Abstract: Cracking occurred in hot upset forging of a 40Cr round steel. The causes of cracking were analyzed by means of macroscopic observation, chemical composition analysis, scanning electron microscope analysis and metallographic examination. The results show that the microstructure of 40Cr round steel crack defect was normal, and the content of non－metallic inclusions in the structure met the requirements of product standards. The defects on the upset forging base metal were caused by the surface scratches of the round steel during the rolling process. Finally, an improved method was proposed to avoid the recurrence of such problems.