How to determine if a cold-rolled sheet is of acceptable quality?
① Appearance: No obvious scratches, pitting, oxidation, or warping;
② Dimensions: Thickness and width measured with calipers, deviations within standard range;
③ Performance: Yield strength and elongation tested through tensile testing, meeting material requirements;
④ Surface roughness: Measured with a roughness meter, meeting usage requirements.
What causes the "delamination" defect in cold-rolled sheets?
Main causes:
① Internal inclusions and bubbles in hot-rolled raw materials;
② Excessive reduction during cold rolling, causing internal separation;
③ Excessively high annealing temperature or prolonged holding time, resulting in coarse and uneven grain size.
What is the difference between cold-rolled sheets and galvanized cold-rolled sheets?
Galvanized cold-rolled sheets have a layer of zinc plated on the surface (hot-dip galvanizing or electroplating). Their core advantage is stronger corrosion resistance, requiring no additional rust prevention treatment, but the cost is higher; ordinary cold-rolled sheets require subsequent rust prevention treatment, which is less expensive.
What are the development trends of cold-rolled sheets?
① High Strength: Develop high-strength cold-rolled sheets (such as DP steel and TRIP steel) to meet the lightweighting requirements of automobiles; ② High Precision: Improve thickness and width tolerance control to adapt to precision manufacturing; ③ Environmental Protection: Adopt environmentally friendly processes such as chromium-free passivation and water-based coating; ④ Multifunctionality: Develop composite cold-rolled sheets that combine high strength, high formability, and corrosion resistance.
What are the main cost components of cold-rolled sheets?
Main costs: Hot-rolled raw material costs (accounting for 60%-70%), cold-rolling processing fees (rolling, annealing, leveling), pickling fees, packaging and transportation fees, taxes, and profit. Prices are greatly affected by steel market conditions, material specifications, and purchase volume.