Microstructure and Mechanical Impact Behavior of Ultra-Low Carbon Microalloyed Pipeline Steel Used in Chemical Pipeline during Welding Heat Treatment with Computer Aid

Abstract

Through optical microscopy, scanning electron microscopy, transmission electron microscopy and impact testing machine and other equipment, this paper study the microstructures and impact properties of ultra-low carbon microalloyed pipeline steel. The results show that the base metal of ultra-low carbon microalloyed pipeline steel is mainly composed of granular bainite and bainite ferrite. The coarse grain structure of HAZ in welded joints mainly includes bainite ferrite, granular bainite, a small amount of polygonal ferrite and fine M-A island, and the grain size is coarse. The acicular ferrite in the weld is mainly induced by complex oxides of titanium, aluminium, silicon and manganese. And the organizational structure is interlaced with the basket weaving structure. The microstructures of weld zone and heat affected zone of ultra-low carbon microalloyed pipeline steel are obviously different.