Jfe Steel Corporation

Kimihiro Nishimura

Masayuki Kasai

Takashi Iwamoto

Kazuaki Fukuoka

Keisuke Ando

Naoya Ihara

Shinichi Suzuki

Nobuyuki Ishikawa

Kazukuni Hase

Mitsuhiro Okatsu

Kunikazu Tomita

Yoshihiro Yazawa

Junji Shimamura

Tatsumi Kimura

Tomoyuki Yokota

Katsuyuki Ichimiya

Minoru Honjo

Seiji Nabeshima

Nobuo Shikanai

Shinji Mitao

Keiji Ueda

Yota Kuronuma

Kazuhiko Shiotani

Akihiko Tanizawa

Hitoshi Sueyoshi

Yuta Imanami

Masayuki Horie

Shunichi Tachibana

Toshiyuki Hoshino

Yasumitsu Kiyoto

Tsutomu Komori

Keiichiro Kishi

Yasuto Inohara

Free-cutting steel that has the same or better machinability compared to low-carbon sulfur-lead composite free-cutting steel, despite of no-addition of Pb, is provided. Free-cutting steel contains, in mass %, C: 0.08% or less, Mn: 0.50 to 1.50%, P: 0.100% or less, S: 0.250 to 0.500%, N: 0.0050 to 0.0150%, O: more than 0.0100% and 0.0500% or less, Cr: 0.50 to 1.50%, at least one of Si, Al, or Ti: 0.050 to 0.500% in total, with the balance being Fe and inevitable impurities, with an A value defined by formula (1) satisfying 0.40 to 2.00, and with a B value defined by formula (2) satisfying 1.10×10to 1.50×10; and a steel microstructure with distributed 3000 or more sulfide particles with an equivalent circular diameter of 5 μm or less per mm.

Free-cutting steel and method for manufacturing same

Free-cutting steel includes a specific composition, with an A value defined by a following formula (1) satisfying 4.0 or more and 20.0 or less, and remainder having Fe and an unavoidable impurity; and texture with 1000 or more sulfide particles with an equivalent circle diameter of less than 1 μm per mm, 500 or more sulfide particles with an equivalent circle diameter of 1 μm or more and 5 μm or less per mm, and 1000 or more Pb particles with an equivalent circle diameter of 1 μm or less per mm, whereinA value=(Mn+5Cr)/S  (1)

Free-cutting steel and manufacturing method thereof

Provided is a steel for nitrocarburizing that ensures mechanical workability before nitrocarburizing treatment. A steel for nitrocarburizing comprises: a chemical composition containing, in mass %, C: &#x2265;0.02% and &#x3c;0.15%, Si: &#x2264;0.30%, Mn: 1.5-2.5%, P: &#x2264;0.025%, S: &#x2264;0.06%, Cr: 0.5-2.0%, Mo: 0.005-0.2%, V: 0.02-0.20%, Nb: 0.003-0.20%, Al: &#x3e;0.020% and &#x2264;1.0%, Ti: &#x3e;0.0050% and &#x2264;0.015%, N: &#x2264;0.0200%, Sb: 0.0030-0.010%, with a balance being Fe and inevitable impurities, satisfying Expression (1) or (2); and a steel microstructure where an area ratio of bainite phase is &#x3e;50%, a prior austenite grain size is &#x2264;100 &#x3bc;m, &#x2265;300/&#x3bc;mTi precipitates with an equivalent circular particle size of &#x2264;30 nm disperse, Sb segregates to prior austenite grain boundaries.

Steel for nitrocarburizing and nitrocarburized component, and methods of producing same

Provided is a wire rod that has superior machinability by cutting regardless of the type of tool material and the type of lubricant and even in the case where no lubricant is used. A wire rod for cutting work comprises: a specific chemical composition; and Vickers hardness that satisfies the following expressions (1) and (2) in the case where an average aspect ratio of ferrite grains at a position of &#xbc; of a diameter from a surface of the wire rod for cutting work is more than 2.8, and satisfies the following expressions (3) and (4) in the case where the average aspect ratio is 2.8 or less,H&#x2264;350&#x2003;&#x2003;(1)H&#x2264;30&#x2003;&#x2003;(2)H&#x2264;250&#x2003;&#x2003;(3)H&#x2264;20&#x2003;&#x2003;(4).

Wire rod for cutting work

Disclosed are a case hardened steel which is suitable as a material for producing mechanical structural parts having high rotating bending fatigue strength and impact fatigue strength at a relatively low cost, and a method of producing the same. The case hardening steel has a chemical composition containing, by mass %, C, Si, Mn, P, S, Cr, Mo, B, Ti, N, and O within a range satisfying a predetermined relationship, and Al in at least a predetermined amount in relation to the B, N, and Ti contents, with the balance being Fe and inevitable impurities, wherein &#x221a;I&#x2264;80 is satisfied, where I represents an area in &#x3bc;mof an oxide-based inclusion located at the center of a fish-eye on a fracture surface of the case hardening steel after being subjected to carburizing-quenching and tempering and subsequently to a rotating bending fatigue test.

