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.

One aspect of the present invention relates to a plated steel sheet for hot press forming, having an excellent impact property.

The invention relates to a turnout rail production technology, in particular to a deeply-hardened-surface turnout rail with high degree of undercooling and the preparation method thereof. The invention aims to solve the technical problem by providing a deeply-hardened-surface turnout rail with high degree of undercooling featured in even hardness distribution and a deeply hardened surface layer and the preparation method thereof. The method is described as follows: feeding molten iron for converter smelting.fwdarw.furnace rear argon blowing station.fwdarw.LF refining.fwdarw.RH vacuumization.fwdarw.casting steel blanks.fwdarw.slow cooling in the slow cooling pit.fwdarw.austenitic homogenization.fwdarw.rail rolling.fwdarw.heat treatment; in the converter smelting process, adding 0.2-0.3% Cr, 0.04-0.06 V and 0.75-0.80% C; the heat treatment process is divided into two cooling stages. The turnout rail prepared with the method described in the invention has a deeper deeply-hardened surface layer; the hardness is distributed more evenly, the anti-contact fatigue performance is higher and the resistance to wearing is ideal.

A rolled steel sheet, for press hardening is provided, having a chemical composition where Ti/N>3.42, and the carbon, manganese, chromium and silicon contents satisfy:

[00001]$2.6C+\frac{\mathrm{Mn}}{5.3}+\frac{\mathrm{Cr}}{13}+\frac{\mathrm{Si}}{15}\ge 1.1\%.$

The sheet has a nickel content Ni.sub.surf at any point of the steel in the vicinity of the surface over a depth Δ, such that: Ni.sub.surf>Ni.sub.nom, Ni.sub.nom denoting the nominal nickel content of the steel, and such that, Ni.sub.max denoting the maximum nickel content within Δ:

[00002]$\frac{\left({\mathrm{Ni}}_{\max }+{\mathrm{Ni}}_{\mathrm{nom}}\right)}{2}\times \left(\Delta \right)\ge 0.6,$

and such that:

[00003]$\frac{\left({\mathrm{Ni}}_{\max }-{\mathrm{Ni}}_{\mathrm{nom}}\right)}{\Delta }\ge 0.01$

and the surface density of all of the particles D.sub.i , and the surface density of the particles D.sub.(>2 μm) larger than 2 micrometers satisfy, at least to a depth of 100 micrometers in the vicinity of the surface of said sheet:

D.sub.i+6.75 D.sub.(>2 μm)<270

D.sub.i and D.sub.(>2 μm) being expressed as number of particles per square millimeter, and said particles denoting all the oxides, sulfides, and nitrides, either pure or combined such as oxysulfides and carbonitrides, present in the steel matrix.

The present disclosure discloses a method for producing high strength hot rolled steel. The method includes casting a steel slab of a composition, comprising in weight %: carbon (C) of about 0.45 wt. %-1.2 wt. %, manganese (Mn) of about 0.0-1.0 wt. %, silicon (Si) of about 0.0-0.5 wt. %, niobium (Nb) up-to 0.03 wt. %, sulphur (S) up-to 0.05 wt. % of S, phosphorous (P) up-to 0.05 wt. %, nitrogen (N) 0.002 wt. %-0.012 wt. % and balance being Iron (Fe) optionally along with incidental elements. The method also involves, heating, hot rolling, cooling, coiling the steel and retaining the steel at an ambient temperature to produce high strength hot rolled steel with 75-95% spheroid microstructure and 5-25% pearlite microstructure.

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: 6% to 30%, bainite: 5% or more, tempered martensite: 5% or more, fresh martensite: 0% to 10%, and pearlite and cementite in total: 0% to 5%, a number density of tempered martensite with a circle equivalent diameter of 5.0 μm or more is 20/1000 μm.sup.2 or less, and an area ratio of fresh martensite with a circle equivalent diameter of 2.0 μm or more after imparting 5% plastic strain is 10% or less, and a method for producing the same.

This hot-rolled steel sheet has a predetermined chemical composition, the number % of crystal grains of bainite that are in contact with both tempered martensite and residual austenite is 80% or more of all crystal grains of the bainite, a C concentration in the residual austenite is 0.80 mass % or more, an average crystal grain size of the residual austenite is 0.70 μm or less, and a standard deviation of Vickers hardness is 25 HV0.01 or less.

Provided are a high-strength thick hot-rolled steel sheet having excellent elongation and a method for manufacturing same. The high-strength thick hot-rolled steel sheet comprises, by weight %: 0.05-0.15% of C; 0.01-1.0% of Si; 1.0-2.0% of Mn; 0.01-0.1% of Sol. Al; 0.005-1.0% of Cr; 0.001-0.02% of P; 0.001-0.01% of S; 0.001-0.01% of N; 0.005-0.07% of Nb; 0.005-0.11% of Ti; and the remainder of Fe and unavoidable impurities, satisfies relation 1, and has a microstructure comprising, by area %: 25-50% of polygonal ferrite; 30-50% of bainitic ferrite and acicular ferrite; 20% or less of bainite; less than 5% of the sum of area fractions of carbide and pearlite structures having a diameter of 0.5 μm or more, observed within a unit area (1 cm.sup.2); and less than 5% of phase MA (martensitic-austenitic constituents).

A steel sheet according to an aspect of the present invention has a predetermined chemical composition, in which a metallographic structure at a ¼ thickness portion includes, by volume percentage, a total of 50% or more of one or both of martensite and bainite and 8% or more of residual austenite, an average value of aspect ratios of prior austenite grains is 5.0 or more, number density of AlN is 3000 pieces/mm.sup.2 or more and less than 6000 pieces/mm.sup.2 at a depth position of 30 μm from a sheet surface, an internal oxidation layer in which at least a part of a crystal grain boundary is coated with an oxide is provided from the sheet surface to a depth of 5.0 μm or more, grain boundary coverage of the oxide is 60% or more in a region from the sheet surface to a depth of 5.0 μm, and a tensile strength is 980 MPa or more.

The present invention relates to a hot stamped component, a precoated steel sheet used for hot stamping, and a hot stamping process. The hot stamped component of the present invention is provided with a coating of aluminium or an aluminium alloy on at least one surface of the base steel, the coating is produced by interdiffusion between the base steel and a precoating of aluminium or aluminium alloy, and the coating has a thickness of 6 to 26 μm.