Study Of The Underlying Technology Of High Strength Pipeline Steel X100

With the development of the industry of oil and nature gas, the pipeline steel for transporting oil and nature gas has been making rapid development. In china, the country economic making great progress and expenditure of oil, nature gas expending continuously, especially a lot of pipage striding over the country and the western pipeline constructing, the demands for variety, specifications and quality are bringing forward.This mainly topic is the fundamental technique researching of the high strength X100 pipeline steel .The main contents are given as follows:(1)Kinetic curves of continuous cooling transformation, both static (without deformation) and dynamic ( after deformation in the non-recrystallized austenitic region), have been measured by the high-resolution dilatometer attached to the thermomechanical simulator Gleeble 3800, at the various cooling rates. Microstructures after different cooling rates were characterized by optical microscope and electronic microscope. Macrohardness on the samples after different thermal processes and microhardness on each phase within microstructures were measured as well. The microstructures in samples change from polygonal ferrite, acicular ferrite, granular bainite to lower bainite with the increasing microharndness when cooling rate increases. It was found that deformation, applied in the non-recrystallized region, shift C-curve to the left side with a wider range of cooling rate for the formation of acicular ferrite, and lead to finer microstructures in samples. It was proposed that the cooling rate should be more than 20℃/s to achieve the strength requirement by X100 pipeline grade.(2)X100 pipeline steel was developed and produced by several patterns of controlled rolling and accelerated cooling process. In particular, effects of finish rolling temperature and finish cooling temperature on the mechanical properties and microstructure of the hot rolled steel were investigated. It was found that microstructures of the developed X100 pipeline steel mainly consists of acicular ferrite, granular bainite and lower bainite at the range of studied finish rolling temperatures and finish cooling temperatures. Lower finish rolling temperature results in a refined microstructure and then the higher strength. Lower finish cooling also leads to a higher strength but worse toughness due to more harder phase of bainite formed. In conclusion, it has been suggested that rolling temperature is 850°C and finish cooling temperature 200°C in the controlled rolling and accelerated cooling process for the industrial production of X100 pipeline steel.