Nippon Steel Corporation

Kohichi Isobe

Masayuki Hashimura

Hiroshi Hirata

Hiroshi Hagiwara

Atsushi Mizuno

Kenichiro Naito

Ken-ichiro Naito

Kenji Fukuyasu

The present invention provides steel superior in machinability comprised of, by wt %, C: 0.005 to 0.2%, Si: 0.001 to 0.5%, Mn: 0.2 to 3.0%, P: 0.001 to 0.2%, S: 0.03 to 1.0%, T.N: 0.002 to 0.02%, T.O: 0.0005 to 0.035%, and the balance of Fe and unavoidable impurities, said steel satisfying one or both of Mn/S in the steel being 1.2 to 2.8 or an area ratio of pearlite over a grain size of 1 &#x3bc;m in a microstructure of the steel being not more than 5%.

Method of production of steel superior in machinability

Superior in machinability and method of production of same

The present invention is a steel, excellent in machinability, wherein forging workability is improved by suppressing the deterioration of mechanical properties in the direction in which the mechanical properties are the lowest, and more specifically, is a steel excellent in forgeability and machinability, characterized in that: the steel contains, in mass, C: 0.1 to 0.85%, Si: 0.01 to 1.5%, Mn: 0.05 to 2.0%, P: 0.003 to 0.2%, S: 0.003 to 0.5%, and Zr: 0.0003 to 0.01%; the following steel components are controlled in the following ranges respectively, in mass, Al: 0.01% or less, total O: 0.02% or less, and total N: 0.02% or less; the average aspect ratio of MnS grains is 10 or less and the maximum aspect ratio of those is 30 or less; and the balance of the steel components consists of Fe and unavoidable impurities.

Steel excellent in forgeability and machinability

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Muroran, Japan

Kohichi Isobe