Difference between CCS FQ51 and CCS FQ63 steel plate

CCS FQ51 is an ultra-high-strength marine steel plate certified by the China Classification Society (CCS) for demanding offshore and shipbuilding applications. The "FQ" designation signifies that it is a quenched and tempered steel with impact toughness tested at -60°C, ensuring exceptional performance in Arctic and polar environments . It has a minimum yield strength of 500 MPa (73 ksi) and a tensile strength range of 610-770 MPa (88-112 ksi), with minimum elongation typically around 16-18% . The chemical composition is strictly controlled with a low carbon equivalent (Ceq) to ensure good weldability. This grade is ideal for critical structural components in self-elevating drilling platforms, icebreakers, and Arctic-class vessels.

CCS FQ63 is also an ultra-high-strength marine steel plate certified by CCS, manufactured through quenching and tempering (QT). The "63" denotes a minimum yield strength of 620 MPa and tensile strength ranging from 720 to 890 MPa, with minimum elongation of approximately 15% . Like FQ51, it is impact tested at -60°C, with minimum impact energy requirements typically around 46J (transverse) and 69J (longitudinal) . The chemical composition is precisely controlled, featuring a low carbon content to maintain high strength while ensuring good weldability. This grade is designed for the most demanding applications such as ultra-large container ships, jack-up rig legs, and critical marine structures requiring maximum strength-to-weight ratio.

Both CCS FQ51 and CCS FQ63 are CCS-certified quenched and tempered marine steels with exceptional low-temperature toughness tested at -60°C, ensuring reliable performance in the most extreme Arctic and harsh marine environments . Their primary difference lies in strength level: FQ51 offers a minimum yield strength of 500 MPa with tensile strength of 610-770 MPa, suitable for high-strength offshore platforms and ice-class vessels, while FQ63 provides a substantially higher minimum yield strength of 620 MPa with tensile strength reaching 720-890 MPa, designed for more demanding load-bearing applications requiring maximum weight reduction. Both grades feature strictly controlled chemical composition and maintain good weldability for critical marine service.

Chemical Composition

Mechanical Property