spore: profile
id: steel-4140
spore_version: 0.2
family: carbon-and-alloy-steels
name: Alloy steel AISI 4140 (chromium-molybdenum)
abbreviation: 4140 (UNS G41400)
role: structural alloy
category: metals
type: steels-and-stainless
summary: AISI 4140 is a medium-carbon chromium-molybdenum alloy steel (UNS G41400) whose strength depends on heat treatment. Quenched and tempered bar of 10 to 100 mm reaches a minimum yield strength of 740 MPa. In hydrogen gas and in dilute sulfuric acid its strength and corrosion resistance suffer, which limits use where those are present.
best_for: Machine parts and structures in medium and large sections that need high strength and toughness after quenching and tempering
weakest_at: Hydrogen gas, which cut notched strength by about 60 percent in one room-temperature study, and dilute sulfuric acid, which corroded it at 176.87 mpy
identity:
  formula: Fe balance; 0.38 to 0.43 C, 0.75 to 1.00 Mn, 0.15 to 0.35 Si, 0.80 to 1.10 Cr, 0.15 to 0.25 Mo, 0.035 max P, 0.040 max S (wt%, ASTM A29 limits as printed in Table 1.1.1 of the Sandia reference)
  source: sandia-1211
  where: Table 1.1.1, Allowable composition ranges (wt%) for Cr-Mo steels, row 4140
  designations:
    - system: AISI
      code: '4140'
      source: voestalpine-4140
      where: NEAREST STANDARDS table, AISI column
    - system: UNS
      code: G41400
      source: voestalpine-4140
      where: NEAREST STANDARDS table, UNS column
    - system: EN
      code: '1.7225'
      source: saky-4140
      where: 'Product description: 1.7225 is the European EN standard'
    - system: EN name
      code: 42CrMo4
      source: metinvest-42crmo4
      where: Steel 42CrMo4 analogues table, EU column
    - system: ISO
      code: 683-2
      source: metinvest-42crmo4
      where: '42CrMo4 page: made in accordance with DIN EN ISO 683-2 (formerly EN 10083-3)'
    - system: JIS
      code: SCM440
      source: elgin-4140
      where: Key Words line
    - system: JIS
      code: SCM 4
      source: elgin-4140
      where: Key Words line, printed as JIS SCM 4
    - system: SAE
      code: '4140'
      source: saky-4140
      where: 'Short Description: AISI SAE 4140 alloy steel'
    - system: SAE
      code: J404
      source: elgin-4140
      where: Key Words line
    - system: SAE
      code: J412
      source: elgin-4140
      where: Key Words line
    - system: SAE
      code: J770
      source: elgin-4140
      where: Key Words line
    - system: ASTM
      code: A29
      source: saky-4140
      where: Specifications table, Standard row
    - system: ASTM
      code: A322
      source: elgin-4140
      where: Key Words line
    - system: ASTM
      code: A331
      source: elgin-4140
      where: Key Words line
    - system: ASTM
      code: A505
      source: elgin-4140
      where: Key Words line
    - system: ASTM
      code: A519
      source: elgin-4140
      where: Key Words line
    - system: ASTM
      code: A646
      source: elgin-4140
      where: Key Words line
    - system: BS
      code: EN19
      source: tachart-709m40
      where: 709M40 page, Alias list, printed En19
    - system: BS
      code: 708M40
      source: elgin-4140
      where: Key Words line, printed B.S. 708 M 40 (UK)
    - system: BS
      code: 708A42
      source: elgin-4140
      where: Key Words line, printed B.S. 708 A 42 (UK)
    - system: BS
      code: 709M40
      source: elgin-4140
      where: Key Words line, printed B.S. 709 M 40 (UK)
    - system: DTD
      code: 167A
      source: tachart-709m40
      where: 709M40 page, Alias list
    - system: AFNOR
      code: 40 CD 4
      source: elgin-4140
      where: Key Words line
    - system: AFNOR
      code: 42 CD 4
      source: elgin-4140
      where: Key Words line, printed AFNOR 42 CD 4 (France)
    - system: SS
      code: 14 2244
      source: elgin-4140
      where: Key Words line, printed SS14 2244 (Sweden)
    - system: MIL
      code: MIL-S-16974
      source: elgin-4140
      where: Key Words line, printed MIL SPEC MIL-S-16974
    - system: MIL
      code: S 5626
      source: aircraft-4140
      where: Specifications list, MIL S 5626
    - system: AMS
      code: S 5626
      source: aircraft-4140
      where: Specifications list, AMS S 5626
    - system: AMS
      code: '6349'
      source: aircraft-4140
      where: Specifications list, AMS 6349
    - system: AMS
      code: '6382'
      source: aircraft-4140
      where: Specifications list, AMS 6382
    - system: AMS
      code: '6381'
      source: elgin-4140
      where: Key Words line
    - system: AMS
      code: '6390'
      source: elgin-4140
      where: Key Words line
    - system: AMS
      code: '6395'
      source: elgin-4140
      where: Key Words line
    - system: AS
      code: 1444-1996
      source: aircraft-4140
      where: Specifications list, AS 1444-1996
    - system: IS
      code: 40Cr1Mo28
      source: elgin-4140
      where: Key Words line, printed IS 1570, IS 4367 and IS 5517 40Cr1Mo28
    - system: DIN
      code: 41CrMo4
      note: nearest equivalent
      source: voestalpine-4140
      where: NEAREST STANDARDS table, DIN column, printed as 41CrMo4
    - system: BS
      code: EN19A
      note: nearest equivalent
      source: voestalpine-4140
      where: NEAREST STANDARDS table, BS column
tags:
  environments: []
  stresses: []
  applications:
    - mechanisms
    - structures
properties:
  - benchmark: yield_strength
    label: Yield strength, quenched and tempered, 10 to 100 mm
    value: 740
    bound: lower
    unit: MPa
    scope: material
    conditions:
      condition: 'quenched and tempered: oil quench from 830 to 860 C, temper 540 to 680 C for at least 1 h, air cool'
      section: 10 to 100 mm
      strength_type: Rp0.2, minimum
      unit_in_source: N/mm2
    method: Mechanical properties (heat treated) table, minimum as printed; N/mm2 is the same number as MPa
    status: ground
    source: voestalpine-4140
    where: Mechanical Properties (heat treated) table, Yield Strength (Rp 0.2), 10-100 mm column
  - benchmark: yield_strength
    label: Yield strength, quenched and tempered, 101 to 250 mm
    value: 665
    bound: lower
    unit: MPa
    scope: material
    conditions:
      condition: 'quenched and tempered: oil quench from 830 to 860 C, temper 540 to 680 C for at least 1 h, air cool'
      section: 101 to 250 mm
      strength_type: Rp0.2, minimum
      unit_in_source: N/mm2
    method: Mechanical properties (heat treated) table, minimum as printed; N/mm2 is the same number as MPa
    status: ground
    source: voestalpine-4140
    where: Mechanical Properties (heat treated) table, Yield Strength (Rp 0.2), 101-250 mm column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, quenched and tempered, 10 to 100 mm
    value: 930
    value_high: 1080
    bound: range
    unit: MPa
    scope: material
