spore: profile
id: stainless-420
spore_version: 0.2
family: stainless-martensitic
name: Stainless steel 420
abbreviation: '420'
role: hardenable martensitic stainless steel for blades, bearings and wear parts
category: metals
type: steels-and-stainless
summary: |
  AISI 420 (UNS S42000, EN 1.4021) is a martensitic stainless steel with 12.0 to 14.0 % chromium and 0.16 to 0.25 % carbon (EN composition). Annealed, its maximum hardness is 241 HB and its yield strength 51.5 ksi. Tempered at 440 °F it reaches a yield strength of 190.1 ksi and 48 HRC. Its density is 7.75 g/cm3, it is magnetic, and it resists corrosion less well than the ferritic and austenitic steels. Tempered at 1000 °F its tensile strength falls to 158.5 ksi.
best_for: Hardened wear parts, blades and bearing-type components that need high strength and edge retention, from one steel that reaches 48 HRC after tempering at 440 °F
weakest_at: 'Corrosion resistance and ductility: it resists corrosion less well than austenitic grades, and it loses strength when tempered at 1000 °F (158.5 ksi tensile)'
identity:
  formula: 'Iron-chromium-carbon steel: Fe balance, Cr 12.0 to 14.0 %, C 0.16 to 0.25 % (EN 1.4021 composition)'
  source: teamedelstahl-1-4021
  where: Chemical composition table, 1.4021 (X20Cr13 / AISI 420) page
  designations:
    - system: UNS
      code: S42000
      source: rolledalloys-420
      where: Specifications box, UNS line
    - system: EN
      code: '1.4021'
      source: rolledalloys-420
      where: Specifications box, W. Nr./EN line
    - system: EN name
      code: X20Cr13
      source: teamedelstahl-1-4021
      where: Standards and nomenclature section, page heading 1.4021 (X20Cr13 / AISI 420)
    - system: AISI
      code: '420'
      source: teamedelstahl-1-4021
      where: Standards and nomenclature section, page heading 1.4021 (X20Cr13 / AISI 420)
    - system: ASTM
      code: A276
      note: listed specification for Type 420
      source: rolledalloys-420
      where: Specifications box, ASTM line
    - system: ASTM
      code: A484
      note: listed specification for Type 420
      source: rolledalloys-420
      where: Specifications box, ASTM line
    - system: AMS
      code: '5621'
      source: rolledalloys-420
      where: Specifications box, AMS line
tags:
  environments: []
  stresses:
    - corrosion
  applications:
    - mechanisms
properties:
  - benchmark: density
    label: Density, 1.4021 bar (EN 10088-3)
    value: 7.75
    unit: g/cm3
    scope: material
    conditions:
      grade: 1.4021 (420) bar, up to 160 mm
      standard: EN 10088-3:2005
      temperature: not stated
    method: Value printed in a stockholder datasheet
    status: ground
    source: aalco-1-4021
    where: Physical Property table, row Density
  - benchmark: density
    label: Density, 1.4021 / AISI 420 (20 °C)
    value: 7.7
    unit: kg/dm3
    scope: material
    conditions:
      grade: 1.4021 (X20Cr13 / AISI 420)
      temperature: 20 °C
    method: Value printed in a steel supplier's material page
    status: ground
    source: teamedelstahl-1-4021
    where: Physical properties at 20 °C table, row Density
  - benchmark: density
    label: Density, Type 420 (ASTM A276)
    value: 0.278
    unit: lb/in3
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temperature: not stated
    method: Value printed in a mill datasheet
    status: ground
    source: rolledalloys-420
    where: Physical Properties, row Density
  - benchmark: melting_point
    label: Melting range, Type 420
    value: 2650
    value_high: 2750
    bound: range
    unit: °F
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      unit_in_source: 2650 - 2750 °F
    method: Range printed in a mill datasheet
    status: ground
    source: rolledalloys-420
    where: Physical Properties, row Melting Range
  - benchmark: poissons_ratio
    label: Poisson's ratio, Type 420
    value: 0.28
    unit: '-'
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temperature: not stated
    method: Value printed in a mill datasheet
    status: ground
    source: rolledalloys-420
    where: Physical Properties, row Poisson Ratio
  - benchmark: elastic_modulus
    label: Modulus of elasticity, 1.4021 bar
    value: 200
    unit: GPa
    scope: material
    conditions:
      grade: 1.4021 (420) bar, up to 160 mm
      standard: EN 10088-3:2005
      temperature: not stated
    method: Value printed in a stockholder datasheet
    status: ground
    source: aalco-1-4021
    where: Physical Property table, row Modulus of Elasticity
  - benchmark: elastic_modulus
    label: Modulus of elasticity, 1.4021 (20 °C)
    value: 215
    unit: kN/mm2
    scope: material
    conditions:
      grade: 1.4021 (X20Cr13 / AISI 420)
      temperature: 20 °C
    method: Value printed in a steel supplier's material page
    status: ground
    note: The other two sources give 200 GPa (Aalco) and 31.2 x 10^6 psi, which is about 215 GPa; the 200 GPa figure is a separate row.
