c
    where: Product description paragraph
  - environment: Tempering between 425 and 565 C
    headline: Avoid this tempering range.
    effect: 'Aalco: tempering in the range 425 to 565 C is to be avoided because of reduced impact resistance and corrosion resistance.'
    rating: moderate
    conditions:
      temperature: 425 to 565 C tempering
    source: aalco-440c-bar
    where: Heat Treatment section
  - environment: General corrosion, rated Marginal by NASA
    headline: NASA rates 440C corrosion resistance Marginal, and hard steels rust.
    effect: NASA Glenn's 2018 comparison rates the corrosion resistance of 440C as Marginal, against Excellent for 60NiTi in aqueous and acidic service, and says hard steels are prone to rusting, even stainless steels like 440C.
    rating: moderate
    source: nasa-2018-ntrs
    where: Technical Properties Comparison table (Corrosion resistance row); Materials Requirements slide
  - environment: Overheating during grinding
    headline: Grinding heat lowers hardness and corrosion resistance.
    effect: 'Rolled Alloys: do not overheat while grinding, since both the hardness and corrosion resistance may be lowered.'
    rating: moderate
    source: rolled-440c
    where: Grinding and Polishing section
  - environment: Above the tempering temperature
    headline: Not recommended above the tempering temperature, because of over-tempering.
    effect: 'Aalco: not recommended for use in temperatures above the relevant tempering temperature, because mechanical properties are reduced by over-tempering.'
    rating: unknown
    source: aalco-440c-bar
    where: Heat Resistance section
risks:
  hazards:
    - text: In a NIOSH-authored study of stainless steel welding fume, the hexavalent chromium fraction ranged from 2800 to 34,000 ppm across eight welding process and shielding-gas combinations, and generation rates ranged from 69 to 7800 ug/min.
      ghs: []
      source: pmc-cr6-welding
      where: Abstract (Cr6+ fraction and generation rate results)
  failure_risks:
    - mode: Ball wear in unlubricated sliding contact
      trigger: 440C in self-mated sliding contact without lubrication (liquid-nitrogen test rig)
      consequence: Wear rates were high enough to explain the ball wear sometimes seen in HPOTP bearings.
      severity: high
      source: nasa-1984-ntrs
      where: Summary
    - mode: Softening from heat
      trigger: Bulk bearing temperatures of 480 C (900 F) or more, or extended time at 540 C (1000 F)
      consequence: 'NASA 1984: hot hardness falls rapidly at 540 C (1000 F) and above, and at 760 C (1400 F) hardness fell from HRC 60 to HRC 44 in 10 s and HRC 40 in 105 s.'
      severity: high
      source: nasa-1984-ntrs
      where: Summary; Hot-Hardness Measurements section; Results text
    - mode: Over-tempering
      trigger: Service or tempering above the tempering temperature
      consequence: 'Aalco: mechanical properties are reduced by over-tempering at elevated temperatures, so use above the tempering temperature is not recommended.'
      severity: moderate
      source: aalco-440c-bar
      where: Martensitic stainless steels paragraph; Heat Resistance section
    - mode: Rusting in moist or wet service
      trigger: Moisture or wet service
      consequence: NASA Glenn says hard steels are prone to rusting, even stainless steels such as 440C.
      severity: moderate
      source: nasa-2018-ntrs
      where: Materials Requirements slide (Technical Challenge list)
    - mode: Soft or hard welds from the wrong filler
      trigger: Choice of welding filler (Aalco lists 420, 309 and 310 fillers)
      consequence: 'Aalco: a grade 420 filler gives a high-hardness weld, while 309 or 310 gives soft welds with higher ductility.'
      severity: moderate
      source: aalco-440c-bar
      where: Weldability section
  side_effects: []
  handling:
    - text: Machine in the annealed condition; once hardened, machining becomes much harder and probably impossible (Aalco). Chips are tough and stringy, so chip breakers matter (Aalco, Rolled Alloys).
      source: aalco-440c-bar
      where: Machinability section
    - text: Do not overheat when grinding, since hardness and corrosion resistance can be lowered (Rolled Alloys).
