spore: profile
id: stainless-17-7ph
spore_version: 0.2
family: stainless-precipitation-hardening
name: 17-7 PH stainless steel
abbreviation: 17-7 PH (UNS S17700, EN 1.4568, Type 631)
role: high-strength semi-austenitic precipitation-hardening stainless steel
category: metals
type: steels-and-stainless
summary: |
  17-7 PH is a chromium-nickel-aluminium stainless steel (16.00 to 18.00 % Cr, 6.50 to 7.75 % Ni, 0.75 to 1.50 % Al) that is formed in the soft annealed condition (Condition A) and then hardened by simple low-temperature heat treatments. The Cleveland-Cliffs 2024 datasheet gives a yield strength of 185 ksi (1276 MPa) after the TH 1050 treatment and 275 ksi (1896 MPa) after the CH 900 treatment, against 45 ksi (310 MPa) when soft. Its density is 7.81 g/cm3 in Condition A. A NASA Goddard study of 1968 tested the alloy for rocket-driven spacecraft and found that its fittings cracked under stress in nitrogen tetroxide and hydrazine propellant, and a NASA Marshall study of 1969 found stress corrosion cracking in 3.5 % salt water in nearly every heat-treated condition except CH 900.
best_for: Springs, Belleville washers, eyelets and flat springs that need high strength and stainless corrosion resistance, with formability in the soft state
weakest_at: Stress corrosion cracking in chloride and in nitrogen tetroxide/hydrazine propellant, in every heat-treated condition except CH 900; ductility in CH 900 (2 % elongation)
identity:
  formula: Fe balance, 16.00 to 18.00 Cr, 6.50 to 7.75 Ni, 0.75 to 1.50 Al, max 0.09 C, max 1.00 Mn, max 1.00 Si, max 0.040 P, max 0.030 S (wt%)
  source: cc-17-7
  where: Composition table (wt %), Cleveland-Cliffs 17-7 PH datasheet, 2024
  designations:
    - system: UNS
      code: S17700
      source: combmet-pdf
      where: 'Header block, UNS: S17700'
    - system: EN
      code: '1.4568'
      source: combmet-pdf
      where: 'Header block, EN DIN: 1.4568'
    - system: EN name
      code: X7CrNiAl17-7
      source: totalmateria-17-7
      where: Grade name line, EN X7CrNiAl17-7 Stainless steels
    - system: JIS
      code: SUS631
      source: totalmateria-17-7
      where: Equivalents list, JIS row
    - system: AISI
      code: '631'
      note: called Type 631 in the datasheet
      source: combmet-pdf
      where: Description paragraph, also Type 631
    - system: ASTM
      code: A693
      note: plate, sheet and strip, Grade 631
      source: combmet-pdf
      where: Applicable Specifications, Strip and Sheet row, ASTM A693 (Type 631)
    - system: ASTM
      code: A313
      note: wire and bar
      source: combmet-wire
      where: Applicable Specifications, Wire and Bar row
    - system: AMS
      code: '5528'
      note: sheet, strip and plate
      source: combmet-pdf
      where: Applicable Specifications, Strip and Sheet row
    - system: AMS
      code: '5529'
      note: cold rolled sheet and strip
      source: combmet-pdf
      where: Applicable Specifications, Strip and Sheet row
    - system: AMS
      code: '5678'
      note: wire
      source: combmet-wire
      where: Applicable Specifications, Wire and Bar row
    - system: Trade name
      code: 17-7 PH
      source: cc-17-7
      where: Document title, 17-7 PH Stainless Steel
tags:
  environments: []
  stresses: []
  applications:
    - structures
    - mechanisms
    - propulsion-and-tanks
properties:
  - benchmark: density
    label: Density, Condition A (annealed)
    value: 7.81
    unit: g/cm3
    scope: material
    conditions:
      condition: A (annealed)
      temperature: not stated in table
      unit_in_source: 0.282 lb/in3
    method: Value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024)
    status: ground
    source: cc-17-7
    where: Table 7 Physical Properties, Density row, Condition A column
  - benchmark: density
    label: Density, Condition TH 1050
    value: 7.65
    unit: g/cm3
    scope: material
    conditions:
      condition: TH 1050
      temperature: not stated in table
      unit_in_source: 0.276 lb/in3
    method: Value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024)
    status: ground
    source: cc-17-7
    where: Table 7 Physical Properties, Density row, TH 1050 column
  - benchmark: melting_point
    label: Melting range
    value: 1404
    value_high: 1440
    bound: range
    unit: °C
    scope: material
    conditions:
      unit_in_source: 2560 to 2625 °F
      basis: melting range printed for the alloy, not a single melting point
    method: Range printed in a manufacturer datasheet (United Performance Metals)
    status: ground
    source: upmet-17-7
    where: Physical Properties of 17-7 PH table, Melting Range row
  - benchmark: thermal_conductivity
    label: Thermal conductivity, Condition TH 1050 at 149 °C
    value: 16.9
    unit: W/(m·K)
    scope: material
    conditions:
      condition: TH 1050
      temperature: 149 °C (300 °F)
      unit_in_source: 117 BTU·in/(hr·ft²·°F)
    method: Value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024), rounded to one decimal as printed
    status: ground
    source: cc-17-7
    where: Table 7 Physical Properties, Thermal Conductivity row, TH 1050 column, 300 °F (149 °C)
  - benchmark: cte
    label: Mean coefficient of thermal expansion, Condition A, 21 to 427 °C
    value: 17.3
    unit: µm/(m·°C)
    scope: material
    conditions:
      condition: A (annealed)
      temperature: 21 to 427 °C (70 to 800 °F), mean
      unit_in_source: 9.6 x 10-6 in/in/°F
    method: Value printed in a manufacturer datasheet (Combined Metals, rev 2022)
    status: ground
    note: The Cleveland-Cliffs 2024 table prints 16.0 µm/m·K for the same Condition A row, which does not match its own 9.6 x 10-6 in/in/°F; this entry uses the Combined Metals value, which matches the inch figure.
