An object of the present invention is to provide a steel wire for mechanical structural parts that is reduced in deformation resistance and improved in crack resistance during cold working, and thus exhibits excellent cold workability. The steel wire for mechanical structural parts of the present invention is a steel wire containing, in mass %, 0.3 to 0.6% of C, (105 to 0.5% of Si, 0.2 to 1.7% of Mn, more than 0% and 0.03% or less of P, 0.001 to 0.05% of S, 0.005 to 0.1% of Al, and 0 to 0.015% of N, the balance being iron and inevitable impurities, wherein steel of the steel wire has a metal structure formed of ferrite and cementite, and the number proportion of cementite particles present in ferrite grain boundaries is 40% or more based on the total number of cementite particles.

The present invention relates to a steel material including: 0.23 mass %?C?0.39 mass %; 0.03 mass %?V?0.30 mass %; 6.60 mass %?Mn+Cr?7.40 mass %; Mn/Cr?0.150; Mn?0.60 mass %; Cr?6.60 mass %; Cu+Ni?0.84 mass %; 0.01 mass %?Si?0.40 mass %; 2.00 mass %?Mo?3.50 mass %; 0.001 mass %?Al?0.080 mass %; and 0.003 mass %?N?0.040 mass %, with the balance being Fe and unavoidable impurities.

The present invention relates to a steel material including: 0.23 mass %?C?0.39 mass %; 0.03 mass %?V?0.30 mass %; 6.60 mass %?Mn+Cr?7.40 mass %; Mn/Cr?0.150; Mn?0.60 mass %; Cr?6.60 mass %; Cu+Ni?0.84 mass %; 0.01 mass %?Si?0.40 mass %; 2.00 mass %?Mo?3.50 mass %; 0.001 mass %?Al?0.080 mass %; and 0.003 mass %?N?0.040 mass %, with the balance being Fe and unavoidable impurities.

An aspect of the present invention relates to a high strength steel sheet having an excellent high-temperature elongation characteristic, wherein the sheet comprises, by weight %, 0.4-0.9% of C, 0.01-1.5% of Cr, 0.03% or less (exclusive of 0%) of P, 0.01% or less (exclusive of 0%) of S, 0.01% or less (exclusive of 0%) of N, 0.01% or less (exclusive of 0%) of sol. Al, and a balance of Fe and inevitable impurities, and comprises at least one among 2.1% or less (exclusive of 0%) of Mn and 1.6% or less (exclusive of 0%) of Si; the sheet has a microcrystalline structure including pearlite having an area fraction of 80% or more and ferrite having an area fraction of 20% or less; and the pearlite includes cementite having a major axis length of 200 nm or shorter.

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>Ae, where Ae=(0.8Ceq)96.75 (Ceq=[C]+0.1[Si]+0.06[Mn]0.11[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 m.

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>Ae, where Ae=(0.8Ceq)96.75 (Ceq=[C]+0.1[Si]+0.06[Mn]0.11[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 m.

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>Ae with an Ae value expressed by a predetermined relational expression, the average equivalent circular diameter of bcc-Fe crystal grains being 15-35 m, and the average of the maximum grain diameter and the second largest grain diameter of the bcc-Fe crystal grains being 50 m or less in terms of equivalent circular diameter.

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>Ae with an Ae value expressed by a predetermined relational expression, the average equivalent circular diameter of bcc-Fe crystal grains being 15-35 m, and the average of the maximum grain diameter and the second largest grain diameter of the bcc-Fe crystal grains being 50 m or less in terms of equivalent circular diameter.

A high strength, high toughness steel alloy is disclosed. The alloy has the following broad weight percent composition.

TABLE-US-00001 Element Broad C 0.35-0.55 Mn 0.6-1.2 Si 0.9-2.5 P 0.01 max. S 0.001 max. Cr 0.75-2.0 Ni 3.5-7.0 Mo + W 0.4-1.3 Cu 0.5-0.6 Co 0.01 max. V + (5/9) Nb 0.2-1.0 Fe Balance

Included in the balance are the usual impurities found in commercial grades of steel alloys produced for similar use and properties. Also disclosed is a hardened and tempered article that has very high strength and fracture toughness. The article is formed from the alloy having the broad weight percent composition set forth above. The alloy article according to this aspect of the invention is further characterized by being tempered at a temperature of about 500 F. to 600 F.

This steel material for bearings includes prescribed components in the steel, the oxide inclusions in the steel that have a minor axis of 1 m or greater satisfying the following conditions (1) and (2). (1) The average composition contains specific respective amounts of CaO, Al.sub.2O.sub.3, SiO.sub.2, and TiO.sub.2, and CaO+Al.sub.2O.sub.3+SiO.sub.2+TiO.sub.260%. (2) The proportion of oxide inclusions in which TiN occurs at the interface of the oxide inclusions and the steel is 30% or more of the total of the oxide inclusions.