| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a thick steel plate excellent in toughness of a weld heat-affected zone in which HAZ toughness is excellent when giving high heat input welding, a low yield ratio can be realized, and further, which can also assure favorable base material toughness. <P>SOLUTION: The thick steel plate satisfies a predetermined chemical composition, includes an oxide which satisfies that in a constituent element except oxygen Ti>10%, Al<20%, 5%<Ca<40%, 5%<REM<50% and/or 5%<Zr<40%, wherein an oxide having less than 2μm of an equivalent circle diameter is at least 200 pieces/mm<SP POS="POST">2</SP>, an oxide having at least 2μm and less than 5μm of an equivalent circle diameter is 30-70 pieces/mm<SP POS="POST">2</SP>, and an oxide having at least 5μm of an equivalent circle diameter is less than 30 pieces/mm<SP POS="POST">2</SP>, and includes at least 5×10<SP POS="POST">6</SP>pieces/mm<SP POS="POST">2</SP>of a Ti containing nitride having at most 100 nm of an equivalent circle diameter. <P>COPYRIGHT: (C)2012,JPO&INPIT</p> |