    source: combmet-pdf
    where: Physical Properties table, Coefficient of Expansion row, Annealed column, 70-800 °F and 21-427 °C line
  - benchmark: cte
    label: Mean coefficient of thermal expansion, Condition TH 1050, 21 to 427 °C
    value: 11.9
    unit: µm/(m·°C)
    scope: material
    conditions:
      condition: TH 1050
      temperature: 21 to 427 °C (70 to 800 °F), mean
      unit_in_source: 6.6 µin/in-°F
    method: Value printed in a manufacturer datasheet (Combined Metals, rev 2022)
    status: ground
    source: combmet-pdf
    where: Physical Properties table, Coefficient of Expansion row, TH 1050 column, 70-800 °F and 21-427 °C line
  - benchmark: elastic_modulus
    label: Modulus of elasticity, Condition TH 1050
    value: 200
    unit: GPa
    scope: material
    conditions:
      condition: TH 1050
      unit_in_source: 29.0 x 10^3 ksi
    method: Value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024); the annealed modulus is not printed
    status: ground
    source: cc-17-7
    where: Table 7 Physical Properties, Modulus of Elasticity row, TH 1050 column
  - benchmark: electrical_resistivity
    label: Electrical resistivity, Condition A (annealed)
    value: 80
    unit: µΩ·cm
    scope: material
    conditions:
      condition: A (annealed)
      temperature: not stated in table
    method: Value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024)
    status: ground
    source: cc-17-7
    where: Table 7 Physical Properties, Electrical Resistivity row, Condition A column
  - benchmark: yield_strength
    label: Yield strength 0.2 % offset, Condition A (annealed)
    value: 310
    unit: MPa
    scope: material
    conditions:
      condition: A (annealed)
      basis: typical, room temperature
      unit_in_source: 45 ksi
      form: not stated in table
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 1)
    status: ground
    note: 'Earlier sheets give other values for the same condition: AK Steel (2007) prints 40 ksi (276 MPa) and Combined Metals (2022) prints 40 ksi (276 MPa). The Cleveland-Cliffs 2024 sheet is used throughout this profile.'
    source: cc-17-7
    where: Table 1 Typical Mechanical Properties, 0.2% YS row, Condition A column
  - benchmark: yield_strength
    label: Yield strength 0.2 % offset, Condition TH 1050
    value: 1276
    unit: MPa
    scope: material
    conditions:
      condition: TH 1050
      basis: typical, room temperature
      unit_in_source: 185 ksi
      form: not stated in table
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 1)
    status: ground
    source: cc-17-7
    where: Table 1 Typical Mechanical Properties, 0.2% YS row, TH 1050 column
  - benchmark: yield_strength
    label: Yield strength 0.2 % offset, Condition RH 950
    value: 1448
    unit: MPa
    scope: material
    conditions:
      condition: RH 950
      basis: typical, room temperature
      unit_in_source: 210 ksi
      form: not stated in table
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 1)
    status: ground
    source: cc-17-7
    where: Table 1 Typical Mechanical Properties, 0.2% YS row, RH 950 column
  - benchmark: yield_strength
    label: Yield strength 0.2 % offset, Condition CH 900
    value: 1896
    unit: MPa
    scope: material
    conditions:
      condition: CH 900
      basis: typical, room temperature
      unit_in_source: 275 ksi
      form: not stated in table
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 1)
    status: ground
    source: cc-17-7
    where: Table 1 Typical Mechanical Properties, 0.2% YS row, CH 900 column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, Condition A (annealed)
    value: 827
    unit: MPa
    scope: material
    conditions:
      condition: A (annealed)
      basis: typical, room temperature
      unit_in_source: 120 ksi
      form: not stated in table
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 1)
    status: ground
    source: cc-17-7
    where: Table 1 Typical Mechanical Properties, UTS row, Condition A column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, Condition TH 1050
    value: 1379
    unit: MPa
    scope: material
    conditions:
      condition: TH 1050
      basis: typical, room temperature
      unit_in_source: 200 ksi
      form: not stated in table
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 1)
    status: ground
    source: cc-17-7
    where: Table 1 Typical Mechanical Properties, UTS row, TH 1050 column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, Condition RH 950
    value: 1586
    unit: MPa
    scope: material
    conditions:
      condition: RH 950
      basis: typical, room temperature
      unit_in_source: 230 ksi
      form: not stated in table
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 1)
    status: ground
    source: cc-17-7
    where: Table 1 Typical Mechanical Properties, UTS row, RH 950 column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, Condition CH 900
    value: 2034
    unit: MPa
    scope: material
    conditions:
      condition: CH 900
      basis: typical, room temperature
      unit_in_source: 295 ksi
      form: not stated in table
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 1)
    status: ground
    source: cc-17-7
    where: Table 1 Typical Mechanical Properties, UTS row, CH 900 column
  - benchmark: elongation
    label: Elongation in 2 in., Condition A (annealed)
    value: 35
    unit: '%'
    scope: material
    conditions:
      condition: A (annealed)
      gauge_length: 2 in. (50.8 mm)
      basis: typical
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 1)
    status: ground
    source: cc-17-7
    where: Table 1 Typical Mechanical Properties, Elongation row, Condition A column
  - benchmark: elongation
    label: Elongation in 2 in., Condition TH 1050
    value: 8
    unit: '%'
    scope: material
    conditions:
      condition: TH 1050
      gauge_length: 2 in. (50.8 mm)
      basis: typical
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 1)
    status: ground
    note: AK Steel (2007) and Combined Metals (2022) print 9 % for the same condition.
