Research Of Process Engineering Of High Quality Pipeline Steel X65

Pipeline transport is a kind of economic, reasonable and advanced mode oftransportation compared with the traditional mode of transportation. As people increasedemand for natural gas, oil and other energy, the number of pipeline construction for oiland gas transportation in domestic and transnational gradually increased, leading toincreasing demand for pipeline steel. Although，there were a lot of research ontechnology of pipeline steel both at home and abroad and production process becameincreasingly mature, but product qualities is not stable in the actual product. This paperstudied the production process of X65pipeline steel in Xinsteel, because there arenumber of problems in final production, such as unstable DWTT results, high yield ratioand inclusion problem. The behavior of hot deformation at high temperature andcontinuous cooling transformation of X65was investigated. The laboratory test andindustrial trial of hot rolling of X65was conducted, the results are as follows:(1) Single pass deformation test show that the temperature, rate and degree ofdeformation are the main factors influencing the dynamic recrystallization softeningbehavior. Higher deformation temperature, lower deformation rate and higherdeformation degree caused dynamic recrystallization more likely to happen.(2) It is created great number of dislocation in deformed austenite, which promotedferrite transformation, raised temperature of ferrite transformation and inhibited bainitetransformation in some degree as same time. Under same condition of transformation,the microstructure of steel gradually transforms from proeutectoid ferrite and pearlite toacicular ferrite and bainite, finally became bainite microstructure, the contents of ferriteand pearlite in steel microstructure are reducing and bainite contents is increasing along with cooling rate increasing, the grain size is reducing as well. For this test, afterdeformation, the microstructure of X65is acicular ferrite when cooling rate at3~40℃/s.(3) The results of hot rolling in laboratory experiment show that mechanicalproperty of testing steel meet specified requirement using established TMCP process toroll. The control parameters of TMCP process of X65pipeline steel as follows: heatingtemperature1200℃. Two stages of rolling, start rolling temperature of first stage is1120℃. start rolling temperature of second stage is less than950℃in order to keepfinish rolling temperature. The thick of intermediate slab is3.5～4times of finalproduction. The temperature of finish rolling is780～820℃. The temperature of finishcooling is780～820℃and cooling rate is12～18℃／s.(4) Industrial trail results show that the quality production can be achieved by take aseries of measures including adjusting chemical composition of steel such as increasingMo content to0.22%, and strictly controlling steelmaking and rolling processparameters.