A steel wire for machine structural parts, may include Fe, inevitable impurities, and, by mass: 0.05 to 0.60% C; 0.005 to 0.50% Si; 0.30 to 1.20% Mn; more than 0 to 0.050% P; more than 0 to 0.050% S; 0.001 to 0.10% Al; more than 0 to 1.5% Cr; and more than 0 to 0.02% N. An area of cementite present at ferrite grain boundaries in an area of all cementite of the steel wire may be 32% or more. When a C content (% by mass) of a steel is expressed as [C], an average circular-equivalent diameter of all the cementite is (1.668-2.13 [C]) ?m or more and (1.863-2.13 [C]) ?m or less.

A steel wire for machine structural parts, may include Fe, inevitable impurities, and, by mass: 0.05 to 0.60% C; 0.005 to 0.50% Si; 0.30 to 1.20% Mn; more than 0 to 0.050% P; more than 0 to 0.050% S; 0.001 to 0.10% Al; more than 0 to 1.5% Cr; and more than 0 to 0.02% N. An area of cementite present at ferrite grain boundaries in an area of all cementite of the steel wire may be 32% or more. When a C content (% by mass) of a steel is expressed as [C], an average circular-equivalent diameter of all the cementite is (1.668-2.13 [C]) ?m or more and (1.863-2.13 [C]) ?m or less.

A cold-workable mechanical structural steel may include: C: 0.30 to 0.45 mass %; Si: 0.10 to 0.40 mass %; Mn: 0.50 to 1.00 mass %; P: 0.050 mass % or less; S: 0.050 mass % or less; Cr: 0.80 to 1.30 mass %; Al: 0.01 to 0.10 mass %; and a balance of iron and inevitable impurity, the steel having an area percentage of pro-eutectoid ferrite of 10% or larger and 70% or smaller; containing at least one selected from the group consisting of bainite, martensite, and pearlite; and having a dislocation density of 3.5?10.sup.14 m.sup.?2 or larger.

A cold-workable mechanical structural steel may include: C: 0.30 to 0.45 mass %; Si: 0.10 to 0.40 mass %; Mn: 0.50 to 1.00 mass %; P: 0.050 mass % or less; S: 0.050 mass % or less; Cr: 0.80 to 1.30 mass %; Al: 0.01 to 0.10 mass %; and a balance of iron and inevitable impurity, the steel having an area percentage of pro-eutectoid ferrite of 10% or larger and 70% or smaller; containing at least one selected from the group consisting of bainite, martensite, and pearlite; and having a dislocation density of 3.5?10.sup.14 m.sup.?2 or larger.

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.

A steel material comprising, by mass%, C: greater than 0.05% to 0.2%, Mn: 1% to 3%, Si: greater than 0.5% to 1.8%, Al: 0.01% to 0.5%, N: 0.001% to 0.015%, Ti or a sum of V and Ti: greater than 0.1% to 0.25%, Ti: 0.001% or more, Cr: 0% to 0.25%, Mo: 0% to 0.35%, the balance: Fe and impurities, comprising a multi-phase structure having a ferrite main phase and a second phase containing one or more of bainite, martensite and austenite, wherein an average nanohardness of the second phase is less than 6.0 GPa, an average grain diameter of all crystal grains in the main phase and the second phase is 3 m or less, and a proportion of a length of small-angle grain boundaries where the misorientation is 2 to less than 15 in a length of all grain boundaries is 15% or more.

A steel wire for machine structural parts, including respective predetermined contents of C, Si, Mn, P, S, Al, Cr, N, and iron, wherein when a total content of Cr and Mn (% by mass) in cementite in the metallurgical microstructure is expressed as {Cr+Mn}, a total content of Cr and Mn (% by mass) in steel is expressed as [Cr+Mn], and a C content (% by mass) of the steel is expressed as [C], a concentration ratio {Cr+Mn}/[Cr+Mn] is (0.5[C] +0.040) or more, and an average circular-equivalent diameter of all the cementite is (1.668-2.13[C]) ?m or more and (1.863-2.13[C]) ?m or less.

A steel wire for machine structural parts, including respective predetermined contents of C, Si, Mn, P, S, Al, Cr, N, and iron, wherein when a total content of Cr and Mn (% by mass) in cementite in the metallurgical microstructure is expressed as {Cr+Mn}, a total content of Cr and Mn (% by mass) in steel is expressed as [Cr+Mn], and a C content (% by mass) of the steel is expressed as [C], a concentration ratio {Cr+Mn}/[Cr+Mn] is (0.5[C] +0.040) or more, and an average circular-equivalent diameter of all the cementite is (1.668-2.13[C]) ?m or more and (1.863-2.13[C]) ?m or less.

A self-lubricating rolling bearing is provided. The chemical compositions in the inner rings and the outer rings of bearing are 3.4-3.7% C, 2.7-2.9% Si, 0.3-0.5% Mn, 0.3-0.5% Cr, ?0.05% S, ?0.05% P, 0.03-0.045% Residual Mg, and the remainder Fe. The total percent of the chemical compositions is 100%. The material for the inner and outer rings of the rolling bearing introduced in the invention is austempered ductile iron (ADI). In the microstructure of ADI, the diameter of the graphite nodules is less than 0.02 mm, the number of graphite spheres per square millimeter is more than 400, and the microstructure of the metal matrix in the ADI can be showed clearly only when it is observed on the microscope with a magnification more than 500. Eventually, the self-lubricating rolling bearings are made from the ADI.

A self-lubricating rolling bearing is provided. The chemical compositions in the inner rings and the outer rings of bearing are 3.4-3.7% C, 2.7-2.9% Si, 0.3-0.5% Mn, 0.3-0.5% Cr, ?0.05% S, ?0.05% P, 0.03-0.045% Residual Mg, and the remainder Fe. The total percent of the chemical compositions is 100%. The material for the inner and outer rings of the rolling bearing introduced in the invention is austempered ductile iron (ADI). In the microstructure of ADI, the diameter of the graphite nodules is less than 0.02 mm, the number of graphite spheres per square millimeter is more than 400, and the microstructure of the metal matrix in the ADI can be showed clearly only when it is observed on the microscope with a magnification more than 500. Eventually, the self-lubricating rolling bearings are made from the ADI.