| 摘要 |
PROBLEM TO BE SOLVED: To produce a steel having high strength of >=1100MPa tensile strength and furthermore excellent in delayed fracture resistance. SOLUTION: This steel has a compsn. contg., by weight, 0.20 to 0.50% C, 0.2 to 2.0% Si, one ore two kinds among Mn, Ni, Cr and Mo respectively by 0.2 to 3.0% one or >= two kinds among Al, Nb, V and Ti respectively by 0.01 to 0.3%, <=0.02% Ni, and the balance Fe with inevitable impurities, in which the main structure is composed of tempered martensite, and the precious austenitic grain boundary is applied with a ferritic layer having 0.1 to 10μm thickness. Its tensile strength is regulated to 1100 to 1500MPa.
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