Steel P690QH QT-HF
Heat-treated state
EN P690QH
QT-HF = hot formed then re-quenched and tempered
For heads, cones and tubular sections hot formed above the tempering temperature, which must be re-austenitised, quenched and tempered to restore properties.
Values for the QT-HF condition
Other P690QH tempers and conditions
P690QH is listed in 5 conditions; see the grade overview at P690QH.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
QT | Thickest standard supply range; use where section size dominates and the lower guaranteed yield is acceptable. | 680 | 790 | 18 | 22 HRC | 6.6 % IACS |
QT | Heavy plate condition — slightly reduced minimum strength because of lower quench severity through thickness. | 700 | 820 | 17 | 24 HRC | 6.6 % IACS |
quenched, tempered and post-weld stress relieved (simulated PWHT) | Choose when the fabricated vessel receives PWHT (typically 530–580 °C); expect a modest drop in yield and hardness. | 710 | 800 | 18 | 24 HRC | 6.6 % IACS |
QT-HFThis page Hot formed then re-quenched and tempered | For heads, cones and tubular sections hot formed above the tempering temperature, which must be re-austenitised, quenched and tempered to restore properties. | 735 | 830 | 17 | 26 HRC | 6.6 % IACS |
QTDefault Quenched and tempered | Standard as-delivered condition for plate up to 50 mm — full 690 MPa minimum yield with 0 °C impact guarantee. | 740 | 830 | 17 | 26 HRC | 6.6 % IACS |
What is P690QH QT-HF?
P690QH QT-HF is P690QH heat treated to QT-HF — for heads, cones and tubular sections hot formed above the tempering temperature, which must be re-austenitised, quenched and tempered to restore properties. P690QH QT-HF has a yield strength of 735 MPa (107 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 83% of steel grades. Elongation at break is 17% and the elastic modulus is 210 GPa (30.5 Msi). P690QH QT-HF has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). QT is the default condition FabDigit quotes; QT-HF is available on request or by drawing note.
Advantages
- High strength — 735 MPa (107 ksi), better than 83% of steel grades
- Tough — resists crack growth — 120 MPa·√m (109.2 ksi·√in), better than 81% of steel grades
Limitations
- Difficult to machine — 40/100, worse than 77% of steel grades
- Low electrical conductivity — 6.6 % IACS, worse than 76% of steel grades
P690QH QT-HF properties
Typical room-temperature values for P690QH QT-HF; 22 are specific to this condition. Other listed values are P690QH reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
P690QH QT-HF has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
P690QH QT-HF has a yield strength of 735 MPa (107 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 83% of steel grades. Elongation at break is 17% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
P690QH QT-HF is rated for continuous service to 400°C (752 °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
P690QH QT-HF conducts electricity at 6.6 % IACS, worse than 76% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of P690QH QT-HF takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 25%.
Manufacturability7
P690QH QT-HF's machinability is fair (40/100, worse than 77% of steel grades); weldability good (63/100); formability fair (38/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with P690QH QT-HF
Is P690QH easy to machine?
Machines like a 250–290 HB quenched-and-tempered alloy steel: rigid setups, coated carbide, moderate speed (~90–140 m/min) and generous feed to stay under the work-hardened skin.
Can P690QH be welded?
Weldable with low-hydrogen processes and matching/undermatching consumables; preheat typically 100–175 °C by thickness and CEV, interpass ≤ 200–250 °C, controlled heat input (~1.0–2.5 kJ/mm) to avoid HAZ softening and hydrogen cracking.
Can P690QH be formed, bent or molded?
Cold bend with the axis across the rolling direction, minimum inner radius about 3–4 t, ground and deburred edges; if hot formed above the tempering temperature the plate must be re-quenched and tempered.
What surface finishes work on P690QH?
No natural corrosion protection — shot blast to Sa 2½ and apply zinc-rich epoxy primer, metallising or paint; hot-dip galvanising is possible but requires review for liquid-metal-assisted cracking at this strength level.
P690QH 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 | ≤ 0.2 | 0.16 |
| Si | ≤ 0.8 | 0.35 |
| Mn | 0.8 – 1.7 | 1.3 |
| PQH grade, tighter than Q | ≤ 0.02 | 0.01 |
| SQH grade | ≤ 0.01 | 0 |
| N | ≤ 0.02 | 0.01 |
| Altotal Al, fine-grain practice | ≥ 0.02 | 0.04 |
| Cr | ≤ 1.5 | 0.5 |
| Cu | ≤ 0.5 | 0.15 |
| Mo | ≤ 0.7 | 0.5 |
| Ni | ≤ 2.5 | 1.2 |
| Nb | ≤ 0.06 | 0.03 |
| Ti | ≤ 0.05 | 0.02 |
| V | ≤ 0.12 | 0.05 |
| Zr | ≤ 0.05 | — |
| Bhardenability boost | ≤ 0.01 | 0 |
| Fe | balance | — |
P690QH QT-HF — frequently asked
What is P690QH QT-HF used for?
P690QH QT-HF is typically used for high-strength structural tubing, mobile crane booms, heavy machinery frames and offshore structural components. In short: 690 MPa hollow section; tubular P690Q equivalent; high strength-to-weight tube.
What is the yield strength of P690QH QT-HF?
P690QH QT-HF has a typical yield strength of 735 MPa (107 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 83% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is P690QH QT-HF easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Machines like a 250–290 HB quenched-and-tempered alloy steel: rigid setups, coated carbide, moderate speed (~90–140 m/min) and generous feed to stay under the work-hardened skin.
Can P690QH QT-HF be welded?
Yes — weldability is rated good (63/100). Weldable with low-hydrogen processes and matching/undermatching consumables; preheat typically 100–175 °C by thickness and CEV, interpass ≤ 200–250 °C, controlled heat input (~1.0–2.5 kJ/mm) to avoid HAZ softening and hydrogen cracking.
What surface finishes work on P690QH QT-HF?
No natural corrosion protection — shot blast to Sa 2½ and apply zinc-rich epoxy primer, metallising or paint; hot-dip galvanising is possible but requires review for liquid-metal-assisted cracking at this strength level.
Can P690QH QT-HF be formed, bent or molded?
Cold bend with the axis across the rolling direction, minimum inner radius about 3–4 t, ground and deburred edges; if hot formed above the tempering temperature the plate must be re-quenched and tempered.
What is the maximum service temperature of P690QH QT-HF?
P690QH QT-HF is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between P690QH-QT and P690QH QT-HF?
QT is the default condition — standard as-delivered condition for plate up to 50 mm — full 690 MPa minimum yield with 0 °C impact guarantee. QT-HF: for heads, cones and tubular sections hot formed above the tempering temperature, which must be re-austenitised, quenched and tempered to restore properties. Yield strength is 740 MPa in QT versus 735 MPa in QT-HF.
Sources
- EN 10028-6 — Flat products made of steels for pressure purposes, Part 6: Weldable fine grain steels, quenched and tempered — CEN (2020)
- EN 10027-2 — Designation systems for steels: material numbers (1.8880) — CEN (2015)
- EN 1011-2 — Welding: arc welding of ferritic steels — CEN (2001)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- Quenched and tempered 690 MPa pressure-vessel plate datasheets (SSAB/Dillinger/voestalpine class data) — various 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.