    source: teamedelstahl-1-4021
    where: Mechanical properties at 20 °C table, row Modulus of elasticity
  - benchmark: elastic_modulus
    label: Modulus of elasticity, Type 420 (68 °F)
    value: 31.2
    unit: 10^6 psi
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temperature: 68 °F
    method: Value printed in a mill datasheet
    status: ground
    source: rolledalloys-420
    where: Physical Properties, row Modulus of Elasticity (68°F)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, 1.4021 bar
    value: 24.9
    unit: W/(m·K)
    scope: material
    conditions:
      grade: 1.4021 (420) bar, up to 160 mm
      temperature: not stated
    method: Value printed in a stockholder datasheet
    status: ground
    source: aalco-1-4021
    where: Physical Property table, row Thermal Conductivity
  - benchmark: thermal_conductivity
    label: Thermal conductivity, 1.4021 (20 °C)
    value: 30
    unit: W/(m·K)
    scope: material
    conditions:
      grade: 1.4021 (X20Cr13 / AISI 420)
      temperature: 20 °C
    method: Value printed in a steel supplier's material page
    status: ground
    note: 'Two sources differ: 24.9 W/(m·K) (Aalco, temperature not stated) and 30 W/(m·K) at 20 °C (teamedelstahl). Both are kept with their conditions.'
    source: teamedelstahl-1-4021
    where: Physical properties at 20 °C table, row Thermal conductivity
  - benchmark: thermal_conductivity
    label: Thermal conductivity, Type 420 (212 °F)
    value: 14.4
    unit: BTU/(hr·ft·°F)
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temperature: 212 °F
    method: Value printed in a mill datasheet
    status: ground
    source: rolledalloys-420
    where: Physical Properties, row Thermal Conductivity (212°F)
  - benchmark: cte
    label: Coefficient of thermal expansion, 1.4021 bar (0 to 100 °C)
    value: 10.3
    unit: 10^-6/K
    scope: material
    conditions:
      grade: 1.4021 (420) bar, up to 160 mm
      temperature_range: not stated in the Aalco table
    method: Value printed in a stockholder datasheet
    status: ground
    source: aalco-1-4021
    where: Physical Property table, row Thermal Expansion
  - benchmark: cte
    label: Coefficient of thermal expansion, Type 420 (68 to 212 °F)
    value: 5.833
    unit: µin/in·°F
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temperature: 68 to 212 °F
    method: Value printed in a mill datasheet
    status: ground
    source: rolledalloys-420
    where: Physical Properties, row Coefficient of Thermal Expansion (68°F - 212°F)
  - benchmark: specific_heat
    label: Specific heat capacity, 1.4021 (20 °C)
    value: 460
    unit: J/(kg·K)
    scope: material
    conditions:
      grade: 1.4021 (X20Cr13 / AISI 420)
      temperature: 20 °C
    method: Value printed in a steel supplier's material page
    status: ground
    source: teamedelstahl-1-4021
    where: Physical properties at 20 °C table, row Specific heat capacity
  - benchmark: electrical_resistivity
    label: Electrical resistivity, 1.4021 bar
    value: 0.55
    unit: µΩ·m
    scope: material
    conditions:
      grade: 1.4021 (420) bar, up to 160 mm
      unit_in_source: x10^-6 Ω.m
      temperature: not stated
    method: Value printed in a stockholder datasheet
    status: ground
    source: aalco-1-4021
    where: Physical Property table, row Electrical Resistivity
  - benchmark: electrical_resistivity
    label: Electrical resistivity, 1.4021 (20 °C)
    value: 0.6
    unit: Ω·mm2/m
    scope: material
    conditions:
      grade: 1.4021 (X20Cr13 / AISI 420)
      temperature: 20 °C
    method: Value printed in a steel supplier's material page
    status: ground
    source: teamedelstahl-1-4021
    where: Physical properties at 20 °C table, row Electrical resistance
  - benchmark: electrical_resistivity
    label: Electrical resistivity, Type 420
    value: 25.6
    unit: µΩ·in
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temperature: not stated
    method: Value printed in a mill datasheet
    status: ground
    source: rolledalloys-420
    where: Physical Properties, row Electrical Resistivity
  - benchmark: yield_strength
    label: Yield strength 0.2 % offset, Type 420 annealed (Condition A)
    value: 51.5
    unit: ksi
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temper: annealed (Condition A, ASTM A276)
      measure: 0.2 % yield strength
    method: Value printed in a mill datasheet, tempered-condition table