    source: cc-17-7
    where: Table 1 Typical Mechanical Properties, Elongation row, TH 1050 column
  - benchmark: elongation
    label: Elongation in 2 in., Condition CH 900
    value: 2
    unit: '%'
    scope: material
    conditions:
      condition: CH 900
      gauge_length: 2 in. (50.8 mm)
      basis: typical
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 1)
    status: ground
    source: cc-17-7
    where: Table 1 Typical Mechanical Properties, Elongation row, CH 900 column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength at 482 °C, Condition TH 1050
    value: 855
    unit: MPa
    scope: material
    conditions:
      condition: TH 1050
      temperature: 482 °C (900 °F)
      unit_in_source: 124 ksi
      basis: typical short-time tensile test
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 4)
    status: ground
    source: cc-17-7
    where: Table 4 Typical Elevated Temperature Short-Time Tensile Properties, UTS row, TH 1050, 900 °F (482 °C) column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength at 482 °C, Condition RH 950
    value: 917
    unit: MPa
    scope: material
    conditions:
      condition: RH 950
      temperature: 482 °C (900 °F)
      unit_in_source: 133 ksi
      basis: typical short-time tensile test
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 4)
    status: ground
    source: cc-17-7
    where: Table 4 Typical Elevated Temperature Short-Time Tensile Properties, UTS row, RH 950, 900 °F (482 °C) column
  - benchmark: yield_strength
    label: Yield strength at 482 °C, Condition TH 1050
    value: 690
    unit: MPa
    scope: material
    conditions:
      condition: TH 1050
      temperature: 482 °C (900 °F)
      unit_in_source: 100 ksi
      basis: typical 0.2 % offset
    method: Typical value printed in a manufacturer datasheet (Cleveland-Cliffs, 2024, Table 4)
    status: ground
    source: cc-17-7
    where: Table 4 Typical Elevated Temperature Short-Time Tensile Properties, 0.2% YS row, TH 1050, 900 °F (482 °C) column
  - benchmark: stress_corrosion_threshold
    label: Threshold stress for stress corrosion cracking in boiling magnesium chloride
    value: 104000
    unit: psi
    scope: material
    conditions:
      environment: boiling 42 % MgCl2 solution at 154 °C, closed reflux
      specimen: stressed as a simple beam, sheet 0.63 in thick
      unit_in_source: 104,000 psi
      note_in_source: below this stress no stress corrosion occurred, regardless of heat treatment
    method: Threshold printed in a NASA technical note (1968) on the heat treatment of 17-7 PH; the name stress_corrosion_threshold is not in the canonical list
    status: ground
    source: ntrs-tn-d4673
    where: Results section, paragraph beginning A threshold stress level (104,000 psi)
corrosion:
  - environment: Boiling magnesium chloride solution (42 %, 154 °C) under sustained tensile stress
    headline: Stress corrosion cracking begins above a threshold of about 104,000 psi in the NASA boiling-chloride test.
    effect: NASA Goddard tested 17-7 PH sheet in a boiling 42 % MgCl2 solution with the stress applied as a beam. Below 104,000 psi no cracking occurred, whichever of the three heat treatments was used. Above that, cracking occurred, and one heat treatment gave longer life than the other two.
    rating: severe
    conditions:
      medium: 42 % MgCl2, boiling, 154 °C, closed reflux
      specimen: beam, sheet
      exposure: stress applied for the test period, duration not stated in the summary
    source: ntrs-tn-d4673
    where: Test method and Results sections; Summary
  - environment: Alternate immersion in 3.5 % salt solution under tensile stress
    headline: In 3.5 % salt water 17-7 PH cracked under stress in every heat-treated condition except CH 900.
    effect: NASA Marshall tested several precipitation-hardening stainless steels by alternate immersion in 3.5 % salt solution. PH 13-8 Mo, PH 14-8 Mo, 15-5 PH, 17-4 PH, A-286, Almar 362 and Unitemp 212 were highly resistant. 17-7 PH was susceptible in nearly all heat-treated conditions, and the only exception was CH 900, which resisted cracking.
    rating: severe
    conditions:
      medium: 3.5 % salt solution
      method: alternate immersion, round tensile, flat tensile and C-ring specimens
      stress: loads up to 100 % of yield in the work described
    source: ntrs-tmx53910
    where: Abstract; Conclusions, item 2
  - environment: Nitrogen tetroxide with hydrazine (MMH) rocket propellant
    headline: Fittings of 17-7 PH cracked under stress corrosion in nitrogen tetroxide and MMH propellant.
    effect: NASA Goddard reports that 17-7 PH has several times shown a tendency to crack under stress corrosion when exposed to the nitrogen-tetroxide/hydrazine (MMH) propellant system, and Figure 1 of the report shows cracking in fittings made from the alloy. The 1968 work set out to reduce this susceptibility by changing the thermal treatment.
    rating: severe
    conditions:
      medium: nitrogen tetroxide with MMH propellant
      part: reaction-motor fittings
    source: ntrs-tn-d4673
    where: Abstract and Introduction; Figure 1 caption
  - environment: General corrosion, compared with other stainless types
    headline: In TH 1050 and RH 950 general corrosion resistance is better than Types 410, 420 and 431, and in CH 900 it is close to Type 304.
    effect: Cleveland-Cliffs says corrosion resistance in Conditions TH 1050 and RH 950 is superior to the hardenable chromium types, and in some environments approximates the austenitic chromium-nickel steels. In Condition CH 900 general corrosion resistance is comparable to Type 304. The sheet gives no corrosion rate.
