Kobe Steel, Ltd.

Masashi Kawauchi

Yoshihiro Yamaguchi

Tsugio Kaneda

Sodai Kita

Yoshihide Fuchino

Sadayashi Furusawa

Takashi Shimohata

Shuzi Iwata

This invention relates to a free-cutting steel that is used as a material for mechanical construction members be manufactured by machining as well as cold working. There has been proposed resulfurized free-machining steels containing large amounts of sulfur to improve the machinability, as well as resulfurized free-machining steels containing sulfur and zirconium to improve machinability and cold workability. None of these steels, however, simultaneously satisfy the machinability cold workability and mechanical properties required of steels used for the construction of machines. The present invention provides a steel comprising 0.08 to 0.6% of carbon, 0.35% or less of silicon, 0.3 to 1.5% of manganese, 0.04 to 0.15% of sulfur, 0.010 to 0.05% of aluminum, 0.01 to 0.08% of niobium, 0.008% or less of oxygen, 0.008% or less of nitrogen, wherein the amount of zirconium being 0.2 to 1.2 in terms of (Zr% -2.9x 0% -6.5x N%)/S%, the steel has a refined grain size and controlled sulfide morphology, and exhibits improved machinability, cold workability and mechanical properties.

Grain refined free-machining steel

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Kobe, Japan

Masashi Kawauchi