Research On Rolling And Tempering Process Of X80 Pipe Line Steel For Hot Induction Bends

The pipeline carries a significant advantage of security,economy,and delivery capacity,the first choice of transportation in the west of the country,to ensure the economic growth of the developed regions of the eastern part of the country.X80 pipeline steel has become the preferred steel grade of pipeline construction.As the X80 for Hot Induction Bends that changes the direction of the pipeline,the mother's hot rolled steel plate in production still has the problem that the impact toughness is not up to standard and the strength is easy to exceed the standard.In this thesis,the transformation and composition of the austenitic was studied by thermal simulation experiment,and the rolling process was determined by experimental rolling and industrial rolling.The main work involved as follows:(1)Using the Gleeble-3800 heat simulator,the influence of the continuous cooling conditions on the phase change and the metallographic structure of the X80 and X80 hot induction bend's austenitic was studied.The study shows that the phase transition products of high temperature transformation are mainly composed of polygon ferrite and pearlite.The phase transition products of medium temperature transition region are mainly acicular ferrite(AF),granular bainite(GB),different proportion of structure in different cooling conditions of bainite.Bend X80 alloy content improve inhibits the polygonal ferrite transformation,promote the bainite transformation,equivalent to increase the proportion of bainite,reduce ferritic proportion,reaction in performance,is characterized by higher strength,hardness,toughness,plasticity decreases.(2)The effects of different AR+ACC,CR+air cooling and TMCP process parameters on the performance were studied through experiment rolling.The experimental results show that AR+ACC rolling process can not meet the requirements of impact toughness.By using CR+air cold rolling process,the original austenite grains can be significantly refined.With the decrease of the final rolling temperature,the strength is increased,and the impact toughness of the steel plate is poor when it enters the two-phase zone rolling.Adopting TMCP process,with the loss of the final cooling temperature,the strength of steel plate rised,cooling rate between 15 to 25?/s,strong toughness of test steel changed little,The decrease of the final rolling temperature is beneficial to the ratio of the steel plate and the impact toughness.(3)Industrial trial production of X80 hot induction bend is carried out in 5000 mills,the test results show that the cooling rate has a direct influence on impact toughness,improve the cooling speed is helpful to control the size of M/A,make the distribution of more dispersion,thus improve the impact resistance;Finishing temperature had significant effect on the control of strength,when finishing temperature control between 740?755?,the intensity distribution is ideal.(4)Laboratory experiments show that the heat treatment QT technology can improve the comprehensive performance of X80 hot induction bend,when the quenching temperature 950? and tempering at 550? temperature,comprehensive performance is best.Industrial rolling steel plate after 600? tempering,the large size of M/A decomposition,forming small M/A,can obviously improve the impact toughness.