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In this study,typical microstructural characteristics of a metastable β Ti alloy(Ti-5Al-5Mo-5V-3Cr-1Fe)forged in a dual-phase region(strain of 54％at 820℃)were investigated in detail by the combined use of X-ray diffraction,energy dispersive spectroscopy,electron channeling contrast imaging and electron backscatter diffraction techniques.Results show that the microstructure of the forged alloy is composed of bulk α grains,α plates and β matrix.The bulk α grains correspond to retained primary α phase(αp,average grain size～2.4 μm),while the α plates are secondary α phase(αs,width～70 nm)precipitated from the β matrix during air cooling.During forging,the β matrix experiences dynamic recovery with many subgrains and significant orientation gradients formed.Analyses of the orientation relationship between the α and β phases show that the Burgers orientation relationship is not maintained between some αp and β phases,which should be related to thermal deformation-induced changes of their orientations.In contrast,all of the αs plates are found to maintain well the Burgers orientation relationship with the β phase.