Influence of annealing on the banded structure of 22Si2MnCrNi2MoA drill steel

22Si2MnCrNi2MoA drill steel was tested by optical microscopy,scanning electron microscopy and energy dispersive spectroscopy to study its dynamic continuous cooling phase transformation law and annealing process optimization,analyze the effect of cooling rate on its continuous cooling transformation(CCT) curves and transformation microstructure,and find out the cause of banded structure formation and measures for quality improvement.It is shown that the steel has high hardenability,and a bainite and martensite duplex microstructure is obtained when the hot rolled material is cooled in air after deformation.The optimal annealing process is at 710℃for 5 h.The composition inhomogeneity of the banded structure in the steel cannot be eliminated by isothermal annealing.The banded structure is caused by the segregation of the alloy elements of Si,Mn,Cr,Ni and Mo,and can be weakened by improving the crosssection deformation uniformity of bars.However,the homogeneous distribution of alloy elements in the metallurgical process is the critical way to reduce or eliminate the composition inhomogeneity of the banded structure.