Stainless Steel SUH3
JIS SUH3
SUH3 is a JIS silicon-chromium martensitic heat-resisting steel with about 2 % Si and higher chromium than SUH1, giving better hot corrosion and scale resistance.
Reference datasheet — SUH3 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 QT condition
SUH3 tempers and conditions
SUH3 is supplied in 6 conditions, soft to hard. QT is the default FabDigit quotes; the values on this page are for it.
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 |
QTDefault 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?
SUH3 is a JIS silicon-chromium martensitic heat-resisting steel with about 2 % Si and higher chromium than SUH1, giving better hot corrosion and scale resistance. Quenched and tempered it provides roughly 780 MPa yield, 1010 MPa tensile, 18 % elongation and 295 HB (31 HRC), with a maximum service temperature of 800 °C; it is supplied as hot-rolled and cold-drawn bar and forged valve stems. The trade-offs are abrasive, work-hardening machining behaviour (score 35), poor fusion weldability and no useful cold formability. SUH1 is the lower-cost option where 750 °C service is sufficient. SUH3 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). SUH3 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).
What is SUH3 used for?
- Engine exhaust valves
- High-temperature valve seats
- Exhaust valve stems
- Hot-forged valve blanks
- Furnace hardware
- Heat-resisting fasteners
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 properties
Typical room-temperature values for SUH3-QT; bars are the position among stainless steel grades.
Physical3
SUH3 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 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 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 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 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'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. 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. SUH3 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SUH3
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.
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 |
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.
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
How much does SUH3 cost?
SUH3 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.
SUH3 — frequently asked
What is SUH3 used for?
SUH3 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?
SUH3 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 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 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?
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 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?
SUH3 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.
How much does SUH3 cost?
SUH3 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 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; 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.