    status: ground
    source: rolledalloys-420
    where: Tempered Condition Properties table, row Annealed, column 0.2% Yield Strength
  - benchmark: yield_strength
    label: Yield strength 0.2 % offset, Type 420 tempered at 440 °F
    value: 190.1
    unit: ksi
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temper: tempered at 440 °F
      measure: 0.2 % yield strength
    method: Value printed in a mill datasheet, tempered-condition table
    status: ground
    source: rolledalloys-420
    where: Tempered Condition Properties table, row 440, column 0.2% Yield Strength
  - benchmark: yield_strength
    label: Yield strength 0.2 % offset, Type 420 tempered at 1000 °F
    value: 137.9
    unit: ksi
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temper: tempered at 1000 °F
      measure: 0.2 % yield strength
    method: Value printed in a mill datasheet, tempered-condition table
    status: ground
    note: 'Over-tempering: the same table gives 36 HRC at this temper, against 48 HRC at 440 °F.'
    source: rolledalloys-420
    where: Tempered Condition Properties table, row 1000, column 0.2% Yield Strength
  - benchmark: yield_strength
    label: Proof stress Rp0.2, 1.4021 bar up to 160 mm
    value: 500
    value_high: 600
    bound: range
    unit: MPa
    scope: material
    conditions:
      grade: 1.4021 (420) bar, up to 160 mm
      standard: EN 10088-3:2005
      temper: not stated
    method: Range printed in a stockholder datasheet
    status: ground
    source: aalco-1-4021
    where: Mechanical Property table under Spec EN 10088-3:2005, row Proof Stress
  - benchmark: yield_strength
    label: Yield strength Rp0.2, 1.4021 (20 °C) lower limit
    value: 460
    bound: lower
    unit: N/mm2
    scope: material
    conditions:
      grade: 1.4021 (X20Cr13 / AISI 420)
      temperature: 20 °C
      temper: not stated
    method: Minimum value printed in a steel supplier's material page
    status: ground
    source: teamedelstahl-1-4021
    where: Mechanical properties at 20 °C table, row Yield point Rp0.2
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, Type 420 annealed (Condition A)
    value: 85.8
    unit: ksi
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temper: annealed (Condition A, ASTM A276)
    method: Value printed in a mill datasheet, tempered-condition table
    status: ground
    source: rolledalloys-420
    where: Tempered Condition Properties table, row Annealed, column Ultimate Tensile Strength
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, Type 420 tempered at 440 °F
    value: 255.2
    unit: ksi
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temper: tempered at 440 °F
    method: Value printed in a mill datasheet, tempered-condition table
    status: ground
    source: rolledalloys-420
    where: Tempered Condition Properties table, row 440, column Ultimate Tensile Strength
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, Type 420 tempered at 1000 °F
    value: 158.5
    unit: ksi
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temper: tempered at 1000 °F
    method: Value printed in a mill datasheet, tempered-condition table
    status: ground
    source: rolledalloys-420
    where: Tempered Condition Properties table, row 1000, column Ultimate Tensile Strength
  - benchmark: ultimate_tensile_strength
    label: Tensile strength Rm, 1.4021 bar up to 160 mm
    value: 700
    value_high: 950
    bound: range
    unit: MPa
    scope: material
    conditions:
      grade: 1.4021 (420) bar, up to 160 mm
      standard: EN 10088-3:2005
      temper: not stated
    method: Range printed in a stockholder datasheet
    status: ground
    source: aalco-1-4021
    where: Mechanical Property table under Spec EN 10088-3:2005, row Tensile Strength
  - benchmark: ultimate_tensile_strength
    label: Tensile strength Rm, 1.4021 (20 °C)
    value: 750
    value_high: 850
    bound: range
    unit: N/mm2
    scope: material
    conditions:
      grade: 1.4021 (X20Cr13 / AISI 420)
      temperature: 20 °C
      temper: not stated
    method: Range printed in a steel supplier's material page
    status: ground
    source: teamedelstahl-1-4021
    where: Mechanical properties at 20 °C table, row Tensile strength Rm
  - benchmark: elongation
    label: Elongation A, 1.4021 bar up to 160 mm
    value: 12
    value_high: 13
    bound: range
    unit: '%'
    scope: material
    conditions:
      grade: 1.4021 (420) bar, up to 160 mm
