Study Of Recrystallization And Precipitates In Different Deformation Process On X100Pipeline Steel

Pipeline steel is one of the most economic and efficient tool to transport oil andnature gas. With the development of transport efficiency and pressure of oil andnature gas, stricter requirements have been put forward to develop the overallperformance of pipeline steel. Recently the grade of pipeline steel has risen to X100and X120according to API-5L or ISO-3183standard. Because X100high gradepipeline steel has the advantage of high strength and toughness, good weldingperformance, excellent resistant HIC and SCC and also low installation cost. Now it isone of the high value-added productions in many steel companies that iscompetitively manufactured.The recrystallization behavior of X100pipeline test steel was studied underdifferent thermal simulation deformation conditions on thermal simulator. Themorphology, components and distributions of precipitates of X100pipeline test steelwere investigated. The main research contents and results are given as follows:(1) Effects on recrystallization behavior of X100pipeline test steel underdifferent deformation temperature, strain quantity and strain rate were investigated byusing single and double pass compression test on MMS-200thermal simulator.(2) In the condition of strain rate of20%, dynamic recrystallization of X100pipeline steel didn’t occur in the single or pass compression test. Staticrecrystallization occurred during the holding time of20s later after deforming. Thecompletely recystallization of X100pipeline steel occurred when deformed incondition of stain of50%and deformation temperature of1150℃and strain rate of0.5s-1, while dynamic recystallization occurred partially in the condition of strain rateof1s-1and5s-1. In the double-pass compression test, static softening rate in differentdeformation condition of X100pipeline steel was concluded. The result shows thatstatic softening rate increased as the interval time prolonged and the deformationtemperature increased. The static recrystalliztion kinetics model was established. The static recrystalliztion activation energy and kinetics equations of X100pipeline steelwere292.42kJ/mol and XS=1－exp[－0.693(t/t0.5)0.34] respectively.(3) The morphology, components and distributions of precipitates of X100pipeline test steel were studied. Three types of precipitates with different shape andcomponents were found in the experiment. The increase of precipitates of Ti and Nbis accompanied by the increase of the quantity of deformation in the condition ofdeformation temperature of950℃. The size of precipitates is much smaller.