Reading the CCSEH620 Grade Designation
CCSEH620 is an ultra high strength marine structural steel plate certified under classification society rules. The designation gives four pieces of information. The prefix identifies the certification society under whose rules the plate is approved. The letter E is the quality grade, and in ship steel designations it corresponds to Charpy V-notch impact testing at minus 40 degrees Celsius. The letter H marks a high strength grade rather than a normal strength grade. The number 620 is the minimum yield strength in megapascals.
The quality letters used in marine steel follow a fixed sequence. For the normal strength grades numbered 235, the letters A, B, D and E mean impact testing at plus 20, zero, minus 20 and minus 40 degrees Celsius. For the high strength and ultra high strength series the same quality letter is attached to the strength number, so EH620 and FH620 share a yield level of 620 MPa but are tested at minus 40 and minus 60 degrees Celsius respectively. A designer chooses between them on the minimum design temperature of the structure, not on strength.
Properties and Delivery Requirements
| Item | EH620 requirement |
|---|---|
| Minimum yield strength | 620 MPa |
| Impact test temperature | Minus 40 degrees Celsius, Charpy V-notch |
| Delivery condition | Quenched and tempered, or thermo-mechanically rolled plus tempering, depending on grade and mill route |
| Typical size range | 3 mm to 80 mm thick, 1500 mm to 4000 mm wide, 4000 mm to 19000 mm long |
| Supplementary options | Through thickness properties to GB/T 5313, ultrasonic testing to GB/T 2970, restricted dimensional tolerances |
The steel is produced to GB/T 712-2011, which lists the grades A, B, D and E, the high strength grades from AH32 to FH40, and the ultra high strength grades including AH420 through FH690, with the 620 MPa level appearing as AH620, DH620, EH620 and FH620. Certification under classification society rules is added when the plate is destined for a classed hull or offshore structure, and the approval mark is applied to the plate along with the heat number, grade and dimensions.
Hull, Deck and Machinery Applications
Hull shells and shell plating in regions where high strength is combined with moderate low temperature exposure.
Deck machinery foundations and seatings, where concentrated loads meet a welded structure.
Internal hull structures, bulkhead stiffeners and heavy brackets.
Cut marine parts, profiles and fabricated components produced from plate rather than from castings.
Flange gears, bearing housings and shafting support components.
Offshore and harbour structures where a 620 MPa class is required at a design temperature above minus 40 degrees Celsius.
These components share a pattern: they carry high local load, they are welded into a restrained structure, and they cannot be replaced in service. That combination is what drives the specification of an ultra high strength plate with a certified low temperature impact result, rather than a higher strength level alone.
Fabrication Practice for a 620 MPa Plate
Welding is the critical operation. The higher strength level brings higher hardenability, so a qualified welding procedure is required, low-hydrogen consumables must be used, and preheat and interpass temperatures have to be controlled within the range established by the procedure qualification. Heat input is kept inside a defined window: too low a heat input raises the cooling rate and the hardness in the heat affected zone, while excessive heat input coarsens the grain and reduces toughness. The steel is normally supplied with a controlled carbon equivalent to make that window practicable.
Cutting should produce a clean edge with minimal thermal damage. Plasma and waterjet cutting are preferred for parts that will be highly stressed, and flame cut edges should be dressed where fatigue loading is present. Where the plate is bent, allowance is made for higher springback than with normal strength ship steel, and the minimum bend radius is increased accordingly.
Ordering, Testing and Documentation
An order for EH620 plate should state the grade, the standard, the impact test temperature, the delivery condition, the plate size and the inspection level, plus the classification society whose certification is required. The same grade can be supplied under the rules of the major international societies, and the marking requirement differs slightly between them, so the certificate and the plate mark must be aligned with the project specification before rolling starts.
Where the connection design produces high restraint through the plate thickness, through thickness properties to GB/T 5313 in the Z15, Z25 or Z35 grades should be ordered to control the short transverse reduction of area and reduce the risk of lamellar tearing. Ultrasonic testing to GB/T 2970 or to the relevant society requirement should be specified for critical plates. Documentation issued with the consignment includes the mill certificate with chemical analysis and mechanical results, the classification certificate, the ultrasonic test report where applicable, and packing and marking details that allow each plate to be identified on site.
Frequently Asked Questions
Q: What is the difference between EH620 and FH620?
A: Both have a minimum yield strength of 620 MPa. EH620 is impact tested at minus 40 degrees Celsius and FH620 at minus 60 degrees Celsius, so the choice depends on the lowest design temperature of the structure.
Q: What does the quality letter E mean in ship steel?
A: In the normal strength series A, B, D and E correspond to impact testing at plus 20, zero, minus 20 and minus 40 degrees Celsius. The same letters carry the same meaning when attached to a high strength grade number.
Q: Is through thickness property testing necessary?
A: It is necessary where heavily restrained welds pull through the plate thickness. Ordering Z15, Z25 or Z35 to GB/T 5313 controls the relevant property and reduces the risk of lamellar tearing.
Q: How is the plate certified?
A: Certification is issued under classification society rules in addition to the mill certificate. The approval mark, heat number, grade and dimensions are marked on the plate so that it can be traced back to the test results.
Q: Can the plate be cut and formed on site?
A: Yes, but plasma or waterjet cutting is preferred for stressed parts, edges should be dressed, and the higher springback of a 620 MPa steel must be allowed for in bending and press work.
