| 摘要 |
PROBLEM TO BE SOLVED: To provide a high cleanliness rolled steel material excellent in cold workability and fatigue characteristic by specifying the numerical value calculated by a specific equation from the size and the number of inclusions existing in minute amounts in a steel material of specific composition and defined by L cross section observation. SOLUTION: This high cleanliness rolled steel material, excellent in cold workability and fatigue characteristic, has the following characteristics: the number of inclusions of >=50% Al2 O3 , content and >=20μm size, among the inclusions detected by applying EPMA analysis to the insoluble inclusions obtained by dissolving a steel material of 0.005% total Al content and 10-40ppm total oxygen content in an aqueous solution of mixed acids consisting of [(250ml of 60% nitric acid)+ (10ml of 96% sulfuric acid)+(550ml of pure water)] heated to 90-95 deg.C, is regulated to <=15 pieces for 50g of the meltage of the steel material; the score, determined by an equation in an additional keyword column (1) with respect to the inclusions detected withion an area of <=110mm<2> , including the whole region of the width of a longitudinal cross section, in an arbitrary longitudinal cross section passing through the axial center of a linear or bar-shaped rolled steel material of the above steel material and parallel to rolling direction, is regulated to <=6.
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