    conditions:
      condition: 'quenched and tempered: oil quench from 830 to 860 C, temper 540 to 680 C for at least 1 h, air cool'
      section: 10 to 100 mm
      unit_in_source: N/mm2
    method: Mechanical properties (heat treated) table, minimum and maximum as printed; N/mm2 is the same number as MPa
    status: ground
    source: voestalpine-4140
    where: Mechanical Properties (heat treated) table, Tensile (Rm), 10-100 mm column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, quenched and tempered, 101 to 250 mm
    value: 850
    value_high: 1000
    bound: range
    unit: MPa
    scope: material
    conditions:
      condition: 'quenched and tempered: oil quench from 830 to 860 C, temper 540 to 680 C for at least 1 h, air cool'
      section: 101 to 250 mm
      unit_in_source: N/mm2
    method: Mechanical properties (heat treated) table, minimum and maximum as printed; N/mm2 is the same number as MPa
    status: ground
    source: voestalpine-4140
    where: Mechanical Properties (heat treated) table, Tensile (Rm), 101-250 mm column
  - benchmark: elongation
    label: Elongation, quenched and tempered, 10 to 100 mm
    value: 12
    bound: lower
    unit: '%'
    scope: material
    conditions:
      condition: 'quenched and tempered: oil quench from 830 to 860 C, temper 540 to 680 C for at least 1 h, air cool'
      section: 10 to 100 mm
      gauge: A5 as labelled in the datasheet
    method: Mechanical properties (heat treated) table, minimum as printed
    status: ground
    source: voestalpine-4140
    where: Mechanical Properties (heat treated) table, Elongation (A5 %), 10-100 mm column
  - benchmark: impact_energy
    label: Charpy impact energy, quenched and tempered, 10 to 100 mm
    value: 42
    bound: lower
    unit: J
    scope: material
    conditions:
      condition: 'quenched and tempered: oil quench from 830 to 860 C, temper 540 to 680 C for at least 1 h, air cool'
      section: 10 to 100 mm
      test: Charpy
      test_temperature: not stated in the datasheet
    method: Mechanical properties (heat treated) table, minimum as printed
    status: ground
    source: voestalpine-4140
    where: Mechanical Properties (heat treated) table, Charpy Impact (J), 10-100 mm column
  - benchmark: hardness_brinell
    label: Hardness, quenched and tempered, 10 to 100 mm
    value: 269
    value_high: 331
    bound: range
    unit: HB
    scope: material
    conditions:
      condition: 'quenched and tempered: oil quench from 830 to 860 C, temper 540 to 680 C for at least 1 h, air cool'
      section: 10 to 100 mm
    method: Mechanical properties (heat treated) table, range as printed
    status: ground
    source: voestalpine-4140
    where: Mechanical Properties (heat treated) table, Hardness (HB), 10-100 mm column
  - benchmark: yield_strength
    label: Yield strength, typical, 50 mm section
    value: 770
    unit: MPa
    scope: material
    conditions:
      condition: hardened and tempered, supplied to condition T (the temper temperature is not stated)
      section: 50 mm
    method: Typical mechanical properties table as printed, row Alloy 4140 at 50 mm; typical values, not minimums
    status: ground
    source: aircraft-4140
    where: Typical Mechanical Properties table, row Alloy 4140, section 50 mm
  - benchmark: yield_strength
    label: Yield strength, typical, 200 mm section
    value: 570
    unit: MPa
    scope: material
    conditions:
      condition: hardened and tempered, supplied to condition T (the temper temperature is not stated)
      section: 200 mm
    method: Typical mechanical properties table as printed, row Alloy 4140 at 200 mm; typical values, not minimums
    status: ground
    source: aircraft-4140
    where: Typical Mechanical Properties table, row Alloy 4140, section 200 mm
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, typical, 50 mm section
    value: 930
    unit: MPa
    scope: material
    conditions:
      condition: hardened and tempered, supplied to condition T (the temper temperature is not stated)
      section: 50 mm
    method: Typical mechanical properties table as printed, row Alloy 4140 at 50 mm; typical values, not minimums
    status: ground
    source: aircraft-4140
    where: Typical Mechanical Properties table, row Alloy 4140, section 50 mm
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, typical, 200 mm section
    value: 850
    unit: MPa
    scope: material
    conditions:
      condition: hardened and tempered, supplied to condition T (the temper temperature is not stated)
      section: 200 mm
    method: Typical mechanical properties table as printed, row Alloy 4140 at 200 mm; typical values, not minimums
    status: ground
    source: aircraft-4140
    where: Typical Mechanical Properties table, row Alloy 4140, section 200 mm
  - benchmark: elongation
    label: Elongation, typical, 50 mm section
    value: 17
    unit: '%'
    scope: material
    conditions:
      condition: hardened and tempered, supplied to condition T (the temper temperature is not stated)
      section: 50 mm
    method: Typical mechanical properties table as printed, row Alloy 4140 at 50 mm
    status: ground
    source: aircraft-4140
    where: Typical Mechanical Properties table, Elongation %, row Alloy 4140, section 50 mm
  - benchmark: impact_energy
    label: Izod impact energy, typical, 50 mm section
    value: 90
    unit: J
    scope: material
    conditions:
      condition: hardened and tempered, supplied to condition T (the temper temperature is not stated)
      section: 50 mm
      test: Izod
    method: Typical mechanical properties table as printed (column headed Izod J)
    status: ground
    source: aircraft-4140
    where: Typical Mechanical Properties table, Izod J, row Alloy 4140, section 50 mm
  - benchmark: hardness_brinell
    label: Hardness, typical, 50 mm section
    value: 275
    unit: HB
    scope: material
    conditions:
      condition: hardened and tempered, supplied to condition T (the temper temperature is not stated)
      section: 50 mm
    method: Typical mechanical properties table as printed, row Alloy 4140 at 50 mm
    status: ground
    source: aircraft-4140
    where: Typical Mechanical Properties table, Hardness HB, row Alloy 4140, section 50 mm
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, normalised at 870 C
    value: 1020
    unit: MPa
    scope: material
    conditions:
      condition: normalised at 870 C, air cooled
      section: 25 mm (1 in.) round
    method: Mechanical properties table of the fact sheet, value as printed for the stated condition
    status: ground
    source: elgin-4140
    where: 'Mechanical Properties, Tensile Strength Ultimate, row 1020 MPa (heading: normalized at 870 C, 25 mm round)'
  - benchmark: yield_strength
    label: Yield strength, normalised at 870 C
    value: 655