      source: rolled-440c
      where: Grinding and Polishing section
    - text: 'Hardening: heat to 1010 to 1065 C, then quench in warm oil or air, with oil for heavy sections (Aalco).'
      source: aalco-440c-bar
      where: Heat Treatment section (Hardening)
    - text: 'Hardening: heat to 1850 to 1950 F, quench in warm oil or air, and temper immediately between 300 and 800 F, depending on the hardness wanted (Rolled Alloys).'
      source: rolled-440c
      where: Hardening section
    - text: 'Weldability: if welding is needed, preheat to about 250 C and follow with a full anneal (Aalco).'
      source: aalco-440c-bar
      where: Weldability section
    - text: 'Weldability: Rolled Alloys preheats to about 500 F, welds, then anneals at 1350 to 1400 F for 6 to 8 hours, cooling slowly in the furnace.'
      source: rolled-440c
      where: Weldability section
  mitigations:
    - text: Keep the temper at or below about 800 F (427 C) where corrosion resistance matters (Carpenter).
      source: carpenter-440c
      where: Product description paragraph
    - text: Avoid tempering between 425 and 565 C, the range that lowers impact and corrosion resistance; 590 to 675 C gives lower hardness and high impact resistance (Aalco).
      source: aalco-440c-bar
      where: Heat Treatment section
    - text: 'Short overheats are tolerable: tempering times of 10 seconds or less can be taken up to 650 C (1200 F) without significant hardness loss (NASA 1984).'
      source: nasa-1984-ntrs
      where: Summary
    - text: Weld with 309 or 310 filler when soft, ductile welds are wanted, since 420 gives a high-hardness weld (Aalco).
      source: aalco-440c-bar
      where: Weldability section
uses:
  - application: mechanisms
    device: Rolling-element bearings (ball and roller)
    example: Carpenter says 440C has been used primarily as a bearing steel, in the hardened plus tempered condition.
    source: carpenter-440c
    where: Product description paragraph
  - application: mechanisms
    device: Valve seats and valve parts
    example: Aalco lists valve seats and says 440C is particularly suited to ball bearings and valve parts; UPMET lists ball bearings and valves.
    source: aalco-440c-bar
    where: Applications list (Valve seats)
  - application: propulsion-and-tanks
    device: High-pressure oxygen turbopump bearings of the Space Shuttle main engine (HPOTP)
    example: NASA's 1984 Battelle report measured 440C wear and tempering for these bearings and found that unlubricated 440C wear could explain the ball wear seen in service.
    source: nasa-1984-ntrs
    where: Introduction and Summary
  - application: mechanisms
    device: Bearing races in spacecraft reaction-wheel assemblies (NASA comparison)
    example: NASA Glenn's 2018 slides compare 440C with 60NiTi and credit 60NiTi bearing races with 2x (against Rex 20) to 5x (against 440C) improvement in a reaction-wheel bearing.
    source: nasa-2018-ntrs
    where: Space Bearing Application slide (Typical Reaction Wheel Assembly)
supply:
  - subject: Chromium
    abundance: World mine production about 51,000 thousand metric tons, gross weight, in 2025 (estimated). World resources are greater than 12 billion tons of shipping-grade chromite, 95 percent in Kazakhstan and southern Africa (USGS 2026).
    producers:
      - country: South Africa
        share_percent: 45.1
        year: 2025
      - country: Turkey
        share_percent: 17.6
        year: 2025
      - country: Kazakhstan
        share_percent: 13.7
        year: 2025
      - country: India
        share_percent: 5.9
        year: 2025
      - country: Brazil
        share_percent: 3.9
        year: 2025
      - country: Zimbabwe
        share_percent: 3.9
        year: 2025
      - country: Finland
        share_percent: 3.7
        year: 2025
    critical_lists: []
    recycling: Recycled chromium in reported stainless-steel scrap receipts was 21 percent of US apparent consumption in 2025 (USGS 2026).
    substitutes:
      - Chromium has no substitute in stainless steel, the leading end use, or in superalloys (USGS 2026)
    source: usgs-chromium-2026
    where: World Mine Production and Reserves table (2025e, gross weight; shares computed from the printed tonnage); World Resources; Substitutes; Recycling
  - subject: Chromium import reliance (United States)
    abundance: US net import reliance was 79 percent of apparent consumption in 2025 (estimated). Chromite imports for 2021 to 2024 came from South Africa (96 percent) and Turkey (3 percent).
