In accordance with one aspect of the present disclosure, there is provided a steel material for a tailor-welded blank, including 0.04 to 0.06 wt % of carbon (C), 1.2 to 1.5 wt % of manganese (Mn), 0.01 to 0.10 wt % of titanium (Ti), 0.01 to 0.10 wt % of niobium (Nb), and the balance of iron (Fe) and inevitable impurities; having a tensile strength (TS) of 550 MPa or greater, a yield strength (YS) of 300 MPa or greater, and an elongation (EL) of 20% or greater; and having a dual-phase structure of ferrite and martensite.

Provided is a low-density clad steel sheet having excellent formability and fatigue properties, including a base material; and cladding materials provided on both side surfaces of the base material, wherein the base material is a lightweight steel sheet including, by weight, C: 0.3 to 1.0%, Mn: 4.0 to 16.0%, Al: 4.5 to 9.0%, and a remainder of Fe and inevitable impurities, and each of the cladding materials is martensitic carbon steel including, by weight, C: 0.1 to 0.45%, Mn: 1.0 to 3.0%, and a remainder of Fe and inevitable impurities.

A hot stamped article excellent in strength having a predetermined composition, having an average crystal grain size of prior austenite of 3 μm or less, containing at least one of lower bainite, martensite, and tempered martensite in an area rate of 90% or more, and having a grain boundary solid solution ratio Z, defined by Z=(mass % of one or both of Nb and Mo at the grain boundaries)/(mass % of one or more of Nb and Mo at time of dissolution) of 0.3 or more.

A steel sheet having a specified chemical composition and a method for producing the steel sheet. The steel sheet has a microstructure including martensite and bainite. The total area fraction of the martensite and the bainite to the entirety of the microstructure is more than 90% and 100% or less. The microstructure includes inclusion clusters A and B, the content of the clusters A in the microstructure being 2 clusters/mm.sup.2 or less, and the content of the clusters B in the microstructure being 5 clusters/mm.sup.2 or less. The microstructure includes carbide particles including Fe as a main constituent which have an aspect ratio of 2.0 or less and a major axis of 0.30 μm or more and 2 μm or less. The content of the carbide particles in the microstructure is 4000 particles/mm.sup.2 or less. The microstructure includes prior γ grains having an average size of 6 to 15 μm.

A strong and ductile automotive steel comprising 8-11 wt. % Mn, 0.1-0.35 wt. % C, 1-3 wt. % Al, 0.05-0.5 wt. % V, and a balance of Fe. By tuning the amount of austenite stabilizers, a dual phase microstructure of martensite and austenite with proper phase fraction can be achieved at room temperature. The martensite partitions C into the retained austenite grains. The martensite matrix can ensure the higher strength of automotive steel while the retained austenite grains with varied mechanical stability can improve the ductility of automotive steel, achieving the strength of 1500 MPa and the ductility of 20% simultaneously. The method for fabricating this automotive steel circumvents the high quenching temperature of conventional Q&P steels and therefore reduces the production price and is easy for mass production.

The present invention presents a steel for hot stamping, a hot stamping process and a hot stamped component. The steel for hot stamping in weight percentage contains C: 0.2-0.4%, Si: 0-0.8%, Al: 0-1.0%, B: 0-0.005%, Mn: 0.5-3.0%, Mo: 0-1%, Cr: 0-2%, Ni: 0-5%, V: 0-0.4%, Nb: 0-0.2%, Ti: 0.01%, and impurity elements such as P, S, N unavoidable during smelting, wherein 29*Mo+16*Mn+14*Cr+5.3*Ni30% is satisfied when B0.0005%, and 0.4-1.0% Al is contained when 0.0005%<B0.005%.

A high strength steel sheet having excellent surface quality and formability with a tensile strength of 980 MPa or more and a TS-El balance of 30000 MPa % or more is provided. A high strength steel sheet comprises: a chemical composition containing C: 0.08% to 0.30%, Si: 2.0% or less, Mn: more than 3.0% and 10.0% or less, P: 0.05% or less, S: 0.01% or less, Al: 1.5% or less, Ti: 0.010% to 0.300%, and N: 0.0020% to 0.0100% in a range satisfying 1.1(Ti+Mn.sup.1/2/400)/(0.01+5N)6.0; and a microstructure including a retained austenite phase and a ferrite phase, wherein a ratio Mn/Mn of an average Mn concentration (Mn) of the retained austenite phase to an average Mn concentration (Mn) of the ferrite phase is 1.5 or more.

Billets and methods for manufacturing them are disclosed. The billets include a cladding member including an alloy selected from the group including stainless steel, nickel-chrome, nickel-copper, and copper-nickel alloys, and a steel body that is positioned so that it has an interface with the cladding member, the steel body having a formation in which the scavenging metal is located and elements being provided for separating the scavenging metal from the cladding member at the interface.

There is provided a hot stamped body including a middle part in sheet thickness and a surface layer arranged at both sides or one side of the middle part in sheet thickness, further including an intermediate layer formed between the middle part in sheet thickness and each surface layer so as to adjoin them, wherein the middle part in sheet thickness has a predetermined composition, the middle part in sheet thickness has a hardness of 500 Hv or more and 800 Hv or less, the surface layer has a hardness change H.sub.1 in the sheet thickness direction of 10 Hv or more and less than 200 Hv, and the intermediate layer has a hardness change H.sub.2 in the sheet thickness direction of 50 Hv or more and less than 200 Hv.

A steel sheet including a steel micro-structure containing, in volume fraction, tempered martensite: 85% or more, retained austenite: 5% or more to less than 15%, and ferrite, pearlite, bainite, and as-quenched martensite being less than 10% in total, when contents of Mn and C in the retained austenite are denoted by Mn.sub.A and C.sub.A, and when contents of Mn and C in a matrix are denoted by Mn.sub.M and C.sub.M, respectively, following Formulas (1) to (3) are satisfied, and the number of carbides having an equivalent circle radius of 0.1 m or more is 100 or less in a region measuring 20000 m.sup.2, and the steel sheet has a tensile strength of 1100 MPa or more. The steel sheet is excellent in crash resistance and formability.
Mn.sub.A/Mn.sub.M1.2(1)
C.sub.A/C.sub.M5.0(2)
C.sub.A1.0(3)