Provided is a plated steel sheet having both strength and workability. In a hot-dip Zn—Al—Mg-based plated steel sheet, the steel substrate contains C in an amount of 0.050 to 0.180% by mass, Si in an amount of 0.001 to 0.50% by mass, Mn in an amount of 1.00 to 2.80% by mass, Ti in an amount of 0.01 to 0.10% by mass, and B in an amount of 0.0005 to 0.0100% by mass, an average grain size of cementite after winding in a hot rolling step is not greater than 2 μm, a metal structure after a continuous hot-dip galvanizing step includes a ferrite phase and not less than 15 and less than 45% by area of a second phase, and the second phase is composed of martensite or composed of martensite and bainite and has an average crystal grain size of not greater than 8 μm.

The present invention relates to a cold rolled steel sheet containing C: 0.15% or more and 0.40% or less, Si: 0.50% or more and 4.00% or less, Mn: 1.00% or more and 4.00% or less, and sol. Al: 0.001% or more and 2.000% or less, having a metallic structure consisting of 35 to 65 area % of ferrite phases, 35 to 65 area % of hard second phases, and 0 to 5 area % of remaining phases, wherein 60% or more of the ferrite phases are recrystallized ferrite phases, an average crystal grain size defined by 15° grain boundaries is 5.0 μm or less, a maximum connecting rate of the hard second phases is 10% or more, and a two-dimensional isoperimetric constant of the hard second phases is 0.20 or less.

A high-strength steel sheet includes a chemical composition including: by mass %, C: 0.080 to 0.500%, Si: 2.50% or less, Mn: 0.50 to 5.00%, P: 0.100% or less, S: 0.0100% or less, Al: 0.001 to 2.500%, N: 0.0150% or less, O: 0.0050% or less, and the balance: Fe and inevitable impurities. The high-strength steel sheet satisfying a predetermined formula has a microstructure in a region from ⅛t to ⅜t from a steel sheet surface. The microstructure includes: by volume %, 20% or more of acicular ferrite, 20% or more of an island-shaped hard structure including residual austenite, 2% to 25% of residual austenite, and 20% or less of aggregated ferrite.

Provided are a hot dip galvanized steel sheet comprising a base steel sheet wherein the base steel sheet has a predetermined chemical composition, and contains ferrite: 50% or less, retained austenite: 30% or less, tempered martensite: 5% or more, fresh martensite: 10% or less, and pearlite and cementite in total: 5% or less, remaining structures consist of bainite, and a number ratio of tempered martensite with a Mn concentration profile satisfying [Mn].sub.b/[Mn].sub.a>1.2 and [Mn].sub.a/[Mn]<2.0 ([Mn] is the Mn content in the base steel sheet, [Mn].sub.a is the average Mn concentration in the tempered martensite, and [Mn].sub.b is the Mn concentration at the interfaces of different phases of the tempered martensite and ferrite phase and bainite phase) is 0.2 or more with respect to the total number of tempered martensite, and a method for producing the same.

Provided are a hot dip galvanized steel sheet comprising a base steel sheet and a hot dip galvanized layer on at least one surface of the base metal steel sheet, wherein the base steel sheet has a predetermined chemical composition, and contains, by volume fraction, ferrite: 0% to 50%, retained austenite: 0% to 30%, tempered martensite: 5% or more, fresh martensite: 0% to 10%, and pearlite and cementite in total: 0% to 5%, when there are remaining structures, the remaining structures consist of bainite, a concentration of B atoms at prior austenite grain boundaries is 2.0 atm % or more, and an average effective crystal grain size is 7.0 μm or less, and a method for producing the same.