    producers: []
    critical_lists: []
    recycling: Recycled chromium was 21 percent of US apparent consumption in 2025.
    substitutes: []
    source: usgs-chromium-2026
    where: Salient Statistics (Net import reliance row); Import Sources (2021-24)
  - subject: Molybdenum
    abundance: World mine production 260,000 t of molybdenum content in 2025 (estimated). Identified resources are about 5.4 million tons in the United States and about 20 million tons in the rest of the world (USGS 2026).
    producers:
      - country: China
        share_percent: 37.3
        year: 2025
      - country: Chile
        share_percent: 16.2
        year: 2025
      - country: United States
        share_percent: 15.4
        year: 2025
      - country: Peru
        share_percent: 15
        year: 2025
      - country: Mexico
        share_percent: 6.5
        year: 2025
    critical_lists: []
    recycling: Molybdenum recycled from steel, superalloy and catalyst scrap may be as much as 30 percent of apparent supply (USGS 2026).
    substitutes:
      - Little substitution in its main use in steels and cast irons; potential substitutes in alloy steels include boron, chromium, niobium and vanadium (USGS 2026)
    source: usgs-molybdenum-2026
    where: World Mine Production and Reserves table (2025e, molybdenum content; shares computed from the printed tonnage); Substitutes; Recycling
  - subject: Molybdenum trade and policy
    abundance: The United States is a net exporter of molybdenum (USGS 2026), with 40,000 t of molybdenum content mine production in 2025 (estimated). China imposed export controls on molybdenum powders in February 2025.
    producers: []
    critical_lists: []
    recycling: ''
    substitutes: []
    source: usgs-molybdenum-2026
    where: Salient Statistics (Net import reliance row, E = net exporter); Events, Trends, and Issues
media: []
documents:
  - title: 'Rolled Alloys: Stainless 440C data sheet (Bulletin No. 1142)'
    type: datasheet
    url: https://www.rolledalloys.ca/wp-content/uploads/440C_stainless-steel-data-sheet.pdf
    year: 2015
  - title: 'AircraftMaterials UK: Stainless Steel 440C technical data sheet'
    type: datasheet
    url: https://www.aircraftmaterials.com/data/alstst/440c.html
  - title: 'Aalco: Stainless Steel - Martensitic - 1.4125 (440C) Bar datasheet (EN 10088-3:2005)'
    type: datasheet
    url: https://www.aalco.co.uk/datasheets/Stainless-Steel-14125-440C-Bar_312.ashx
  - title: 'United Performance Metals: Alloy 440C datasheet'
    type: datasheet
    url: https://www.upmet.com/sites/default/files/datasheets/440c.pdf
  - title: 'Carpenter Technology: 440C alloy page'
    type: datasheet
    url: https://www.carpentertechnology.com/alloy-finder/440c
  - title: 'NASA Glenn (DellaCorte, 2018): Ni-Ti Next Generation Bearings for Space Applications'
    type: report
    url: https://ntrs.nasa.gov/api/citations/20180002168/downloads/20180002168.pdf
    year: 2018
  - title: 'Battelle for NASA (Dufrane et al., 1984): Measurements of elastohydrodynamic film thicknesses, wear, and tempering behavior of high pressure oxygen turbopump bearings'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19840014892/downloads/19840014892.pdf
    year: 1984
  - title: Effects of Heat Treatment on the Properties of SS440C for Blades Applications (Springer Proceedings in Physics 289; UniMAP repository copy)
    type: paper
    url: https://ris.unimap.edu.my/entities/publication/1eddb8c2-050b-427f-8b49-0de618f67a03
  - title: 'USGS Mineral Commodity Summaries 2026: Chromium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Molybdenum'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-molybdenum.pdf
    year: 2026
  - title: 'Keane et al. (NIOSH): Selecting Processes to Minimize Hexavalent Chromium from Stainless Steel Welding'
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC4681305
  - title: Google Patents JP6207408B2 (background text naming SUS440C and JIS G4303)
    type: paper
    url: https://patents.google.com/patent/JP6207408B2/en
gaps:
  - ASTM A582 is not printed by any fetched 440C source (Rolled Alloys, Carpenter, Aalco, Aircraft Materials, UPMET, NASA 2018), so it is not in designations. Aalco names 440F (UNS S44020) as a free-machining variant, which is a different grade.
