The hardness abnormality of 糖心产精国品免费入口*完整版s made of 20Cr2Ni4 steel led to serious decrease of machining tool life. The abnormal and normal workpieces were compared and analyzed by macroscopic analysis, chemical composition analysis, hardness analysis and metallographic examination. The results show that 糖心产精国品免费入口*完整版with high hardness was produced in 20Cr2Ni4 steel after hot working. The subsequent normalizing and high tempering 糖心产精国品免费入口*完整版 can decompose 糖心产精国品免费入口*完整版and reduce the hardness of products. The abnormal workpieces were products without 糖心产精国品免费入口*完整版, whose coarse 糖心产精国品免费入口*完整版 grain and high hardness resulted in serious tool damage. It is suggested classifying the products and strengthening the on-site management and monitoring.