Difference between CCS FQ51 and CCS FQ56 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 the extremely low temperature of -60°C . 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 of 16-18% . This grade features strictly controlled chemical composition, with a maximum carbon content of approximately 0.16% to enhance weldability . It is designed for critical structural components in self-elevating drilling platforms, icebreakers, and Arctic-class vessels.

CCS FQ56 is also an ultra-high-strength marine steel plate certified by CCS, manufactured through quenching and tempering (QT) . The "56" denotes a minimum yield strength of 550 MPa and tensile strength ranging from 670 to 835 MPa, with minimum elongation of 16% . 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 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 FQ56 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 FQ56 provides a substantially higher minimum yield strength of 550 MPa with tensile strength reaching 670-835 MPa, designed for more demanding load-bearing applications requiring superior strength . Both grades feature strictly controlled chemical composition and maintain good weldability for critical marine service. The selection between them depends on whether the project requires the balanced strength of FQ51 or the superior performance of FQ56 for more extreme structural demands.

CCS Grade FQ51 Chemical Composition

CCS Grade FQ56 Chemical Composition

CCS Grade FQ51 Mechanical Property

CCS Grade FQ56 Mechanical Property