Stainless Steel SUS431-QT900
Heat-treated state
JIS SUS431 · UNS S43100 · EN 1.4057
Higher-strength shaft/fastener condition where wear and fatigue loading are more severe but some impact ductility is still needed.
Values for the QT900 condition
Other SUS431 tempers and conditions
SUS431 is listed in 7 conditions; see the grade overview at SUS431.
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 |
QT900This page 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-QT900?
SUS431-QT900 is SUS431 heat treated to QT900 — higher-strength shaft/fastener condition where wear and fatigue loading are more severe but some impact ductility is still needed. SUS431-QT900 has a yield strength of 790 MPa (115 ksi) and a tensile strength of 970 MPa (141 ksi) — stronger than 96% of stainless steel grades. Elongation at break is 13% and the elastic modulus is 200 GPa (29 Msi). SUS431-QT900 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). QT800 is the default condition FabDigit quotes; QT900 is available on request or by drawing note.
Advantages
- High strength — 790 MPa (115 ksi), better than 96% of stainless steel grades
- Low embodied carbon — 3.6 kg CO₂/kg, better than 83% 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
- 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-QT900 properties
Typical room-temperature values for SUS431-QT900; 11 are specific to this condition. Other listed values are SUS431 reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
SUS431-QT900 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-QT900 has a yield strength of 790 MPa (115 ksi) and a tensile strength of 970 MPa (141 ksi) — stronger than 96% of stainless steel grades. Elongation at break is 13% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
SUS431-QT900 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-QT900 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-QT900 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-QT900's machinability is poor (33/100, worse than 57% of stainless steel grades); weldability poor (25/100); formability poor (25/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SUS431-QT900
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.
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.
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 | — |
SUS431-QT900 — frequently asked
What is SUS431-QT900 used for?
SUS431-QT900 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-QT900?
SUS431-QT900 has a typical yield strength of 790 MPa (115 ksi) and a tensile strength of 970 MPa (141 ksi) — stronger than 96% of stainless steel grades. Strength varies by condition: see the 7 listed tempers.
Is SUS431-QT900 easy to machine?
Not especially — machinability is rated poor (33/100, worse than 57% 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-QT900 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-QT900?
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-QT900 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-QT900?
SUS431-QT900 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.