    rating: moderate
    conditions:
      basis: comparison with other stainless grades, no test data printed
    source: cc-17-7
    where: Product Description paragraph, page 1
risks:
  hazards:
    - text: 'The Washington Alloy stainless wire and rod safety data sheet lists 17-7PH among its products. It says the welding product is not GHS classified, and that welding fumes and gases cannot be classified simply: they depend on the metal welded and the process, and may affect eyes, skin, the respiratory system, the pancreas and the liver. This describes welding fume, not the base metal in solid form.'
      ghs: []
      source: stoody-ss-sds
      where: Section II, GHS Hazard Classification and Other Hazards; Section on welding fumes and gases
    - text: The same data sheet says chromium in fume may form hexavalent chromium, and that acute overexposure to welding fume can cause metal fume fever while chronic overexposure can lead to siderosis.
      ghs: []
      source: stoody-ss-sds
      where: Hazards to health paragraphs (acute and chronic symptoms) and the OSHA hexavalent chromium note
  failure_risks:
    - mode: Stress corrosion cracking in salt water
      trigger: Tensile stress in heat-treated 17-7 PH exposed to chloride (3.5 % salt, alternate immersion), in any condition except CH 900
      consequence: NASA found cracking in nearly all heat-treated conditions; CH 900 was the only condition that resisted it in that test.
      severity: high
      source: ntrs-tmx53910
      where: Abstract; Conclusions, item 2
    - mode: Stress corrosion cracking of propulsion fittings
      trigger: Stressed reaction-motor fittings in contact with nitrogen tetroxide and MMH propellant
      consequence: Fittings cracked in the Goddard work, which led to a search for a better heat treatment.
      severity: high
      source: ntrs-tn-d4673
      where: Abstract and Introduction; Figure 1 caption
    - mode: Cracking above the chloride threshold stress
      trigger: Tensile stress above about 104,000 psi in boiling 42 % magnesium chloride at 154 °C
      consequence: Cracking above the threshold in the test; none was seen below it, whichever heat treatment was used.
      severity: moderate
      source: ntrs-tn-d4673
      where: Results section, threshold paragraph
    - mode: Low strength in welded joints
      trigger: Welding without the full heat-treatment sequence afterwards
      consequence: AK Steel says austenite conditioning and precipitation hardening must both be carried out after welding to reach high strength levels, and that the alloy has poorer weldability than 17-4 PH, mainly because of its high aluminium content.
      severity: moderate
      source: ak-17-7
      where: Weldability section
  side_effects:
    - text: On heat treatment from Condition A to RH 950 or TH 1050 the alloy expands by about 0.004 in/in, which matters for the size of machined or formed parts.
      affects: Dimensions of finished parts
      source: cc-17-7
      where: Dimensional Changes paragraph, page 4
  handling:
    - text: Form the part in Condition A (annealed), then heat treat it. The datasheet says the alloy works harden rapidly and may need intermediate annealing for deep drawing or intricate parts.
      source: ak-17-7
      where: Formability section
    - text: 'Heat treatments printed for the standard routes: TH 1050 at 1050 ± 10 °F (566 ± 5.5 °C) for 90 min; RH 950 at 950 ± 10 °F (510 ± 5.5 °C) for 60 min; CH 900 at 900 ± 10 °F (482 ± 5.5 °C) for 60 min, all followed by air cooling.'
      source: cc-17-7
      where: Standard Heat Treatments, Figure 1
    - text: Mill annealing (Condition A) is at 1950 ± 25 °F (1066 ± 14 °C). For TH 1050, austenite conditioning is at 1400 ± 25 °F (760 ± 14 °C) for 90 min before cooling to form martensite.
      source: cc-17-7
      where: Standard Heat Treatments, Figure 1
    - text: The NASA 1969 work found CH 900 to be the only heat-treated condition that resisted stress corrosion cracking in salt water. The Cleveland-Cliffs sheet gives CH 900 an elongation of 2 %, so it has the least ductility.
      source: ntrs-tmx53910
      where: Conclusions, item 2; ductility from Table 1 of cc-17-7
  mitigations:
    - text: 'Use the aging condition for the environment as well as the strength: NASA reported that CH 900 was the one heat-treated condition that resisted cracking in 3.5 % salt water, and the Cleveland-Cliffs sheet gives it the lowest elongation of the aged conditions.'
      source: ntrs-tmx53910
      where: Abstract and Conclusions
uses:
  - application: propulsion-and-tanks
    device: Reaction-motor and support-equipment fittings for rocket-driven spacecraft
    example: NASA Goddard's 1968 report says the alloy was considered for reaction-motor and support equipment in rocket-driven spacecraft, where fittings made of it were tested with nitrogen tetroxide and MMH propellant, and the report notes that fittings cracked under stress corrosion.
    source: ntrs-tn-d4673
    where: Abstract, Introduction, Figure 1 caption
  - application: mechanisms
    device: Flat springs, Belleville (conical spring) washers and eyelets
    example: Cleveland-Cliffs lists aerospace parts, Belleville washers, eyelets and flat springs among the uses of 17-7 PH, with excellent properties for these parts up to 600 °F (316 °C).
    source: cc-17-7
    where: Cover page application list and introduction paragraph
  - application: structures
    device: Aerospace bulkheads, retaining rings and tooling
    example: Smiths Metal Centres lists aerospace tooling, bulkheads, retaining rings and springs among the typical applications of 17-7 PH.
    source: smith-17-7
    where: Typical Applications list
  - application: mechanisms
    device: Springs and washers from wire and bar
    example: Elgiloy Specialty Metals lists springs, rings, washers, heat exchangers and tubing among the applications of 17-7 PH wire and bar, with spring temper strengths of 240 to 300 ksi (1655 to 2070 MPa) for diameters up to 0.100 in, with use up to 650 °F (343 °C).
