Steel Q690-QT (Quenched and tempered)
Heat-treated state · default condition
GB Q690
Standard supply condition for thick high-strength plate; best strength/toughness balance for crane booms and heavy equipment.
Values for the QT condition
Other Q690 tempers and conditions
Q690 is listed in 2 conditions; see the grade overview at Q690.
- TMCP
- QT
Compare all 2 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Thermomechanically controlled processed | Pick for lower carbon equivalent and easier field welding (less/no preheat) in medium thickness plate and welded box sections. | 715 | 830 | 17 | 22 HRC | 7.8 % IACS |
QTDefaultThis page Quenched and tempered | Standard supply condition for thick high-strength plate; best strength/toughness balance for crane booms and heavy equipment. | 730 | 850 | 16 | 25 HRC | — |
What is Q690-QT?
Q690-QT is Q690 heat treated to QT — standard supply condition for thick high-strength plate; best strength/toughness balance for crane booms and heavy equipment. Q690-QT has a yield strength of 730 MPa (106 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 83% of steel grades. Elongation at break is 16% and the elastic modulus is 206 GPa (29.9 Msi). Q690-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 — 730 MPa (106 ksi), better than 83% of steel grades
Limitations
- Difficult to machine — 40/100, worse than 77% of steel grades
Q690-QT properties
Typical room-temperature values for Q690-QT; 11 are specific to this condition. Other listed values are Q690 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
Q690-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
Q690-QT has a yield strength of 730 MPa (106 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 83% of steel grades. Elongation at break is 16% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
Q690-QT is rated for continuous service to 400°C (752 °F). It conducts heat at 40 W/m·K (23.1 BTU/hr·ft·°F), worse than 64% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
Q690-QT conducts electricity at 7.6 % IACS, worse than 65% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of Q690-QT takes about 26 MJ of energy and emits 2.1 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 25%.
Manufacturability5
Q690-QT's machinability is fair (40/100, worse than 77% of steel grades); weldability good (65/100); formability fair (40/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Q690-QT
Is Q690 easy to machine?
Machine as a ~255 HB Q&T alloy steel: rigid setups, coated carbide, 80–140 m/min turning, moderate feeds; avoid dry grinding that can re-temper or crack the surface.
Can Q690 be welded?
Use low-hydrogen consumables matching ~690 MPa, preheat 100–150 °C (thickness/CEV dependent), interpass ≤250 °C and controlled heat input to protect HAZ toughness; no PWHT above the tempering temperature.
Can Q690 be formed, bent or molded?
Cold-bend transverse to rolling direction with minimum inner radius ≈3t (roll-form rather than press where possible); hot forming above ~580 °C destroys the Q&T condition and requires re-heat-treatment.
What surface finishes work on Q690?
No inherent corrosion resistance — shot-blast to Sa 2.5 and apply epoxy/zinc-rich primer systems; if hot-dip galvanizing, watch for liquid-metal-assisted and hydrogen embrittlement risks in high-strength sections.
Q690 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 some thick Q&T plate per GB/T 16270 | ≤ 0.18 | 0.15 |
| Si | ≤ 0.6 | 0.3 |
| Mn | ≤ 2 | 1.5 |
| P≤0.020 for D, ≤0.020/0.018 for E/F | ≤ 0.03 | 0.01 |
| S≤0.010 for E, ≤0.008 for F | ≤ 0.02 | 0.01 |
| Nbmicro-alloying | ≤ 0.11 | 0.04 |
| V | ≤ 0.2 | 0.05 |
| Ti | ≤ 0.05 | 0.02 |
| Cr | ≤ 1 | 0.4 |
| Nihigher for E/F grades | ≤ 0.8 | 0.3 |
| Cu | ≤ 0.8 | 0.2 |
| Mo | ≤ 0.3 | 0.2 |
| Bhardenability booster in Q&T plate | ≤ 0 | 0 |
| Altotal Al | ≥ 0.02 | 0.03 |
| N | ≤ 0.02 | 0.01 |
| Fe | balance | — |
Q690-QT — frequently asked
What is Q690-QT used for?
Q690-QT is typically used for excavator arms, mobile crane sections and mining equipment. In short: 690 MPa-class Q&T plate; maximum structural strength-to-weight; restricted cold formability.
What is the yield strength of Q690-QT?
Q690-QT has a typical yield strength of 730 MPa (106 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 83% of steel grades. Strength varies by condition: see the 2 listed tempers.
Is Q690-QT easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Machine as a ~255 HB Q&T alloy steel: rigid setups, coated carbide, 80–140 m/min turning, moderate feeds; avoid dry grinding that can re-temper or crack the surface.
Can Q690-QT be welded?
Yes — weldability is rated good (65/100). Use low-hydrogen consumables matching ~690 MPa, preheat 100–150 °C (thickness/CEV dependent), interpass ≤250 °C and controlled heat input to protect HAZ toughness; no PWHT above the tempering temperature.
What surface finishes work on Q690-QT?
No inherent corrosion resistance — shot-blast to Sa 2.5 and apply epoxy/zinc-rich primer systems; if hot-dip galvanizing, watch for liquid-metal-assisted and hydrogen embrittlement risks in high-strength sections.
Can Q690-QT be formed, bent or molded?
Cold-bend transverse to rolling direction with minimum inner radius ≈3t (roll-form rather than press where possible); hot forming above ~580 °C destroys the Q&T condition and requires re-heat-treatment.
What is the maximum service temperature of Q690-QT?
Q690-QT 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 Q690-QT and Q690 TMCP?
QT is the default condition — standard supply condition for thick high-strength plate; best strength/toughness balance for crane booms and heavy equipment. TMCP: pick for lower carbon equivalent and easier field welding (less/no preheat) in medium thickness plate and welded box sections. Yield strength is 730 MPa in QT versus 715 MPa in TMCP.
Sources
- EN 10025-6 Hot rolled products of structural steels — quenched and tempered plates (S690Q/QL/QL1) — CEN (2019)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- High-strength quenched & tempered structural plate datasheets (S690Q/Q690 class) — Steel plate producers (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.