GB/T 6394-2017 outlines methods for determining grain size in steel round bars, critical for assessing mechanical properties:
Test methods: Specifies comparison charts (ASTM E112 equivalent) and intercept methods for measuring grain size.
Grain size classification: Uses 0–12 scale, with 0 being coarsest (≥50μm) and 12 finest (≤3μm).
Sampling: Requires transverse sections from the center of bars ≥20mm diameter to ensure representative grain structure.
Requirements: Structural steels like Q355 require minimum 6 级 (6th grade, ~10μm) grain size for good toughness.
This standard ensures consistent grain size measurement, as grain size directly affects strength, toughness, and weldability.