Study on Banded Structures Evolution of Microalloyed Steel during Isothermal Holding Process

The evolution of banded structures of microalloyed steel during isothermal holding process was studied by thermal simulation test machine, optical microscope and scanning electron microscope, and its formation mechanism was analyzed.The results show that the banded structure is ferrite/martensite at 650-700 ℃.At 550-600 ℃, the banded structure is acicular ferrite / martensite, and the volume fraction of acicular ferrite increases with the decrease of holding temperature.Mn segregation is the main reason for the incomplete transformation. When the isothermal temperature drops to 450 ℃, the microstructure is all acicular ferrite, and the banded structure almost disappears.