What CCS Grade DQ63 Shipbuilding Steel Plate Is
CCS Grade DQ63 is an extra high strength hull structural steel plate approved under the China Classification Society rules for sea-going steel ships. In the CCS designation the letter D fixes the charpy impact test temperature at −20 °C, the letter Q states that the plate is quenched and tempered, and the number 63 identifies the nominal minimum yield strength level of 630 MPa. The grade therefore sits at the top of the extra high strength group and is used where ordinary AH or DH grades cannot carry the design stress.
Because strength is obtained by quenching and tempering rather than by alloying alone, the plate combines a very high yield point with good toughness and weldability, provided the fabricator controls heat input and interpass temperature.
Chemical Composition
| Element | Content, % max |
|---|---|
| Carbon, C | 0.20 |
| Silicon, Si | 0.55 |
| Manganese, Mn | 1.70 |
| Phosphorus, P | 0.025 |
| Sulfur, S | 0.025 |
| Nitrogen, N | 0.020 |
The lean carbon and sulphur limits keep the heat-affected zone tough after welding, while manganese provides solid-solution strengthening. Fine-grain practice and a low nitrogen level are essential for meeting the impact requirement at −20 °C.
Mechanical Properties and Delivery Condition
| Property | Requirement |
|---|---|
| Minimum yield strength | 620 MPa |
| Tensile strength | 720–890 MPa |
| Minimum elongation | 15% |
| Impact test temperature | −20 °C, charpy V-notch, longitudinal |
| Delivery condition | Quenched and tempered |
Yield strength is the property that drives the design of this grade: at 620 MPa minimum it allows plate thickness to be reduced compared with a DH36 or EH40 hull, which lowers steel weight and improves payload. Tensile strength is controlled in a narrow band because both under-matching and over-matching cause problems in welded connections.
Processing and inspection options
Quenching and tempering: the mandatory route for DQ63; plate is austenitized, water quenched and tempered to a fine tempered-martensite or bainitic structure.
Ultrasonic examination: normally required for extra high strength plate used in primary hull structure.
Thickness-direction testing: Z15, Z25 or Z35 properties can be supplied for joints loaded through the plate thickness.
Charpy V-notch impact testing: performed at −20 °C in the longitudinal direction as standard, with transverse testing available.
Surface protection: shot blasting, painting or shop primer can be applied before shipment.
Where DQ63 Plate Is Used
Hull structure: shell plating and longitudinals of bulk carriers, oil tankers, container ships and general cargo vessels, where high design stress and heavy loads occur.
Decks and superstructures: strength decks, superstructure sides and bulkheads that must resist deformation under bending and torsion.
Offshore engineering: offshore platform structures, drilling rigs and floating production storage and offloading units operating in deep water.
Reinforcement and safety components: keels, ribs, frames, brackets, hatch coamings and other critical details that determine the global safety of the vessel.
DQ63 in the CCS Extra Strength Family
| Quality letter | Impact temperature | Strength levels | Delivery condition |
|---|---|---|---|
| A quality | 0 °C | AQ43 to AQ70 | As-rolled or normalized |
| D quality | −20 °C | DQ43 to DQ70 | Quenched and tempered |
| E quality | −40 °C | EQ43 to EQ70 | Quenched and tempered |
| F quality | −60 °C | FQ43 to FQ70 | Quenched and tempered |
Within the 63 strength level the DQ grade is the economical choice for temperate and tropical service areas; where the design temperature falls further, EQ63 or FQ63 should be substituted for the same strength.
Frequently Asked Questions
Q: What does the letter D mean in CCS Grade DQ63?
It defines the charpy impact test temperature of the grade, which for D quality is −20 °C.
Q: What is the minimum yield strength of DQ63 plate?
620 MPa minimum yield, with tensile strength between 720 MPa and 890 MPa and minimum elongation of 15%.
Q: Is DQ63 plate quenched and tempered?
Yes. The Q in the designation means the plate is supplied in the quenched and tempered condition, which is mandatory for all DQ, EQ and FQ extra high strength grades.
Q: Can DQ63 be welded in the same way as AH36 hull steel?
It is weldable with matching extra high strength consumables, but lower heat input, controlled interpass temperature and preheat in thick sections are needed to protect the heat-affected zone.
Q: What thickness is DQ63 available in?
Plates are commonly supplied from 6 mm to about 150 mm, in widths of 1,500 mm to 3,000 mm and lengths up to about 12,000 mm, depending on the mill rolling programme.
Q: Does the plate come with classification society certification?
Plate is supplied with the mill inspection certificate and can be issued under CCS approval for the intended hull or offshore application.
