Patent ID: 7338630

Claim:
A free-cutting steel consisting essentially of, in % by mass, C: 0.1-0.5%, Si: 0.05-2.5%, Mn: 0.1-3.5%, S: 0.0005-0.004%, Al: 0.01-0.06% Ti: 0.003-0.01%, O: up to 0.0015%, N: 0.003-0.01%, Bi: 0.015-0.025%, and the balance of Fe and inevitable impurities, wherein the formula (1) below is satisfied: −4.8≦log(([ N]− 0.0015)×[ Ti] 0.98 )≦−4.3 formula (1); wherein these inclusions reside in the steel texture: a composite inclusion, in which a sulfide-base inclusion and a Bi metal inclusion are hybridized, has a maximum diameter √{square root over ( )}AREAmax (MnS+Bi), estimated by the extreme value statistics, of 25 μm or less; the sulfide-base inclusion as a single entity has a maximum diameter √{square root over ( )}AREAmax (MnS), estimated by the extreme value statistics, of 20 μm or less; and the Bi metal inclusion as a single entity has a maximum diameter √{square root over ( )}AREAmax (Bi), estimated by the extreme value statistics, of 20 μm or less.