HIGH-STRENGTH COLD ROLLED STEEL SHEET EXCELLING IN CHEMICAL TREATABILITY

摘要

A high-strength cold rolled steel sheet that even when doped with Mo in order to attain a strength increase, exhibits stable excellent chemical treatability. With respect to the surface properties of the cold rolled steel sheet, there is satisfied the characteristic that not only is the maximum depth of unevenness (Ry) 10 µm or more but also the average spacing of the unevenness (Sm) is 30 µm or less. Further, there is satisfied either the characteristic that the load length ratio of surface unevenness (tp40) is 20% or below, or the characteristic that the difference between mentioned load length ratios (tp60) and (tp40) is 60% or above; preferably, there are satisfied both the characteristics.Still further, the surface has no cracks of 3 µm or less width and 5 µm or more depth.