  - The JIS standard itself was not reached. SUS440C and JIS G4303 come from the background text of Japanese patent JP6207408B2. The Nachi-Fujikoshi SUS440C table returned a 404 error.
  - No tensile, yield or elongation value for annealed 440C was taken from a fetched source. Wikipedia's annealed row was not used, because the brief limits Wikipedia to composition and history.
  - No tensile or yield values across the 300 to 800 F temper range were found. The only 600 F strength values are representative values from two datasheets (Rolled Alloys and Aircraft Materials), and no strength temper curve was read.
  - Aalco's EN 10088-3 ranges (proof stress 448 to 1900 MPa, tensile 758 to 2030 MPa, elongation 4 to 14 %) span several tempers, so they are not used as single values.
  - UPMET's 440C datasheet prints yield 448 MPa, tensile 75 MPa (probably a typo), elongation 14 % and hardness 269 HB max with no heat-treatment condition, so none are used. Its density (7650 kg/cm3) has a unit slip, and its thermal conductivity (24.2 at 212 F) and electrical resistivity (600) have no unit.
  - The Carpenter 440C page gives composition, specifications and uses only, with no property values.
  - 'The UniMAP copy of the Springer paper prints an as-received annealed hardness of 11.4 HRC, which does not fit the other annealed data (Rolled Alloys: about 223 HB), so it is not used. Its tensile results are not given as numbers in the abstract.'
  - The NASA 2018 slides give 440C electrical resistivity as about 0.60 x10^-6 ohm.m in one table and about 36 x10^-6 ohm.cm in the other; only the first is used. Its 1900 MPa tensile value has no temper, so it is not used.
  - No specific heat value was read from any fetched 440C source.
  - No 440C safety data sheet was reached. The PubChem chromium and molybdenum records fetched in this run carry no hazard codes in their text, so they are not cited. OSHA (403), DOL (blocked) and CDC stacks (access denied) could not be read. The hazard source is a NIOSH-authored study of stainless steel welding fume, not a 440C study.
  - No source for dust or fume from grinding or machining 440C was read.
  - USGS critical-mineral list status for chromium and molybdenum was not checked (the MCS chapters do not print the lists), so critical_lists is empty.
  - Supply shares are computed by hand from printed tonnage (basis given per producer); they are not printed percentages.
  - 'No ESA or ECSS source for 440C was found. The space links come from two NASA reports only: a Space Shuttle main engine turbopump bearing study (1984) and a 2018 reaction-wheel bearing comparison.'
  - hardness and fracture_toughness are not in property-canon.yaml, so short names are used for them.
  - 'Not usable in this run: Starrapid 440C PDF (download failed), ASM Alloy Digest SS-101 (no text), Hudson Tool Steel 440C page (no text), AZoM 440C bar page (supplier list, no property values), SB Specialty Metals 440C data sheet (no values in text).'
  - No cryogenic tensile data and no high-temperature tensile data for 440C were found beyond the 1984 hardness tests.
