Difference between CCS FQ47 and CCS FQ51 steel plate

CCS FQ47 is an extra-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 460 MPa and a tensile strength range of 570-720 MPa, with minimum elongation of 17-19% . Its chemical composition includes carbon ≤0.21% and manganese ≤1.70% . 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 FQ51 is an ultra-high-strength marine steel plate also certified by CCS, manufactured through quenching and tempering (QT) or thermomechanical control processing (TMCP) . The "51" denotes a minimum yield strength of 500 MPa and a tensile strength range of 610-770 MPa, with minimum elongation of 16-18% . Like FQ47, it is impact tested at -60°C, with impact energy requirements typically ranging from 46J to 69J depending on specimen orientation . It has a lower maximum carbon content of 0.16% compared to FQ47, which contributes to enhanced weldability . This grade is ideal for more 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 FQ51 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 FQ51 provides a higher minimum yield strength of 500 MPa with tensile strength reaching 610-770 MPa, designed for more demanding load-bearing applications requiring superior strength . Additionally, FQ51 has a lower maximum carbon content (0.16% vs. 0.21%), which can offer enhanced weldability for critical fabrication . Both grades feature strictly controlled chemical composition and maintain good weldability for critical marine service.

CCS Grade FQ47 Chemical Composition

CCS Grade FQ51 Chemical Composition

CCS Grade FQ47 Mechanical Property

CCS Grade FQ51 Mechanical Property