SS400????????????????????

 针对SS400钢板在生产过程中产生的表面纵向裂纹现象进行宏观观察和微观的测试与分析。结果表明：钢板表面纵向裂纹大部分是以平行束或网状形式集中分布在钢板宽度方向的两个1/4区域内，裂纹的长度一般在0.5~2 m，宽度均小于1 mm，深度为0.1~0.2 mm。无论是纵向裂纹还是横向裂纹，其裂纹沟内均含有由Na、Mg、Al、Si、Cl、K、Ca等元素组成的复合夹杂物相，而在裂纹的内部却只有氧化铁夹杂物。进一步分析后认为，该表面缺陷产生于连铸结晶器内，在随后二冷区的强冷和加热炉的加热过程中，裂纹得到了进一步的扩展。

Surface Longitudinal Crack Measurement and Analysis for SS400 Steel Sheet

Surface longitudinal cracks were macroscopically observed and macroscopically analyzed for SS400 steal sheet which occurred in the production process.The results showed that most of the longitudinal cracks were distributed in the couple of 1/4 areas along the width direction of the steal sheet as parallel beam or reticulate form.The length and the depth of the cracks were 0.5-2 mm and 0.1-0.2 mm,respectively,and the width was less than 1 mm.Complex inclusions which composed of Na、Mg、Al、Si、Cl、K、Ca,etc.were found along the width of the cracks,whatever it is longitudinal crack or transverse crack,while only ferric oxide was found inside the cracks.Further analysis showed that such surface cracks originally formed in the successive mould,and further enlarged by the following secondary cooling and furnace heating.