| 摘要 |
PROBLEM TO BE SOLVED: To realize a steel sheet or a steel pipe excellent in hydrogen-induced crack resistance, and further to realize a steel sheet or a steel pipe allowing evaluation of hydrogen-induced crack resistance from an internal quality of a cast slab without conducting a hydrogen-induced crack test after rolling.SOLUTION: A steel sheet excellent in hydrogen-induced crack resistance satisfies regular C, Si, Mn, P, S, Al, Ca, N and O, and further, includes one or more elements selected from a group consisting of regular REM and Zr, and the balance consists of iron and inevitable impurities. The ratio of the Ca and the S (Ca/S) is 2.0 or higher. The Ca, the S and the O satisfy (Ca-1.25S)/O≤1.80. A Ca drop amount obtained by subtracting a Ca concentration of a slab from a Ca concentration of molten steel within a tundish is a threshold value Caor lower. The threshold value Cais the maximum Ca drop amount capable of avoiding a hydrogen-induced crack in a steel sheet obtained by rolling the slab.SELECTED DRAWING: Figure 6 |