    unit: MPa
    scope: material
    conditions:
      condition: normalised at 870 C, air cooled
      section: 25 mm (1 in.) round
    method: Mechanical properties table of the fact sheet, value as printed for the stated condition
    status: ground
    source: elgin-4140
    where: 'Mechanical Properties, Tensile Strength Yield, row 655 MPa (heading: normalized at 870 C, 25 mm round)'
  - benchmark: elongation
    label: Elongation, normalised at 870 C
    value: 17.7
    unit: '%'
    scope: material
    conditions:
      condition: normalised at 870 C, air cooled
      section: 25 mm (1 in.) round
      gauge: 50 mm
    method: Mechanical properties table of the fact sheet, value as printed for the stated condition
    status: ground
    source: elgin-4140
    where: Mechanical Properties, Elongation at Break, row 17.70% in 50 mm
  - benchmark: reduction_of_area
    label: Reduction of area, normalised at 870 C
    value: 46.8
    unit: '%'
    scope: material
    conditions:
      condition: normalised at 870 C, air cooled
      section: 25 mm (1 in.) round
    method: Mechanical properties table of the fact sheet, value as printed for the stated condition
    status: ground
    source: elgin-4140
    where: Mechanical Properties, Reduction of Area, row 46.80%
  - benchmark: hardness_brinell
    label: Hardness, Brinell, normalised at 870 C
    value: 302
    unit: HB
    scope: material
    conditions:
      condition: normalised at 870 C, air cooled
      section: 25 mm (1 in.) round
    method: Mechanical properties table of the fact sheet; the Brinell value is printed and the other scales are converted by the datasheet
    status: ground
    source: elgin-4140
    where: Mechanical Properties, Hardness Brinell, row 302
  - benchmark: density
    value: 7.85
    unit: g/cc
    scope: material
    conditions:
      basis: physical properties table; no temperature or heat treatment stated
    method: Physical properties table as printed (metric column)
    status: ground
    source: elgin-4140
    where: Physical Properties, Density, row 7.85 g/cc
  - benchmark: elastic_modulus
    label: Modulus of elasticity
    value: 205
    unit: GPa
    scope: material
    conditions:
      basis: datasheet comment Typical for steel; no temperature or heat treatment stated
    method: Mechanical properties table as printed; the datasheet marks the value as typical for steel
    status: ground
    source: elgin-4140
    where: Mechanical Properties, Modulus of Elasticity, row 205 GPa
  - benchmark: shear_modulus
    value: 80
    unit: GPa
    scope: material
    conditions:
      basis: datasheet comment Typical for steel; no temperature or heat treatment stated
    method: Mechanical properties table as printed; the datasheet marks the value as typical for steel
    status: ground
    source: elgin-4140
    where: Mechanical Properties, Shear Modulus, row 80.0 GPa
  - benchmark: bulk_modulus
    value: 160
    unit: GPa
    scope: material
    conditions:
      basis: datasheet comment Typical for steel; no temperature or heat treatment stated
    method: Mechanical properties table as printed; the datasheet marks the value as typical for steel
    status: ground
    source: elgin-4140
    where: Mechanical Properties, Bulk Modulus, row 160 GPa
  - benchmark: poissons_ratio
    value: 0.29
    unit: '-'
    scope: material
    conditions:
      basis: datasheet marks the value as calculated; no temperature stated
    method: Mechanical properties table as printed; the datasheet notes the value is calculated
    status: calculated
    source: elgin-4140
    where: Mechanical Properties, Poissons Ratio, row 0.29 (comment Calculated)
  - benchmark: cte
    label: Coefficient of thermal expansion, 0 to 100 C
    value: 12.2
    unit: ppm/K
    scope: material
    conditions:
      temperature: 0 to 100 C (32 to 212 F)
      unit_in_source: µm/m-°C, numerically the same as ppm/K
    method: Thermal properties table as printed; the unit is the same number as ppm/K
    status: ground
    source: elgin-4140
    where: Thermal Properties, CTE linear, row 12.2 µm/m-°C at 0.000 to 100 °C
  - benchmark: cte
    label: Coefficient of thermal expansion, 20 to 600 C
    value: 14.6
    unit: ppm/K
    scope: material
    conditions:
      temperature: 20 to 600 C (68 to 1110 F)
      unit_in_source: µm/m-°C, numerically the same as ppm/K
    method: Thermal properties table as printed; the unit is the same number as ppm/K
    status: ground
    source: elgin-4140
    where: Thermal Properties, CTE linear, row 14.6 µm/m-°C at 20.0 to 600 °C
  - benchmark: specific_heat
    value: 0.473
    unit: J/gK
    scope: material
    conditions:
      temperature: 150 to 200 C (302 to 392 F)
      unit_in_source: J/g-°C
    method: Thermal properties table as printed; J/g-°C is the same number as J/gK
    status: ground
    source: elgin-4140
    where: Thermal Properties, Specific Heat Capacity, row 0.473 J/g-°C at 150 to 200 °C
  - benchmark: thermal_conductivity
    value: 42.6
    unit: W/mK
    scope: material
    conditions:
      temperature: 100 C (212 F)
      unit_in_source: W/m-K, with the W lost in text extraction; the BTU column on the same row (296 BTU-in/hr-ft2-F) confirms W/m-K
    method: Thermal properties table as printed; unit inferred from the BTU-in column on the same row
    status: ground
    source: elgin-4140
    where: Thermal Properties, Thermal Conductivity, row 42.6 at 100 C (296 BTU-in/hr-ft2-F)
  - benchmark: yield_strength
    label: Yield strength, high-strength condition, smooth bar
    value: 1235
    unit: MPa
    scope: material
    conditions:
      heat_treatment: A 1116 K/60 min, water quench, T 755 K/120 min (A 843 C 1 h, water quench, temper 482 C 2 h); strength level high
      environment: 69 MPa helium gas
      test: smooth tensile, room temperature, strain rate 3.3e-5 per s
      yield_definition: deviation from linearity on load vs time plot
    method: Table 3.1.1.1 row 4140 (69 MPa He); the same value appears in Table 1.1.3 high-strength row; kelvin converted to C by subtracting 273.15 and rounding
    status: ground
    source: sandia-1211
    where: Table 3.1.1.1, 4140 row, 69 MPa He; Table 1.1.3, 4140 high strength row
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, high-strength condition, helium
    value: 1283
    unit: MPa
    scope: material
    conditions:
      heat_treatment: A 1116 K/60 min, water quench, T 755 K/120 min (A 843 C 1 h, water quench, temper 482 C 2 h); strength level high
      environment: 69 MPa helium gas
      test: smooth tensile, room temperature
    method: Table 3.1.1.1 row 4140, 69 MPa He
    status: ground
    source: sandia-1211
    where: Table 3.1.1.1, 4140 row, 69 MPa He, Su column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, high-strength condition, hydrogen
