Cast steel material for pressure vessels and method of making a pressure vessel by using same

摘要

The present invention provides a cast steel material for pressure vessels which has improved impact resistance (weldability) and toughness while maintaining its creep rupture strength at a level equal to or higher than the excellent creep rupture strength currently possessed by CrMoV cast steel, as well as a method of making a pressure vessel (or cast steel article) by using this cast steel material which permits a pressure vessel to be made without requiring a material working step such as forging. Specifically, the present invention relates to a cast steel material for pressure vessels which contains C, Si, Mn, Ni, Cr, Mo, V, W, Nb and/or Ta, B, Ti, Al, N, O, P and S in predetermined proportions, the balance being Fe and incidental impurities, provided that the contents of Ti, Al, O and N satisfies the following relationship: N - 0.29äTi - 1.5(O - 0.89Al)ü ≤ 0.0060%, and to a method of making a pressure vessel wherein the aforesaid cast steel material is cast and then heat-treated under predetermined conditions.