X65, X70, and X80 belong to high grade pipeline steels. Toughness is one of the mostimportant properties of pipeline steels when the pipeline transports the gas or oil, and the means to control toughness is very important for exploring even higher grade pipeline steels. We established the relationship between toughness and crystallographic parameters of high grade pipeline steels by studying the crystallographicparameters of X65, X70, and X80 using EBSD and analyzing Charpy CVN of X65, X70 and X80. The resultsshow that the effective grain size, the frequency distribution of grain boundary misorientation and the ratio ofhigh angle grain boundary to small angle grain boundary are important parameters. The finer the effective grainsize, and the higher the frequency distribution of grain boundaries(≥ 50°), the more excellent toughness of highgrade pipeline steels will be.
