Stainless Steel SUS431-QT700
Heat-treated state
JIS SUS431 · UNS S43100 · EN 1.4057
Choose when toughness and machinability matter more than strength — large sections, impact-loaded shafts.
Values for the QT700 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 | — |
QT700This page 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-QT700?
SUS431-QT700 is SUS431 heat treated to QT700 — choose when toughness and machinability matter more than strength — large sections, impact-loaded shafts. SUS431-QT700 has a yield strength of 560 MPa (81.2 ksi) and a tensile strength of 780 MPa (113 ksi) — stronger than 85% of stainless steel grades. Elongation at break is 18% and the elastic modulus is 200 GPa (29 Msi). SUS431-QT700 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; QT700 is available on request or by drawing note.
Advantages
- High strength — 560 MPa (81.2 ksi), better than 85% 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
- Needs corrosion protection — 45/100, worse than 85% of stainless steel grades
- Limited ductility — 18%, worse than 83% 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-QT700 properties
Typical room-temperature values for SUS431-QT700; 10 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-QT700 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-QT700 has a yield strength of 560 MPa (81.2 ksi) and a tensile strength of 780 MPa (113 ksi) — stronger than 85% of stainless steel grades. Elongation at break is 18% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
SUS431-QT700 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-QT700 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-QT700 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-QT700's machinability is fair (42/100, better than 79% 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-QT700
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-QT700 — frequently asked
What is SUS431-QT700 used for?
SUS431-QT700 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-QT700?
SUS431-QT700 has a typical yield strength of 560 MPa (81.2 ksi) and a tensile strength of 780 MPa (113 ksi) — stronger than 85% of stainless steel grades. Strength varies by condition: see the 7 listed tempers.
Is SUS431-QT700 easy to machine?
Not especially — machinability is rated fair (42/100, better than 79% 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-QT700 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-QT700?
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-QT700 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-QT700?
SUS431-QT700 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.