      standard: EN 10088-3:2005
      temper: not stated
    method: Range printed in a stockholder datasheet
    status: ground
    source: aalco-1-4021
    where: Mechanical Property table under Spec EN 10088-3:2005, row Elongation A
  - benchmark: elongation
    label: Elongation A5.65, 1.4021 (20 °C) lower limit
    value: 12
    bound: lower
    unit: '%'
    scope: material
    conditions:
      grade: 1.4021 (X20Cr13 / AISI 420)
      temperature: 20 °C
      temper: not stated
    method: Minimum value printed in a steel supplier's material page
    status: ground
    source: teamedelstahl-1-4021
    where: Mechanical properties at 20 °C table, row Elongation A5,65
  - benchmark: hardness_brinell
    label: Hardness Brinell maximum, Type 420 annealed (Condition A)
    value: 241
    bound: upper
    unit: HB
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temper: annealed (Condition A, ASTM A276)
    method: Maximum value printed in a mill datasheet
    status: ground
    source: rolledalloys-420
    where: Mechanical Properties, row Hardness MAX, Brinell (Condition A footnote)
  - benchmark: hardness_brinell
    label: Hardness Brinell maximum, 1.4021 (20 °C)
    value: 230
    bound: upper
    unit: HB
    scope: material
    conditions:
      grade: 1.4021 (X20Cr13 / AISI 420)
      temperature: 20 °C
      temper: not stated
    method: Maximum value printed in a steel supplier's material page
    status: ground
    source: teamedelstahl-1-4021
    where: Mechanical properties at 20 °C table, row Hardness HB
  - benchmark: hardness_rockwell_c
    label: Hardness Rockwell C, Type 420 tempered at 440 °F
    value: 48
    unit: HRC
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temper: tempered at 440 °F
    method: Value printed in a mill datasheet, tempered-condition table
    status: ground
    source: rolledalloys-420
    where: Tempered Condition Properties table, row 440, column Rockwell Hardness HRC
  - benchmark: hardness_rockwell_c
    label: Hardness Rockwell C, Type 420 tempered at 1000 °F
    value: 36
    unit: HRC
    scope: material
    conditions:
      grade: Type 420, UNS S42000
      temper: tempered at 1000 °F
    method: Value printed in a mill datasheet, tempered-condition table
    status: ground
    source: rolledalloys-420
    where: Tempered Condition Properties table, row 1000, column Rockwell Hardness HRC
  - benchmark: max_service_temp
    label: Scaling resistance limit, continuous (1.4021)
    value: 675
    bound: upper
    unit: °C
    scope: material
    conditions:
      grade: 1.4021 (420)
      basis: scaling resistance, continuous
      intermittent_limit: 760 °C
      note_in_source: use above the tempering temperature is not recommended if mechanical properties must be kept
    method: Value printed in a stockholder datasheet, corrosion resistance section
    status: ground
    note: A scaling limit, not a structural service limit. The Aalco page says mechanical properties fall above the tempering temperature.
    source: aalco-1-4021
    where: Corrosion Resistance section, Heat resistance paragraph
corrosion:
  - environment: Air and humid atmospheres
    headline: Martensitic steels resist corrosion less well than ferritic and austenitic grades because their chromium is low.
    effect: Wikipedia says martensitic stainless steels are not as corrosion-resistant as ferritic and austenitic grades due to their low chromium content, and lists Type 420 as a representative grade. Rolled Alloys says 420 offers corrosion resistance comparable to that of Type 410.
    rating: moderate
    conditions:
      basis: general comparison; no corrosion rate or test environment given in the sources
    source: wikipedia-stainless
    where: Families, Martensitic section
  - environment: Hardened condition
    headline: Maximum corrosion resistance is reached in the fully hardened condition, not the annealed one.
    effect: Aalco states that maximum corrosion resistance is achieved in the hardened condition, and the Rolled Alloys sheet describes 420 as similar to 410 in corrosion resistance. No corrosion rate is given.
    rating: moderate
    conditions:
      basis: qualitative statement; no test environment given
    source: aalco-1-4021
    where: Corrosion Resistance section
  - environment: High-temperature scaling in air
    headline: 420 scales in air at high temperature, with a continuous limit of 675 °C.
