| 摘要 |
<p>A steel thin plate which contains, in wt %, 0.04 to 0.1 % of C, 0.5 % or less of Si, 0.5 to 2 % of Mn, 0.05 % or less of P, 0.005 % or less of O and 0.005 % or less of S, and has an average ferrite grain diameter of 10 ν m or less and a frequency of formation A, which is defined as the total length of a second phase structure in the form of a band observed per 1 mm2 of the cross section of a plate along the direction of rolling, of 20 mm/mm2 or less. The steel thin plate can be produced, for example, by a method comprising a step of subjecting a continuously cast slab containing the above-mentioned components, directly or after re-heating, to a hot rolling at its Ar3 transformation temperature or higher, and a step of cooling the hot rolled steel plate to a temperature of 600 to 750C within 2 seconds at a cooling rate of 100 - 2000 °C / s and winding it up at a temperature of 450 to 650C. The steel thin plate has a high strength of 340 Mpa or higher, and also is excellent in ductility, stretch-flanging property and impact resistance even after hot dip zinc plating and can be wound into a coil having good surface properties.</p> |
