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An open crack was found in a Ti-6Al-4V alloy forging ring. Optical observation, scanning electron microscopy analysis, energy-dispersive X-ray spectroscopy, hardness test and X-ray photoelectron spectroscopy were applied to find out the reason. It was found there was an obvious transition zone from the edge of the crack to the matrix on one side of the crack, where the shape and size of the microstructure changed from big block to elongated wattle. In addition, the microstructure inside the crack appeared non-compact and porous. Microhardness tests showed that the hardness of the area near the crack was remarkably higher than that of matrix. The results of energy-dispersive X-ray spectroscopy showed that the content of Al and V was much smaller near the crack compared to the matrix. The surface of the crack is basically composed of Ti, Al and V, and no other elements were found in the precision range. X-ray photoelectron spectroscopy results showed that the blocky α-phase area near the crack contained oxygen, carbon and nitrogen. However, no carbon and nitrogen were found in the matrix and the oxygen content was lower.