sources:
  rolled-440c:
    title: 'Rolled Alloys: Stainless 440C data sheet (Bulletin No. 1142, 08/15)'
    id: Bulletin No. 1142
    url: https://www.rolledalloys.ca/wp-content/uploads/440C_stainless-steel-data-sheet.pdf
    kind: datasheet
    year: 2015
    license: cited, not reproduced
  aircraft-materials-440c:
    title: 'AircraftMaterials UK: Stainless Steel 440C technical data sheet (Alloy 440C, AISI 440C, AMS 5630)'
    id: Alloy 440C page
    url: https://www.aircraftmaterials.com/data/alstst/440c.html
    kind: datasheet
    license: cited, not reproduced
  aalco-440c-bar:
    title: 'Aalco: Stainless Steel - Martensitic - 1.4125 (440C) Bar, EN 10088-3:2005 datasheet'
    id: EN 10088-3:2005 bar
    url: https://www.aalco.co.uk/datasheets/Stainless-Steel-14125-440C-Bar_312.ashx
    kind: datasheet
    license: cited, not reproduced
  upmet-440c:
    title: 'United Performance Metals: Alloy 440C datasheet (AMS 5630 chemistry)'
    id: ALLOY 440C
    url: https://www.upmet.com/sites/default/files/datasheets/440c.pdf
    kind: datasheet
    license: cited, not reproduced
  carpenter-440c:
    title: 'Carpenter Technology: 440C alloy page (type analysis, applicable specifications, uses)'
    id: UNS S44004
    url: https://www.carpentertechnology.com/alloy-finder/440c
    kind: datasheet
    license: cited, not reproduced
  nasa-2018-ntrs:
    title: 'NASA Glenn: DellaCorte, Ni-Ti Next Generation Bearings for Space Applications (Schaeffler International Bearing Conference, 24 January 2018)'
    id: NTRS 20180002168
    url: https://ntrs.nasa.gov/api/citations/20180002168/downloads/20180002168.pdf
    kind: report
    year: 2018
    license: public domain (NASA)
  nasa-1984-ntrs:
    title: 'Dufrane et al., Battelle for NASA: Measurements of elastohydrodynamic film thicknesses, wear, and tempering behavior of high pressure oxygen turbopump bearings (AISI 440C)'
    id: NTRS 19840014892 (report dated 2 April 1984)
    url: https://ntrs.nasa.gov/api/citations/19840014892/downloads/19840014892.pdf
    kind: report
    year: 1984
    license: public domain (NASA)
  springer-unimap-440c:
    title: Effects of Heat Treatment on the Properties of SS440C for Blades Applications (Springer Proceedings in Physics 289, pp. 145-152; UniMAP repository copy)
    id: Springer Proc. Phys. 289, 145-152
    url: https://ris.unimap.edu.my/entities/publication/1eddb8c2-050b-427f-8b49-0de618f67a03
    kind: paper
    license: cited, not reproduced
  usgs-chromium-2026:
    title: 'USGS Mineral Commodity Summaries 2026: Chromium'
    id: mcs2026-chromium
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    kind: report
    year: 2026
    license: public domain (USGS)
  usgs-molybdenum-2026:
    title: 'USGS Mineral Commodity Summaries 2026: Molybdenum'
    id: mcs2026-molybdenum
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-molybdenum.pdf
    kind: report
    year: 2026
    license: public domain (USGS)
  pmc-cr6-welding:
    title: 'Keane M, Siert A, Stone S, Chen B, et al. (NIOSH): Selecting Processes to Minimize Hexavalent Chromium from Stainless Steel Welding (Welding Journal)'
    id: PMC4681305
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC4681305
    kind: paper
    license: open access (PMC)
  patent-jp6207408:
    title: 'Google Patents JP6207408B2: background text naming SUS440C and JIS G4303'
    id: JP6207408B2
    url: https://patents.google.com/patent/JP6207408B2/en
    kind: web
    license: public patent text
  wiki-440c:
    title: 'Wikipedia: 440C (composition cross-check only)'
    id: 440C
    url: https://en.wikipedia.org/wiki/440C
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
license: CC-BY-4.0
updated: '2026-10-24'
review:
  status: draft
  method: assistant
  checked_values: 44
  unreachable: 0
  caveats: 6
  note: 'Read by an AI assistant on 2026-10-24 from pages fetched in this run: Rolled Alloys bulletin 1142, AircraftMaterials 440C sheet, Aalco EN 10088-3 bar datasheet, UPMET 440C datasheet, Carpenter 440C page, NASA Glenn 2018 slides, NASA/Battelle 1984 turbopump bearing report, UniMAP copy of the Springer SS440C paper, USGS MCS 2026 chromium and molybdenum, the NIOSH-authored welding fume study (PMC), Google Patents JP6207408B2 (JIS name only) and Wikipedia (composition only).'