    source: combmet-wire
    where: Description and Typical Mechanical Properties table, Spring row
supply:
  - subject: Nickel (mine production, 2025 estimate), main source of the 6.50 to 7.75 % nickel in the alloy
    abundance: World mine production 3,900,000 t in 2025 (estimate); world reserves more than 140,000,000 t (USGS 2026).
    producers:
      - country: Indonesia
        share_percent: 66.7
        year: 2025
        basis: 2,600,000 t of 3,900,000 t, computed
      - country: Philippines
        share_percent: 6.9
        year: 2025
        basis: 270,000 t of 3,900,000 t, computed
      - country: Russia
        share_percent: 5.1
        year: 2025
        basis: 200,000 t of 3,900,000 t, computed
      - country: Canada
        share_percent: 3.6
        year: 2025
        basis: 140,000 t of 3,900,000 t, computed
      - country: New Caledonia
        share_percent: 3.6
        year: 2025
        basis: 140,000 t of 3,900,000 t, computed
    critical_lists: []
    recycling: 'USGS: nickel recovered from scrap, mainly stainless steel scrap, accounted for about 60 % of 2025 apparent consumption.'
    substitutes:
      - 'USGS: low-nickel, duplex and ultrahigh-chromium stainless steels have been substituted for austenitic grades in construction.'
    source: usgs-ni
    where: World Mine Production and Reserves table, 2025e column; Recycling; Substitutes
  - subject: Chromium (mine production, 2025 estimate), main source of the 16.00 to 18.00 % chromium in the alloy
    abundance: World chromite mine production 51,000 thousand t in 2025 (estimate, gross weight); world ore reserves more than 1,200,000 thousand t, gross weight (USGS 2026).
    producers:
      - country: South Africa
        share_percent: 45.1
        year: 2025
        basis: 23,000 of 51,000 thousand t, computed
      - country: Turkey
        share_percent: 17.6
        year: 2025
        basis: 9,000 of 51,000 thousand t, computed
      - country: Brazil
        share_percent: 3.9
        year: 2025
        basis: 2,000 of 51,000 thousand t, computed
      - country: Finland
        share_percent: 3.7
        year: 2025
        basis: 1,900 of 51,000 thousand t, computed
    critical_lists: []
    substitutes: []
    source: usgs-cr
    where: World Mine Production and Reserves table, 2025e column; Events, Trends, and Issues; reserves column
documents:
  - title: Cleveland-Cliffs 17-7 PH Stainless Steel product data bulletin (2024)
    type: datasheet
    url: https://www.clevelandcliffs.com/_assets/_eb15314af477616a40b17eafbaeabe27/clevelandcliffs/db/1190/10504/file/CLF_ProductData_17-7-PH+Stainless+Steel_72024.pdf
    year: 2024
  - title: Combined Metals material datasheet, 17-7PH stainless steel (rev 2022)
    type: datasheet
    url: https://www.combmet.com/wp-content/uploads/2023/02/cmc_17-7ph_data_sheet.pdf
    year: 2022
  - title: Elgiloy Specialty Metals, 17-7 PH wire products datasheet (rev 6/17/2020)
    type: datasheet
    url: https://www.combmet.com/wp-content/uploads/2023/06/Wire-17-7-PH-Apr-2020-1.pdf
    year: 2020
  - title: United Performance Metals, Alloy 17-7 PH datasheet (AMS 5528, UNS S17700)
    type: datasheet
    url: https://www.upmet.com/sites/default/files/products/datasheet/17-7-ph-datasheet.pdf
  - title: AK Steel 17-7 PH Stainless Steel Data Sheet, 7100-0096 7/07 (copy on AWS server)
    type: datasheet
    url: https://app.aws.org/mwf/attachments//82/222882/17-7_PH_Data_Sheet.pdf
    year: 2007
  - title: Smiths Metal Centres, 17-7PH Technical Datasheet (2023)
    type: datasheet
    url: https://www.smithmetal.com/pdf/stainless/ph/17-7ph.pdf
    year: 2023
  - title: Total Materia, X7CrNiAl17-7 (EN) material page, grade name and equivalents
    type: database
    url: https://www.totalmateria.com/en-us/material/1050855
  - title: NASA TN D-4673, Heat Treatment for Improved Stress-Corrosion Resistance of 17-7 PH Stainless Steel (Johnson and Grimsley, Goddard, 1968)
    type: report
    url: https://ntrs.nasa.gov/api/citations/19680019907/downloads/19680019907.pdf
    year: 1968
  - title: NASA TM X-53910, Stress Corrosion Cracking Evaluation of Several Precipitation Hardening Stainless Steels (Humphries and Nelson, MSFC, 1969)
    type: report
    url: https://ntrs.nasa.gov/api/citations/19690028850/downloads/19690028850.pdf
    year: 1969
  - title: 'USGS Mineral Commodity Summaries 2026: Nickel'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Chromium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
  - title: Washington Alloy, Stainless Steel Solid Wire and Rods safety data sheet, SDS 005-SS (rev 6-2015)
    type: sds
    url: https://www.stoodyind.com/Safety/MSDS/Stainless.pdf
    year: 2015
gaps:
  - No fracture toughness, Charpy impact or fatigue endurance value was entered. The Cleveland-Cliffs endurance-limit table prints its cycle count in a way that is hard to read (15 x 10 with a superscript 6), so it was left out rather than guessed.
  - No hardness value is a property entry. Rockwell values are printed in the datasheets (for example B85 soft, C43 TH 1050, C48 RH 950, C52 CH 900) and are quoted in the story text only, because the canonical list has no hardness name.
