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利用Gleeble热模拟实验机模拟了铁素体-贝氏体双相X100管线钢在不同的单道次热循环临界峰值温度(760℃和800℃)下生成的临界热影响区(ICHAZ)的组织,利用光学显微镜、扫描电镜、透射电镜等对显微组织进行了表征,尤其是对马氏体-奥氏体(M-A)组元的分布状态进行了研究.同时对不同峰值温度的样品在-20℃的冲击韧度进行了测试.结果表明,铁素体-贝氏体双相X100管线钢ICHAZ的冲击韧度较高,在760℃时平均为163 J,800℃时平均为201 J.800℃时的冲击韧度高于760℃,这是因为760℃时形成的M-A组元的分布较为连续,而加热至800℃时逆转组织含量更高,部分逆转组织转变为贝氏体,从而使得M-A组元的分布较为分散.贝氏体-铁素体双相组织X100管线钢的ICHAZ的冲击韧度明显高于传统的单相贝氏体组织管线钢,这是由于双相组织的ICHAZ处的M-A组元沿着铁素体-贝氏体边界形成,尺寸较小并且比较分散,因此对冲击韧度的危害程度显著降低.

Microstructure of single pass intercritically reheated heat affected zone (ICHAZ) of an X100 pipeline steel at different peak temperatures (760 ℃ and 800 ℃) was simulated on a Gleeble thermal simulation machine,and the microstructure of the samples,especially distribution of martensite-austenite (M-A) constituent,was studied by means of optical microscope (OM),scanning electron microscopy (SEM) and transmission electron microscopy (TEM).Meanwhile,Charpy impact toughness at-20 ℃ of the samples was evaluated.The results show that ICHAZ toughness of the ferrite-bainite dual phase X100 pipeline steel is relatively high,which is 163 Jin average when the peak temperature is 760 ℃ and 201 J in average at peak temperature of 800 ℃.The toughness of the sample heated at peak temperature of 800 ℃ is higher than that of heated at peak temperature of 760 ℃,which is attributed to that the M-A constituent in 760 ℃ sample is continuously distributed while in the 800 ℃ sample the M-A constituent is discrete.At 800 ℃,more reverted austenite is formed during reheating and part of the reverted austenite decomposes into bainite during cooling which induced the scattering of M-A constituent.Impact toughness of the ICHAZ of the ferrite-bainite dual phase X100 pipeline steel is much higher than that of single phase bainite pipeline steel.The reason is that,in the ICHAZ of dual phase steel,M-A constituent distributes at the border of ferrite and bainite and hence the M-A constituent is small in size and discrete,therefore,the impact toughness is not notably deteriorated.