story:
  recipe:
    line: 440C is an iron-based martensitic stainless steel. Carbon (0.95 to 1.20 percent) is the highest of the 400 series, and chromium (16 to 18 percent) gives the stainless film. Rolled Alloys, Carpenter and Aalco print the same carbon and chromium limits, and Wikipedia gives the same ranges. Molybdenum is 0.75 percent maximum in Rolled Alloys and Carpenter, while EN 10088-3 (Aalco) allows 0.40 to 0.80 percent. The record gives limits, not a single analysis.
    parts:
      - name: Iron
        symbol: Fe
        share_note: balance (the rest)
        role: The matrix. As a martensitic stainless steel it can be hardened by heat treatment (Rolled Alloys).
        source: rolled-440c
        where: Chemical composition table (Fe balance)
      - name: Carbon
        symbol: C
        share_percent: 0.95
        share_high: 1.2
        role: Gives the high hardness; Rolled Alloys calls 440C the highest carbon content of the 400 series stainless steels.
        source: rolled-440c
        where: Chemical composition table (C, min 0.95, max 1.2); Features list
      - name: Chromium
        symbol: Cr
        share_percent: 16
        share_high: 18
        role: Keeps the stainless characteristics despite the high carbon (Rolled Alloys).
        source: rolled-440c
        where: Chemical composition table (Cr, min 16.0, max 18.0)
      - name: Molybdenum
        symbol: Mo
        share_percent: 0
        share_high: 0.75
        role: Maximum 0.75 (Rolled Alloys and Carpenter); EN 10088-3 allows 0.40 to 0.80 (Aalco).
        source: rolled-440c
        where: Chemical composition table (Mo, max 0.75)
      - name: Manganese
        symbol: Mn
        share_percent: 0
        share_high: 1
        role: Residual element, held to a maximum.
        source: rolled-440c
        where: Chemical composition table (Mn, max 1.00)
      - name: Silicon
        symbol: Si
        share_percent: 0
        share_high: 1
        role: Residual element, held to a maximum.
        source: rolled-440c
        where: Chemical composition table (Si, max 1.00)
      - name: Phosphorus
        symbol: P
        share_percent: 0
        share_high: 0.04
        role: Impurity held to a maximum.
        source: rolled-440c
        where: Chemical composition table (P, max 0.04)
      - name: Sulfur
        symbol: S
        share_percent: 0
        share_high: 0.03
        role: Impurity held to a maximum.
        source: rolled-440c
        where: Chemical composition table (S, max 0.03)
  risk_groups:
    - title: For people
      level: 1
      verdict: Welding fume is the main human-health watch point
      lead: No safety data sheet for 440C was reached. The hazard source found is a NIOSH-authored study of stainless steel welding fume.
      points:
        - label: Welding fume
          line: In the NIOSH-authored study, the hexavalent chromium fraction of stainless steel welding fume ranged from 2800 to 34,000 ppm across eight process and shielding-gas combinations.
        - label: Scope
          line: The study covers welding fume in general, not 440C alone, so treat it as a guide until a 440C safety data sheet is checked.
    - title: In service
      level: 2
      verdict: Heat and poor lubrication are the failure routes
      lead: NASA's 1984 study of turbopump bearings found that 440C softens with heat and wears fast when unlubricated.
      points:
        - label: Heat
          line: Bulk bearing temperatures of 480 C (900 F) or more could not be tolerated, and hot hardness falls rapidly from 540 C (1000 F).
        - label: Wear
          line: Unlubricated 440C wear rates were high enough to explain the ball wear seen in service.
    - title: Corrosion and temper
      level: 1
      verdict: Temper choice sets corrosion resistance
      lead: Corrosion resistance is best in the hardened, tempered and passivated condition (Aalco).
      points:
        - label: Avoid
          line: Tempering between 425 and 565 C reduces impact and corrosion resistance (Aalco).
