Stainless Steel 431 · heat-treated state
Stainless Steel 431 +QT900
Properties of the +QT900 condition, compared with the other 431 tempers.
Highest standard EN QT class; use where strength governs and impact requirement is modest (KV ≥ 15 J).
What is 431 +QT900?
431 +QT900 is 431 heat treated to +QT900 — highest standard EN QT class; use where strength governs and impact requirement is modest (KV ≥ 15 J). 431 +QT900 has a yield strength of 750 MPa (109 ksi) and a tensile strength of 970 MPa (141 ksi) — stronger than 93% of stainless steel grades. Elongation at break is 13% and the elastic modulus is 200 GPa (29 Msi). 431 +QT900 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; +QT900 is available on request or by drawing note.
Advantages
- High strength — 750 MPa (109 ksi), better than 93% 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 — 13%, worse than 93% 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
- Needs corrosion protection — 48/100, worse than 81% of stainless steel grades
- Limited formability — 25/100, worse than 79% of stainless steel grades
431 +QT900 properties
Typical room-temperature values for 431 +QT900 — 9 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 +QT900 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 +QT900 has a yield strength of 750 MPa (109 ksi) and a tensile strength of 970 MPa (141 ksi) — stronger than 93% of stainless steel grades. Elongation at break is 13% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
431 +QT900 is rated for continuous service to 450°C (842 °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 +QT900 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 +QT900 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 +QT900's machinability is fair (35/100, better than 51% 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 +QT900
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 +QT900 — frequently asked
What is 431 +QT900 used for?
431 +QT900 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 +QT900?
431 +QT900 has a typical yield strength of 750 MPa (109 ksi) and a tensile strength of 970 MPa (141 ksi) — stronger than 93% of stainless steel grades. Strength varies by condition: see the 8 listed tempers.
Is 431 +QT900 easy to machine?
Not especially — machinability is rated fair (35/100, better than 51% 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 +QT900 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 +QT900?
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 +QT900 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 +QT900?
431 +QT900 is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in 431 +QT900?
Yes — 431 +QT900 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.