GB/T 1979-2001 establishes criteria for evaluating surface quality of steel round bars, ensuring consistency:
Defect classification: Categorizes defects as cracks (rejectable), folds (rejectable if >0.5mm deep), and minor scratches (acceptable if ≤0.1mm deep).
Inspection methods: Mandates visual inspection under 1000 lux lighting, with magnetic particle testing for critical applications to detect subsurface defects.
Surface roughness: Specifies Ra values for different finishes (e.g., hot-rolled: Ra ≤12.5 μm; cold-drawn: Ra ≤3.2 μm).
Acceptance criteria: Bars with surface defects exceeding 5% of total length are rejected, with critical applications requiring 100% defect-free surfaces.
This standard ensures surface quality meets application requirements, from structural bars (tolerating minor defects) to bearing bars (requiring perfect surfaces).