热轧工艺对X80管线钢组织及低温韧性的影响

Effect of hot-rolling processes on microstructures and low-temperature toughness in X80 grade pipe-line steel

利用D450试验轧机,对X80管线钢开展控轧控冷实验。采用光学显微镜、透射电镜、扫描电镜以及电子背散射衍射技术分析不同TMCP工艺条件下的管线钢组织结构,研究形变热处理工艺对管线钢组织及低温韧性的影响。研究结果表明:在较高压下率及较大冷速条件下,管线钢组织以细小的针状铁素体作为主要组元,奥氏体/马氏体(M/A)组元数量较少,粒径较小;相反,在低压下率及较小冷速情况下,管线钢组织主要是由粒径较大的准多边形铁素体构成,M/A组元数量多,粒径大;与准多边形铁素体为主的组织相比,以针状铁素体作为主要组元的管线钢由于具有细小的有效晶粒粒径、高的大角度晶界比例以及细小的M/A组元,表现出良好的低温韧性。

Using a pilot rolling mill with twin rolls of 450 mm in diameter, thermo-mechanical controlled processing（TMCP） experiments were performed in X80 grade pipe-line steel. The microstructural characteristics for different TMCP conditions were analyzed by means of optical microscope（OM）, transmission electron microscope（TEM）, scanning electron microscope（SEM） as well as electron back-scatter diffraction（EBSD）, and the effect of TMCP conditions on microstructures and low-temperature toughness was investigated. The results show that during higher reduction in austenite non-recrystallization region and faster cooling rate during accelerated cooling, the microstructure is dominated by acicular ferrite（AF） accompanied with small amount of fine martensite/austenite（M/A） constituents. In contrast,lower reduction and slower cooling rate lead to a predominantly quasi-polygonal ferrite（QF） microstructure with coarse M/A islands. Compared with the microstructure mainly consisting of QF, the pipe-line steel with the microstructure primarily characterized by AF exhibits excellent low-temperature toughness because of its fine effective grain size, high fraction of high angle grain boundaries and fine M/A islands.