The present disclosure relates to the technical field of rails welding, and particularly to a method for optimizing microstructure of a rail welded joint, the method comprises the following steps: step 1): subjecting a rail web area of a to-be-cooled welded joint which is obtained by flash butt welding to an accelerated cooling by means of an accelerated cooling device and by using compressed air as a cooling medium, measuring and monitoring temperature of a central position of the rail web of the welded joint while cooling; step 2): stopping the accelerated cooling when the temperature of the central position of the rail web drops to a preset temperature, then placing the welded joint in air and naturally cooling to room temperature, wherein the rail is a pearlite rail having a carbon content of 0.6-0.9 wt %.

This steel sheet has a predetermined chemical composition, a microstructure contains, in terms of a volume fraction, ferrite: 10% to 75%, martensite: 20% to 90%, retained austenite: 0% to 5%, bainite and bainitic ferrite in total: 0% to 50%, and pearlite: 0% to 5%, a proportion of unrecrystallized ferrite in the ferrite is 0% to 25%, cementite that is contained in the martensite satisfies a predetermined relational expression, a density of transition carbide included in the martensite is 1.0×10.sup.13 pieces/m.sup.3 or more, a density of coarse inclusion having an equivalent circle diameter of 10 μm or more is 0.50 pieces/mm.sup.2 or less, in a surface parallel to the surface at a position ¼ of the sheet thickness deep from the surface in the sheet thickness direction, a ratio of a maximum value Hv.sub.max of Vickers hardness to a minimum value Hv.sub.min of the Vickers hardness is 1.40 or less, and an average value of minimum distances between peaks of the Vickers hardness in a distribution map of the Vickers hardness is 1.00 mm or less.

The railway wheel according to the present embodiment has a chemical composition consisting of: in mass %, C: 0.80 to 1.15%, Si: 0.45% or less, Mn: 0.10 to 0.85%, P: 0.050% or less, S: 0.030% or less, Al: 0.200 to 1.500%, N: 0.0200% or less, Nb: 0.005 to 0.050%, Cr: 0 to 0.25%, and V: 0 to 0.12%, with the balance being Fe and impurities, wherein at least in the microstructure of the rim part and the web part, the amount of pro-eutectoid cementite defined by Formula (1) is 2.00 pieces/100 μm or less:

Amount of pro-eutectoid cementite (pieces/100 μm)=a total sum of the number of pieces of pro-eutectoid cementite which intersect with two diagonal lines in a square visual field of 200 μm×200 μm/(5.66×100 μm)×100  (1)

A galvannealed steel sheet according to one aspect of the present invention has a hot-dip galvannealed layer on at least one surface of the steel sheet, and the steel sheet has a predetermined chemical composition, in which the steel sheet contains 10% or more and 90% or less of ferrite, and 10% or more of tempered martensite and tempered bainite in terms of an area ratio, a sum of the ferrite, the tempered martensite, and the tempered bainite is 90% or more, carbides having a major axis of 50 nm or more and 300 nm or less are contained in grains of the ferrite in a number density of 20/μm.sup.2 or more, and a two-dimensional homogeneous dispersion ratio S of Mn is 0.75 or more and 1.30 or less.

Provided is a steel material which can achieve excellent fatigue strength even when a carburized steel component is produced by welding before carburizing treatment. The steel material has a chemical composition containing: in mass %, C: 0.09 to 0.16%, Si: 0.01 to 0.50%, Mn: 0.40 to 0.60%, P: 0.030% or less, S: 0.025% or less, Cr: 0.90 to 2.00%, Mo: 0.10 to 0.40%, Al: 0.005 to 0.030%, Ti: 0.010 to less than 0.050%, Nb: 0.010 to 0.030%, N: 0.0080% or less, O: 0.0030% or less, B: 0.0003 to 0.0030%, Ca: 0.0005 to 0.0050%, and the balance: Fe and impurities, and satisfying Formula (1) to Formula (3) according to the description. In a cross section parallel to an axial direction of the steel material, an amount of Mn sulfide is 70.0 pieces/mm.sup.2 or less, and an amount of oxide is 25.0 pieces/mm.sup.2 or less.