    value: 1228
    unit: MPa
    scope: material
    conditions:
      heat_treatment: A 1116 K/60 min, water quench, T 755 K/120 min (A 843 C 1 h, water quench, temper 482 C 2 h); strength level high
      environment: 69 MPa hydrogen gas
      test: smooth tensile, room temperature
    method: Table 3.1.1.1 row 4140, 69 MPa H2
    status: ground
    source: sandia-1211
    where: Table 3.1.1.1, 4140 row, 69 MPa H2, Su column
  - benchmark: reduction_of_area
    label: Reduction of area, high-strength condition, helium
    value: 48
    unit: '%'
    scope: material
    conditions:
      heat_treatment: A 1116 K/60 min, water quench, T 755 K/120 min (A 843 C 1 h, water quench, temper 482 C 2 h); strength level high
      environment: 69 MPa helium gas
      test: smooth tensile, room temperature
    method: Table 3.1.1.1 row 4140, 69 MPa He, RA column
    status: ground
    source: sandia-1211
    where: Table 3.1.1.1, 4140 row, 69 MPa He, RA column
  - benchmark: reduction_of_area
    label: Reduction of area, high-strength condition, hydrogen
    value: 8.8
    unit: '%'
    scope: material
    conditions:
      heat_treatment: A 1116 K/60 min, water quench, T 755 K/120 min (A 843 C 1 h, water quench, temper 482 C 2 h); strength level high
      environment: 69 MPa hydrogen gas
      test: smooth tensile, room temperature
    method: Table 3.1.1.1 row 4140, 69 MPa H2, RA column
    status: ground
    source: sandia-1211
    where: Table 3.1.1.1, 4140 row, 69 MPa H2, RA column
  - benchmark: elongation
    label: Elongation, high-strength condition, hydrogen
    value: 2.6
    unit: '%'
    scope: material
    conditions:
      heat_treatment: A 1116 K/60 min, water quench, T 755 K/120 min (A 843 C 1 h, water quench, temper 482 C 2 h); strength level high
      environment: 69 MPa hydrogen gas
      test: smooth tensile, room temperature
    method: Table 3.1.1.1 row 4140, 69 MPa H2, Elt column; the footnote for a 32 mm gauge is printed against the helium value, not this one
    status: ground
    source: sandia-1211
    where: Table 3.1.1.1, 4140 row, 69 MPa H2, Elt column
  - benchmark: yield_strength
    label: Yield strength, low-strength condition
    value: 642
    unit: MPa
    scope: material
    conditions:
      heat_treatment: A 1116 K/60 min, oil quench, T 977 K/120 min, air cool (A 843 C 1 h, oil quench, temper 704 C 2 h, air cool); strength level low
      environment: not stated for the smooth yield value
    method: Table 1.1.3 low-strength 4140 row; kelvin converted to C by subtracting 273.15 and rounding; the same Sy* is listed in Table 3.1.2.1
    status: ground
    source: sandia-1211
    where: Table 1.1.3, 4140 low strength row, Sy column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, low-strength condition
    value: 745
    unit: MPa
    scope: material
    conditions:
      heat_treatment: A 1116 K/60 min, oil quench, T 977 K/120 min, air cool (A 843 C 1 h, oil quench, temper 704 C 2 h, air cool); strength level low
      environment: not stated in Table 1.1.3
    method: Table 1.1.3 low-strength 4140 row
    status: ground
    source: sandia-1211
    where: Table 1.1.3, 4140 low strength row, Su column
  - benchmark: reduction_of_area
    label: Reduction of area, low-strength condition
    value: 68
    unit: '%'
    scope: material
    conditions:
      heat_treatment: A 1116 K/60 min, oil quench, T 977 K/120 min, air cool (A 843 C 1 h, oil quench, temper 704 C 2 h, air cool); strength level low
      environment: not stated in Table 1.1.3
    method: Table 1.1.3 low-strength 4140 row
    status: ground
    source: sandia-1211
    where: Table 1.1.3, 4140 low strength row, RA column
  - benchmark: notched_tensile_strength
    label: Notched tensile strength, low-strength condition, air
    value: 1345
    unit: MPa
    scope: material
    conditions:
      heat_treatment: A 843 C 1 h, oil quench, temper 704 C 2 h, air cool; strength level low
      environment: air
      specimen: V-notch, 60 degree included angle, notch root radius 0.024 mm, Kt 8.4
      displacement_rate: about 4e-4 mm/s
    method: Table 3.1.2.1 row 4140 (low strength), air
    status: ground
    source: sandia-1211
    where: Table 3.1.2.1, 4140 low strength row, air, sigma s column
  - benchmark: notched_tensile_strength
    label: Notched tensile strength, low-strength condition, helium
    value: 1259
    unit: MPa
    scope: material
    conditions:
      heat_treatment: A 843 C 1 h, oil quench, temper 704 C 2 h, air cool; strength level low
      environment: 69 MPa helium gas
      specimen: V-notch, 60 degree included angle, notch root radius 0.024 mm, Kt 8.4
      displacement_rate: about 4e-4 mm/s
    method: Table 3.1.2.1 row 4140 (low strength), 69 MPa He
    status: ground
    source: sandia-1211
    where: Table 3.1.2.1, 4140 low strength row, 69 MPa He, sigma s column
  - benchmark: notched_tensile_strength
    label: Notched tensile strength, low-strength condition, hydrogen
    value: 1074
    unit: MPa
    scope: material
    conditions:
      heat_treatment: A 843 C 1 h, oil quench, temper 704 C 2 h, air cool; strength level low
      environment: 69 MPa hydrogen gas
      specimen: V-notch, 60 degree included angle, notch root radius 0.024 mm, Kt 8.4
      displacement_rate: about 4e-4 mm/s
    method: Table 3.1.2.1 row 4140 (low strength), 69 MPa H2
    status: ground
    source: sandia-1211
    where: Table 3.1.2.1, 4140 low strength row, 69 MPa H2, sigma s column
  - benchmark: notched_tensile_strength
    label: Notched tensile strength, high-strength condition, helium
    value: 2160
    unit: MPa
    scope: material
    conditions:
      heat_treatment: A 843 C 1 h, water quench, temper 482 C 2 h; strength level high
      environment: 69 MPa helium gas
      specimen: V-notch, 60 degree included angle, notch root radius 0.024 mm, Kt 8.4
      displacement_rate: about 4e-4 mm/s
    method: Table 3.1.2.1 row 4140 (high strength), 69 MPa He
    status: ground
    source: sandia-1211
    where: Table 3.1.2.1, 4140 high strength row, 69 MPa He, sigma s column
  - benchmark: notched_tensile_strength
    label: Notched tensile strength, high-strength condition, hydrogen
    value: 862
    unit: MPa
    scope: material
    conditions:
      heat_treatment: A 843 C 1 h, water quench, temper 482 C 2 h; strength level high
      environment: 69 MPa hydrogen gas
      specimen: V-notch, 60 degree included angle, notch root radius 0.024 mm, Kt 8.4
      displacement_rate: about 4e-4 mm/s
    method: Table 3.1.2.1 row 4140 (high strength), 69 MPa H2
    status: ground
    source: sandia-1211
    where: Table 3.1.2.1, 4140 high strength row, 69 MPa H2, sigma s column
  - benchmark: notched_reduction_of_area
    label: Notched reduction of area, low-strength condition, air
    value: 10
    unit: '%'
