Stainless Steel 431 · heat-treated state
Stainless Steel 431 Hardened
Properties of the Hardened condition, compared with the other 431 tempers.
Intermediate state only — must be tempered before use; retained stresses make it crack-prone.
What is 431 Hardened?
431 Hardened is 431 heat treated to Hardened — intermediate state only — must be tempered before use; retained stresses make it crack-prone. 431 Hardened has a yield strength of 1,200 MPa (174 ksi) and a tensile strength of 1,500 MPa (218 ksi) — stronger than 98% of stainless steel grades. Elongation at break is 5% and the elastic modulus is 200 GPa (29 Msi). 431 Hardened has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 66% of stainless steel grades. It melts at 1,425°C (2,597 °F). Hardened & Tempered is the default condition FabDigit quotes; Hardened is available on request or by drawing note.
Advantages
- High strength — 1,200 MPa (174 ksi), better than 98% of stainless steel grades
- Conducts heat well — 20.2 W/m·K (11.7 BTU/hr·ft·°F), better than 75% of stainless steel grades
Limitations
- Limited ductility — 5%, worse than 100% of stainless steel grades
- Limited service temperature — 150°C (302 °F), worse than 100% of stainless steel grades
- Difficult to machine — 10/100, worse than 100% of stainless steel grades
- Difficult to weld — 25/100, worse than 92% of stainless steel grades
- Low fracture toughness — 80 MPa·√m (72.8 ksi·√in), worse than 83% of stainless steel grades
431 Hardened properties
Typical room-temperature values for 431 Hardened — 8 properties are specific to this condition; the rest are grade-level values shared by every 431 temper. Each bar shows where the value sits among the stainless steel grades in FabDigit's library — further right is higher.
Physical3
431 Hardened has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 66% of stainless steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
431 Hardened has a yield strength of 1,200 MPa (174 ksi) and a tensile strength of 1,500 MPa (218 ksi) — stronger than 98% of stainless steel grades. Elongation at break is 5% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
431 Hardened is rated for continuous service to 150°C (302 °F). It conducts heat at 20.2 W/m·K (11.7 BTU/hr·ft·°F), better than 75% of stainless steel grades. Thermal expansion is 11.7 µm/m·K (6.5 µin/in·°F).
Electrical3
431 Hardened conducts electricity at 2.4 % IACS, better than 67% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is fair (48/100), worse than 81% of stainless steel grades.
Sustainability4
Producing a kilogram of 431 Hardened takes about 53 MJ of energy and emits 4.2 kg of CO₂ — less than 67% of stainless steel grades. Typical recycled content is 50%.
Manufacturability7
431 Hardened's machinability is not recommended (10/100, worse than 100% of stainless steel grades); weldability poor (25/100); formability poor (25/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 431 tempers and conditions
431 is also supplied in 7 other conditions. The full side-by-side table is on the 431 overview.
- Hardened & TemperedDefaultThe normal supply and service condition: best balance of strength, toughness and corrosion resistance for shafts, stems and fasteners.760 MPa yield · 31 HRC
- HardenedIntermediate state only — must be tempered before use; retained stresses make it crack-prone.1,200 MPa yield · 46 HRC
- Q&T 40-45 HRCMaximum-strength/wear condition for stems, bushings and cutlery-type parts; accept low impact toughness and no notches.1,080 MPa yield · 42 HRC
- +QT900Highest standard EN QT class; use where strength governs and impact requirement is modest (KV ≥ 15 J).750 MPa yield · 31 HRC
- AnnealedStock condition for machining and subsequent heat treatment; note 431 is still quite strong when annealed because it air-hardens.655 MPa yield · 26 HRC
- +QT800Common European bar condition for pump/valve shafts, KV ≥ 20 J with good corrosion resistance.650 MPa yield · 27 HRC
- +QT700Lowest-strength QT class in EN 10088-3; pick for large sections or where machining and toughness matter more than strength.540 MPa yield · 22 HRC
Working with 431 Hardened
Is 431 easy to machine?
