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采用电解、萃取复型、透射电镜以及能谱分析等方法研究了不同温度等温过程中X120管线钢中第二相粒子的回溶规律,并测定了相应条件下的奥氏体晶粒尺寸。结果表明:在锻态组织中存在两种类型的碳氮化物,一类是在凝固过程中形成的粗大富Ti颗粒;另一类是在变形过程中形变诱导析出产生的富Nb第二相粒子,其尺寸更加细小,此类粒子经1000℃保温60 min后消失。1000~1220℃保温过程中含Nb和Mo的碳氮化物发生回溶,导致奥氏体晶粒快速长大,但此时未回溶的碳氮化Nb、Ti粒子仍阻碍晶界的迁移。当再加热温度达到1270℃并保温120 min后,只有极少量的含Nb的Ti N颗粒能够保持稳定,故第二相粒子的钉扎作用明显减弱,使得奥氏体晶粒异常长大。
The law of second phase particles dissolution in X120 pipeline steel during different temperature isothermal process was studied by means of electrolysis, extraction complexing, transmission electron microscopy and energy spectrum analysis. The austenite grain size under the corresponding conditions was also measured. The results show that there are two types of carbonitrides in the as-cast microstructure, one is the coarse Ti-rich particles formed during solidification and the other is the Nb-rich second phase particles induced by deformation induced precipitation during the deformation , Its size is more small, such particles disappear after 60 min incubation at 1000 ℃. The carbonitrides containing Nb and Mo during the heat preservation process from 1000 ℃ to 1220 ℃ are dissolved back into solution, resulting in the rapid growth of austenite grains. However, Nb and Ti carbonitrides which are not dissolved at this time still hinder the migration of grain boundaries. When the reheating temperature reaches 1270 ℃ and holding time is 120 min, only a very small amount of TiN particles containing Nb can maintain stable, so the pinning effect of the second phase particles is obviously weakened, resulting in the abnormal growth of austenite grains.