    scope: material
    conditions:
      heat_treatment: A 843 C 1 h, oil quench, temper 704 C 2 h, air cool; strength level low
      environment: air
      specimen: V-notch, Kt 8.4
    method: Table 3.1.2.1 row 4140 (low strength), air, RA column
    status: ground
    source: sandia-1211
    where: Table 3.1.2.1, 4140 low strength row, air, RA column
  - benchmark: notched_reduction_of_area
    label: Notched reduction of area, low-strength condition, helium
    value: 14
    unit: '%'
    scope: material
    conditions:
      heat_treatment: A 843 C 1 h, oil quench, temper 704 C 2 h, air cool; strength level low
      environment: 69 MPa helium gas
      specimen: V-notch, Kt 8.4
    method: Table 3.1.2.1 row 4140 (low strength), 69 MPa He, RA column
    status: ground
    source: sandia-1211
    where: Table 3.1.2.1, 4140 low strength row, 69 MPa He, RA column
  - benchmark: notched_reduction_of_area
    label: Notched reduction of area, low-strength condition, hydrogen
    value: 7.1
    unit: '%'
    scope: material
    conditions:
      heat_treatment: A 843 C 1 h, oil quench, temper 704 C 2 h, air cool; strength level low
      environment: 69 MPa hydrogen gas
      specimen: V-notch, Kt 8.4
    method: Table 3.1.2.1 row 4140 (low strength), 69 MPa H2, RA column
    status: ground
    source: sandia-1211
    where: Table 3.1.2.1, 4140 low strength row, 69 MPa H2, RA column
  - benchmark: notched_reduction_of_area
    label: Notched reduction of area, high-strength condition, helium
    value: 2.8
    unit: '%'
    scope: material
    conditions:
      heat_treatment: A 843 C 1 h, water quench, temper 482 C 2 h; strength level high
      environment: 69 MPa helium gas
      specimen: V-notch, Kt 8.4
    method: Table 3.1.2.1 row 4140 (high strength), 69 MPa He, RA column
    status: ground
    source: sandia-1211
    where: Table 3.1.2.1, 4140 high strength row, 69 MPa He, RA column
  - benchmark: notched_reduction_of_area
    label: Notched reduction of area, high-strength condition, hydrogen
    value: 0.9
    unit: '%'
    scope: material
    conditions:
      heat_treatment: A 843 C 1 h, water quench, temper 482 C 2 h; strength level high
      environment: 69 MPa hydrogen gas
      specimen: V-notch, Kt 8.4
    method: Table 3.1.2.1 row 4140 (high strength), 69 MPa H2, RA column
    status: ground
    source: sandia-1211
    where: Table 3.1.2.1, 4140 high strength row, 69 MPa H2, RA column
corrosion:
  - environment: Immersion in 0.5 M sulfuric acid (H2SO4), 48 to 144 h, weight-loss test
    headline: AISI 4140 corroded at 132.65 to 176.87 mpy in 0.5 M sulfuric acid, and its rate rose with exposure time.
    effect: Rates were 132.65 mpy at 48 h, 143.7 mpy at 96 h and 176.87 mpy at 144 h, from weight loss (Table 1). The paper reports obvious rust on all AISI 4140 specimens at every time and XRD shows metal oxides as the corrosion products. Only AISI 1045 corroded faster, at 183.7 mpy at 144 h. The severe rating is an assistant judgement from the mpy values, not a rating in the paper.
    rating: severe
    conditions:
      solution: 0.5 M H2SO4
      exposure_times_h: 48, 96, 144
      specimen: 25 mm diameter by 30 mm high, three per material (as printed)
      heat_treatment: not stated in the paper
      method: weight loss in mg; corrosion rate in mpy
    source: itats-2021
    where: Table 1 (AISI 4140 rows); Results, Corrosion Rate; Macrostructure results
  - environment: Hydrogen gas at 69 MPa, room temperature (one study compiled by Sandia)
    headline: Hydrogen gas at 69 MPa cuts the notched tensile strength of high-strength 4140 from 2160 to 862 MPa, and its notched reduction of area from 2.8 to 0.9 percent.
    effect: The Sandia reference says hydrogen severely degrades reduction of area in smooth tension (80% lower than in helium), while ultimate strength barely changes (1283 to 1228 MPa). Hydrogen lowers notched tensile strength by about 60% for high-strength 4140 and by about 15% for low-strength 4140. The yield strength of 4140 sets how severe the loss is, so the high-strength condition suffers most.
    rating: severe
    conditions:
      environment: 69 MPa hydrogen gas, room temperature
      comparison: 69 MPa helium gas
      notch: V-notch, Kt 8.4
      heat_treatment_high: A 843 C 1 h, water quench, temper 482 C 2 h
      heat_treatment_low: A 843 C 1 h, oil quench, temper 704 C 2 h
    source: sandia-1211
    where: Sections 3.1.1 and 3.1.2 (text); Tables 3.1.1.1 and 3.1.2.1
risks:
  hazards:
    - text: 'PubChem aggregated GHS for elemental chromium (signal word Danger): H317 (20.7%), H319 (19.1%) and H334 (20.3%) are the reported codes above 10%; H335, H320, H341, H371, H400 and H410 also appear in notifications. About half of 2404 company reports (1202) say it does not meet GHS criteria. The data cover the element, not the alloy.'
      ghs:
        - H317
        - H319
        - H334
        - H335
        - H320
        - H341
        - H371
        - H400
        - H410
      source: pubchem-chromium
      where: Safety and Hazards, GHS Classification (CID 23976)
    - text: 'PubChem aggregated GHS for elemental molybdenum: 57.4% (874 of 1523) of reports say it does not meet GHS criteria. Reported codes include H228 flammable solid (30%), H361 suspected of damaging fertility or the unborn child (29.5%), H225 (11.6%), H315, H319 and H335. The data cover the element, not the alloy.'
      ghs:
        - H228
        - H361
        - H225
        - H315
        - H319
        - H335
      source: pubchem-molybdenum
      where: Safety and Hazards, GHS Classification (CID 23932)
  failure_risks:
    - mode: Hydrogen embrittlement in gaseous hydrogen
      trigger: Hydrogen gas at 69 MPa, room temperature, notched and smooth specimens
      consequence: Notched tensile strength of high-strength 4140 fell from 2160 to 862 MPa, and its notched reduction of area from 2.8 to 0.9 percent. The source ties the loss to yield strength.
      severity: high
      source: sandia-1211
      where: Table 3.1.2.1; Section 3.1.2
    - mode: Acid corrosion with weight loss
      trigger: Immersion in 0.5 M sulfuric acid for 48 to 144 h
      consequence: Mass fell from 4000 mg to 1600 mg after 144 h, a corrosion rate of 176.87 mpy, with visible rust on the specimens.
      severity: high
      source: itats-2021
      where: Table 1, AISI 4140 rows
    - mode: Temper brittleness
      trigger: Tempering in the 200 to 420 C range
      consequence: Brittleness. The supplier says this tempering range should be avoided.
      severity: moderate
      source: aircraft-4140
      where: Heat Treatments, Tempering note
  side_effects: []
  handling:
    - text: Harden at 830 to 860 C and oil quench, then temper at 540 to 680 C for at least 1 hour and air cool (recommended for the quenched and tempered condition).
