| 摘要 |
PROBLEM TO BE SOLVED: To provide steel which has satisfactory toughness, and to provide a production method therefor. SOLUTION: In the steel, the cleanliness of nonmetallic inclusions with a length of >=2μm is <=0.050%, and the average value of inclusion indexes A expressed by formula (1) as for nonmetallic inclusions with a length of <2μm is 5,000 nm; wherein, (m) in formula (1) is the number (pieces) of nonmetallic inclusions of <2μm present in the field at an angle of 10μm when an optional position of the steel is observed in the above field; LX is the length (nm) of nonmetallic inclusions of <2μm observed on the Xth when the optional position of the steel is observed in the field at an angle of 10μm; and (n) is a coefficient satisfying 0 in the case of LX<=20 nm, 1 in the case of 0.20 nm<LX<=250 nm, 3 in the case of 250 nm<LX<=500 nm, and 4 in the case of 500 nm<LX<2μm.
|
