Difference between CCS FQ56 and CCS FQ70 steel plate

CCS FQ56 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, ensuring exceptional performance in Arctic and polar environments. It has a minimum yield strength of 550 MPa and a tensile strength range of 670-830 MPa, with a typical minimum elongation of 16-18%. Its chemical composition is strictly controlled, with carbon typically ≤0.21% and manganese ≤1.70%. This grade is designed for critical structural components in self-elevating drilling platforms, icebreakers, and Arctic-class vessels.

CCS FQ70 is an ultra-high-strength marine steel plate also certified by CCS, manufactured through quenching and tempering . The "70" denotes a minimum yield strength of 690 MPa and a tensile strength range of 770-940 MPa, with a minimum elongation of 14% . Like FQ56, it is impact tested at -60°C, with minimum impact energy requirements typically around 46J (transverse) and 62J (longitudinal) . Its chemical composition includes carbon 0.125-0.165%, Ni 0.8-1.5%, Cr 0.6-1.0%, and B 0.0008-0.0030% . 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 FQ56 and CCS FQ70 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: FQ56 offers a minimum yield strength of 550 MPa with tensile strength of 670-830 MPa, while FQ70 provides a substantially higher minimum yield strength of 690 MPa with tensile strength reaching 770-940 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