Stainless Steel SUS431
JIS SUS431 · UNS S43100 · EN 1.4057
SUS431 (S43100) is the JIS equivalent of AISI 431, a Cr-Ni martensitic stainless that combines high strength with better corrosion resistance than the 410/420 grades.
Reference datasheet — SUS431 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the QT800 condition
SUS431 tempers and conditions
SUS431 is supplied in 7 conditions, soft to hard. QT800 is the default FabDigit quotes; the values on this page are for it.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest supply condition for machining, drilling or subsequent hardening; still relatively hard because the alloy is air-hardening. | 520 | 800 | 20 | 24 HRC | — |
hardened and high-temperature tempered, Rm 700–850 MPa | Choose when toughness and machinability matter more than strength — large sections, impact-loaded shafts. | 560 | 780 | 18 | 21 HRC | — |
QT800Default +QT800 / JIS heat-treated | The standard stocked bar condition — best all-round balance of strength, toughness and corrosion resistance for pump/valve shafts and studs. | 680 | 880 | 16 | 27 HRC | — |
Cold drawn | Precision-size bright bar for small shafts and screw-machine parts where tight tolerance matters more than peak strength. | 750 | 900 | 12 | 29 HRC | 2.4 % IACS |
hardened and tempered, Rm 900–1050 MPa, ~30–34 HRC | Higher-strength shaft/fastener condition where wear and fatigue loading are more severe but some impact ductility is still needed. | 790 | 970 | 13 | 31 HRC | — |
Q&T low-temper | Low tempering (≈250–350 °C) for maximum strength, wear and best retained corrosion resistance; toughness is low, avoid shock loads. | 1,000 | 1,250 | 10 | 38 HRC | — |
Hardened | Intermediate condition only — must be tempered promptly; quoted for hardenability reference (≈43–46 HRC). | 1,100 | 1,450 | 5 | 44 HRC | 2.2 % IACS |
What is SUS431?
SUS431 (S43100) is the JIS equivalent of AISI 431, a Cr-Ni martensitic stainless that combines high strength with better corrosion resistance than the 410/420 grades. It is chosen for precision shafts, valve stems and high-strength fasteners, and is on file annealed, cold-drawn, hardened and in QT700–QT900 and QT-38HRC tempers; the default condition gives 680 MPa yield, 880 MPa tensile, 16 % elongation and 270 HB (27 HRC), with service to 550 °C. Being air-hardening, it welds and cold-forms poorly, and the 400–580 °C range must be avoided to prevent embrittlement. 17-4 PH is the usual alternative when higher strength and easier fabrication are both needed. SUS431 has a density of 7.7 g/cm³ (0.278 lb/in³), lighter than 83% of stainless steel grades. It melts at 1,425°C (2,597 °F). SUS431 has a yield strength of 680 MPa (98.6 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 91% of stainless steel grades. Elongation at break is 16% and the elastic modulus is 200 GPa (29 Msi).
What is SUS431 used for?
- precision shafts
- valve stems
- high-strength fasteners
Advantages
- High strength — 680 MPa (98.6 ksi), better than 91% of stainless steel grades
- Low embodied carbon — 3.6 kg CO₂/kg, better than 83% of stainless steel grades
Limitations
- Difficult to weld — 25/100, worse than 92% of stainless steel grades
- Limited ductility — 16%, worse than 88% of stainless steel grades
- Needs corrosion protection — 45/100, worse than 85% of stainless steel grades
- Low fracture toughness — 70 MPa·√m (63.7 ksi·√in), worse than 83% of stainless steel grades
- Limited formability — 25/100, worse than 78% of stainless steel grades
SUS431 properties
Typical room-temperature values for SUS431-QT800; bars are the position among stainless steel grades.
Physical3
SUS431 has a density of 7.7 g/cm³ (0.278 lb/in³), lighter than 83% of stainless steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
SUS431 has a yield strength of 680 MPa (98.6 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 91% of stainless steel grades. Elongation at break is 16% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
SUS431 is rated for continuous service to 550°C (1,022 °F). It conducts heat at 20 W/m·K (11.6 BTU/hr·ft·°F), better than 74% of stainless steel grades. Thermal expansion is 10.3 µm/m·K (5.72 µin/in·°F).
Electrical3
SUS431 conducts electricity at 2.4 % IACS, better than 67% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is fair (45/100), worse than 85% of stainless steel grades.
