Kobe Steel, Ltd.

Sugita Wire, Ltd.

Kabushiki Kaisha Kobe Seiko Sho

Masamichi Chiba

Koji Yamashita

Kenichi Inoue

Takuya Kochi

Hiroyuki Mitani

Hideo Fujii

Takehiro Tsuchida

Atsushi Inada

Yosuke Matsumoto

Nobuaki Akagi

Hirofumi Hojo

Masato Kaiso

Tomotsuna Kamijo

Kei Masumoto

Kouji Yamashita

Yousuke Matsumoto

Ichiro Sugita

Masaru Tanimoto

Yoshimasa Ureshino

Yuki Sasaki

Reiko Kato

Masayuki Sakata

Shogo Murakami

Shingo Kasai

Provided is a steel for a mechanical structure for cold working, which contains C, Si, Mn, P, S, Al and N and in which the metal structure includes pearlite and ferrite, the total areal proportion of pearlite and ferrite relative to the overall structure is 90% or higher, the average circle-equivalent diameter of bcc-Fe crystal grains surrounded by large angle grain boundaries is 5-15 &#x3bc;m, the average aspect ratio of pro-eutectoid ferrite crystal grains is 3.0 or lower, and the average spacing at the narrowest pearlite lamellar spacing is 0.20 &#x3bc;m or less.

Steel for mechanical structure for cold working, and method for producing same

To provide a steel for high-strength bolts, which can exhibit the sufficient delayed fracture resistance under the severe environment, and also has excellent bolt formability. The steel for high-strength bolts of the present invention includes C: 0.10 to 0.30%; and Ni: 0.4 to 0.7%, with the chemical composition being appropriately adjust, and satisfies the following formulas (1) and (2):0.85&#x2264;[C]+[Si]/7+[Mn]/5+[Ni]/20+[Cr]/9+[Mo]/2&#x2264;1.3&#x2003;&#x2003;(1)[C]&#x2212;(0.07&#xd7;[Mo]+0.20&#xd7;[V])&#x2264;0.20&#x2003;&#x2003;(2).

Steel for high-strength bolts which has excellent delayed fracture resistance and bolt formability, and bolt

The present invention is a steel for a mechanical structure for cold working, the steel characterized in containing C, Si, Mn, P, S, Al, N, and Cr, the remainder being iron and inevitable impurities; the metal composition having pearlite and pro-eutectoid ferrite; the combined area of the pearlite and pro-eutectoid ferrite being 90% or more of the total composition; the area percentage A of the pro-eutectoid ferrite having the relationship A&#x3e;Ae, where Ae=(0.8&#x2212;Ceq)&#xd7;96.75 (Ceq=[C]+0.1&#xd7;[Si]+0.06&#xd7;[Mn]&#x2212;0.11&#xd7;[Cr], and '(element names)' indicates the element content (percent in mass); and the mean grain size of the pro-eutectoid ferrite and the ferrite in the pearlite being 15 to 25 &#x3bc;m.

Steel for mechanical structure for cold working, and method for manufacturing same

Provided are a steel for a mechanical structure for cold working, and a method for manufacturing the same, whereby softening and variations in hardness can be reduced even when a conventional spheroidizing annealing process is performed. A steel having a predetermined chemical composition, the total area ratio of pearlite and pro-eutectoid ferrite being at least 90 area % with respect to the total metallographic structure of the steel, the area ratio (A) of pro-eutectoid ferrite satisfying the relationship A&#x3e;Ae with an Ae value expressed by a predetermined relational expression, the average equivalent circular diameter of bcc-Fe crystal grains being 15-35 &#x3bc;m, and the average of the maximum grain diameter and the second largest grain diameter of the bcc-Fe crystal grains being 50 &#x3bc;m or less in terms of equivalent circular diameter.

Provided are: a boron-added high strength steel for bolt excellent in delayed fracture resistance even having a tensile strength of 1100 MPa or more without addition of large amounts of expensive alloy elements such as Cr and Mo: and a high strength bolt made from the boron-added high strength steel for bolt. The high strength steel for bolt contains C of 0.23% to less than 0.40%, Si of 0.23% to 1.50%, Mn of 0.30% to 1.45%, P of 0.03% or less (excluding 0%), S of 0.03% or less (excluding 0%), Cr of 0.05% to 1.5%, V of 0.02% to 0.30%, Ti of 0.02% to 0.1%, B of 0.0003% to 0.0050%, Al of 0.01% to 0.10%, and N of 0.002% to 0.010%, with the remainder being iron and inevitable impurities. The steel has a ratio ([Si]/[C]) of the Si content [Si] to the C content [C] of 1.0 or more and has a ferrite-pearlite mixed microstructure.

