Formation of the adiabatic shear band in sheet metal is investigated with experiments for high strength steel sheets, 60 C and 60 TRIP. Since the adiabatic shear band is formed as a result of adiabatic shear failure with a narrow band of concentrated shear strain, the adiabatic shear band plays an important role in the analysis of high speed deformation phenomena. For shear band experiments with a tension split Hopkinson bar, specimens are designed to induce large shear strain. The experimental results show that the shear deformation modes of two sheet metals, 60 TRIP and 60 C, are quite different from each other in that the adiabatic shear band is observed only in 60 C. The shear deformation in 60 TRIP is restrained by the abrupt increase of strength due to the plastic strain, which interferes with propagation of the shear crack. Instead, a tensile crack developed at the corner where the shear crack should have been initiated. As a result, the load-displacement curves show that the tensile load of 60 TRIP specimens becomes higher than that of 60 C at the same displacement.