      source: voestalpine-4140
      where: Heat Treatment (recommended), Harden and Temper rows
    - text: Stress relieve about 30 to 50 C below the tempering temperature for the quenched and tempered condition, or at 600 to 650 C for the annealed condition, then air cool.
      source: voestalpine-4140
      where: Heat Treatment (recommended), Stress Relieve row
    - text: Avoid tempering between 200 and 420 C; the supplier says this causes temper brittleness.
      source: aircraft-4140
      where: Heat Treatments, Tempering note
  mitigations:
    - text: The source ties the hydrogen damage to yield strength. In the room-temperature study the lower-strength 4140 lost about 15% of its notched tensile strength, against about 60% for the high-strength condition, so keep the yield strength of the chosen condition in view wherever hydrogen may be present.
      source: sandia-1211
      where: Section 3.1.2 (text); Table 3.1.2.1
    - text: Molybdenum in the grade prevents temper brittleness, per the supplier; keep the Mo content within the datasheet limits.
      source: voestalpine-4140
      where: Description
uses:
  - application: mechanisms
    device: Axles, gears, shafts, spindles, pinions, sprockets and studs
    example: Aircraft Materials lists these among the other typical applications of alloy 4140 bar. No test data are given for them.
    source: aircraft-4140
    where: Description, other typical applications
  - application: structures
    device: Rams, crowbars and oil-patch and logging parts
    example: The supplier calls alloy 4140 the most widely used alloy for oil-patch applications and lists logging parts and rams among its uses.
    source: aircraft-4140
    where: Description
  - application: structures
    device: Aerospace bar to AMS 6349 and AMS 6382
    example: Alloy 4140 bar is supplied to AMS 6349 and AMS 6382, with AMS S 5626 and MIL S 5626 also listed. The Elgin fact sheet lists AMS 6381, 6382, 6390 and 6395.
    source: aircraft-4140
    where: Specifications list; Elgin keywords list
supply:
  - subject: Chromium
    abundance: World resources are greater than 12 billion t of shipping-grade chromite, with 95% of world chromium resources in Kazakhstan and southern Africa. US net import reliance was 79% of apparent consumption in 2025 (estimated). US chromite imports in 2021 to 2024 came from South Africa (96%) and Turkey (3%).
    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
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (chromium, used in stainless steel)
        listed: true
    recycling: Recycled chromium in stainless-steel scrap receipts was 21% of US apparent consumption in 2025.
    substitutes:
      - Chromium has no substitute in stainless steel, the leading end use, or in superalloys (USGS 2026).
    source: usgs-chromium-2026
    where: Salient Statistics; World Mine Production and Reserves (2025e; shares computed as printed tonnage over the 51,000 t world total); World Resources; Substitutes; Recycling
  - subject: Molybdenum
    abundance: World reserves were 17,000 thousand t (2025e). Identified resources are about 5.4 million t in the United States and about 20 million t in the rest of the world. Molybdenum is used principally as an alloying agent in cast iron, steel and superalloys. The Government of China imposed export controls on molybdenum powders in February 2025.
    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 is recycled in ferrous scrap, superalloy scrap and catalysts; USGS says recycled molybdenum may be as much as 30% of apparent supply.
    substitutes:
      - 'USGS: there is little substitution in steels; potential substitutes in alloy steels include boron, chromium, niobium (columbium) and vanadium.'
    source: usgs-molybdenum-2026
    where: Domestic Production and Use; Events, Trends and Issues; World Mine Production and Reserves (2025e; shares computed over the 260,000 t world total); World Resources; Substitutes; Recycling
media: []
documents:
  - title: 'voestalpine High Performance Metals: AISI 4140 / 1.7225 / G41400 datasheet (Australia)'
    type: datasheet
    url: https://www.voestalpine.com/highperformancemetals/australia/app/uploads/sites/265/2024/08/Datasheet-4140-2026-v1.pdf
    year: 2026
  - title: Alloy Steel Grade 4140 Fact Sheet (Elgin, mwcomponents.com)
    type: datasheet
    url: https://www.mwcomponents.com/uploads/Resource-Center/Elgin-Material-Sheets/Alloy-Steel-Grade-4140-Fact-Sheet_Elgin-Website.pdf
  - title: Aircraft Alloy Steel AISI 4140 (AMS 6349 / AMS 6382) Technical Data Sheet (Aircraft Materials)
    type: datasheet
    url: https://aircraftmaterials.com/data/alstst/4140.html
  - title: 'Technical Reference on Hydrogen Compatibility of Materials: Low-Alloy Ferritic Steels, Tempered Fe-Cr-Mo Alloys (code 1211), Sandia National Laboratories'
    type: report
    url: https://www.sandia.gov/app/uploads/sites/158/2021/12/1211TechRef_FeCrMo_T.pdf
    year: 2005
  - title: 'Rosidah et al. 2021: The effect of time variation on the steels corrosion rate in 0.5 M H2SO4 solution (JMESI)'
    type: paper
    url: https://ejournal.itats.ac.id/jmesi/article/download/2183/1989
    year: 2021
  - 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: 'USGS: About the 2025 List of Critical Minerals'
    type: report
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
  - title: 'PubChem: Chromium (CID 23976), GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23976/JSON/?heading=GHS+Classification
    year: 2026
  - title: 'PubChem: Molybdenum (CID 23932), GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23932/JSON/?heading=GHS+Classification
    year: 2026
  - title: 'Saky Steel: AISI 4140 1.7225 42CrMo4 SCM440 B7 Steel Bar (stockist page)'
    type: datasheet
    url: https://www.sakysteel.com/aisi-4140-1-7225-42crmo4-scm440-b7-steel-bar.html
  - title: 'Metinvest: Steel 42CrMo4 characteristics, properties and analogues (manufacturer page)'
    type: datasheet
    url: https://metinvestholding.com/en/products/steel-grades/42crmo4
  - title: 'Tachart: 709M40 grade page with alias list (stockist page)'
    type: datasheet
    url: https://www.tachart.com/?p=1110
gaps:
  - No safety data sheet for AISI 4140 bar was read in this run. The hazard entries are PubChem records for elemental chromium and molybdenum. Welding, grinding and fume hazards of the steel itself are not sourced.
  - Composition sources disagree. Elgin lists carbon as max 0.33 and manganese as 0.40 to 0.60; voestalpine gives maximum limits (carbon 0.40, manganese 1.00, silicon 0.40, chromium 1.10, molybdenum 0.30); Aircraft Materials gives single values (carbon 0.40, silicon 0.25, manganese 0.85, chromium 1.00, molybdenum 0.25). The recipe uses the ASTM A29 ranges printed in the Sandia reference; the other values are kept in their sources as printed.
  - 'No annealed-condition strength value was found. Annealing temperatures also differ: voestalpine gives 680 to 720 C, and Aircraft Materials gives 830 to 850 C with furnace cooling.'
  - The Aircraft Materials typical rows do not state a temper temperature, so they are recorded as condition T with the temper temperature not stated.
