항복점 연신이 저탄소강의 Fluting 현상에 미치는 영향

Effect of Yield Point Elongation at Fluting Effect of Low Carbon Steel

Low-carbon steel plates that are often used in the external plates of home electronics generally undergo annealing, plating and skin pass rolling after cold rolling. Most of them are made into painted steel plates in a manufacturing line and then formed into the final parts. The manufacturing process of painted steel plate consists of pre-treatment, primer coating, top coating, and tension leveling. During baking after painting, they stay at approximately 230℃ for about 60 seconds. In this heating process, aging of the steel plates is accelerated and a high degree of yield point elongation (YPE) occurs. When YPE occurs, the strength of the material is improved, but if a seriously aged steel plate is bended, a discontinuous bending deformation occurs on the bended steel plate. This deformation can be regarded as a kind of plastic hinge, and it is called fluting. This non-uniform plastic deformation is treated as an important defect in home electronics because it not only causes a problem in their functions but also takes away their commercial value. There are not many studies on this fluting in bending process. Aratani and Tosaka studied on the relationship between YPE and fluting in bending process and the influence of post-processing on the forming of the body of a 3-piece can. They experimented with a 0.18t material and found that bending at the diameter of 45 mm generated fluting at 4.5% or higher YPE. However, there have bee no studies on low-carbon steel plates with the thickness of 0.5∼0.6t which are often used in home electronics. Further studies are still necessary on the controlling method for the onset conditions and size of YPE, and some studies have been reported. This study reviewed the influence of the size of YPE on the generation of fluting. The section of YPE for controlling defects was determined by comparing the lengths of the YPE sections of defective and good PCM steel plates.