| 摘要 |
PROBLEM TO BE SOLVED: To provide a non-refining steel reduced in toughness and ductility and excellent in breaking splittability by allowing the specified number of sulfide inclusions having the specified width or above to exist on the longitudinal section at the position to a specified thickness from the surface of a forging material and controlling the average aspect ratio (length/width) of the sulfide inclusions to the specified value or below. SOLUTION: On the longitudinal section at the position apart by 1/4 of the thickness from the surface of a forging material, sulfide inclusions of >=1μm width are present by 100 to 4000 pieces/mm2, and, moreover, the average aspect ratio of the sulfide inclusions is <=10. This invention preferably has a compsn. contg., by mass (including no 0%), <=2.0% Mn and <=0.11% S, moreover contg. at least one kind selected from the groups of <=0.2% Zr, <=0.1% Ti, <=0.01% Mg, <=0.01% Ca, <=0.1% Se, <=0.1% Te and <=0.3% rare earth metals and furthermore contg. 0.15 to 0.6% C, <=1.5% Si, <=0.15% P, <=2% Cr, <=0.06% Al and 0.03% N.
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