| 摘要 |
<p>A steel plate which has a thickness of 4 mm or more and less than 10 mm, wherein interior portions thereof having distances from its surface of 1/4 and 3/4 of its thickness have a ferrite proportion of 30 to 90 %, and an interior portion having a distance from the surface thereof of 1/2 of its thickness has a ferrite proportion of 20 to 90 %; and a steel plate which has a thickness of 10 to 100 mm, wherein interior portions thereof having distances from the surface and the back surface thereof of 2 mm have a ferrite proportion of 30 to 90 %, and interior portions thereof having distances from its surface of 1/4, 1/2 and 3/4 of its thickness have a ferrite proportion of 20 to 90 %. The above steel plate is produced by a method comprising using a steel having the contents of C, Si, Mn, P, S, Al and N being limited to prescribed ranges and optionally further containing Mo, Cr, Nb, Ti, V, Cu, Ni, B, REM, Ca, Zr and/or Mg, and strictly specifying the balance between components of the steel, and comprising strictly controlling the conditions in rolling, washing with water, and the like, and is excellent in machinability, toughness and weldability. ® KIPO & WIPO 2007</p> |