    effect: Aalco gives fair scaling resistance up to 760 °C intermittently and 675 °C continuously, and says use above the tempering temperature is not recommended if mechanical properties must be kept.
    rating: moderate
    conditions:
      basis: scaling resistance in air; no weight-gain or rate values given
    source: aalco-1-4021
    where: Corrosion Resistance section, Heat resistance paragraph
risks:
  hazards:
    - text: 'Generic stainless steel SDS (Parker Steel, Metric Metal), not a 420-specific sheet: solid metal products are generally articles and not hazardous materials under the OSHA Hazard Communication Standard. Small chips, fines and dust may ignite readily, and hazardous elements can be released during cutting, grinding and welding. Do not breathe dust or fume.'
      ghs: []
      source: metric-sds
      where: Section 2 Hazards Identification, General Hazard Statement and Hazard Statements; generic SDS, GHS classes not applied to 420 here
    - text: Welding, torch cutting or grinding of stainless steel can generate hexavalent chromium. The SDS notes that chromium metal in the zero valence state does not present an unusual health hazard.
      ghs: []
      source: metric-sds
      where: Asterisked footnote to the composition table on chromium metal
  failure_risks:
    - mode: Loss of strength from over-tempering
      trigger: Tempering or service at 1000 °F (538 °C)
      consequence: The Rolled Alloys table gives 158.5 ksi tensile and 137.9 ksi yield at 1000 °F, against 255.2 ksi tensile at 440 °F, and 36 HRC against 48 HRC. Aalco also warns of strength loss from over-tempering at elevated temperature.
      severity: high
      source: rolledalloys-420
      where: Tempered Condition Properties table, rows 440 and 1000; Aalco Temperature notes
    - mode: Brittleness at sub-zero temperature
      trigger: Service below zero degrees Celsius
      consequence: Aalco says the useful temperature range is limited by loss of ductility below zero.
      severity: moderate
      source: aalco-1-4021
      where: Operating range paragraph, Temperature notes
    - mode: Cracking during hot working
      trigger: Hot working below 1700 °F (927 °C)
      consequence: Aalco says hot work below 1700 °F may cause cracking; work should start after uniform heating to 2100 to 2250 °F (1149 to 1232 °C).
      severity: moderate
      source: aalco-1-4021
      where: Hot working paragraph, Temperature notes
    - mode: Weld joint strength
      trigger: Welding high-strength joints without post-weld heat treatment
      consequence: Aalco recommends post-weld hardening and tempering for high-strength joints, with preheat at 150 to 320 °C and post-heat at 610 to 760 °C.
      severity: low
      source: aalco-1-4021
      where: Weldability section
  side_effects:
    - text: 420 is magnetic, in both the annealed and hardened condition, so it cannot be used where a nonmagnetic material is required.
      affects: Magnetic response of parts and assemblies
      source: wikipedia-stainless
      where: Properties, Magnetism section; Families, Martensitic section
  handling:
    - text: 'Specify the temper with the order: strength and hardness follow the tempering temperature, from 255.2 ksi tensile at 440 °F to 158.5 ksi at 1000 °F (Rolled Alloys table).'
      source: rolledalloys-420
      where: Tempered Condition Properties table
    - text: Harden and temper after fabrication. The supplier's thermal-treatment table gives hardening at 950 to 1050 °C with oil, polymer or air cooling, and tempering at 600 to 700 °C or 650 to 750 °C.
      source: teamedelstahl-1-4021
      where: Thermal treatment table
  mitigations:
    - text: Ventilate or enclose cutting, grinding and welding to limit dust and fume, as the generic stainless SDS advises.
      source: metric-sds
      where: Engineering controls paragraph in the handling section
uses:
  - application: mechanisms
    device: Bearings and industrial chains
    example: Rolled Alloys lists industrial chains and bearings among the applications of Type 420, which it says is used for high strength, high wear resistance or good edge retention.
    source: rolledalloys-420
    where: Applications list
  - application: mechanisms
    device: Pumps and valves
    example: Rolled Alloys lists pumps and valves, and plastic injection moulds and dies, among the applications of Type 420.
    source: rolledalloys-420
    where: Applications list
supply:
  - subject: Chromium (mine production, the alloying element in 420)
    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
    critical_lists: []
    recycling: 'USGS: in 2025 recycled chromium contained in stainless-steel scrap receipts accounted for 21 % of apparent consumption. The United States imported 79 % of its apparent consumption (2025e net import reliance).'
