Q: What are the common surface defects of cold-rolled coils?
A: Main defects include: oxide scale, pitting, scratches, roll marks, creases, rust spots, inclusions, edge/center waviness (shape defects), color difference, etc.
Q: How to determine whether surface scratches on cold-rolled coils are caused during the rolling process or later?
A: Rolling scratches are mostly continuous, regular longitudinal scratches (consistent with the rolling direction), with relatively uniform depth; later scratches are mostly random and irregular, possibly accompanied by oil/impurity residue.
Q: What are the mechanical property testing items for cold-rolled coils?
A: Core testing items: tensile strength (σb), yield strength (σs), elongation (δ), hardness (HRB). For deep-drawing materials, the n value (work hardening index) and r value (plastic strain ratio) also need to be tested.
Q: What are the effects of poor "sheet shape" on cold-rolled coils?
A: Poor sheet shape (such as waviness, warping, or kinking) can lead to inaccurate positioning and dimensional deviations during leveling/stamping, rendering the material unusable in severe cases and requiring correction using a leveling machine.
Q: What is the typical rust-proof period for cold-rolled coils?
A: The standard rust-proof period is 3-6 months (applied rust-preventive oil + moisture-proof packaging). If stored in a dry and well-ventilated environment, this can be extended to 12 months. Stainless steel cold-rolled coils have an even longer rust-proof period (they are not prone to rust even without a coating).