GB/T 18394-2001 outlines precise methods for measuring carbon content in steel round bars, a critical parameter for grade verification:
Testing techniques: Mandates combustion infrared absorption spectrometry (the primary method) for accuracy, with wet chemical analysis (e.g., volumetric method) as a backup for disputes.
Sample preparation: Requires drillings from the center of bars ≥20mm diameter (to avoid surface decarburization) or 1/4 depth for larger bars, with samples ground to 100 mesh to ensure uniform combustion.
Accuracy limits: Allows ±0.005% tolerance for carbon contents ≤0.10%, and ±0.01% for 0.10–1.00% C-ensuring compliance with grade specifications (e.g., 0.42–0.50% C for 45#).
Calibration: Requires daily calibration using certified reference materials (e.g., CRM with 0.25% C) to maintain instrument precision.
This standard ensures consistent carbon measurement across Chinese steel mills, preventing grade misclassification in critical applications.