Study On Rolling Methods And The Properties Of X70 Pipeline Steel

With the rising demand to natural gas and oil, the technique and the technology of producing pipeline steel have been developed rapidly, which is due to that long linepipe is one of the economical, fast and convenient the way for transporitng natural gas and oil. Excellent combination of strength and toughness and low ratio of yield strength to tensile strength are required to meet long distance transportation at high pressure. Thus, X70 pipeline steel was researched and the hot simulation and experimental rolling (QingHuangDao ShouGang Commpany 3454 Rolling) are used to develop the technics of X70 pipeline steel which processes the high mechanical properties.The main outcomes are involved as follows:First of all,Two different kinds of chemical components of X70 pipeline steel are designed. CCT curve is measured using mmS-200 hot simulation experiment machine. Based on the CCT curve, we know that when cooling ratio is between 15℃/s~20℃/s, the acicular ferrite pipeline steel would be obtained.Secondly,The TMCP technics is applied in the Mo series X70 pipeline steel, and HTP technics for the Nb series X70 pipeline steel in the rolling experiment. The influences of control rolling and control colling process parameters (fine rolling process, initiate cooling temperature, final cooling temperature, cooling ratio) on experimental steel microstructure and properties are researched, which provide theoretical support to the next industrial production experiment.Third,Based on the tensile experiment, I MPact experiment and the microstructure observation, we can know that appropriate control rolling and control colling process can produce X70 pipeline steel with good integrated mechanical property. Finally,The appropriate producing technics of X70 pipeline steel are obtained according to the laboratory result analysis and some steel's capacity . The best TMCP processing parameters are: The rough rolling temperature is about 1150℃, the final coarse rolling temperature is less than 950℃, the final rolling temperature is 780℃~820℃, the final cooling temperature is about 540℃~580℃, the final cooling speed is 15℃/s~20℃/s. The best HTP processing parameters: The start rolling temperature is about 1120℃, the final coarse rolling temperature is less than 950℃, the final rolling temperature is 830℃~850℃, the final cooling temperature is about 550℃~600℃, the final cooling speed is 15℃/s~20℃/s..