【摘要】 研究F550级船板钢在820、850和910℃淬火,600℃回火条件下的热处理工艺对其低温韧性的影响。通过光学显微镜、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等实验方法,分析了组织中多边形铁素体以及M/A岛体积分数、M/A岛的形貌、尺寸及分布情况。结果表明:选择在亚温区850℃淬火后600℃回火试验钢的-80℃低温韧性最佳,达到220 J左右。在完全淬火区910℃淬火后回火,钢的主要组织为贝氏体,且大于2μm的M/A岛数量较多,这些M/A岛在晶间聚集或呈细条状或点列状分布在贝氏体铁素体板条间,这对钢的韧性起到破坏作用。经亚温处理后实验钢的组织为多边形铁素体和粒状贝氏体,铁素体细小且弥散分布。粒状贝氏体中的M/A岛体积分数较完全淬火低,且呈细小圆点状,弥散分布在贝氏体铁素体板条间,可以有效的阻止裂纹的扩展。更多还原

【Abstract】 Microstructure and mechanical properties of F550 ship plate steel after guenching at 820 ℃,850 ℃,910 ℃ and tempering at 600 ℃ were investigared.The effects of quenching temperature on low temperature toughness of F550 ship plate steel were examined.The morphology,size and distribution of martensite-austenite(M/A) constituents and the volume fraction of M/A islands and polygonal ferrite obtained after different heat treatment processes were observed by optical microscope,scanning electron microscopy(SEM),transmission electron microscopy(TEM) and quantitative metallographic methods.The results show that after intercritical quenching at 850 ℃ and tempering at 600℃,the low temperature toughness at-80 ℃ of the steel is the best,which is about 220 J.After complete quenching at 910 ℃ and tempering at 600 ℃,the main microstructure of the steel is bainite,and the amount of M/A islands with the size above 2 μm increases and the M/A islands are distributed at grain boundaries or between bainitic ferrite lathes with the form of elongated block and dots,which lead to the decrease of toughness.After sub-critical heat treatment,the microstructure consists of polygonal ferrite(QF) and granular bainite,and polygonal ferrite is fine and distributed uniformly.The amount of M/A islands is smaller compared with that of complete quenching and tempering,and the M/A islands with dot-shape disperse uniformly between bainitic ferrite lathes acting as effective barriers to crack propagation.更多还原