| 摘要 |
PURPOSE:To obtain a steel having superior hydrogen attack resistance and superior allowable stress characteristics at high temp. and maintaining the high toughness even through stress relief annealing after welding by adding B and Cr to 1/2Mo or further adding Cu or Ni. CONSTITUTION:This steel consists of, by wt., 0.07-0.22% C, 0.05-0.50% Si, 0.10-0.95% Mn, 0.26-0.75% Cr, 0.45-0.60% Mo, 0.010-0.100% sol. Al, 0.00015-0.0010% B and the balance Fe with inevitable impurities or further contains >=1 kind of 0.10-0.50% Cu and 0.10-1.00% Ni. B enhances the hardenability during normalizing, and the lower limit or more of B is required, yet more than the upper limit of B deteriorates the toughness. Cr prevents carbide from coarsening during stress relief annealing and use, yet less than the lower limit of Cr produces an insufficient effect, and more than the upper limit of Cu deteriorates the weldability. Cu and Ni enhance the hardenability during normalizing, and they improve the strength and toughness, respectively, yet less than the lower limits of Cu and Ni do not produce the effects. More than the upper limit of Cu causes deterioration in the toughness, surface cracking and weld hot cracking, and more than the upper limit of Ni results in a higher cost. |
