| 摘要 |
PROBLEM TO BE SOLVED: To obtain a steel sheet free from flaws caused by surface cracking in continuous casting and excellent in surface properties by allowing it to contain specified weight ratios of chemical components such as C, Si, Mn, Al and N. SOLUTION: This steel sheet has a chemical compsn. contg., by weight, <=0.2% C, 0 to 2.0% Si, 0.05 to 2.0% Mn, 0.3 to 2.5% Al and 0.002 to 0.01% N. The coarsening of AlN in the grains in a low temp.γregion is promoted to suppress then hardening in the grains, the difference in the strength with nonsegregated zones in the vicinities of the grain boundaries is eliminated, and the concentration of strains on the nonsegregated zones is suppressed to prevent the embrittlement therein. In theα+γregions, the formation of ferrite onto the grain boundaries is suppressed by Al, the conversion into film-shaped ferrite is suppressed, the amt. of ferrite increases, and the concentration of strains is suppressed to prevent the embrittlement therein. In this way, the maintenance of a slab before hot rolling is made needless, so that the working cost and the energy cost can be reduced. In the case the strength and formability of the steel sheet are required, Nb, V, Cr, Mo, Zr or rare earth elements may be added thereto.
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