Two 690 MPa Steels from Two Standard Systems
A514 Grade B is one of the high-yield-strength quenched and tempered alloy plate grades defined in ASTM A514/A514M, with a companion ASME edition. Q690E is defined in GB/T 1591, the Chinese standard for high-strength low-alloy structural steels, and is also produced under GB/T 16270 for quenched and tempered plate. Both deliver a minimum yield strength of about 690 MPa, and both are used where a structure must carry heavy loads without excessive weight, but they reach that strength by different alloy routes and carry different toughness and certification regimes.
Chemical Composition
| Element, % | A514 Grade B, ladle | A514 Grade B, product | Q690E, max |
|---|---|---|---|
| C | 0.12-0.21 | 0.10-0.23 | 0.20 |
| Mn | 0.70-1.00 | 0.66-1.04 | 1.70 |
| P | 0.035 max | 0.043 max | 0.020 |
| S | 0.035 max | 0.043 max | 0.010 |
| Si | 0.40-0.80 | 0.35-0.85 | 0.80 |
| Cr | 0.40-0.65 | 0.35-0.70 | 1.50 |
| Mo | 0.15-0.30 | 0.12-0.33 | 0.70 |
| V | 0.03-0.08 | 0.01-0.10 | 0.12 |
| B | 0.0005-0.005 | 0.0000-0.0055 | 0.005 |
| Ni | - | - | 2.00 |
| Cu | - | - | 0.50 |
| Nb / Ti | - | - | 0.06 / 0.05 |
A514 Grade B relies on a chromium-molybdenum-boron alloy recipe with a carbon range that starts at 0.12% to secure hardening, and the specification publishes separate product analysis tolerances that allow the finished plate to deviate slightly from the ladle figures. Q690E uses a wider alloy window with defined maxima for chromium, molybdenum, nickel, copper and microalloying elements, and the standard sets tighter phosphorus and sulphur ceilings, which reflects the modern practice of producing the grade from desulphurized, calcium-treated steel for improved toughness and weldability.
Mechanical Properties
| A514 Grade B | Thickness up to 2.5 in (63 mm) | Thickness 2.5-6 in (63-150 mm) |
|---|---|---|
| Yield strength min | 100 ksi (690 MPa) | 90 ksi (620 MPa) |
| Tensile strength | 110-130 ksi (760-895 MPa) | 100-130 ksi (690-895 MPa) |
| Elongation min, % | 18 | 16 |
| Brinell hardness | 235-293 HBW | 235-293 HBW |
| Q690E | Up to 50 mm | >50-100 mm | >100-150 mm |
|---|---|---|---|
| Yield strength min, MPa | 690 | 650 | 630 |
| Tensile strength, MPa | 770-940 | 760-930 | 710-900 |
| Elongation min, % | 14 | 14 | 14 |
The two strength ladders are closely comparable in the light and medium thickness range. The important practical difference appears in the toughness regime: Q690E must satisfy Charpy V-notch testing at -40 °C, the condition indicated by the letter E in the GB/T 1591 quality system, whereas impact testing in ASTM A514 is a supplementary requirement that the purchaser has to order explicitly, typically at -20 °F for Grade B. For equipment operating in cold climates, that difference decides the specification.
Applications and Grade Selection
Both grades are used for mobile and crawler crane booms and outriggers, excavator and loader structures, mining truck bodies, conveyor and crushing equipment, pressure vessel supports, bridge components and heavy transport frames. A514 Grade B is common in North American and ASME-governed projects where the design drawing already carries the ASTM or ASME designation. Q690E appears in equipment built to Chinese and GB design codes and is widely used in mining and construction machinery manufactured in Asia.
Where static strength is the only requirement, either grade can be substituted after checking that the design code, the toughness demand and the welding procedure are satisfied. Where fatigue or low-temperature toughness governs, the grade with the higher certified impact energy at the actual service temperature should be chosen, and the heat-affected zone toughness of the qualified welding procedure should be reviewed alongside the parent metal data.
Fabrication and Quality Control
Both steels are sensitive to heat input. Welding is carried out with low-hydrogen consumables matched to the 690 MPa class, with preheat, interpass temperature control and a qualified procedure qualification record. Excess heat input softens the heat-affected zone below the parent metal strength; insufficient heat input raises hardness and hydrogen cracking risk, so both upper and lower limits are written into the procedure. Where the joint carries through-thickness stress, plate with thickness-direction properties should be specified.
Cutting is done by plasma, laser, waterjet or abrasive methods, and thermally cut edges on thick plate are dressed to remove the hardened layer before welding. Forming is normally cold, with generous radii; any hot forming must be followed by re-quenching and tempering if the mechanical properties are to be maintained.
Inspection for both grades covers heat analysis, product analysis, tensile testing, Charpy testing at the ordered temperature, hardness verification and dimensional checks, documented on an inspection certificate to EN 10204. Ultrasonic examination of the plate to EN 10160 is normally available as an addition for thick plate, and third-party witnessed testing is commonly requested for crane and lifting structures where the design authority requires independent verification.
Frequently Asked Questions
Q: Are A514 Grade B and Q690E interchangeable?
A: They are comparable in strength, but substitution requires confirmation of the design code, the required impact test temperature and the welding procedure, because the toughness and certification requirements differ.
Q: Which grade has the better low-temperature toughness?
A: Q690E carries a mandatory Charpy requirement at -40 °C, while impact testing in ASTM A514 is supplementary, so Q690E is normally the simpler choice for cold service.
Q: What hardness range does A514 Grade B have?
A: The specification requires a Brinell hardness of 235-293 HBW, which also serves as a practical check that the plate has been correctly quenched and tempered.
Q: Do both grades need preheat for welding?
A: Yes for most thicknesses. A qualified procedure with preheat, controlled heat input and low-hydrogen consumables is required for both.
Q: What is the yield strength fall-off with thickness?
A: A514 Grade B drops from 690 MPa to 620 MPa above 63 mm, and Q690E falls from 690 MPa to 650 MPa above 50 mm and to 630 MPa above 100 mm.
Q: Can these plates be bent?
A: Yes, cold bending is normal with adequate radii. Hot forming above the tempering temperature requires re-quenching and tempering to restore properties.
