Steel Q690Q-QT (Quenched and tempered)
Heat-treated state · default condition
GB Q690Q · EN S690Q
Standard stocked condition for crane booms and machinery frames up to 50 mm plate.
Values for the QT condition
Other Q690Q tempers and conditions
Q690Q is listed in 7 conditions; see the grade overview at Q690Q.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Q&T | Very heavy sections where 630 MPa minimum yield is acceptable; check hardenability with the mill. | 690 | 780 | 17 | 23 HRC | 7.2 % IACS |
Q&T | Heavy plate for thick booms and base frames; slightly lower guaranteed strength due to reduced quench rate. | 710 | 810 | 16 | 24 HRC | 7.2 % IACS |
QTDefaultThis page Quenched and tempered | Standard stocked condition for crane booms and machinery frames up to 50 mm plate. | 750 | 830 | 16 | 26 HRC | 7.2 % IACS |
Quality class C | Cheapest quality class for indoor or mild-climate structures with no low-temperature toughness demand. | 750 | 830 | 16 | 26 HRC | 7.2 % IACS |
Quality class D | Most common Chinese stock class for mobile cranes and pump-truck booms. | 750 | 830 | 16 | 26 HRC | 7.2 % IACS |
Quality class E | Cold-climate equipment (northern China, mining, offshore support); equivalent to S690QL. | 750 | 830 | 16 | 26 HRC | 7.2 % IACS |
Quality class F | Extreme low-temperature / arctic service; equivalent to S690QL1, mill order only. | 750 | 830 | 17 | 26 HRC | 7.2 % IACS |
What is Q690Q-QT?
Q690Q-QT is Q690Q heat treated to QT — standard stocked condition for crane booms and machinery frames up to 50 mm plate. Q690Q-QT has a yield strength of 750 MPa (109 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 84% of steel grades. Elongation at break is 16% and the elastic modulus is 210 GPa (30.5 Msi). Q690Q-QT 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).
Advantages
- High strength — 750 MPa (109 ksi), better than 84% of steel grades
Q690Q-QT properties
Typical room-temperature values for Q690Q-QT; 22 are specific to this condition. Other listed values are Q690Q reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
Q690Q-QT 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
Q690Q-QT has a yield strength of 750 MPa (109 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 84% of steel grades. Elongation at break is 16% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
Q690Q-QT is rated for continuous service to 350°C (662 °F). It conducts heat at 38 W/m·K (22 BTU/hr·ft·°F), worse than 69% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
Q690Q-QT conducts electricity at 7.2 % IACS, worse than 71% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (14/100), better than 70% of steel grades.
Sustainability4
Producing a kilogram of Q690Q-QT takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 22%.
Manufacturability7
Q690Q-QT's machinability is fair (42/100, worse than 73% of steel grades); weldability good (62/100); formability fair (45/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Q690Q-QT
Is Q690Q easy to machine?
Machine as ~260 HB Q&T alloy steel: rigid setups, coated carbide, moderate speeds; avoid heavy grinding heat that tempers the surface.
Can Q690Q be welded?
Low-hydrogen consumables matched to 690 MPa, preheat ~100–150 °C (CEV ≈0.55–0.65), control interpass ≤200 °C and heat input ≤2.0 kJ/mm to protect HAZ toughness; no post-weld heat treatment above the tempering temperature.
Can Q690Q be formed, bent or molded?
Cold bend transverse to rolling direction with min inner radius ≈3t (thin) to 4–5t (thick); allow for large springback and deburr flame-cut edges before bending.
What surface finishes work on Q690Q?
Shot blast and paint or zinc-rich primer; hot-dip galvanizing possible but screen for liquid-metal embrittlement and residual stress.
Q690Q 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≤0.20 for t≤50 mm | ≤ 0.2 | 0.16 |
| Si | ≤ 0.8 | 0.3 |
| Mn | ≤ 1.7 | 1.3 |
| P≤0.020 for E/F classes | ≤ 0.03 | 0.01 |
| S≤0.010 for E/F classes | ≤ 0.02 | 0.01 |
| Cr | ≤ 1.5 | 0.5 |
| Ni | ≤ 2 | 0.6 |
| Mo | ≤ 0.7 | 0.35 |
| Cu | ≤ 0.5 | 0.15 |
| V | ≤ 0.12 | 0.04 |
| Nb | ≤ 0.06 | 0.03 |
| Ti | ≤ 0.05 | 0.02 |
| B | ≤ 0.01 | 0 |
| Altotal Al, grain refining | ≥ 0.02 | 0.03 |
| N | ≤ 0.02 | 0.01 |
| Fe | balance | — |
Q690Q-QT — frequently asked
What is Q690Q-QT used for?
Q690Q-QT is typically used for cranes, excavator structures and heavy trailers. In short: entry-level high-strength Q&T; best weldability in family; S690Q equivalent.
What is the yield strength of Q690Q-QT?
Q690Q-QT has a typical yield strength of 750 MPa (109 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 84% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is Q690Q-QT easy to machine?
Not especially — machinability is rated fair (42/100, worse than 73% of steel grades). Machine as ~260 HB Q&T alloy steel: rigid setups, coated carbide, moderate speeds; avoid heavy grinding heat that tempers the surface.
Can Q690Q-QT be welded?
Yes — weldability is rated good (62/100). Low-hydrogen consumables matched to 690 MPa, preheat ~100–150 °C (CEV ≈0.55–0.65), control interpass ≤200 °C and heat input ≤2.0 kJ/mm to protect HAZ toughness; no post-weld heat treatment above the tempering temperature.
What surface finishes work on Q690Q-QT?
Shot blast and paint or zinc-rich primer; hot-dip galvanizing possible but screen for liquid-metal embrittlement and residual stress.
Can Q690Q-QT be formed, bent or molded?
Cold bend transverse to rolling direction with min inner radius ≈3t (thin) to 4–5t (thick); allow for large springback and deburr flame-cut edges before bending.
What is the maximum service temperature of Q690Q-QT?
Q690Q-QT 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 Q690Q-QT and Q690Q-Q690C?
QT is the default condition — standard stocked condition for crane booms and machinery frames up to 50 mm plate. Q690C: cheapest quality class for indoor or mild-climate structures with no low-temperature toughness demand. Yield strength is 750 MPa in QT versus 750 MPa in Q690C.
Sources
- EN 10025-6 Hot rolled products of structural steels — Flat products of high yield strength structural steels in the quenched and tempered condition — CEN (2019)
- S690QL / high-strength Q&T plate datasheet and welding recommendations — SSAB / Dillinger / (2023)
- 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)
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.