GB/T 4340.1-2009 specifies hardness testing procedures for steel round bars, ensuring accurate and consistent measurement:
Testing methods: Covers Brinell (HB), Rockwell (HR), and Vickers (HV) hardness, with method selection based on bar diameter (Brinell for ≥10mm, Rockwell for ≥5mm).
Sample preparation: Specimens must be ground to a flat surface (Ra ≤0.8 μm) to eliminate surface irregularities; for round bars, testing is done on a flattened or cross-sectional surface.
Testing load: Brinell uses 3000kgf for hard steels (e.g., GCr15) and 1000kgf for soft steels (e.g., Q235); Rockwell uses HRC scale for hardened steels and HRB for annealed grades.
Accuracy: Requires calibration against certified hardness blocks, with maximum allowable deviation ±2 HB or ±1 HRC.
This standard ensures hardness data reliably reflects material properties, critical for quality control in heat-treated components like gears and bearings.