Difference between CCS FQ51 and CCS FQ70 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 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 and a tensile strength range of 610-770 MPa, with minimum elongation of approximately 16%. Its chemical composition is precisely controlled to ensure good weldability and low-temperature toughness. This grade is ideal 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 . Like FQ51, it is impact tested at -60°C, with minimum impact energy requirements of 46J (transverse) and 62J (longitudinal) . Its chemical composition includes carbon ≤0.18%, manganese ≤1.60%, and alloying elements such as Ni, Cr, Mo, and B to achieve superior strength and toughness . This grade is designed for the most demanding applications, including ultra-large container ships, jack-up rig legs, and critical marine structures requiring maximum strength-to-weight ratio.

Both CCS FQ51 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: 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 FQ70 provides a substantially higher minimum yield strength of 690 MPa with tensile strength reaching 770-940 MPa, designed for the most 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