Effects of Ultra Fast Cooling Ending Temperature on Microstructure and Mechanical Properties of X80 Pipeline Steel

Hot rolling test for X80 pipeline steel was carried out at experimental rolling mills. And the test steel was cooled by ultra fast cooling and laminar cooling after rolling. Combined with the microstructure observation, effects of ultra fast cooling ending temperature on mechanical properties were investigated. Results show that when the ultra fast cooling ending temperature was about 670 ℃, polygonal ferrite was found and yield ratio of test steel was lower. With the decreasing of ultra fast cooling ending temperature, the amount of precipitates increased, the size of precipitates was finer and dispersion, the strength and toughness increaseed, elongation first increased and then decreased.