Case hardening steel, method of producing the same, and method of producing gear parts

Provided is a steel for nitrocarburizing that can ensure hardened case depth by suppressing precipitation of Cr, V, and Nb in a part of the surface layer very close to the surface. The provided steel comprises: a specific chemical composition satisfying 9.5&#x2264;([Cr]/52+[V]/50.9+[Nb]/92.9+M)&#xd7;10&#x2264;18.5, with the balance being Fe and inevitable impurities; and a steel microstructure in which an area ratio of bainite phase with respect to the entire microstructure is more than 50%.

Steel for nitrocarburizing, and component

A case hardening steel suitable as raw material for producing a mechanical structural part having high rotating bending fatigue strength and pitting fatigue strength at relatively low cost and a method of producing the case hardening steel are provided. A case hardening steel comprises a chemical composition containing, in mass %, C, Si, Mn, P, S, Cr, Mo, Al, N, and O in a predetermined relationship, with a balance being Fe and inevitable impurities, wherein &#x221a;I&#x2264;80 (where I denotes an area (&#x3bc;m) of an oxide-based inclusion located in a fish eye central portion at a fracture surface after subjecting the case hardening steel to carburizing-quenching and tempering and then performing a rotating bending fatigue test).

Case hardening steel, method of producing case hardening steel, and method of producing gear part

A steel plate has a chemical composition containing, by mass %, C: 0.03% or more and 0.08% or less, Si: 0.01% or more and 1.0% or less, Mn: 1.2% or more and 3.0% or less, P: 0.015% or less, S: 0.005% or less, Al: 0.08% or less, Nb: 0.005% or more and 0.07% or less, Ti: 0.005% or more and 0.025% or less, N: 0.010% or less, O: 0.005% or less and the balance being Fe and inevitable impurities, a structure being a dual-phase structure consisting of a bainite phase and island martensite, wherein the area fraction of the island martensite is 3% to 15%, the equivalent circle diameter of the island martensite is 3.0 &#x3bc;m or less, and the remainder of the structure is a bainite phase.

High strength steel plate having low yield ratio excellent in terms of strain ageing resistance, method of manufacturing the same and high strength welded steel pipe made of the same

A steel plate has a chemical composition containing, by mass %, C: 0.03% or more and 0.08% or less, Si: 0.01% or more and 1.0% or less, Mn: 1.2% or more and 3.0% or less, P: 0.015% or less, S: 0.005% or less, Al: 0.08% or less, Nb: 0.005% or more and 0.07% or less, Ti: 0.005% or more and 0.025% or less, N: 0.010% or less, O: 0.005% or less and the balance being Fe and inevitable impurities, a metallographic structure including a bainite phase and island martensite, and a polygonal ferrite in surface portions within 5 mm from the upper and lower surfaces, wherein the area fraction of the island martensite is 3% to 15%, the equivalent circle diameter of the island martensite is 3.0 &#x3bc;m or less, the area fraction of the polygonal ferrite in the surface portions is 10% to less than 80%.

Provided are a steel pipe for a linepipe with high compressive strength and a heavy wall thickness, and a method of manufacturing the same. Lowering of yield stress caused by a Bauschinger effect can be suppressed by optimizing the metal microstructure of a steel plate without requiring particular forming conditions in forming the steel pipe, and without requiring heat treatment after pipe making. A steel pipe has the composition which contains by mass % 0.03 to 0.10% C, 0.30% or less Si, 1.00 to 2.00% Mn, 0.015% or less P, 0.003% or less S, 0.080% or less Al, 0.005 to 0.035% Nb, 0.005 to 0.020% Ti, and Fe and unavoidable impurities as a balance. The steel pipe has metal microstructure where a fraction of bainite is 60% or more, a fraction of rolled ferrite is 5% or less, and a fraction of M-A constituent (MA) is 3% or less.

Welded steel pipe for linepipe with high compressive strength and manufacturing method thereof

An internal high hardness type pearlitic rail that has a composition containing 0.73% to 0.85% by mass C, 0.5% to 0.75% by mass Si, 0.3% to 1.0% by mass Mn, 0.035% by mass or less P, 0.0005% to 0.012% by mass S, 0.2% to 1.3% by mass Cr, and the balance being Fe and incidental impurities, in which the value of [% Mn]/[% Cr] is greater than or equal to 0.3 and less than 1.0, where [% Mn] represents the Mn content, and [% Cr] represents the Cr content, and in which the internal hardness of a rail head that is defined by the Vickers hardness of a portion located from a surface layer of the rail head to a depth of at least 25 mm is greater than or equal to 380 Hv and less than 480 Hv.

Internal high hardness type pearlitic rail with excellent wear resistance and rolling contact fatigue resistance and method for producing same

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Tokyo, Japan

Kimihiro Nishimura