        - label: Above 800 F
          line: Hardened and tempered above about 800 F (427 C), or annealed, the corrosion resistance is reduced (Carpenter).
  why: '440C is a high-carbon martensitic stainless steel built for hardness. It is hardened by heat treatment, and Carpenter says it is used in the hardened plus tempered condition. Its main use is bearings and valve parts, and NASA studied 440C bearings in the Space Shuttle main engine''s high-pressure oxygen turbopump. The trade-off is corrosion resistance: Carpenter says it falls in the annealed state and after tempering above about 800 F (427 C), and NASA''s 2018 comparison rates it marginal.'
  uses:
    - where: Bearings and valve parts
      line: 'Rolled Alloys, Aalco and UPMET all list bearings and valve parts (UPMET: ball bearings and valves). Aalco also lists high-quality knife blades, surgical instruments and chisels.'
    - where: Space Shuttle main engine turbopump bearings
      line: A 1984 NASA report on the high-pressure oxygen turbopump bearings measured 440C wear and tempering. It found that wear in unlubricated contact could explain the ball wear seen in service.
    - where: Space reaction-wheel bearing comparison (2018)
      line: NASA Glenn's 2018 slides compare 440C with 60NiTi for space bearings. They credit 60NiTi bearing races with 2x (against Rex 20) to 5x (against 440C) improvement in a reaction-wheel bearing.
  can_do:
    - label: Hardness
      line: 'Hardened and tempered, 440C reaches about HRC 60, the highest hardness of any stainless steel (Carpenter, Rolled Alloys). The temper sets it: 60 HRC after a one-hour temper at 300 F, and 56 HRC after tempering at 600 to 800 F (Rolled Alloys).'
    - label: Strength
      line: At the 600 F temper, Aircraft Materials gives 1965 MPa tensile and 1896 MPa yield, and Rolled Alloys gives 285 ksi and 275 ksi for the same heat treatment, with 2 percent elongation.
    - label: Stiffness
      line: Young's modulus is 200 GPa in the Aalco, UPMET and NASA 2018 records.
    - label: Heat tolerance
      line: In NASA's 1984 tests, tempering at 540 C (1000 F) for 10 to 945 s dropped hardness from HRC 60 only to HRC 57 to 58. Bulk bearing temperatures of 480 C (900 F) or more could not be tolerated in the turbopump bearings.
    - label: Service temperature
      line: NASA Glenn gives about 400 C as the maximum use temperature of 440C in its 2018 comparison.
  compare: Against common stainless steels, 440C trades corrosion resistance for hardness. Aalco says its corrosion resistance approximates that of 304 in many environments, and that martensitic grades resist corrosion less than the common austenitic grades. NASA's 2018 comparison rates 440C corrosion resistance as marginal and calls the austenitic 304 soft, while it lists 60NiTi, a superelastic bearing alloy, as excellent in aqueous and acidic service.
  compare_rows:
    - label: Tensile strength at the 600 F temper
      benchmark: ultimate_tensile_strength
    - label: Density
      benchmark: density
    - label: Melting range
      benchmark: melting_point
  handling:
    - Machine in the annealed condition. Once hardened, machining becomes much harder and probably impossible (Aalco).
    - Do not overheat when grinding, since hardness and corrosion resistance can fall (Rolled Alloys).
    - Temper straight after quenching, at the temperature that gives the hardness you need (Rolled Alloys, Aalco).
    - Welding is seldom needed. If it is, preheat (about 250 C, or 500 F) and anneal afterwards (Aalco, Rolled Alloys).
  good_for:
    - Bearings, where hardness and wear resistance matter (Carpenter, Aalco, Rolled Alloys).
    - Valve seats and valve parts (Aalco, Rolled Alloys, UPMET).
    - Knife blades, surgical instruments and chisels (Aalco, UPMET).
  watch_out:
    - Corrosion. NASA rates it marginal, and Aalco says it is less corrosion resistant than the common austenitic grades.
    - Tempering between 425 and 565 C, which reduces impact and corrosion resistance (Aalco).
    - Long holds at 540 C (1000 F), or bulk temperatures of 480 C (900 F) and above, which take bearing hardness to unusable levels (NASA 1984).
    - Welding, which is seldom done. Filler choice changes the weld hardness (Aalco, Rolled Alloys).
  verdict: Of the stainless steels in these sources, 440C is the hardest when heat-treated, so it is the bearing and valve choice when hardness matters most. Accept its marginal corrosion resistance, keep the temper at or below about 800 F (427 C), and keep service below about 400 C.