Study On Bending Properties Of Cold-rolled SPCC Steel Sheet

Compared with the hot rolling product, the cold rolling product has the following advantages. First, the size is accurate and the thickness is uniform. Second, it meets the requirements of good surface quality and excellent shape of strip. Next, it is covering a wide range of variety and application. Finally, its production efficiency is high. As the representative of cold rolled plates, cold-rolled SPCC steel sheet has been widely used in such trades as automobile, household appliance, chemical and construction with the features of excellent drawing properties and aesthetic appearances. It has increasingly become one of the important steel material products in modern industry because of its high production, excellent quality and good economic benefit.The bending fracture defect was found in a batch of cold-rolled SPCC steel sheets which were produced by Shandong Taishan Steel. After sampling from these defective products, bending tests were done for these samples which have different chemical compositions and different reduction rates. By means of chemical composition analysis, microstructure analysis of the bending specimen, fracture morphology analysis and inclusion testing, this article studies systematically the influence rule of smelting process, reduction rate, annealing process and bending direction on bending property of cold-rolled SPCC steel sheet.The main production process of cold-rolled SPCC steel sheet includes smelting, hot rolling, pickling, cold rolling, annealing and finishing. Tests revealed that it was the nonmetallic inclusion that wrecked continuity of the base. When the cold rolled sheet began to bend, the tiny cracks were developed more easily at where inclusion was distributed. LF refining process can effectively decrease the inclusion content and control the inclusion distribution. So, the use of LF refining process is one of the most effective ways to improve the quality of the steel and reduce the bending fracture defect. During the cold rolling process, reduction rate has little influence on the bending property of SPCC steel sheet. Experiments show that the bending property of the samples is the worst when the bending line goes parallel to the rolling direction, but the bending property becomes better when the bending line and the rolling direction forms an angle of 45 or 90 degrees.According to the results, LF refining process can improve the quality of the cold rolling plate by effectively controlling inclusion content. When designing blanking process, technology engineers should pay attention to the bending direction of the product. The problem of bending fracture can be effectively avoided by making the bending line perpendicular to the rolling direction. Currently the most popular cold-rolled SPCC steel sheet on the market is usually annealed, but the tests showed that SPCC sheet which has not yet been annealed can also has good performance by controlling the non-metallic inclusion content. The unannealed SPCC steel sheet can be used in the real application especially when it only needs to be bended less than 90 degrees. This can effectively help reduce costs.