Heavy steel plates for offshore structure and shipbuilding with yield strengths of approximately 690 MPa and low yield-ratio

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• 作者：LIU DongshengCHENG Binggui
• 会议时间：2013-06-01
• 关键词：ultrahigh strength heavy plate for shipbuilding ; intercritical annealing and quenching ; strengthening and toughening
• 作者单位：Institute of Research of Iron and Steel,Shasteel,Jinfeng Town,Zhangjiagang 215625,Jiangsu,China
• 母体文献：第五届宝钢学术年会论文集
• 会议名称：第五届宝钢学术年会
• 会议地点：上海
• 主办单位：中国金属学会
• 语种：chi

摘要

A steel composition substantially leaner than that of HSLA-100 steel was proposed in our previous work[1-5] to produce heavy plates with thickness of - 100 mm and mechanical properties equivalent to that of the HSLA-IOO.The as quenched microstructure of the industrially produced plates consisted of fine granular bainite ( GB) and lathlike bainite ( LB).Excellent combinations of room temperature yield strength ( YS) and subzero temperature Charpy V-notch toughness (CVN) ( YS >690 MPa,CVN > 100 J at -80℃ ) were achieved across the thickness section of the plates after isothermal tempering.However,the yield ratio ( YR) of quenched and tempered plates were higher than 0.95.The present work aimed to improve the stress ratio of the plates.For that,intercritical annealing followed by water quenching ( L) was inserted between quenching and tempering ( QLT) to tailor the microstructure.Integrated industrial production trials via continuous casting,thermomechanical control rolling,and varying heat treatments were conducted.The QLT-treated microstructure of the heavy plates with increased fraction of high angle grain boundaries ( HAGBs) consists of ferrite as soft phase and tempered martensite as hard phase.The martensite formed during L treatment is strengthened by Cu-bearing precipitates after tempering.The industrially produced QLT-plate exhibits YS greater than 690 MPa,improved YR lower than 0.83,and CVN toughness higher than 150 J at - 80℃.It is also proven that direct quenching followed by L ( DQ-L) is a potential substitute for the reheating and quenching steps for efficient production of the heavy plates.