Machine in the annealed or ≤32 HRC condition with rigid setups, sharp carbide, positive rake, heavy flood coolant and constant feed to avoid work hardening; expect ~40 % of 1212 and use ground/turned bar for finish-critical diameters.
Can 431 be welded?
Best avoided — air-hardening HAZ cracks readily; if required, preheat 200–300 °C, use 309/310 or matching 431 filler, weld hot and immediately post-weld temper at 620–650 °C, then slow cool.
Can 431 be formed, bent or molded?
Hot work 1150–900 °C then slow cool/anneal; cold forming is limited to gentle bends in the annealed state, and all forming should be done before hardening.
What surface finishes work on 431?
Passivate per ASTM A967 after machining/grinding; polishes to a bright finish and takes hard chrome, electroless nickel or nitriding — do not bake or plate-relieve in the 370–570 °C embrittlement window.
431 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CASTM A276 S43100: 0.20 max; EN 1.4057: 0.12–0.22 | 0.12 – 0.2 | 0.17 |
| Si | ≤ 1 | 0.5 |
| Mn | ≤ 1 | 0.6 |
| P | ≤ 0.04 | 0.03 |
| SEN 1.4057 S ≤ 0.015; free-machining sulphurised versions (BS 431S29 type) run higher | ≤ 0.03 | 0.02 |
| Cr | 15 – 17 | 16 |
| NiEN 1.4057: 1.5–2.5 | 1.25 – 2.5 | 2 |
| Monot specified in ASTM; EN permits residual Mo ≤ 0.8 | ≤ 0.8 | — |
| Fe | balance | — |
431 Hardened — frequently asked
What is 431 Hardened used for?
431 Hardened is typically used for marine propeller and rudder shafts, pump and mixer shafts, high-strength bolts and studs, valve stems and spindles, steam and gas turbine blades and aerospace fittings and linkages. In short: high-strength martensitic shafting.
What is the yield strength of 431 Hardened?
431 Hardened has a typical yield strength of 1,200 MPa (174 ksi) and a tensile strength of 1,500 MPa (218 ksi) — stronger than 98% of stainless steel grades. Strength varies by condition: see the 8 listed tempers.
Is 431 Hardened easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 100% of stainless steel grades). Machine in the annealed or ≤32 HRC condition with rigid setups, sharp carbide, positive rake, heavy flood coolant and constant feed to avoid work hardening; expect ~40 % of 1212 and use ground/turned bar for finish-critical diameters.
Can 431 Hardened be welded?
Not readily — weldability is rated poor (25/100). Best avoided — air-hardening HAZ cracks readily; if required, preheat 200–300 °C, use 309/310 or matching 431 filler, weld hot and immediately post-weld temper at 620–650 °C, then slow cool.
What surface finishes work on 431 Hardened?
Passivate per ASTM A967 after machining/grinding; polishes to a bright finish and takes hard chrome, electroless nickel or nitriding — do not bake or plate-relieve in the 370–570 °C embrittlement window.
Can 431 Hardened be formed, bent or molded?
Hot work 1150–900 °C then slow cool/anneal; cold forming is limited to gentle bends in the annealed state, and all forming should be done before hardening.
What is the maximum service temperature of 431 Hardened?
431 Hardened is rated for continuous use to about 150°C (302 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in 431 Hardened?
Yes — 431 Hardened is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A276/A276M — Stainless Steel Bars and Shapes — ASTM International (2023)
- ASTM A582/A582M — Free-Machining Stainless Steel Bars — ASTM International (2021)
- EN 10088-3 — Stainless steels: semi-finished products, bars, rods (X17CrNi16-2, 1.4057) — CEN (2014)
- AMS 5628 — Steel Bars, Forgings, 16Cr–2.0Ni — SAE International (2018)
- GB/T 1220 — (14Cr17Ni2) — SAC (2007)
- ASM Handbook Vol. 1: Properties and Selection — Irons, Steels and High-Performance Alloys — ASM International (1990)
- Martensitic stainless steel 1.4057/431 bar datasheet — European long-product mill (typical values) (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.