  - 'No annealed (Condition A) modulus of elasticity is printed in any read source: the datasheets show a dash in that cell.'
  - No specific heat, emissivity or outgassing value was found for this alloy.
  - No vacuum, atomic oxygen, radiation or cryogenic data was looked up for this alloy.
  - No usable limit for hydrogen sulfide (sour service) was found. A search summary said the Upmet sheet warns of cracking in hydrogen sulfide, but that sentence is not in the Upmet datasheet text read in this run, so it is not recorded. NACE MR0175 and ISO 15156 were not opened.
  - The threshold stress entry uses the non-canonical name stress_corrosion_threshold, because no canonical name fits a stress-corrosion threshold.
  - The Cleveland-Cliffs 2024 sheet and the AK Steel 2007 sheet print different typical values for the same conditions (for example Condition A ultimate tensile strength 120 ksi against 130 ksi, and TH 1050 elongation 8 % against 9 %). The profile uses the 2024 sheet and records the differences in notes.
  - The Cleveland-Cliffs metric column prints 16.0 µm/m·K for Condition A at 70 to 800 °F, which does not match its own inch figure. The profile uses the Combined Metals value 17.3 µm/m·°C for the same row, with a note.
  - The EN 10088 part number for 1.4568 was not confirmed. Search results disagreed (EN 10088-1 against EN 10088-2 and EN 2540 for aerospace sheet and strip), and no standard page was opened.
  - No AISI page was opened. The Type 631 number is taken from the Combined Metals datasheet, which calls the alloy also Type 631.
  - The Wikipedia article for 17-7 PH could not be read (HTTP 404). No history of development (for example the Armco origin) was read in this run, so none is recorded.
  - The DTIC report on precipitation-hardening stainless steels could not be read (the PDF failed to parse), so the semi-austenitic classification comes from the Cleveland-Cliffs sheet only.
  - The aircraftmaterials.com AMS 5528 page was read, but its TH 1050 tensile range is printed in reversed order, so none of its numbers are used.
  - No critical-mineral list entry for nickel or chromium was read in the USGS summaries that were opened, so critical_lists is empty.
  - The hazard entries come from a welding-wire safety data sheet that lists 17-7PH among its products, not from a safety data sheet for the solid alloy. No base-metal SDS was read.
  - The Aalco page for 1.4568 was not found in search results, so no Aalco value is used.
  - The makeitfrom.com EN 1.4568 page returned HTTP 403 and was not read; its value ranges are not used.
  - The Armco datasheet is held only behind an ASM Alloy Digest login, so it was not read.
sources:
  cc-17-7:
    title: Cleveland-Cliffs 17-7 PH Stainless Steel product data bulletin, Tables 1, 4 and 7 and Standard Heat Treatments
    id: UNS S17700, AMS 5528, AMS 5529, ASTM A 693 (Grade 631)
    url: https://www.clevelandcliffs.com/_assets/_eb15314af477616a40b17eafbaeabe27/clevelandcliffs/db/1190/10504/file/CLF_ProductData_17-7-PH+Stainless+Steel_72024.pdf
    year: 2024
    kind: datasheet
    license: Manufacturer product bulletin (cited, not reproduced)
  combmet-pdf:
    title: Combined Metals of Chicago, 17-7PH material datasheet (REV 2022 08 05)
    id: UNS S17700, EN DIN 1.4568, Type 631
    url: https://www.combmet.com/wp-content/uploads/2023/02/cmc_17-7ph_data_sheet.pdf
    year: 2022
    kind: datasheet
    license: Distributor datasheet with typical values, not for design (cited, not reproduced)
  combmet-wire:
    title: Elgiloy Specialty Metals (Combined Metals), 17-7 PH wire products datasheet (rev 6/17/2020)
    id: UNS S17700, W. Nr 1.4568, ASTM A313, AMS 5678
    url: https://www.combmet.com/wp-content/uploads/2023/06/Wire-17-7-PH-Apr-2020-1.pdf
    year: 2020
    kind: datasheet
    license: Distributor datasheet with typical values, not for design (cited, not reproduced)
  upmet-17-7:
    title: United Performance Metals, Alloy 17-7 PH datasheet (AMS 5528 / UNS S17700)
    id: AMS 5528, UNS S17700, Grade 631, W.NR. 1.4568
    url: https://www.upmet.com/sites/default/files/products/datasheet/17-7-ph-datasheet.pdf
    year: 2026
    kind: datasheet
    license: Distributor datasheet, information only (cited, not reproduced)
  ak-17-7:
    title: AK Steel 17-7 PH Stainless Steel Data Sheet (7100-0096 7/07)
    id: UNS S17700, AK Steel PH data sheet
    url: https://app.aws.org/mwf/attachments//82/222882/17-7_PH_Data_Sheet.pdf
    year: 2007
    kind: datasheet
    license: Manufacturer datasheet, 2007 (cited, not reproduced)
  smith-17-7:
    title: Smiths Metal Centres, 17-7PH technical datasheet (2023)
    id: 17-7PH precipitation hardening stainless steel
    url: https://www.smithmetal.com/pdf/stainless/ph/17-7ph.pdf
    year: 2023
    kind: datasheet
    license: Distributor datasheet (cited, not reproduced)
  totalmateria-17-7:
    title: Total Materia, X7CrNiAl17-7 (EN) stainless steel equivalents
    id: EN X7CrNiAl17-7, UNS S17700, JIS SUS631
    url: https://www.totalmateria.com/en-us/material/1050855
    kind: database
    license: Database page (cited, not reproduced)
  ntrs-tn-d4673:
    title: 'NASA TN D-4673: Heat Treatment for Improved Stress-Corrosion Resistance of 17-7 PH Stainless Steel (Johnson and Grimsley, Goddard Space Flight Center, 1968)'
    id: NASA TN D-4673, NTRS 19680019907
    url: https://ntrs.nasa.gov/api/citations/19680019907/downloads/19680019907.pdf
    year: 1968
    kind: report
    license: Public domain (NASA)
