| 摘要 |
An electron-beam welded joint including, as a composition of a steel, by mass%, at least, C: 0.02% to 0.10%, Si: 0.03% to 0.30%, Mn: 1.5% to 2.5%, Ti: 0.005% to 0.015%, N: 0.0020% to 0.0060%, O: 0.0010% to 0.0035%, Mg: 0.0003% to 0.0027%, Ca: 0.0003% to 0.0027%, Nb: 0% to 0.020%, V: 0% to 0.030%, Cr: 0% to 0.50%, Mo: 0% to 0.50%, Cu: 0% to 0.25%, Ni: 0% to 0.50%, B: 0% to 0.0030%, Al: limited to 0.015% or less, P: limited to 0.015% or less, S: limited to 0.010% or less, a balance consisting of iron and unavoidable impurities, wherein amounts in mass% of Mg and Ca in the composition of the steel satisfy 0.0006% ‰¤ Mg + Ca ‰¤ 0.0040%, an index value CeEB of hardenability after electron-beam welding obtained by the composition of the steel is 0.49% to 0.60%, a number of oxides having an equivalent circle diameter of 1.0 µm or more is 20 pieces/mm 2 or less at a thickness center portion in a cross-section along a thickness direction of the steel, and a number of oxides containing Mg of 7% or more and having an equivalent circle diameter of 0.05 µm or more and less than 0.5 µm is 1 × 10 3 to 1 × 10 5 pieces/mm 2 at the thickness center portion. |