    substitutes:
      - 'USGS: chromium has no substitute in stainless steel, the leading end use, or in superalloys. Chromium-containing scrap can substitute for ferrochromium in some metallurgical uses.'
    source: usgs-mcs2026-chromium
    where: 'World Mine Production and Reserves table, 2025e column (world total 51,000 thousand t, gross weight: South Africa 23,000, Turkey 9,000, Kazakhstan 7,000); shares calculated by Space Mushroom from those values; Recycling; Substitutes; Domestic Production and Use'
documents:
  - title: Rolled Alloys data sheet 420 (UNS S42000, W. Nr./EN 1.4021), 2022
    type: datasheet
    url: https://rolledalloys.com/wp-content/uploads/420_DS_USA.pdf
    year: 2022
  - title: Aalco datasheet, Stainless Steel 1.4021 (420) Bar
    type: datasheet
    url: https://www.aalco.co.uk/datasheets/Stainless-Steel-14021-420-Bar_311.ashx
  - title: teamedelstahl material page, 1.4021 (X20Cr13 / AISI 420)
    type: datasheet
    url: https://www.teamedelstahl.de/en/materials/1-4021/
  - title: Righton Blackburns datasheet, Stainless Steel 1.4021 (420) Bar
    type: datasheet
    url: https://www.rightonblackburns.co.uk/datasheets/view/stainless-steel-1-4021-420-bar
  - title: 'USGS Mineral Commodity Summaries 2026: Chromium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
  - title: Metric Metal safety data sheet, Stainless Steels (Parker Steel, issue 2/1/2016)
    type: sds
    url: https://www.metricmetal.com/wp-content/uploads/2018/08/G-SDS-Stainless-Steel.pdf
    year: 2016
  - title: 'Wikipedia: Martensitic stainless steel'
    type: database
    url: https://en.wikipedia.org/wiki/Martensitic_stainless_steel
  - title: 'Wikipedia: Stainless steel'
    type: database
    url: https://en.wikipedia.org/wiki/Stainless_steel
gaps:
  - Atomic weights for the recipe parts (Fe, Cr, C) were not read from a fetched page, so the recipe gives weight shares only.
  - No primary ASTM A276 or EN 10088-3 table was opened; the mechanical values come from a stockholder page (Aalco), a supplier page (teamedelstahl) and a mill sheet (Rolled Alloys), each for a different temper or product size.
  - The Aalco page describes its bar as a sulphur-enhanced machining grade. The sulphur figure (0.030 % maximum) is the same as the other sources, but the free-machining claim was not checked against a second source.
  - Heat-treated hardness for 1.4021 (quench plus temper) in HRC was not found in a 1.4021-specific source. The 45 to 50 HRC and 52 to 55 HRC figures seen on other pages are for a different grade (420J1) or are not tied to a grade, so they are not used.
  - Tensile and yield values from the Saky Steel SUS 420 table (650 MPa max) conflict with the EN figures (700 to 950 MPa) and are for a JIS grade with a different carbon range; they are not used.
  - Atlas Quality Management, makeitfrom.com (403), the Combined Metals PDF and the Timken SDS could not be read in this run.
  - No ISO 9223 corrosion rate, salt-spray result or pitting test for 420 was found in a fetched source.
  - No cryogenic, impact (Charpy) or fatigue values for 420 were found in a fetched source.
  - Radiation, outgassing, atomic oxygen and cold-welding data for 420 in vacuum were not looked up.
  - The USGS 2026 chromium summary does not state whether chromium is on the U.S. critical minerals list, so critical_lists is empty.
  - Hardness is recorded as hardness_brinell and hardness_rockwell_c because the canonical file has no hardness entry; these names are not in the canonical list.
  - No PubChem or Wikipedia GHS record for the alloy was opened; the PubChem chromium page was blocked by a CAPTCHA.
