What are difference between CCS FQ47 and CCS FQ70 steel plate？

CCS FQ47 is an extra-high-strength marine steel plate certified by the China Classification Society (CCS) . 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 460 MPa and tensile strength ranging from 570 to 720 MPa . Minimum elongation is typically 17% . Its chemical composition is strictly controlled to ensure good weldability, with carbon equivalent (Ceq) limits specified by CCS rules . This grade is designed for critical structural components in offshore drilling rigs, ice-class vessels, and Arctic marine environments requiring exceptional low-temperature toughness.

CCS FQ70 is an ultra-high-strength marine steel plate also certified by CCS, manufactured through quenching and tempering (QT) or thermomechanical control processing (TMCP) . The "70" denotes a minimum yield strength of 690 MPa and tensile strength ranging from 770 to 940 MPa, with minimum elongation of 14% . Like FQ47, it is impact tested at -60°C, with minimum impact energy requirements of 46J (transverse) and 62J (longitudinal) . The chemical composition features a maximum carbon content of 0.18% , which is lower than FQ47's typical limit, contributing to enhanced weldability while maintaining high strength . This grade is designed for the most demanding applications such as self-elevating drilling platforms, ultra-large container ships, and critical marine structures requiring maximum strength-to-weight ratio.

Both CCS FQ47 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: FQ47 offers a minimum yield strength of 460 MPa with tensile strength of 570-720 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 . Additionally, FQ70 typically has a lower maximum carbon content (0.18% vs. approximately 0.21% for FQ47), which can offer enhanced weldability for critical fabrication . Both grades feature strictly controlled chemical composition and maintain good weldability for critical marine service.

Chemical Composition

Mechanical Property