Stainless Steel SUH3-QT (Quenched and tempered)
Heat-treated state · default condition
JIS SUH3
Standard delivered condition for engine valves: best balance of hot strength, tempering stability and toughness.
Values for the QT condition
Other SUH3 tempers and conditions
SUH3 is listed in 6 conditions; see the grade overview at SUH3.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Pick for machining, hot-worked bar stock or forging blanks before final hardening. | 550 | 830 | 22 | 22 HRC | — |
Hot rolled | Pick for as-supplied hot-rolled bar or extruded/forged valve pre-forms that will be heat treated later. | 620 | 900 | 18 | 27 HRC | 2.5 % IACS |
QTDefaultThis page Quenched and tempered | Standard delivered condition for engine valves: best balance of hot strength, tempering stability and toughness. | 780 | 1,010 | 18 | 31 HRC | — |
Q&T + gas/salt-bath nitrided stem | Pick for valve stems needing scuff/wear resistance in the guide; core stays in the Q&T condition. | 780 | 1,010 | 16 | 31 HRC | 2.5 % IACS |
Cold drawn | Pick for close-tolerance straight bar for valve stem machining where final Q&T follows. | 800 | 980 | 12 | 31 HRC | 2.5 % IACS |
Hardened + low temper (~600–650 °C), 38–45 HRC | Pick when maximum wear resistance on stem tip / seat face is needed and service temperature stays below ~550 °C. | 1,100 | 1,350 | 11 | 42 HRC | — |
What is SUH3-QT?
SUH3-QT is SUH3 heat treated to QT — standard delivered condition for engine valves: best balance of hot strength, tempering stability and toughness. SUH3-QT has a yield strength of 780 MPa (113 ksi) and a tensile strength of 1,010 MPa (146 ksi) — stronger than 95% of stainless steel grades. Elongation at break is 18% and the elastic modulus is 213 GPa (30.9 Msi). SUH3-QT has a density of 7.7 g/cm³ (0.278 lb/in³), lighter than 83% of stainless steel grades. It melts at 1,420°C (2,588 °F).
Advantages
- High strength — 780 MPa (113 ksi), better than 95% of stainless steel grades
- Low embodied carbon — 3.6 kg CO₂/kg, better than 83% of stainless steel grades
- Conducts heat well — 22 W/m·K (12.7 BTU/hr·ft·°F), better than 77% of stainless steel grades
Limitations
- Low fracture toughness — 45 MPa·√m (41 ksi·√in), worse than 95% of stainless steel grades
- Needs corrosion protection — 40/100, worse than 93% of stainless steel grades
- Difficult to weld — 25/100, worse than 92% of stainless steel grades
- Limited ductility — 18%, worse than 83% of stainless steel grades
- Limited formability — 25/100, worse than 78% of stainless steel grades
SUH3-QT properties
Typical room-temperature values for SUH3-QT; 12 are specific to this condition. Other listed values are SUH3 reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
SUH3-QT has a density of 7.7 g/cm³ (0.278 lb/in³), lighter than 83% of stainless steel grades. It melts at 1,420°C (2,588 °F).
Mechanical15
SUH3-QT has a yield strength of 780 MPa (113 ksi) and a tensile strength of 1,010 MPa (146 ksi) — stronger than 95% of stainless steel grades. Elongation at break is 18% and the elastic modulus is 213 GPa (30.9 Msi).
Thermal6
SUH3-QT is rated for continuous service to 800°C (1,472 °F). It conducts heat at 22 W/m·K (12.7 BTU/hr·ft·°F), better than 77% of stainless steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
SUH3-QT conducts electricity at 2.5 % IACS, better than 75% of stainless steel grades.
Chemical & Environmental2
Corrosion resistance is fair (40/100), worse than 93% of stainless steel grades.
Sustainability4
Producing a kilogram of SUH3-QT takes about 52 MJ of energy and emits 3.6 kg of CO₂ — less than 76% of stainless steel grades. Typical recycled content is 55%.
