| 摘要 |
PROBLEM TO BE SOLVED: To obtain a sprit T shape steel having mechanical strength and toughness approximately equal to those of an extremely thick gauge H steel by specifying the compositional components in a steel, furthermore specifying the thickness of the specified region from the surface therein and imparting specified high tensile strength and Charpy absorbed energy thereto. SOLUTION: This steel is the one having a compsn. contg., by weight, 0.15 to 0.20% C, 0.05 to 0.25% Si, 0.8 to 1.4% Mn, <0.5% Cr, <0.05% Nb, <0.025% Ti, <0.08% Al, <0.4% Mo, <0.003% B, <0.006% N, and the balance Fe with inevitable impurities, having >=0.5mm thickness with >420Hv hardness within a depth of 3mm from the surface and having >=490MPa high tensile strength and >=47H Charpy absorbed energy at 0 deg.C. If required, one or >= two kinds among <1.0% Cu, <1.0% Ni and <0.1% V may furthermore be incorporated therein. |
