To ensure compliance with GB/T 1591 and GB/T 706, a comprehensive set of quality inspection tests is performed on each certified batch of Q355B I-beams. These tests are typically conducted by the steel mill's quality department and are documented in the Mill Test Certificate (MTC). The tests can be categorized as follows:
1. Chemical Analysis: A spectroscopic analysis is performed on a sample taken from the molten steel (heat analysis) or from the finished product (product analysis). It verifies compliance with the limits for C, Si, Mn, P, S, and other specified elements, and calculates the Carbon Equivalent (CEV).
2. Mechanical Tests (Destructive): These are performed on test pieces machined from a sample taken from a representative I-beam (usually from the web end) of the rolling batch.
* Tensile Test (per GB/T 228.1): Determines Yield Strength (ReH), Tensile Strength (Rm), and Elongation after Fracture (A). A longitudinal test piece is standard.
* Charpy V-Notch Impact Test (per GB/T 229): For Q355B, a set of three specimens are tested at +20°C. The reported value is the average of the three, with individual values typically not falling below a specified minimum (e.g., 70% of the average). This verifies toughness.
* Bend Test (per GB/T 232): A sample is bent to a specified angle (180°) around a mandrel of a diameter related to the sample thickness. It checks for soundness and ductility, revealing surface or internal defects like cracks or laminations.
3. Dimensional and Visual Inspection (Non-Destructive):
* Dimensional Check: Using calipers, gauges, and templates to verify height, flange width, web/flange thickness, length, camber, sweep (deviation from straightness), and twist against the tolerances in GB/T 706.
* Visual Inspection: Checking for surface defects like deep scratches, rolling laps, cracks, excessive pitting, or uneven mill scale.
* Weight Verification: Checking the theoretical weight per meter against the actual weight.
4. Non-Destructive Testing (NDT): While not always mandatory for all batches per the base standard, it may be specified in supplementary requirements (e.g., for critical applications). Common NDT includes Ultrasonic Testing (UT) to detect internal flaws like inclusions or laminations, particularly in the web-flange junction (the "k-area").