Manufacturability8
SUH3-QT's machinability is fair (35/100, better than 51% of stainless steel grades); weldability poor (25/100); formability poor (25/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SUH3-QT
Is SUH3 easy to machine?
Machine in the annealed or Q&T state with rigid setups, carbide tooling, moderate speeds and heavy coolant; the ~2 % Si and Cr carbides are abrasive and work-harden the surface.
Can SUH3 be welded?
Poor fusion weldability — hardenable martensite requires 250–350 °C preheat and 700–760 °C PWHT; production practice is friction (inertia) welding of the SUH3 stem to an austenitic valve head.
Can SUH3 be formed, bent or molded?
Hot forge/extrude at 1050–1150 °C, finish above 900 °C and cool slowly to avoid quench cracks; cold forming is essentially limited to thread rolling and stem straightening.
What surface finishes work on SUH3?
Grind and polish stems, then nitride, chromize or hard-chrome plate for wear surfaces; no anodizing — use phosphate or oxide coatings for storage protection.
SUH3 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 |
|---|---|---|
| C | 0.35 – 0.45 | 0.4 |
| Sihigh Si for oxidation/scaling resistance | 1.8 – 2.5 | 2.1 |
| Mn | ≤ 0.6 | 0.4 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Niresidual | ≤ 0.6 | — |
| Cr | 10 – 12 | 11 |
| Motempering stability / hot strength | 0.7 – 1.3 | 1 |
| Fe | balance | — |
SUH3-QT — frequently asked
What is SUH3-QT used for?
SUH3-QT is typically used for engine exhaust valves, high-temperature valve seats, exhaust valve stems, hot-forged valve blanks, furnace hardware and heat-resisting fasteners. In short: 800 °C valve stem steel; higher Cr than SUH1; forge hot, no cold forming.
What is the yield strength of SUH3-QT?
SUH3-QT has a typical yield strength of 780 MPa (113 ksi) and a tensile strength of 1,010 MPa (146 ksi) — stronger than 95% of stainless steel grades. Strength varies by condition: see the 6 listed tempers.
Is SUH3-QT easy to machine?
Not especially — machinability is rated fair (35/100, better than 51% of stainless steel grades). Machine in the annealed or Q&T state with rigid setups, carbide tooling, moderate speeds and heavy coolant; the ~2 % Si and Cr carbides are abrasive and work-harden the surface.
Can SUH3-QT be welded?
Not readily — weldability is rated poor (25/100). Poor fusion weldability — hardenable martensite requires 250–350 °C preheat and 700–760 °C PWHT; production practice is friction (inertia) welding of the SUH3 stem to an austenitic valve head.
What surface finishes work on SUH3-QT?
Grind and polish stems, then nitride, chromize or hard-chrome plate for wear surfaces; no anodizing — use phosphate or oxide coatings for storage protection.
Can SUH3-QT be formed, bent or molded?
Hot forge/extrude at 1050–1150 °C, finish above 900 °C and cool slowly to avoid quench cracks; cold forming is essentially limited to thread rolling and stem straightening.
What is the maximum service temperature of SUH3-QT?
SUH3-QT is rated for continuous use to about 800°C (1,472 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SUH3-QT and SUH3 QT-H?
QT is the default condition — standard delivered condition for engine valves: best balance of hot strength, tempering stability and toughness. QT-H: pick when maximum wear resistance on stem tip / seat face is needed and service temperature stays below ~550 °C. Yield strength is 780 MPa in QT versus 1,100 MPa in QT-H.
Sources
- JIS G4311 — Heat-resisting steel bars — Japanese Standards Association (2019)
- JIS G4312 — Heat-resisting steel plates and sheets — Japanese Standards Association (2019)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (valve steels) — ASM International (1990)
- ASM Specialty Handbook: Stainless Steels (martensitic Cr steels) — ASM International (1994)
- GB/T 1221 — Heat-resisting steel bars (42Cr9Si2 / 40Cr10Si2Mo) — SAC (2007)
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.