Provided are a bolt that exhibits excellent delayed fracture resistance at a high strength level of from 1,200 MPa to less than 1,600 MPa in tensile strength, where the possibility of delayed fracture is generally quite high, and a steel material for a bolt to be used as the material for such a bolt. The bolt has a composition satisfying Formulae (1) and (2), and a tensile strength of from 1,200 MPa to less than 1,600 MPa. In Formula (1) and Formula (2), Mo and V represent the contents (% by mass) of Mo and V contained in the steel for a bolt, respectively.

0.48≤Mo/1.4+V<1.10   (1)

0.8<Mo/V<3.0   (2)

An object of the present invention is to provide a semi-hard magnetic white powder having characteristics suitable as a security pigment, such as the magnetic powder contained in magnetic inks used for MICR. The white powder includes base particles made of a semi-hard magnetic Alnico alloy, the base particles having a titanium oxide film and a metallic silver film in this order on the surfaces thereof.

An object of the present invention is to provide a semi-hard magnetic white powder having characteristics suitable as a security pigment, such as the magnetic powder contained in magnetic inks used for MICR. The white powder includes base particles made of a semi-hard magnetic Alnico alloy, the base particles having a titanium oxide film and a metallic silver film in this order on the surfaces thereof.

The chemical composition of the railway wheel of the present embodiment consists of: in mass %, C: 0.80 to 1.60%, Si: 1.00% or less, Mn: 0.10 to 1.25%, P: 0.050% or less, S: 0.030% or less, Al: 0.010 to 0.650%, and N: 0.0030 to 0.0200%, with the balance being Fe and impurities, and wherein, in a microstructure of the web part of the railway wheel, an area fraction of pearlite is 85.0% or more, an area fraction of pro-eutectoid cementite is 0.90 to 15.00%, and an average value of a width W of the pro-eutectoid cementite defined by Formula (1) is less than 0.70 μm:

W=½×(P/2−((P/2).sup.2−4A).sup.1/2)  (1) where, in Formula (1), A is an area (μm.sup.2) of the pro-eutectoid cementite, and P is a circumference length (μm) of the pro-eutectoid cementite.

This free-cutting copper alloy contains Cu: 58.5 to 63.5%, Si: more than 0.4% and 1.0% or less, Pb: 0.003 to 0.25%, and P: 0.005 to 0.19%, with the remainder being Zn and inevitable impurities, a total amount of Fe, Mn, Co and Cr is less than 0.40%, a total amount of Sn and Al is less than 0.40%, a relationship of 56.3≤f1=[Cu]−4.7×[Si]+0.5×[Pb]−0.5×[P]≤59.3 is satisfied, constituent phases of a metal structure have relationships of 20≤(α)≤75, 25≤(β)≤80, 0≤(γ)<2, 20≤(γ).sup.1/2×3+(β)×(−0.5×([Si]).sup.2+1.5×[Si])≤78, and 33≤(γ).sup.1/2×3+(β)×(−0.5×([Si]).sup.2+1.5×[Si])+([Pb]).sup.1/2×33+([P]).sup.1/2×14, and a compound including P is present in β phase.

This free-cutting copper alloy contains Cu: 58.5 to 63.5%, Si: more than 0.4% and 1.0% or less, Pb: 0.003 to 0.25%, and P: 0.005 to 0.19%, with the remainder being Zn and inevitable impurities, a total amount of Fe, Mn, Co and Cr is less than 0.40%, a total amount of Sn and Al is less than 0.40%, a relationship of 56.3≤f1=[Cu]−4.7×[Si]+0.5×[Pb]−0.5×[P]≤59.3 is satisfied, constituent phases of a metal structure have relationships of 20≤(α)≤75, 25≤(β)≤80, 0≤(γ)<2, 20≤(γ).sup.1/2×3+(β)×(−0.5×([Si]).sup.2+1.5×[Si])≤78, and 33≤(γ).sup.1/2×3+(β)×(−0.5×([Si]).sup.2+1.5×[Si])+([Pb]).sup.1/2×33+([P]).sup.1/2×14, and a compound including P is present in β phase.

According to the present invention, an aluminum alloy comprises 18 to 50 parts by weight of Zinc (Zn), 0.05 to 5 parts by weight of Copper (Cu), 0.001 to 0.3 parts by weight of crystal micronization elements which are at least one of vanadium (V), zirconium (Zr), titanium (Ti) and Boron (B), the rest being aluminum (Al) and other unavoidable impurities, based on the total weight of the alloy.

According to the present invention, an aluminum alloy comprises 18 to 50 parts by weight of Zinc (Zn), 0.05 to 5 parts by weight of Copper (Cu), 0.001 to 0.3 parts by weight of crystal micronization elements which are at least one of vanadium (V), zirconium (Zr), titanium (Ti) and Boron (B), the rest being aluminum (Al) and other unavoidable impurities, based on the total weight of the alloy.

Systems and methods for annealing, carburizing and/or other treatments of metallic articles include a retort furnace having a retort. The metallic articles are fed into a chamber of the retort through an inlet section of the retort and are subjected to heating. The retort is oscillated and/or rotated back and forth as the metallic articles are heated, causing the metallic articles to be moved along the chamber of the retort to a discharge.

This high strength austenitic stainless steel having excellent resistance to hydrogen embrittlement includes, in terms of mass %, C: 0.2% or less, Si: 0.2% to 1.5%, Mn: 0.5% to 2.5%, P: 0.06% or less, S: 0.008% or less, Ni: 10.0% to 20.0%, Cr: 16.0% to 25.0%, Mo: 3.5% or less, Cu: 3.5% or less, N: 0.01% to 0.50%; and O: 0.015% or less, with the balance being Fe and unavoidable impurities, in which an average size of precipitates is 100 nm or less and an amount of the precipitates is 0.001% to 1.0% in terms of mass %.