| 摘要 |
PROBLEM TO BE SOLVED: To prevent the softening of the weld heat affected zone in a thin steel sheet used for a structural member such as chassis line of an automobile accompanied with welding. SOLUTION: This high tensile strength thin steel sheet narrow in the weld heat affected softened zone is the one having a compsn. contg., by weight, 0.01 to 0.05% C, 0.5 to 3.0% Si, 0.8 to 3.0% Mn, 0.02 to 0.10% Nb, 0.002 to 0.010% N, and the balance Fe with inevitable impurities and satisfying 7.0×10-4>= [N wt.%] [Nb wt.%]>=5.0×10-5 and having a structure of ferrite and martensite.
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