Boron-added high strength steel for bolt and high strength bolt having excellent delayed fracture resistance

A steel wire for high-strength bolts is used for a non heat-treatment bolt with an excellent cold forgeability for which quenching and tempering steps have been omitted after bolt formation, and which has a tensile strength of 1200 MPa or more and an excellent delayed fracture resistance. The steel wire includes C, Si, Mn, P, S, Cr, Al, N, and B, at least one selected from the group consisting of Ti, V, and Nb with the balance consisting of iron and inevitable impurities. The steel wire has a microstructure wherein ferrite and perlite have a total area rate of 98% or more, perlite lamellar spacing is 250 nm or less, and an area rate of the perlite is more than 40%, and 80% or less. The steel wire has a tensile strength of 1300 MPa or less.

Steel wire for bolt, bolt, and manufacturing processes therefor

A steel is used for providing a bolt that has a high strength and still exhibits excellent hydrogen embrittlement resistance. The steel contains C of 0.30% to 0.50%, Si of 1.0% to 2.5%, Mn of 0.1% to 1.5%, P of greater than 0% to 0.015%, S of greater than 0% to 0.015%, Cr of 0.15% to 2.4%, Al of 0.010% to 0.10%, N of 0.001% to 0.10%, Cu of 0.1% to 0.50%, Ni of 0.1% to 1.0%, Ti of 0.05% to 0.2%, and V of 0% to 0.2%, with the remainder including iron and inevitable impurities, in which a ratio [Ni]/[Cu] is 0.5 or more, and a total content [Ti]+[V] is 0.085% to 0.30%.

Steel for bolt use, bolt, and method for manufacturing bolt

Provided is an iron-based soft magnetic powder for dust core having a less coercive force, which is obtained by specifying the amount of inclusions in the iron-based powder for dust core, and at the same time, capable of decreasing the coercive force of a dust core produced using the iron-based soft magnetic powder. The iron-based soft magnetic powder for dust core is characterized by that when the cross-section of the iron-based soft magnetic powder particle is observed with a scanning electron microscope, the number of inclusions having an equivalent circle diameter from 0.1 to 3 &#x3bc;m is 1&#xd7;10pieces/mmor less and the number of inclusions having an equivalent circle diameter exceeding 3 &#x3bc;m is 10 pieces/mmor less.

Iron-based soft magnetic powder for dust core, preparation process thereof, and dust core

A soft magnetic steel has, on the mass basis, a carbon content of 0.0015% to 0.02%, a manganese content of 0.15% to 0.5%, and a sulfur content of 0.015% to 0.1%, has a ratio Mn/S of 5.7 or more, and contains a single-phase ferrite microstructure as its metallographic structure, in which the density of precipitated FeS grains having a major axis of 0.1 &#x3bc;m or more is 5000 grains/mmor less. This steel ensures excellent magnetic properties with less variation after magnetic annealing, exhibits excellent machinability and cold forgeability during production processes, and can thereby yield a steel part even having a complicated shape and a large size in a high yield.

Soft magnetic steels excellent in cold forgeability, machinability and magnetic properties, and soft magnetic steel parts excellent in magnetic properties

A soft magnetic low-carbon steel has a chemical composition having a C content of 0.05% by mass or below, Si content of 0.1% or below, a Mn content in the range of 0.10 to 0.50% by mass, a P content of 0.030% by mass or below, a S content in the range of 0.010 to 0.15% by mass, an Al content of 0.01% by mass or below, a N content of 0.005% by mass or below, and an 0 content of 0.02% by mass or below. In the soft magnetic low-carbon steel, Mn/S mass ratio is 3.0 or above, ferrite grain size is 100 &#x3bc;m or above, ferrite grains contain precipitated MnS grains of grain sizes of 0.2 &#x3bc;m or above in a density in the density range of 0.02 to 0.5 grains/&#x3bc;m and the precipitated MnS grains have a mean grain size in the range of 0.05 to 4 &#x3bc;m. The soft magnetic low-carbon steel is excellent in cold-rollability and machinability. Steel parts of the soft magnetic low-carbon steel having complicated shapes can be produced at a high yield.

Soft magnetic low-carbon steel excellent in machinability and magnetic characteristic, method of manufacturing the same and method of manufacturing soft magnetic low-carbon part

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Kobe, Japan

Masamichi Chiba