sources:
  rolledalloys-420:
    title: Rolled Alloys Data Sheet, 420 (UNS S42000, W. Nr./EN 1.4021, ASTM A276), rev. 11/22
    url: https://rolledalloys.com/wp-content/uploads/420_DS_USA.pdf
    year: 2022
    kind: datasheet
    license: Manufacturer data sheet, no warranty (cited, not reproduced)
  aalco-1-4021:
    title: Aalco Stainless Steel 1.4021 (420) Bar datasheet
    url: https://www.aalco.co.uk/datasheets/Stainless-Steel-14021-420-Bar_311.ashx
    kind: datasheet
    license: Stockholder datasheet (cited, not reproduced)
  teamedelstahl-1-4021:
    title: teamedelstahl material page, 1.4021 (X20Cr13 / AISI 420)
    url: https://www.teamedelstahl.de/en/materials/1-4021/
    kind: datasheet
    license: Supplier material page (cited, not reproduced)
  rightonblackburns-1-4021:
    title: Righton Blackburns datasheet, Stainless Steel 1.4021 (420) Bar
    url: https://www.rightonblackburns.co.uk/datasheets/view/stainless-steel-1-4021-420-bar
    kind: datasheet
    license: Stockholder datasheet (cited, not reproduced)
  usgs-mcs2026-chromium:
    title: Mineral Commodity Summaries 2026, Chromium
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  metric-sds:
    title: Metric Metal safety data sheet, Stainless Steels (Parker Steel), issue 2/1/2016
    url: https://www.metricmetal.com/wp-content/uploads/2018/08/G-SDS-Stainless-Steel.pdf
    year: 2016
    kind: datasheet
    license: Manufacturer safety data sheet (cited, not reproduced)
  wikipedia-martensitic:
    title: 'Wikipedia: Martensitic stainless steel'
    url: https://en.wikipedia.org/wiki/Martensitic_stainless_steel
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
  wikipedia-stainless:
    title: 'Wikipedia: Stainless steel (Families and Properties sections)'
    url: https://en.wikipedia.org/wiki/Stainless_steel
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
license: CC-BY-4.0
updated: '2026-10-25'
review:
  status: draft
  method: assistant
  checked_values: 37
  unreachable: 4
  caveats: 6
  note: 'Values were read by an AI assistant on 2026-10-25 from the pages and PDFs named in each entry. The Rolled Alloys sheet was read from the PDF text. Unreachable in this run: Atlas Quality Management PDF, makeitfrom.com (403), Combined Metals PDF (image-only), Timken SDS (HTML). Caveats: values differ between sources and tempers; the Rolled Alloys tempering table uses ksi; the Metric Metal SDS is generic stainless and not 420-specific; the Aalco bar is sulphur-enhanced; hardness names are not canonical.'
story:
  risk_groups:
    - title: For people
      lead: The sources describe a generic stainless steel SDS for solid stock, and the risk comes from dust, fume and processing rather than from the solid.
      level: 1
      verdict: Low for solid stock, higher for dust and fume
      points:
        - label: Solid stock
          line: A generic stainless steel SDS says solid metal articles are generally not hazardous materials under the OSHA Hazard Communication Standard. Small chips, fines and dust may ignite readily.
        - label: Processing
          line: Cutting, grinding and welding can release hazardous elements, and welding or grinding can generate hexavalent chromium. Ventilation is the control the SDS names.
    - title: If it fails
      lead: The failure routes in the sources are about temper and temperature, not about a single corrosion rate.
      points:
        - label: Over-tempering
          line: Tempered at 1000 °F, 420 falls to 158.5 ksi tensile and 36 HRC, against 255.2 ksi and 48 HRC at 440 °F (Rolled Alloys).
        - label: Sub-zero service
          line: Aalco says ductility is lost below zero, which limits the useful range.
        - label: Corrosion
          line: Wikipedia says martensitic steels resist corrosion less well than ferritic and austenitic grades. Aalco says maximum corrosion resistance is reached in the hardened condition.
    - title: Handling and storage
      points:
        - label: Keep the temper in view
          line: Strength and hardness follow the tempering temperature. The order should name the temper.
        - label: Welds
          line: Aalco recommends preheat at 150 to 320 °C and post-heat at 610 to 760 °C for high-strength joints.
  why: AISI 420 (UNS S42000, EN 1.4021) is a martensitic stainless steel with 12.0 to 14.0 % chromium and 0.16 to 0.25 % carbon. The carbon lets it be hardened, so it reaches about 48 HRC after tempering at 440 °F (Rolled Alloys), while annealed it is soft, at most 241 HB. Its density is 7.75 g/cm3, and it is magnetic. It is chosen where a steel must be hard and wear-resistant and still stainless enough for blades, chains, bearings and valves. Its weak points are corrosion resistance, which is lower than that of austenitic steels, and strength loss if it is over-tempered.
  uses:
    - where: Bearings and chains
      line: Rolled Alloys lists industrial chains and bearings among the applications of Type 420, which is used for high strength, high wear resistance or good edge retention.
