控冷工艺下组织及M/A岛对管线钢韧性的影响  

Influence of microstructure and M/A island evolution on toughness of pipeline steel under controlled cooling process

作　　者：牛延龙[1] 刘清友[1] 贾书君[1] 童帅 汪兵[1] 任毅 NIU Yan-long;LIU Qing-you;JIA Shu-jun;TONG Shuai;WANG Bing;REN Yi(Institute of Structural Steels,Central Iron and Steel Research Institute,Beijing 100081,China;State Key Laboratory of Metal Materials and Applications for Marine Equipment,Anshan 114009,Liaoning,China)

机构地区：[1]钢铁研究总院工程用钢研究所,北京100081 [2]海洋装备用金属材料及其应用国家重点实验室,辽宁鞍山114009

出　　处：《钢铁》2020年第6期91-100,共10页Iron and Steel

基　　金：国家重点研发计划资助项目(2018YFC0310302)。

摘　　要：为了研究微观组织、M/A岛体积分数和长宽比对管线钢低温韧性的影响,用OM、SEM、EBSD和TEM等多尺度手段对材料进行了表征。结果表明,不同冷却速度工艺下均得到针状铁素体(AF)+准多边形铁素体(QF)+M/A岛+粒状贝氏体(GB)的组织结构。但随着冷却速度的增加,组织得到显著细化,有效晶粒尺寸由3.21降低到2.88μm。M/A岛体积分数从11.2%降低到5.8%,M/A岛长宽比也从3.5降低到1.2。在温度不低于-40℃时,随着有效晶粒尺寸减小和M/A岛尺寸、长宽比的减小,管线钢的低温韧性大幅提高。但在温度降低到-80^-60℃时,以马氏体为主的类圆形M/A岛易脆化断裂,造成材料在M/A岛体积分数最低和长宽比最低时冲击韧性出现最低值,管线钢的低温韧性与大角度晶界所占的百分比没有直接关系。针对试验用高强管线钢,在冷却速度为20℃/s、M/A岛体积分数为9.8%左右、长宽比为2.5时,材料具有韧性优异的综合性能。In order to study the influence of microstructures,volume percent and length/width ratio of M/A islands on low temperature toughness of pipeline steels,the multiscale means including optical microscope(OM),scanning electron microscopy(SEM),electron back scattering diffraction(EBSD)and transmission electron microscopy(TEM)were used.The results showed that the microstructure of three different cooling process was the same and all contained of acicular ferrite(AF)+quasi-polygonal ferrite(QF)+M/A island+grain bainite(GB).However,with the increase of cooling rate,the microstructure was refined remarkably,and the effective grain size decreased from 3.21 to 2.88μm,the volume percent of M/A islands decreased from 11.2%to 5.8%,and the length/width ratio of M/A islands also decreased from 3.5 to 1.2.When the temperature was above-40℃,the low temperature toughness of pipeline steel increased greatly with the decrease of effective grain size and decrease of M/A island size and length/width ratio.However,when the temperature decreased to-80--60℃,the circular M/A islands dominated by martensite tended to embrittle and fracture,resulting in the lowest impact toughness,when the volume percent and the length/width ratio of M/A islands and were the lowest.However,the low temperature toughness of pipeline steel was not directly related to the percentage of large angle grain boundaries.For the high strength pipeline steel in this experiment,when the cooling process was 20℃/s,the M/A volume percent was about 9.8%,and the length/width ratio is 2.5,the material had excellent comprehensive toughness.

关 键 词：M/A岛 夏比冲击 大角度晶界 低温韧性 有效晶粒尺寸 

分 类 号：TE973[石油与天然气工程—石油机械设备] TG335[金属学及工艺—金属压力加工]