GB/T 3078-2008 governs cold-drawn high-quality carbon steel round bars, ensuring precision for machinery components:
Dimensions: Tight tolerances (±0.01mm for 10–30mm diameters) and straightness (≤0.5mm/m) to minimize machining allowances.
Surface finish: Ra ≤1.6 μm for polished bars, achieved via multi-pass drawing and surface treatment to reduce friction in moving parts.
Mechanical properties: Varies by grade (e.g., 20#: 410 MPa tensile strength, 245 MPa yield strength) with mandatory hardness testing (≤156 HB for 20#).
Testing: 100% magnetic particle inspection for bars ≥20mm diameter to detect surface cracks, critical for safety-critical parts like hydraulic shafts.
The standard covers grades 10# to 60#, with cold-drawn 45# being particularly popular for precision shafts. It aligns with ASTM A108, ensuring compatibility with global machinery manufacturing.