Development of X60 and X100 Linepipe Steels with High Deformation Capacity for Strain-based Design

摘要

Recent linepipe steel is required to have enough deformation capacity through longitudinal direction at severe environments such as permafrost or seismic region, even though after anti-corrosion coating treatment in pipe. Under this background, X60 and X100 linepipe steels with high strain aging resistance have been developed. With thermodynamic calculation and pilot plant rolling, optimal chemical compositions were determined, and it was studied that the effects of hot rolling conditions such as finish cooling temperatures on strengths and uniform elongations after coating simulation. Mo, Ni, and V alloying elements were employed to obtain enough strength and improve uniform elongation by producing microstructures consisting of ferrite, bainite and MA constituent. Such microstructures were characterized by EBSD (electron back scattered diffraction) technique. Pipes with 1m length were manufactured with an UOE simulator which can do U-ing, O-ing and expansion at the same machine. After pipe forming, coating simulation to evaluate strain aging characteristics of pipes was performed.