BV E620 and BV E690 are extra high strength quenched and tempered steel plates used in shipbuilding and offshore construction. Both grades belong to the high-strength family of the Bureau Veritas rules for the classification of steel ships, and both are delivered in the quenched and tempered condition with impact toughness verified at -40 °C. The number in each designation states the minimum yield strength in megapascals, so the whole difference between the two products can be read directly from their names: E690 offers about 70 MPa more minimum yield strength than E620.
That strength gap decides where each grade is used. E620 covers heavily loaded primary structures in which the design stress is already well above ordinary hull steel, while E690 is reserved for the most critically loaded nodes and members, where extra load-bearing capacity allows section thickness to be reduced without losing safety margin.
Chemical Composition
E620 and E690 share an identical set of maximum limits, which is typical of a quenched and tempered family: the strength difference is produced by processing and by small, tightly controlled micro-alloying adjustments rather than by a different base chemistry.
| Element, max % | BV E620 | BV E690 |
|---|---|---|
| C | 0.20 | 0.20 |
| Si | 0.55 | 0.55 |
| Mn | 1.70 | 1.70 |
| P | 0.030 | 0.030 |
| S | 0.030 | 0.030 |
| Al, min | 0.015 | 0.015 |
| N | 0.020 | 0.020 |
The low carbon content, the minimum aluminium addition and the tight sulphur limit are all there for weldability and toughness. A carbon level capped at 0.20 % keeps the carbon equivalent low enough for field welding of thick sections, while the aluminium addition ensures a fine grain size that supports the -40 °C Charpy requirement.
Mechanical Properties and Impact Energy
| Property | BV E620 | BV E690 |
|---|---|---|
| Yield strength, min | 620 MPa | 690 MPa |
| Tensile strength | 720-890 MPa | 770-940 MPa |
| Elongation, min | 15% | 14% |
| Impact test temperature | -40 °C | -40 °C |
| Impact energy, transverse | 41 J | 46 J |
| Impact energy, longitudinal | 62 J | 69 J |
The impact figures are the minimum absorbed energy values for the two test directions. As with all quenched and tempered plate, the values must be achieved in the delivered condition, and any subsequent hot forming or post-weld heat treatment has to be evaluated against the class rules before the material properties can be relied on.
Quenching and Tempering: Why E690 Is Stronger
Both grades are produced by heating the plate to the austenitizing range, quenching it rapidly in water to form a hard martensitic structure, and then tempering it at a controlled temperature. The tempering step is what restores ductility and notch toughness after the quench, and the exact combination of quench severity, tempering temperature and micro-alloying additions is what separates a 620 MPa product from a 690 MPa product.
The consequence for fabrication is a steeper demand on the workshop. Higher strength means a higher yield-to-tensile consideration, greater restraint stress around welds, and tighter limits on heat input. Welding procedures for E690 normally require controlled preheat, low-hydrogen consumables matched to the base metal, and careful qualification of any repair welding.
Applications and Selection
Choose BV E620 for primary hull structures, decks, hatch coamings and offshore components where a 620 MPa minimum yield strength satisfies the design stress with a practical plate thickness.
Choose BV E690 for the most highly stressed nodes, heavy lift structures, crane pedestals and offshore connection details where reducing section thickness or weight is a real design benefit.
Stay with the lower strength grade wherever the design permits it, because E620 is easier to weld, easier to form and more widely available than E690.
Confirm the grade marking, the delivery condition and the impact test temperature on the class certificate before plate is released to fabrication, and verify that the welding procedure qualification covers the grade actually supplied.
Frequently Asked Questions
Q: What is the main difference between BV E620 and BV E690?
Strength level. E620 has a minimum yield strength of 620 MPa, and E690 has 690 MPa. Tensile ranges follow the same pattern, at 720-890 MPa and 770-940 MPa respectively.
Q: Are E620 and E690 welded the same way?
No. E690 needs stricter welding control, including qualified procedures, low-hydrogen consumables, controlled heat input and usually preheat. E620 is less demanding but still calls for a procedure qualified for quenched and tempered plate.
Q: What does the E in BV E620 and BV E690 mean?
The letter identifies the high-strength quenched and tempered family in the classification rules, and the number gives the minimum yield strength in MPa. Both grades in this family are verified with Charpy impact testing at -40 °C.
Q: Do both grades have the same chemical composition?
Yes. E620 and E690 share the same maximum limits for carbon, silicon, manganese, phosphorus, sulphur, aluminium and nitrogen. The higher strength of E690 comes from processing control and small micro-alloying adjustments within those limits.
Q: Can E620 be replaced by E690 to save weight?
Only through a design review. The higher yield strength allows thinner sections, but the substitution changes stiffness, buckling behaviour, fatigue performance and weldability, so it has to be approved under the applicable design and class rules.
Q: Why is the elongation requirement lower for E690?
Elongation falls as strength rises, so the rules set a minimum of 15 % for E620 and 14 % for E690. Actual mill results are normally well above the minimum, but the certified value is what the design must assume.
Q: Is impact testing required for both grades?
Yes. Both grades are delivered with Charpy V-notch impact testing at -40 °C, with minimum energy values quoted separately for transverse and longitudinal specimens.
