Steel SHY785 QT-THK
Finish state
Use for thick penstock shells/branch pipes; mid-thickness properties fall slightly due to lower quench severity.
Values for the QT-THK condition
Other SHY785 tempers and conditions
SHY785 is listed in 5 conditions; see the grade overview at SHY785.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Quenched, tempered and post-weld stress relieved | Condition of the finished weldment after SR annealing; expect a modest strength drop and slightly higher toughness. | 820 | 940 | 19 | 29 HRC | 7.2 % IACS |
QT-THKThis page QT | Use for thick penstock shells/branch pipes; mid-thickness properties fall slightly due to lower quench severity. | 820 | 950 | 17 | 29 HRC | 7.2 % IACS |
Q&T, low carbon-equivalent grade for improved weldability | Pick when field welding with reduced preheat is required; lower Ceq/Pcm at the same strength class. | 840 | 960 | 18 | 30 HRC | 7.3 % IACS |
Q&T grade qualified for post-weld stress-relief service | Choose for heavy weldments that must be PWHT/SR-annealed after fabrication without losing the 785 MPa yield class. | 845 | 960 | 18 | 30 HRC | 7.2 % IACS |
QTDefault Quenched and tempered | Standard mill-supplied condition for penstock and heavy welded structures up to ~50 mm thick. | 855 | 980 | 17 | 31 HRC | 7.2 % IACS |
What is SHY785 QT-THK?
SHY785 QT-THK is SHY785 supplied in the QT-THK condition — use for thick penstock shells/branch pipes; mid-thickness properties fall slightly due to lower quench severity. SHY785 QT-THK has a yield strength of 820 MPa (119 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 87% of steel grades. Elongation at break is 17% and the elastic modulus is 206 GPa (29.9 Msi). SHY785 QT-THK has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,450°C (2,642 °F). QT is the default condition FabDigit quotes; QT-THK is available on request or by drawing note.
Advantages
- High strength — 820 MPa (119 ksi), better than 87% of steel grades
Limitations
- Difficult to machine — 35/100, worse than 84% of steel grades
SHY785 QT-THK properties
Typical room-temperature values for SHY785 QT-THK; 22 are specific to this condition. Other listed values are SHY785 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SHY785 QT-THK has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,450°C (2,642 °F).
Mechanical16
SHY785 QT-THK has a yield strength of 820 MPa (119 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 87% of steel grades. Elongation at break is 17% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
SHY785 QT-THK is rated for continuous service to 350°C (662 °F). It conducts heat at 36 W/m·K (20.8 BTU/hr·ft·°F), worse than 73% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
SHY785 QT-THK conducts electricity at 7.2 % IACS, worse than 71% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of SHY785 QT-THK takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 25%.
Manufacturability5
SHY785 QT-THK's machinability is fair (35/100, worse than 84% of steel grades); weldability fair (48/100); formability poor (25/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SHY785 QT-THK
Is SHY785 easy to machine?
Machine as a ~300 HB Q&T steel: rigid setup, coated carbide, moderate speed (60–110 m/min) and generous feed to stay below the work-hardened skin.
Can SHY785 be welded?
Weldable with low-hydrogen SMAW/FCAW/SAW consumables of matching 780–890 MPa class; use 100–150 °C preheat (higher for thick sections), control interpass ≤230 °C and limit heat input to protect HAZ toughness.
Can SHY785 be formed, bent or molded?
Cold bend with inside radius ≥3–4 t across the rolling direction; hot forming above the tempering temperature destroys the Q&T properties and requires re-heat-treatment.
What surface finishes work on SHY785?
Blast-clean and apply epoxy/zinc-rich coating systems (penstock interiors) — the steel has no inherent corrosion resistance; avoid electroplating processes that risk hydrogen embrittlement at this strength.
SHY785 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 |
|---|---|---|
| Cladle analysis; low C for weldability | ≤ 0.18 | 0.14 |
| Si | 0.15 – 0.55 | 0.3 |
| Mn | 0.6 – 1.5 | 1.05 |
| P | ≤ 0.03 | 0.01 |
| S | ≤ 0.03 | 0.01 |
| Cuoptional | ≤ 0.5 | 0.2 |
| Nitoughness | 0.3 – 1.5 | 0.9 |
| Crhardenability | 0.3 – 1 | 0.55 |
| Motemper resistance | 0.2 – 0.7 | 0.45 |
| Voptional microalloy | 0.01 – 0.1 | 0.04 |
| Boptional, hardenability | 5×10⁻⁴ – 0.01 | 0 |
| CeqIIW carbon equivalent, thickness dependent | ≤ 0.62 | 0.56 |
| Fe | balance | — |
SHY785 QT-THK — frequently asked
What is SHY785 QT-THK used for?
SHY785 QT-THK is typically used for penstocks, pressure pipe structures and heavy welded frames. In short: 890 MPa-class structural plate; higher yield than SHY685; penstock-grade weldable steel.
What is the yield strength of SHY785 QT-THK?
SHY785 QT-THK has a typical yield strength of 820 MPa (119 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 87% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is SHY785 QT-THK easy to machine?
Not especially — machinability is rated fair (35/100, worse than 84% of steel grades). Machine as a ~300 HB Q&T steel: rigid setup, coated carbide, moderate speed (60–110 m/min) and generous feed to stay below the work-hardened skin.
Can SHY785 QT-THK be welded?
With care — weldability is rated fair (48/100). Weldable with low-hydrogen SMAW/FCAW/SAW consumables of matching 780–890 MPa class; use 100–150 °C preheat (higher for thick sections), control interpass ≤230 °C and limit heat input to protect HAZ toughness.
What surface finishes work on SHY785 QT-THK?
Blast-clean and apply epoxy/zinc-rich coating systems (penstock interiors) — the steel has no inherent corrosion resistance; avoid electroplating processes that risk hydrogen embrittlement at this strength.
Can SHY785 QT-THK be formed, bent or molded?
Cold bend with inside radius ≥3–4 t across the rolling direction; hot forming above the tempering temperature destroys the Q&T properties and requires re-heat-treatment.
What is the maximum service temperature of SHY785 QT-THK?
SHY785 QT-THK is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SHY785-QT and SHY785 QT-THK?
QT is the default condition — standard mill-supplied condition for penstock and heavy welded structures up to ~50 mm thick. QT-THK: use for thick penstock shells/branch pipes; mid-thickness properties fall slightly due to lower quench severity. Yield strength is 855 MPa in QT versus 820 MPa in QT-THK.
Sources
- JIS G3128 Higher yield strength steel plates for welded structure — JSA (2009)
- EN 10025-6 Hot rolled products of structural steels — Flat products of high yield strength structural steels in the quenched and tempered condition (S890Q) — CEN (2019)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.19: Fatigue and Fracture — ASM International (1996)
- High-strength quenched and tempered plate datasheets (WEL-TEN / Q&T penstock plate class) — Japanese and Chinese plate mills (2023)
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.