GB/T 702-2016 sets strict surface quality standards for hot-rolled round steel:
1) No harmful defects: Surface must be free of cracks, folds, scabs, delaminations, and (inclusions)-these defects reduce strength and can cause fracture under load;
2) Allowable minor defects: Small scratches, indentations, or oxide scales are permitted if their depth does not exceed 10% of the diameter (e.g., ≤2mm for Φ20) and do not affect dimensional accuracy;
3) Rust limits: Light rust (surface discoloration without pitting) is acceptable, but heavy rust (pitting depth >0.1mm) is not, as it reduces cross-sectional area;
4) Edge quality: For cut-length round steel, the end face must be flat (perpendicular to the axis, deviation ≤1°) to ensure proper assembly (e.g., shaft mounting).