  - The hydrogen data come from one room-temperature study, compiled in the Sandia reference (its reference 4), at 69 MPa gas only. No temperature dependence, hydrogen concentration or cathodic-charging data were read. The Colombo 2020 paper (doi 10.1016/j.tafmec.2020.102810) returned a Cloudflare challenge, MDPI Materials 18(2), 339 returned Access Denied, and the arXiv 2012.10112 PDF was truncated.
  - No chloride or salt-spray corrosion data for AISI 4140 were read. The Springer brake-disc paper (doi 10.1186/s44147-025-00702-z, NaCl immersion) returned an automated-access challenge. The only corrosion values here are in 0.5 M sulfuric acid, from a 2021 journal paper that does not state the heat treatment of its 4140 specimens.
  - Mechanical values come from manufacturer datasheets, not from a standard such as AMS 6382 or ASTM A29. MatWeb and Total Materia were not reached in this run.
  - 'Properties not in property-canon were given snake_case names: hardness_brinell, impact_energy, reduction_of_area, notched_tensile_strength and notched_reduction_of_area.'
  - 'Thermal conductivity: the W glyph was lost in text extraction. W/mK is inferred from the BTU-in column on the same row (296 BTU-in/hr-ft2-F matches 42.6 W/mK).'
  - Elgin's density, modulus, bulk and shear moduli, and Poisson's ratio carry no temperature or heat treatment; they are recorded as typical or calculated, as the datasheet marks them.
  - 'Critical minerals: the USGS 2025 list page was read through a fetch summary, not raw text. Chromium is recorded as listed; the summary names no molybdenum entry, so molybdenum has no list entry. The EU critical raw materials list was not read.'
  - No flight, spacecraft or vacuum use of AISI 4140 was found in these sources. The uses are terrestrial machinery and aerospace specifications.
  - Sandia's tables give temperatures in kelvin. The C values in the conditions are conversions (minus 273.15, rounded), and the printed kelvin values are kept beside them.
  - The Sandia composition in Table 1.1.2 (0.40 C, 0.93 Cr, 0.20 Mo) is one test heat, not a specification, and it is not used in the recipe.
  - 'Designations: no Aalco or Sandvik grade page was reached in this run; the web searches returned neither.'
  - 'Designations: voestalpine prints 41CrMo4 beside 1.7225 under DIN, while Metinvest and Saky print 42CrMo4 for 1.7225. Both are kept as printed; check the DIN name before relying on it.'
  - 'Designations: no source in this run calls 708M40, 709M40, 708A42 or EN19 a nearest equivalent, so they carry no note. Tachart lists AISI 4140 as an alias of its 709M40 page.'
  - 'Designations not added: SCM440H and the Russian grades 38XM and 40XFA appear only in the Metinvest 42CrMo4 analogues table. AISI 4137 and SAE 4137 are aliases of 709M40 on Tachart and are a different grade.'
sources:
  voestalpine-4140:
    title: 'voestalpine High Performance Metals: AISI 4140 / 1.7225 / G41400 datasheet'
    id: AISI 4140 / 1.7225 / G41400
    url: https://www.voestalpine.com/highperformancemetals/australia/app/uploads/sites/265/2024/08/Datasheet-4140-2026-v1.pdf
    year: 2026
    kind: datasheet
    license: supplier datasheet, cited not reproduced
  elgin-4140:
    title: Alloy Steel Grade 4140 Fact Sheet (Elgin, mwcomponents.com), normalized at 870 C, 25 mm round
    id: AISI 4140 normalized 870 C, 25 mm round
    url: https://www.mwcomponents.com/uploads/Resource-Center/Elgin-Material-Sheets/Alloy-Steel-Grade-4140-Fact-Sheet_Elgin-Website.pdf
    kind: datasheet
    license: supplier datasheet, cited not reproduced
  aircraft-4140:
    title: Aircraft Alloy Steel AISI 4140 (AMS 6349 / AMS 6382) Technical Data Sheet (Aircraft Materials)
    id: AMS 6349 / AMS 6382
    url: https://aircraftmaterials.com/data/alstst/4140.html
    kind: datasheet
    license: supplier web page, cited not reproduced
  sandia-1211:
    title: 'Technical Reference on Hydrogen Compatibility of Materials: Low-Alloy Ferritic Steels, Tempered Fe-Cr-Mo Alloys (code 1211)'
    id: Sandia National Laboratories, Somerday, revised 12/05
    url: https://www.sandia.gov/app/uploads/sites/158/2021/12/1211TechRef_FeCrMo_T.pdf
    year: 2005
    kind: report
    license: US government report, public
  itats-2021:
    title: The effect of time variation on the steels corrosion rate in 0.5 M H2SO4 solution (Rosidah et al., JMESI 1(2))
    id: doi:10.31284/j.jmesi.2021.v1i2.2183
    url: https://ejournal.itats.ac.id/jmesi/article/download/2183/1989
    year: 2021
    kind: paper
    license: CC BY-NC 4.0
  usgs-chromium-2026:
    title: 'USGS Mineral Commodity Summaries 2026: Chromium'
    id: mcs2026-chromium
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
    kind: report
    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
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-critical-2025:
    title: 'USGS: About the 2025 List of Critical Minerals'
    id: 2025 List of Critical Minerals (60 minerals)
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  pubchem-chromium:
    title: 'PubChem: Chromium (CID 23976), Safety and Hazards, GHS Classification'
    id: CID 23976
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23976/JSON/?heading=GHS+Classification
    year: 2026
    kind: database
    license: PubChem terms (public)
  pubchem-molybdenum:
    title: 'PubChem: Molybdenum (CID 23932), Safety and Hazards, GHS Classification'
    id: CID 23932
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23932/JSON/?heading=GHS+Classification
    year: 2026
    kind: database
    license: PubChem terms (public)
  saky-4140:
    title: 'Saky Steel: AISI 4140 1.7225 42CrMo4 SCM440 B7 Steel Bar'
    id: AISI 4140 1.7225 42CrMo4 SCM440 B7 Steel Bar
    url: https://www.sakysteel.com/aisi-4140-1-7225-42crmo4-scm440-b7-steel-bar.html
    kind: datasheet
    license: supplier web page, cited not reproduced
  metinvest-42crmo4:
    title: 'Metinvest: Steel 42CrMo4 characteristics, properties and analogues'
    id: Steel 42CrMo4 analogues table
    url: https://metinvestholding.com/en/products/steel-grades/42crmo4
    kind: datasheet
    license: manufacturer web page, cited not reproduced
  tachart-709m40:
    title: 'Tachart: 709M40 grade page with alias list'
    id: 709M40 alias list
    url: https://www.tachart.com/?p=1110
    kind: datasheet
    license: supplier web page, cited not reproduced
license: CC-BY-4.0
updated: '2026-10-24'
review:
  status: draft
  method: assistant
  checked_values: 47
  unreachable: 4
  caveats: 3
  note: 'Read by an AI assistant on 2026-10-24 from pages fetched in this run. Strength values are each tied to their heat treatment. Unreachable: Colombo 2020 (Cloudflare), MDPI Materials 18(2) 339 (Access Denied), Springer 10.1186/s44147-025-00702-z (challenge), arXiv 2012.10112 (truncated PDF).'
story:
  recipe:
    line: AISI 4140 is an iron-based chromium-molybdenum steel. The composition limits printed for it (ASTM A29, in the Sandia reference) are 0.38 to 0.43 wt% carbon, 0.75 to 1.00 manganese, 0.15 to 0.35 silicon, 0.80 to 1.10 chromium and 0.15 to 0.25 molybdenum, with phosphorus at 0.035 maximum, sulfur at 0.04 maximum and iron as the balance. Its strength comes from heat treatment (austenitize, quench, temper) as much as from its composition.
    parts:
      - name: Iron
        symbol: Fe
        share_note: balance (the rest)
        role: The matrix of the steel; heat treatment changes its structure from austenite to martensite and then tempered martensite.
