GB/T 18449.4-2009 "Metal materials, Knoop Hardness test, Part 4: Hardness value table", for metal materials Knoop hardness testing supporting key data. This standard details the Knoop Hardness value corresponding to the diagonal length of the indentation under different test forces. In the process of metal material research and development, production and mass testing, users can quickly and accurately convert the Knoop Hardness of materials based on actual test data. It provides a convenient and reliable numerical reference for evaluating the performance of metal materials and effectively promotes industry standardization.