| 摘要 |
PROBLEM TO BE SOLVED: To obtain a steel plate restraining the development of a notch at the time of machining with a laser beam and excellent in the laser beam machnability by developing a specific quantity of magnetite on the steel plate surface from the interface between a scale and the baser steel. SOLUTION: In order to improve the laser beam machinability of the stele plate, the scale having <= about 20μm thickness is formed and the developing quantity of the magnetite in the scale is made to >=15vol%. Further, when growing the magnetite from the interface between the scale and the baser steel, the machinability is further improved due to the stickiness of the scale. In order to control the development of such a scale, at the time of hot-rolling by direct heating or reheating of a hot steel slab, sufficient descaling is executed before the rolling and during the rolling to remove the scale developed during the rolling. Further, parameters of general producing condition composed of the last draft and rolling temp. in a finish-rolling, and the cooling speed and the cooling temp. just after the finish-rolling, are controlled. |
