Research on Banded Microstructure of Steel for Oil Casing Pipe

Center segregation in strand for J55 oil casing pipe is analyzed and the influences of heating temperature, finish rolling temperature, deformation rate in noncrystallization area, cooling rate after finish rolling and coiling temperature etc.on the reduction or elimination of banded microstructure are researched by means of sulfur print, hot acid erosion, OPA, SEM and EDS.The result shows that it is the segregation of Mn that directly leads to the formation of banded microstructure in hot rolled strip, and the problem can be reduced or eliminated by increasing finish rolling temperature, deformation rate in noncrystallization area, cooling rate after finish rolling and coiling temperature and lowering coiling temperature, etc.