  ntrs-tmx53910:
    title: 'NASA TM X-53910: Stress Corrosion Cracking Evaluation of Several Precipitation Hardening Stainless Steels (Humphries and Nelson, Marshall Space Flight Center, 1969)'
    id: NASA TM X-53910, NTRS 19690028850
    url: https://ntrs.nasa.gov/api/citations/19690028850/downloads/19690028850.pdf
    year: 1969
    kind: report
    license: Public domain (NASA)
  usgs-ni:
    title: 'USGS Mineral Commodity Summaries 2026: Nickel'
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.pdf
    year: 2026
    kind: report
    license: Public domain (USGS)
  usgs-cr:
    title: 'USGS 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)
  stoody-ss-sds:
    title: Washington Alloy stainless steel solid wire and rods, safety data sheet SDS 005-SS (rev 6-2015)
    id: SDS 005-SS
    url: https://www.stoodyind.com/Safety/MSDS/Stainless.pdf
    year: 2015
    kind: datasheet
    license: Manufacturer safety data sheet (cited, not reproduced)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 23
  unreachable: 4
  caveats: 6
  note: 'Values were read by an AI assistant on 2026-10-26 from the pages and PDFs named in each entry (PDF text extracted with pdftotext). Unreachable: makeitfrom.com (HTTP 403), Wikipedia (HTTP 404), the DTIC PDF (did not parse) and the Armco datasheet (login). Caveats: the Cleveland-Cliffs 2024 and AK Steel 2007 sheets differ on some typical values; the mechanical values are typical, not minimums; the hazard entries are for welding wire; the chloride and propellant cracking entries come from 1968 and 1969 NASA tests on one or two sheet heats; the EN 10088 part number is unconfirmed.'
story:
  risk_groups:
    - title: For people
      lead: The alloy is a solid stainless steel, and the sources read do not describe health effects of the solid metal in use. Welding is the exposure route the sources describe.
      level: 1
      verdict: Welding fume is the concern
      points:
        - label: Solid alloy
          line: The sources do not give a hazard classification for the solid alloy. The welding wire data sheet that lists 17-7PH says the product is not GHS classified, but that welding fume may affect the eyes, skin, lungs, pancreas and liver.
        - label: Welding fume
          line: The same data sheet says chromium in fume may form hexavalent chromium, and that acute overexposure can cause metal fume fever while chronic overexposure can cause siderosis.
    - title: If it fails
      lead: The failure routes in the sources are stress corrosion cracking. The NASA results are the strongest, because they are measured tests.
      points:
        - label: Salt water
          line: In NASA's 1969 test in 3.5 % salt water, 17-7 PH cracked under stress in nearly every heat-treated condition. CH 900 was the exception.
        - label: Rocket propellant
          line: In NASA's 1968 study, 17-7 PH fittings cracked under stress when exposed to nitrogen tetroxide and hydrazine (MMH). That result is why the heat treatment was studied.
        - label: Threshold
          line: In boiling 42 % magnesium chloride at 154 °C, NASA found no cracking below about 104,000 psi, whichever heat treatment was used.
    - title: Handling and storage
      points:
        - label: Form soft, then harden
          line: Form the part in Condition A, then heat treat. Heat treating changes the size by about 0.004 in/in on the Cleveland-Cliffs figures, so allow for it.
        - label: Choose the condition for the job
          line: TH 1050 and RH 950 give a balance of strength and corrosion resistance. CH 900 gives the highest strength and the best result in the salt test, but only 2 % elongation.
        - label: Welding
          line: After welding, both austenite conditioning and precipitation hardening must be repeated to get high strength (AK Steel). Filler W 17-7 PH is the one most often specified.
  why: 17-7 PH is a stainless steel that can be formed soft and then made much stronger by simple heat treatments. In Condition A it has a yield strength of 310 MPa and an elongation of 35 %; in CH 900 it reaches a yield strength of 1896 MPa, with 2 % elongation. Its chromium (16 to 18 %) gives corrosion resistance in TH 1050 and RH 950 that is better than the hardenable Types 410, 420 and 431. That combination is why it is used for springs, Belleville washers and aerospace parts. The NASA work of 1968 looked at it for rocket-driven spacecraft, where the fittings cracked in propellant, and the 1969 work found cracking in 3.5 % salt water in nearly all heat-treated conditions except CH 900.
  uses:
    - where: Rocket and spacecraft propulsion
      line: NASA Goddard considered 17-7 PH for reaction-motor and support equipment in rocket-driven spacecraft, and studied its stress corrosion cracking in nitrogen tetroxide and MMH propellant. The report shows cracked fittings.
    - where: Springs and washers
      line: Cleveland-Cliffs lists flat springs, Belleville washers and eyelets for use up to 600 °F (316 °C). Elgiloy lists spring wire at 240 to 300 ksi for diameters up to 0.100 in, with use up to 650 °F (343 °C).
    - where: Aerospace hardware
      line: Smiths lists aerospace tooling, bulkheads, retaining rings and springs as typical applications.
  can_do:
    - label: Strength
      value: 1379 MPa at TH 1050
      benchmark: ultimate_tensile_strength
      line: In TH 1050 the tensile strength is 1379 MPa (200 ksi) and the 0.2 % yield strength is 1276 MPa (185 ksi), with 8 % elongation.
