A steel alloy for bearings contains: 0.6 to 0.9 wt. % carbon, 0.1 to 0.5 wt. % silicon, 0.1 to 1.5 wt. % manganese, 1.5 to 2.0 wt. % chromium, 0.2 to 0.6 wt. % molybdenum, 0 to 0.25 wt. % nickel, 0 to 0.3 wt. % copper, 0 to 0.2 wt. % vanadium, 0 to 0.2 wt. % cobalt, 0 to 0.2 wt. % aluminium, 0 to 0.1 wt. % niobium, 0 to 0.2 wt. % tantalum, 0 to 0.05 wt. % phosphorous, 0 to 0.03 wt. % sulphur, 0 to 0.075 wt. % tin, 0 to 0.075 wt. % antimony, 0 to 0.075 wt. % arsenic, 0 to 0.01 wt. % lead, up to 350 ppm nitrogen, up to 100 ppm oxygen, up to 50 ppm calcium, up to 50 ppm boron, up to 50 ppm titanium, the balance being iron, together with any other unavoidable impurities. Furthermore, the steel alloy contains (i) molybdenum and silicon in a weight ratio of 0.4<Mo/Si<6.0 and (ii) molybdenum and chromium in a weight ratio of 0.1<Mo/Cr<0.4.

There is provided a rolling bearing capable of suppressing the occurrence of white structure spalling. A rolling bearing contains a structure having a solid solution carbon amount in a martensitic structure after heat treatment of 0.35 mass % or more and 0.65 mass % or less and a volume ratio of spheroidized carbides having a diameter of 200 nm or more of 4.5% or less.

A steel wire for springs includes a main steel body and having a line shape, and an oxidized layer covering an outer peripheral surface of the main body. The steel constituting the main body contains between 0.6 and 0.7 mass % C, between 1.7 and 2.5 mass % Si, between 0.2 and 1 mass % Mn, between 0.6 and 2 mass % Cr, and between 0.08 and 0.25 mass % V, with the balance consisting of Fe and unavoidable impurities. The steel constituting the main body has a tempered martensitic structure. The oxidized layer includes a high Si concentration layer having a maximum concentration of Si of not less than 2.5 times and not more than 5.5 times that of the main body. The main body includes an intergranular oxidized layer arranged to constitute the outer peripheral surface and having a thickness of not less than 0.5 ?m and not more than 2.5 ?m.

This disclosure provides a high-strength thin steel sheet excellent in both tensile strength and elongation with small elongation anisotropy. The high-strength thin steel sheet has a specific chemical composition and a microstructure where a total area ratio of ferrite, tempered bainitic ferrite and bainitic ferrite is 40% or more and 70% or less, an area ratio of martensite is 5% or more and 30% or less, an area ratio of retained austenite is 10% or more and 35% or less, an average equivalent circular diameter of martensite and retained austenite (secondary phase) grains is 2.0 m or less, an area ratio of secondary phase grains having an equivalent circular diameter of 2.0 m or more is 10% or less, and an average minor axis length of secondary phase grains is 0.40 m or less.

A steel plate improved in formability and wear resistance, having a predetermined chemical composition, having a metal structure of the steel plate having a ratio of number of carbides at ferrite grain boundaries with respect to a number of carbides in ferrite grains of over 1 and having a ferrite grain size of 5 m to 50 m, and having a Vickers hardness of steel plate of 100 HV to 170 HV.

According to an embodiment, the described hot mold steel may be excellent in high thermal conductivity to decrease the temperature difference in materials at high temperature, thereby making heat-checking properties excellent. When the hot mold steel according to the present disclosure is used for die casting, the cooling rate of the product produced using the die casting is quick, thereby improving the physical properties of the produced product and shortening the cooling time to improve productivity. Furthermore, the hot mold steel may have excellent high temperature durability, such that the die casting produced using the hot mold steel may have characteristics of a long life cycle.

According to an embodiment, the described hot mold steel may be excellent in high thermal conductivity to decrease the temperature difference in materials at high temperature, thereby making heat-checking properties excellent. When the hot mold steel according to the present disclosure is used for die casting, the cooling rate of the product produced using the die casting is quick, thereby improving the physical properties of the produced product and shortening the cooling time to improve productivity. Furthermore, the hot mold steel may have excellent high temperature durability, such that the die casting produced using the hot mold steel may have characteristics of a long life cycle.

A steel alloy comprising from: (a) 0.6 to 0.9 wt. % carbon, (b) 0.1 to 0.5 wt. % silicon, (c) 0.1 to 1.5 wt. % manganese, (d) 1.5 to 2.0 wt. % chromium, (e) 0.2 to 0.6 wt. % molybdenum, and up to: (f) 0.25 wt. % nickel, (g) 0.3 wt. % copper, (h) 0.2 wt. % vanadium, (i) 0.2 wt. % cobalt, (j) 0.2 wt. % aluminum, (k) 0.1 wt. % niobium, (l) 0.2 wt. % tantalum, (m) 0.05 wt. % phosphorous, (n) 0.03 wt. % sulphur, (o) 0.075 wt. % tin, (p) 0.075 wt. % antimony, (q) 0.075 wt. % arsenic, (r) 0.01 wt. % lead, (s) 350 ppm nitrogen, (t) 100 ppm oxygen, (u) 50 ppm calcium, (v) 50 ppm boron, (w) 50 ppm titanium, the balance iron, including any other unavoidable impurities, wherein the alloy comprises molybdenum and silicon in a weight ratio of 0.4Mo/Si6.0 and comprises molybdenum and chromium in a weight ratio of 0.1Mo/Cr0.4.

A steel alloy comprising from: (a) 0.6 to 0.9 wt. % carbon, (b) 0.1 to 0.5 wt. % silicon, (c) 0.1 to 1.5 wt. % manganese, (d) 1.5 to 2.0 wt. % chromium, (e) 0.2 to 0.6 wt. % molybdenum, and up to: (f) 0.25 wt. % nickel, (g) 0.3 wt. % copper, (h) 0.2 wt. % vanadium, (i) 0.2 wt. % cobalt, (j) 0.2 wt. % aluminum, (k) 0.1 wt. % niobium, (l) 0.2 wt. % tantalum, (m) 0.05 wt. % phosphorous, (n) 0.03 wt. % sulphur, (o) 0.075 wt. % tin, (p) 0.075 wt. % antimony, (q) 0.075 wt. % arsenic, (r) 0.01 wt. % lead, (s) 350 ppm nitrogen, (t) 100 ppm oxygen, (u) 50 ppm calcium, (v) 50 ppm boron, (w) 50 ppm titanium, the balance iron, including any other unavoidable impurities, wherein the alloy comprises molybdenum and silicon in a weight ratio of 0.4Mo/Si6.0 and comprises molybdenum and chromium in a weight ratio of 0.1Mo/Cr0.4.

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.