| 摘要 |
PURPOSE:To improve weldability and toughness and also to secure the desired tensile strength after SR, by incorporating small amounts of Cr, Mo, and Nb to a carbon-steel plate with a specific composition and regulating the values of Pcm and CE and the value of ferrite grain size after normalizing, respectively. CONSTITUTION:A carbon-steel plate for boiler has a composition containing, by weight, 0.12-0.18% C, 0.10-0.50% Si, 0.10-2.0% Mn, 0.005-0.08% V, and <=0.030% SolAl, also containing 0.10-0.39% Cr, 0.05-0.20% Mo, and 0.005-0.08% Nb, and having the balance Fe with inevitable impurities. Further, the value of Pcm (index showing low-temp. cracking sensitivity at the time of welding) represented by equation I and the value of CE represented by equation II are regulated to <=0.25% and >=0.36%, respectively. Moreover, the ferrite grain size No. in the structure after normalizing is limited to >=8.
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