Abstract: This paper discussed the main causes of defects such as cracks, central holes or others involved in the productive process of 40Mn2 forging grinding ball. The instruments such as scanning electron microsope(SEM),energy dispersive spectrometer(EDS),optical metallographic microscope and spectrometer were employed to analyze the microstructure and determine the chemical composition for 40Mn2 forging billets. The results showed that many defects including shrinkage porosity, inclusions and severe banded structure were observed in forging billets. In addition, unreasonable quenching process parameters led to the coarse widmanstatten structure formation inside the forged grinding balls. In order to avoid forming the widmanstatten structure, the suggestions are following: adding deslagging agent in smelting process, homogenization annealing treatment after the rolling production, adjusting the heating and cooling conditions in forging production.