    - label: Hot strength
      value: 855 MPa at 482 °C
      benchmark: ultimate_tensile_strength
      line: At 482 °C (900 °F) the TH 1050 tensile strength is 855 MPa (124 ksi), and RH 950 gives 917 MPa (133 ksi).
    - label: Weight
      value: 7.81 g/cm3
      benchmark: density
      line: Density is 7.81 g/cm3 in Condition A and 7.65 g/cm3 in TH 1050 and RH 950.
    - label: Heat conduction
      value: 16.9 W/(m·K)
      benchmark: thermal_conductivity
      line: Thermal conductivity in TH 1050 is 16.9 W/(m·K) at 149 °C, as printed in the Cleveland-Cliffs table.
    - label: Melting
      value: 1404 to 1440 °C
      benchmark: melting_point
      line: The melting range is 1404 to 1440 °C (2560 to 2625 °F), according to United Performance Metals.
  compare: AK Steel calls 17-4 PH the most common alloy of this class and says 17-7 PH has poorer weldability than 17-4 PH, mainly because its high aluminium content degrades penetration and enhances weld slag in arc welding. Cleveland-Cliffs describes 17-7 PH as a semi-austenitic precipitation-hardening grade that is formed in the annealed condition. The NASA 1969 work rated 17-4 PH as highly resistant to stress corrosion cracking in 3.5 % salt water, while 17-7 PH cracked in nearly all heat-treated conditions, so chloride cracking is the main difference that work reports between the two.
  compare_rows:
    - label: Yield strength
      benchmark: yield_strength
    - label: Elastic modulus
      benchmark: elastic_modulus
    - label: Thermal expansion
      benchmark: cte
  handling:
    - Form the part in Condition A and heat treat it afterwards. Condition C is described as extremely hard and strong, so it needs suitable fabrication techniques (AK Steel).
    - 'Use the datasheet temperatures: TH 1050 at 1050 °F (566 °C) for 90 min, RH 950 at 950 °F (510 °C) for 60 min, CH 900 at 900 °F (482 °C) for 60 min.'
    - Mill annealing (Condition A) is at 1950 ± 25 °F (1066 ± 14 °C). For TH 1050, austenite conditioning is at 1400 ± 25 °F (760 ± 14 °C) for 90 min before cooling to form martensite (Cleveland-Cliffs Figure 1).
    - Keep tensile stress low in chloride or propellant service. NASA found cracking in salt water in nearly every heat-treated condition except CH 900.
    - After welding, repeat both the austenite conditioning and the precipitation hardening treatment.
  good_for:
    - Springs and washers that must stay stiff and stainless in a range up to about 600 °F (316 °C).
    - Aerospace parts that need high strength with a formable soft state, from one heat-treatment step.
    - Hot strength to 482 °C (900 °F) in the TH 1050 and RH 950 conditions.
  watch_out:
    - 'Chloride: NASA found cracking under stress in 3.5 % salt water in nearly all heat-treated conditions except CH 900.'
    - 'Propellant: fittings of 17-7 PH cracked under stress in nitrogen tetroxide and MMH in the 1968 NASA work.'
    - 'Ductility: CH 900 gives the highest strength (1896 MPa yield) but only 2 % elongation.'
    - Welding needs the full heat-treatment sequence afterwards to reach high strength.
    - No fatigue, toughness or outgassing values are entered in this profile.
  verdict: 17-7 PH is a formable, high-strength stainless steel with 1276 MPa yield in TH 1050 and 1896 MPa in CH 900. Its general corrosion resistance is better than Types 410, 420 and 431 in TH 1050 and RH 950. NASA's 1969 test found stress corrosion cracking in 3.5 % salt water in nearly every heat-treated condition except CH 900, and NASA's 1968 fittings cracked in nitrogen tetroxide and MMH, so the aging condition must be chosen for the environment as well as the load.
  recipe:
    line: 17-7 PH is an iron-based precipitation-hardening stainless steel (UNS S17700, EN 1.4568) made to the composition limits in the identity record, with iron as the balance. It is mill annealed at 1950 ± 25 °F (1066 ± 14 °C) (Condition A). For TH 1050, the austenite is conditioned at 1400 ± 25 °F (760 ± 14 °C) for 90 min, cooled to 60 ± 10 °F (16 ± 5.5 °C) to form martensite, then aged at 1050 ± 10 °F (566 ± 5.5 °C) for 90 min. CH 900 is cold rolled to Condition C at the mill and then aged at 900 °F (482 °C) for 60 min (Cleveland-Cliffs).
    parts:
      - name: Iron
        symbol: Fe
        share_note: balance
        role: Matrix of the alloy; the austenite conditioning and cooling steps transform it to martensite before ageing.
      - name: Chromium
        symbol: Cr
        share_percent: 16
        share_high: 18
        role: Chromium content of the stainless class; the datasheet compares its corrosion resistance with Types 410, 420, 431 and 304.
      - name: Nickel
        symbol: Ni
        share_percent: 6.5
        share_high: 7.75
        role: Alloying element in the composition table; the datasheet calls the alloy semi-austenitic.
      - name: Aluminium
        symbol: Al
        share_percent: 0.75
        share_high: 1.5
        role: Alloying element in the composition table; AK Steel names its high aluminium content as the main weldability difference from 17-4 PH.
      - name: Carbon
        symbol: C
        share_note: max 0.09
        role: Residual element limit in the composition table.
      - name: Manganese, silicon, phosphorus, sulphur
        symbol: Mn, Si, P, S
        share_note: max 1.00 Mn, max 1.00 Si, max 0.040 P, max 0.030 S
        role: Residual and deoxidation elements, limited by the specification.