GB/T 231.3-2022 "Metallic materials - Brinell hardness test - Part 3: Calibration of reference blocks" specifies the calibration method for reference blocks used in indirect verification and periodic inspection of Brinell hardness testing machines, as well as the traceability procedure. The reference blocks must ensure homogeneity, structural stability, and uniform surface hardness, be non-magnetic, and meet requirements for flatness and parallelism. Calibration is conducted within a specified temperature range, with clear specifications for the approach speed of the indenter, the duration of test force application, and the dwell time. Each test surface of the reference block must have a certain number of uniformly distributed indentations. Additionally, the identification and certification requirements for reference blocks are standardized.