Effect Of Quenching Temperature On Microstructure And Mechanical Properties Of Low-alloyed Corrosion Resistance Octg

In this work, the effect of quenching temperature on microstructure and mechanicalproperties of a QT-treated24CrMo48VNb steel has been investigated with the aim todesign a reasonable procedure of heat treatment for a low-alloyed corrosion-resistantOCTG. The morphologies of martensite and precipitate in quenched samples at differenttemperatures from870℃to1200℃and the samples followed by a tempering at700℃were observed using optical microscope, field emission scanning electron microscopeequipped with electron backscatter diffraction and transmission electron microscope. Themartensitic substructures were quantitatively analysed and their dependences on the prioraustenite grain were estimated. Moreover, the longitudinal tensile and low-temperatureimpact properties of all the QT-treated samples were measured. The morphology of impactfracture was observed by scanning electron microscope. The relationship between yieldstrength and microstructure and the dependence of impact energy on martensiticsubstructures were analysed. Based on the above investigations, the trial production oflow-alloyed corrosion resistant OCTG in an industrial scale was carried out and theproduct performances were evaluated.The results show that the size of prior austenite grain, martensitic packet and block of24CrMo48VNb steel increase with the increasing quenching temperature, while the lathwidth does not change significantly. After tempering, the martensitic packet and block areslightly enlarged, and the martensitic lath is widen significanty. In addition, there exhibitsa linear relationship between the size of prior austenite grain and the size of packet orblock.The results also reveal that with the increased quenching temperature, the strength of24CrMo48VNb steel is improved obviously by an increased quantity of fine precipitates,while the impact energy decrease due to the coarsening of prior austenite grain, matensitic packet and block. Therefore, the quenching temperatures from870℃to1000℃arerecommended.Finally, the mechanical and sulfide stress corrosion resistant properties of the trialproducts have satisfied the technical requirements.