Effects of finish rolling temperature on the microstructure and mechanical properties of X80 high deformability pipeline steel

The finish rolling temperature was determined at 830, 800 and 775℃ to investigate its effect on the microstructure and mechanical properties of high deformability pipeline steel. The grain size and volume fraction of ferrite and M/A islands in the steels were measured by metallographic microscopy and image processing software. Electron backscatter diffraction (EBSD) analysis was conducted to ascertain the effective grain size and the volume fraction of high angle grain boundaries. The M/A island forms were observed by transmission electron microscopy (TEM). A quasi-static tensile testing machine was used to test the yield strength, tensile strength and uniform elongation of the three steels. It is indicated that when the finish rolling temperature is 800℃, the steel has the best mechanical properties and can meet the requirements of X80 high deformability pipeline steel.