      - name: Carbon
        symbol: C
        share_percent: 0.38
        share_high: 0.43
        role: Sets how hard the steel can become when quenched; medium carbon gives the strength range.
      - name: Manganese
        symbol: Mn
        share_percent: 0.75
        share_high: 1
        role: Deoxidiser and hardenability aid in the melt.
      - name: Silicon
        symbol: Si
        share_percent: 0.15
        share_high: 0.35
        role: Deoxidiser in the melt.
      - name: Chromium
        symbol: Cr
        share_percent: 0.8
        share_high: 1.1
        role: Adds hardenability and corrosion resistance; the grade is still a low-alloy steel, not stainless.
      - name: Molybdenum
        symbol: Mo
        share_percent: 0.15
        share_high: 0.25
        role: Adds hardenability and, per the supplier, prevents temper brittleness.
      - name: Phosphorus
        symbol: P
        share_percent: 0
        share_high: 0.035
        limit: maximum
        role: Impurity held low.
      - name: Sulfur
        symbol: S
        share_percent: 0
        share_high: 0.04
        limit: maximum
        role: Impurity held low.
  risk_groups:
    - title: For people
      level: 0
      verdict: Alloy not checked against an SDS
      lead: The PubChem records below are for elemental chromium and molybdenum. No safety data sheet for AISI 4140 bar was read in this run.
      points:
        - label: Chromium
          line: PubChem lists elemental chromium as Danger, with H317, H319 and H334 among the reported codes. About half of 2404 company reports say it does not meet GHS criteria.
        - label: Molybdenum
          line: PubChem lists elemental molybdenum with H361 (suspected of damaging fertility or the unborn child) and H228 (flammable solid) among the reported codes. 57.4% of reports say it does not meet GHS criteria.
    - title: In service
      level: 1
      verdict: Hydrogen and acid are the watch points
      lead: These come from two laboratory tests, not from field incidents.
      points:
        - label: Hydrogen gas
          line: In 69 MPa hydrogen gas at room temperature, high-strength 4140 lost about 60% of its notched tensile strength, from 2160 to 862 MPa (Sandia).
        - label: Dilute acid
          line: In 0.5 M sulfuric acid, 4140 rusted over its surface and corroded at 176.87 mpy after 144 h (Rosidah et al., 2021).
    - title: Heat treatment
      level: 1
      verdict: Keep out of the tempering brittle range
      lead: Heat treatment sets the strength, and two windows need care.
      points:
        - label: Temper brittleness
          line: Tempering between 200 and 420 C causes temper brittleness, per the supplier. Avoid that range.
        - label: Stress relief
          line: After quenching and tempering, stress relieve about 30 to 50 C below the tempering temperature, then air cool.
  why: 'AISI 4140 (UNS G41400) is a medium-carbon chromium-molybdenum steel. It is chosen for a balance of strength, toughness and wear resistance after quenching and tempering, and molybdenum keeps it free of temper brittleness, according to the supplier. Its strength depends on the condition: a normalised 25 mm bar, a quenched and tempered bar of 10 to 100 mm and a room-temperature hydrogen study each give different numbers, so every value in this profile carries its own condition. Its main weakness is hydrogen gas, which cut notched strength sharply in one room-temperature study.'
  uses:
    - where: Gears, shafts and spindles
      line: Aircraft Materials lists axles, gears, shafts, pump shafts, pinions, sprockets, studs and ring gears among the typical uses of alloy 4140 bar.
    - where: Oil-patch and logging parts
      line: The same supplier calls alloy 4140 the most widely used alloy for oil-patch applications.
    - where: Aerospace bar
      line: Alloy 4140 bar is supplied to the aerospace specifications AMS 6349 and AMS 6382 (Aircraft Materials).
  can_do:
    - label: Strength
      line: Quenched and tempered bar of 10 to 100 mm is specified at a minimum yield strength of 740 MPa and a tensile strength of 930 to 1080 MPa (voestalpine).
    - label: Toughness
      line: In the same condition the minimum Charpy impact energy is 42 J (voestalpine).
    - label: Normalised
      line: A 25 mm round normalised at 870 C gives 1020 MPa tensile strength, 655 MPa yield strength and 17.7% elongation (Elgin).
    - label: Stiffness
      line: The modulus of elasticity is 205 GPa, typical for steel (Elgin).
    - label: Hydrogen
      line: In 69 MPa hydrogen gas at room temperature, high-strength 4140 still reached 1228 MPa tensile strength, but its notched tensile strength fell to 862 MPa (Sandia).
  compare: In the same 0.5 M sulfuric acid test, AISI 4140 corroded at a rate second only to AISI 1045 (176.87 mpy against 183.7 mpy at 144 h), while the stainless steel in the same test corroded least, because its chromium oxide film protects it (Rosidah et al., 2021). The fetched sources give no direct comparison with another grade on strength or hydrogen behaviour, so this paragraph is limited to that acid test.
  compare_rows:
    - label: Strength
      benchmark: yield_strength
    - label: Stiffness
      benchmark: elastic_modulus
    - label: Density
      benchmark: density
  handling:
    - Quote the heat-treatment condition with every strength value, because the normalised, quenched and tempered, and hydrogen-tested rows differ.
    - Avoid tempering between 200 and 420 C; the supplier says this causes temper brittleness.
    - 'In hydrogen service, do not assume the notched strength of high-strength 4140: the room-temperature study lost about 60%.'
    - Take the safety data sheet for the specific bar before cutting, grinding or welding; no 4140 SDS was read here.
  good_for:
    - Medium and large sections that need high strength with toughness after quenching and tempering (voestalpine).
    - Gears, shafts, spindles, pinions and sprockets, the machine parts the supplier lists (Aircraft Materials).
  watch_out:
    - 'Hydrogen gas: notched tensile strength of high-strength 4140 fell from 2160 to 862 MPa at 69 MPa and room temperature.'
    - 'Dilute acid: 4140 rusted and corroded at 176.87 mpy in 0.5 M sulfuric acid after 144 h.'
    - Tempering between 200 and 420 C causes temper brittleness, so avoid that range.
  verdict: AISI 4140 is a strong, tough steel whose properties depend on heat treatment. Quote the condition with each value, keep hydrogen exposure in mind when choosing the strength level, and protect it from acid. The hydrogen data here come from one room-temperature study, so treat them as a warning, not a design allowable.