Microstructural constituents as well as distribution of precipitates in pipeline steel X100 produced by thermo mechanical control process (TMCP) technology were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, etc. Results show that X100 is polyphase-structured steel which is mainly constituted of GB (granular bainite)、 BF (bainite ferrite)、 M/A (martensite-austensite), conformation and proportion of each phase have significant influence on the performances of X100. It is proved that GB based structure with a few BF and dispersed fine M/A inside has excellent effects on strength and toughness. High density of dislocations, bainite lathes with different orientations and M/A hardening phase were found by means of TEM observation. It also found two types of precipitate, one with big size mainly constitute of Ti, the other with small size mainly constitute of Nb; each type of precipitate have big effects on hindering the recrystallization of austenite and on the precipitation strengthening.%本文利用光学显微康、扫描电镜、透射电镜等,对实验室TMCP工艺生产的X100管线钢的组织构成、微观结构、析出物的形态和分布等进行了研究.研究结果表明,X100为GB(Granular Bainite)、BF(Bainite Ferrite)、M/A构成的复相组织,且各相比例和形态对性能影响较大,以GB为主的基体加上少量BF及弥散分布的细小M/A构成的组织具有较好的强度和韧性匹配.TEM微观形貌观察发现,贝氏体晶粒内部具有高密度位错和不同位向的板条束及M/A硬化相;萃取复形实验发现,X100中主要有两种类型的析出物:一类尺寸较大为Ti的析出,一类尺寸较小为Nb的析出物;这两种析出物起阻碍奥氏体再结晶和晶粒长大及析出强化的作用.
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