Stainless Steel SUH4-QT (Quenched and tempered)
Heat-treated state · default condition
JIS SUH4
Standard delivery/service condition for exhaust valves and high-temperature fasteners: ~300 HB with stable high-temperature strength.
Values for the QT condition
Other SUH4 tempers and conditions
SUH4 is listed in 6 conditions; see the grade overview at SUH4.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Choose for hot forging of valve blanks or for rough machining before final hardening. | 500 | 820 | 18 | 27 HRC | — |
Cold drawn | Pick for close-tolerance valve-stem or fastener blanks where a bright, straight bar is machined before final heat treatment. | 650 | 900 | 10 | 31 HRC | 2.2 % IACS |
Hot rolled | Mill-supplied stock condition for re-heating and forging; hard and low in toughness, normally annealed or Q&T before use. | 700 | 1,050 | 8 | 36 HRC | 2.1 % IACS |
QTDefaultThis page Quenched and tempered | Standard delivery/service condition for exhaust valves and high-temperature fasteners: ~300 HB with stable high-temperature strength. | 730 | 950 | 12 | 32 HRC | — |
Quenched, tempered and gas/salt-bath nitrided stem surface | Standard finish for exhaust-valve stems: hard nitrided case for wear/scuffing resistance on a tempered martensitic core. | 730 | 950 | 11 | 32 HRC | 2.2 % IACS |
Quenched and low-temperature tempered | Use when maximum wear/seat hardness is needed at moderate temperature; not for sustained service above ~550 °C (tempering softening). | 1,050 | 1,300 | 5 | 41 HRC | 2.1 % IACS |
What is SUH4-QT?
SUH4-QT is SUH4 heat treated to QT — standard delivery/service condition for exhaust valves and high-temperature fasteners: ~300 HB with stable high-temperature strength. SUH4-QT has a yield strength of 730 MPa (106 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 93% of stainless steel grades. Elongation at break is 12% and the elastic modulus is 215 GPa (31.2 Msi). SUH4-QT has a density of 7.7 g/cm³ (0.278 lb/in³), lighter than 83% of stainless steel grades. It melts at 1,400°C (2,552 °F).
Advantages
- High strength — 730 MPa (106 ksi), better than 93% of stainless steel grades
- Low embodied carbon — 3.6 kg CO₂/kg, better than 83% of stainless steel grades
- Conducts heat well — 21 W/m·K (12.1 BTU/hr·ft·°F), better than 76% of stainless steel grades
Limitations
- Low fracture toughness — 25 MPa·√m (22.8 ksi·√in), worse than 99% of stainless steel grades
- Limited ductility — 12%, worse than 95% of stainless steel grades
- Difficult to machine — 22/100, worse than 95% of stainless steel grades
- Difficult to weld — 20/100, worse than 95% of stainless steel grades
- Limited formability — 15/100, worse than 91% of stainless steel grades
SUH4-QT properties
Typical room-temperature values for SUH4-QT; 12 are specific to this condition. Other listed values are SUH4 reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
SUH4-QT has a density of 7.7 g/cm³ (0.278 lb/in³), lighter than 83% of stainless steel grades. It melts at 1,400°C (2,552 °F).
Mechanical16
SUH4-QT has a yield strength of 730 MPa (106 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 93% of stainless steel grades. Elongation at break is 12% and the elastic modulus is 215 GPa (31.2 Msi).
Thermal6
SUH4-QT is rated for continuous service to 800°C (1,472 °F). It conducts heat at 21 W/m·K (12.1 BTU/hr·ft·°F), better than 76% of stainless steel grades. Thermal expansion is 10.8 µm/m·K (6 µin/in·°F).
Electrical3
SUH4-QT conducts electricity at 2.2 % IACS, worse than 61% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is fair (48/100), worse than 80% of stainless steel grades.
Sustainability4
Producing a kilogram of SUH4-QT takes about 55 MJ of energy and emits 3.6 kg of CO₂ — more than 50% of stainless steel grades. Typical recycled content is 40%.
Manufacturability7
SUH4-QT's machinability is poor (22/100, worse than 95% of stainless steel grades); weldability poor (20/100); formability poor (15/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SUH4-QT
Is SUH4 easy to machine?
Machine in the annealed condition with rigid setups, coated carbide, low speed and heavy positive feed; hard Cr carbides cause rapid edge wear, so finish-grind after hardening.
Can SUH4 be welded?
Poor weldability — preheat 250–350 °C, use matched or Ni-base filler and temper immediately after welding; avoid welded joints in service parts wherever possible.
Can SUH4 be formed, bent or molded?
Hot forge 1050–1150 °C with slow cooling to avoid quench cracks; essentially no cold formability.
What surface finishes work on SUH4?
Not anodizable; typical finishes are nitriding or QPQ of stems, hard-facing (Stellite) of seat faces, and aluminizing/chromizing for extra scale resistance.
SUH4 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 | 0.75 – 0.85 | 0.8 |
| Sihigh Si for scaling resistance | 1.75 – 2.25 | 2 |
| Mn | ≤ 0.6 | 0.4 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Ni | 1.15 – 1.65 | 1.4 |
| Cr | 19 – 20.5 | 19.8 |
| Fe | balance | — |
SUH4-QT — frequently asked
What is SUH4-QT used for?
SUH4-QT is typically used for engine exhaust valves, valve heads with hard-faced seats, high-temperature engine components, hot-forged valve blanks and heat-resisting wear parts. In short: most oxidation-resistant valve steel; lowest machinability of group; hot forge only.
What is the yield strength of SUH4-QT?
SUH4-QT has a typical yield strength of 730 MPa (106 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 93% of stainless steel grades. Strength varies by condition: see the 6 listed tempers.
Is SUH4-QT easy to machine?
Not especially — machinability is rated poor (22/100, worse than 95% of stainless steel grades). Machine in the annealed condition with rigid setups, coated carbide, low speed and heavy positive feed; hard Cr carbides cause rapid edge wear, so finish-grind after hardening.
Can SUH4-QT be welded?
Not readily — weldability is rated poor (20/100). Poor weldability — preheat 250–350 °C, use matched or Ni-base filler and temper immediately after welding; avoid welded joints in service parts wherever possible.
What surface finishes work on SUH4-QT?
Not anodizable; typical finishes are nitriding or QPQ of stems, hard-facing (Stellite) of seat faces, and aluminizing/chromizing for extra scale resistance.
Can SUH4-QT be formed, bent or molded?
Hot forge 1050–1150 °C with slow cooling to avoid quench cracks; essentially no cold formability.
What is the maximum service temperature of SUH4-QT?
SUH4-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 SUH4-QT and SUH4 QT-High?
QT is the default condition — standard delivery/service condition for exhaust valves and high-temperature fasteners: ~300 HB with stable high-temperature strength. QT-High: use when maximum wear/seat hardness is needed at moderate temperature; not for sustained service above ~550 °C (tempering softening). Yield strength is 730 MPa in QT versus 1,050 MPa in QT-High.
Sources
- JIS G 4311 — Heat-resisting steel bars — JSA (2019)
- JIS G 4312 — Heat-resisting steel plates and sheets — JSA (2019)
- EN 10090 — Valve steels and alloys for internal combustion engines (X80CrSiNi20-2, 1.4747) — CEN (1998)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- Valve steel grade datasheets (X80CrSiNi20-2 / SUH4) — Aichi Steel / Daido Steel / Böhler (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.