Microstructure and impact toughness of X80 grade high strength low alloy pipeline steel
NIU Yan-long1， LIU Qing-you1， JIA Shu-jun1， WANG Bing1， REN Yi2
（1. Institute of Structural Steels， Central Iron and Steel Research Institute， Beijing 100081， China； 2. State Key Laboratory of Metal Materials and Applications for Marine Equipment， Anshan 114009， Liaoning， China）
Abstract：In order to study the low-temperature toughness and related impact crack propagation characteristics of a high strength low-alloyed X80 pipe steel that contains mainly quasi-polygon ferrite/lath bainite，the multiscale means including optical microscope（OM），scanning electron microscopy （SEM），electron back scattering diffraction （EBSD） and transmission electr on microscopy （TEM）were used. The results showed that when the temperature was above －60 ℃，the quasi polyg on ferrite/lath bainite pipeline steel obtained the stronger ability to prevent crack growth in comparison with the acicular ferrite/granular bainite pipe steel. Because of the existence of quasi polygon ferrite，the effective grain size of the tissue could be divided into thin sections. The large angle proportion of the grain boundary could be increased. And the grain boundary of the tissue could be harmonize constraint. Therefore，the crack propagation energy of the material was enhanced and the toughness of the material was improved significantly. When the temperature was below －60 ℃，the coordination of the quasi polygon ferrite/lath bainite was weak and turn into the soft area of the materials.
2019, Vol. 54 