Sustainability4
Producing a kilogram of SUS431 takes about 53 MJ of energy and emits 3.6 kg of CO₂ — less than 67% of stainless steel grades. Typical recycled content is 60%.
Manufacturability7
SUS431's machinability is fair (38/100, better than 63% of stainless steel grades); weldability poor (25/100); formability poor (25/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. SUS431 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SUS431
Is SUS431 easy to machine?
Machine in the annealed or ≤30 HRC tempered condition with rigid setups, sharp positive-rake carbide, heavy coolant and constant feed to avoid work hardening; expect ~35 % of AISI 1212 and use chip-breaking geometry for its stringy chips.
Can SUS431 be welded?
Poor weldability — preheat 200–300 °C, use 430/309L or matching 431 filler, keep interpass hot and temper immediately after (≥650 °C) to avoid martensitic cold cracking; avoid welding in the fully hardened state.
Can SUS431 be formed, bent or molded?
Only mild cold forming in the annealed state (air-hardening alloy); hot work at 1150–1200 °C down to ~900 °C, then slow-cool/anneal before further processing.
SUS431 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 |
|---|---|---|
| CJIS G4303 SUS431 | ≤ 0.2 | 0.16 |
| Si | ≤ 1 | 0.4 |
| Mn | ≤ 1 | 0.6 |
| P | ≤ 0.04 | 0.03 |
| S | ≤ 0.03 | 0.02 |
| Ni | 1.25 – 2.5 | 2 |
| Cr | 15 – 17 | 16 |
| Fe | balance |
What surface finishes work on SUS431?
Passivate per ASTM A967 after machining; takes a good mechanical polish when hardened, and accepts hard chrome or electroless nickel for shaft wear surfaces — do not temper or bake in the 400–580 °C embrittlement range.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Passivation
Organic Coating
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel SUS431 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
How much does SUS431 cost?
SUS431 is a standard-cost stainless steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SUS431 — frequently asked
What is SUS431 used for?
SUS431 is typically used for precision shafts, valve stems and high-strength fasteners. In short: strongest 400-series martensitic; better corrosion than 420; air-hardening, poor weldability.
What is the yield strength of SUS431?
SUS431 has a typical yield strength of 680 MPa (98.6 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 91% of stainless steel grades. Strength varies by condition: see the 7 listed tempers.
Is SUS431 easy to machine?
Not especially — machinability is rated fair (38/100, better than 63% of stainless steel grades). Machine in the annealed or ≤30 HRC tempered condition with rigid setups, sharp positive-rake carbide, heavy coolant and constant feed to avoid work hardening; expect ~35 % of AISI 1212 and use chip-breaking geometry for its stringy chips.
Can SUS431 be welded?
Not readily — weldability is rated poor (25/100). Poor weldability — preheat 200–300 °C, use 430/309L or matching 431 filler, keep interpass hot and temper immediately after (≥650 °C) to avoid martensitic cold cracking; avoid welding in the fully hardened state.
What surface finishes work on SUS431?
Passivate per ASTM A967 after machining; takes a good mechanical polish when hardened, and accepts hard chrome or electroless nickel for shaft wear surfaces — do not temper or bake in the 400–580 °C embrittlement range.
Can SUS431 be formed, bent or molded?
Only mild cold forming in the annealed state (air-hardening alloy); hot work at 1150–1200 °C down to ~900 °C, then slow-cool/anneal before further processing.
What is the maximum service temperature of SUS431?
SUS431 is rated for continuous use to about 550°C (1,022 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SUS431-QT800 and SUS431-H?
QT800 is the default condition — the standard stocked bar condition — best all-round balance of strength, toughness and corrosion resistance for pump/valve shafts and studs. H: intermediate condition only — must be tempered promptly; quoted for hardenability reference (≈43–46 HRC). Yield strength is 680 MPa in QT800 versus 1,100 MPa in H.
How much does SUS431 cost?
SUS431 is a standard-cost stainless steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- JIS G4303 Stainless steel bars — JSA (2021)
- EN 10088-3 X17CrNi16-2 (1.4057) — CEN (2014)
- ASTM A276 / A479 (UNS S43100) — ASTM (2023)
- GB/T 1220 1Cr17Ni2 (14Cr17Ni2) — SAC (2007)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- Martensitic stainless bar datasheet (431 / 1.4057) — Sandvik / Outokumpu (2020)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.