    - where: Pumps and valves
      line: Rolled Alloys lists pumps and valves, and plastic injection moulds and dies, among the applications of Type 420.
  can_do:
    - label: Carry load when hard
      value: 255.2 ksi tensile
      benchmark: ultimate_tensile_strength
      line: Tempered at 440 °F, Type 420 has a tensile strength of 255.2 ksi and a yield strength of 190.1 ksi (Rolled Alloys tempered-condition table).
    - label: Stay hard
      value: 48 HRC
      benchmark: hardness_rockwell_c
      line: The same tempered condition gives 48 HRC. Tempering at 1000 °F drops this to 36 HRC.
    - label: Soft to form
      value: 241 HB maximum
      benchmark: hardness_brinell
      line: Annealed (Condition A), the maximum hardness is 241 HB, and the yield strength is 51.5 ksi.
    - label: Weight
      value: 7.75 g/cm3
      benchmark: density
      line: Density is 7.75 g/cm3 in the Aalco datasheet, and 7.7 kg/dm3 at 20 °C in the teamedelstahl page.
    - label: Heat to 675 °C
      value: 675 °C continuous
      benchmark: max_service_temp
      line: Aalco gives a scaling limit of 675 °C continuous and 760 °C intermittent. This is a scaling limit; above the tempering temperature the mechanical properties fall.
  compare: 'Among the stainless steels, 420 trades corrosion resistance for hardness: Wikipedia says martensitic steels are less corrosion-resistant than ferritic and austenitic grades. Its density of 7.75 g/cm3 (Aalco) is close to the value of 7.7 kg/dm3 given by teamedelstahl for the same grade. The compare rows use the figures printed by the sources, not a ranking of different alloys.'
  compare_rows:
    - label: Density
      benchmark: density
    - label: Thermal conductivity
      benchmark: thermal_conductivity
    - label: Thermal expansion
      benchmark: cte
  handling:
    - Specify the temper, because strength and hardness follow the tempering temperature (Rolled Alloys table).
    - Harden and temper after fabrication, following the thermal-treatment table (hardening 950 to 1050 °C, then tempering).
    - Keep tempering below 1000 °F for useful strength, since 1000 °F tempering drops tensile strength to 158.5 ksi.
    - Ventilate cutting, grinding and welding to limit dust and fume.
  good_for:
    - 'Hard, wear-resistant parts: 48 HRC after tempering at 440 °F (Rolled Alloys).'
    - 'Stainless service with a magnetic response: 420 is magnetic in both conditions (Wikipedia).'
    - Scaling in air up to 675 °C continuous (Aalco).
  watch_out:
    - 'Corrosion: lower than that of austenitic grades, and best in the hardened condition (Aalco, Wikipedia).'
    - Over-tempering at 1000 °F drops tensile strength to 158.5 ksi.
    - Sub-zero ductility is lost (Aalco), so brittle failure is a risk in cold service.
    - Sources differ on thermal conductivity (24.9 W/(m·K) against 30 W/(m·K)) and modulus (200 GPa against 215 GPa).
  verdict: AISI 420 (UNS S42000, EN 1.4021) is a hardenable stainless steel for blades, chains, bearings and valves. It reaches 48 HRC when tempered at 440 °F, weighs 7.75 g/cm3 and is magnetic. It resists corrosion less well than austenitic steels and loses strength when over-tempered. This profile lacks a 1.4021-specific corrosion rate, impact values and vacuum data.
  recipe:
    line: Martensitic stainless steel of iron with about 12 to 14 % chromium and 0.16 to 0.25 % carbon (EN 1.4021 composition). The steel is hot-worked after uniform heating to 1149 to 1232 °C (Aalco), then hardened and tempered (teamedelstahl).
    parts:
      - name: Iron
        symbol: Fe
        share: balance
        role: Matrix of the steel
      - name: Chromium
        symbol: Cr
        share: 12.0 to 14.0 wt%
        role: Gives the steel its stainless character; low chromium makes it less corrosion-resistant than ferritic and austenitic grades (Wikipedia)
      - name: Carbon
        symbol: C
        share: 0.16 to 0.25 wt%
        role: Makes the steel hardenable; gives higher heat-treated strength at some cost in ductility (Rolled Alloys)
      - name: Manganese
        symbol: Mn
        share: up to 1.5 wt%
        role: Maximum allowed in the composition (teamedelstahl composition table)
      - name: Silicon
        symbol: Si
        share: maximum listed in the composition table
        role: Maximum allowed in the composition (teamedelstahl composition table)
      - name: Sulphur
        symbol: S
        share: up to 0.030 wt%
        role: Limit on the impurity; Aalco describes its bar as sulphur-enhanced for machining