This application discloses thin metal strips and methods of making thin metal strip. Particular embodiments of such methods include cooling the thin metal strip to a temperature equal to or less than a bainite or a martensite start transformation temperature B.sub.S or M.sub.S to thereby form bainite and/or martensite, respectively, within the thin metal strip, reheating the thin metal strip to a reheat temperature equal to or greater than transformation temperature Ac.sub.3 and holding the thin metal strip at the reheat temperature for at least 2 seconds and thereby forming austenite within the thin metal strip with at least 75% of austenite grains having a grain size equal to or less than 15 μm, and rapidly recooling the thin metal strip to a temperature equal to or less than the martensite start transformation temperature M.sub.S and thereby providing finer martensite within the thin metal strip from a finer prior austenite.

A steel sheet has a predetermined chemical composition, in which a metallographic structure in a surface layer region ranging from a surface to a position of 20 μm from the surface in a sheet thickness direction consists of ferrite and a secondary phase having a volume fraction of 0.01% to 5.0%, a metallographic structure in an internal region ranging from a position of more than 20 μm from the surface in the sheet thickness direction to a ¼thickness position from the surface in the sheet thickness direction consists of ferrite and a secondary phase having a volume fraction of 2.0% to 10.0%, the volume fraction of the secondary phase in the surface layer region is less than the volume fraction of the secondary phase in the internal region, and in the surface layer region, an average grain size of the secondary phase is 0.01 μm to 4.0 μm, and a texture in which an X.sub.ODF{001}/{111} as the ratio of the intensity of {001} orientation to an intensity of {111} orientation in the ferrite is 0.60 or more and less than 2.00 is included.

The high-strength hot-dip galvanized steel sheet, which includes a hot-dip galvanized coating layer on a surface of the steel sheet, has a component composition containing, in mass %, C: 0.07% to 0.20%, Si: 0.1% to 2.0%, Mn: 2.0% to 3.5%, P: 0.05% or less, S: 0.05% or less, and sol. Al: 0.005% to 0.1%, with the balance being Fe and incidental impurities; and has a steel microstructure containing, in area fraction, 60% or less of ferrite, 40% or more of tempered martensite, and 10% or less of fresh martensite and having a void number density of 1,500/mm.sup.2 or less in a bent portion in the VDA bending test.

The en-bloc heat treatment of a manganese steel product whose alloy has a carbon fraction (C) in the following range 0.02≦C≦0.35% by weight, and a manganese content (Mn) in the following range of 3.5% by weight≦Mn≦6% by weight. The en-bloc annealing method has the following substeps: heating (E1) the steel product to a first holding temperature (T1) which is in the range of 820° C.±20° C., first holding (H1) of the steel product during a first holding period (δ1) at the first holding temperature (T1), faster first cooling (A1) of the steel product to a second holding temperature (T2) which is in the range between 350° C. and 450° C., second holding (H2) of the steel product during a second holding period (δ2) in the range of the second holding temperature (T2), performing a slower second cooling (A2).

A vapor phase growth method of an embodiment is a vapor phase growth method using a vapor phase growth apparatus including a reactor, an exhaust pump, a pressure control valve, and an exhaust pipe. The vapor phase growth method includes: loading a first substrate into the reactor, heating the first substrate, supplying a process gas, and forming a silicon carbide film on a surface of the first substrate and depositing a by-product containing carbon in the first portion or the second portion by adjusting a pressure in the reactor by controlling the pressure control valve; unloading the first substrate from the reactor; removing the by-product by supplying a gas including a gas containing fluorine to the exhaust pipe by controlling a pressure in the exhaust pipe; and then loading a second substrate into the reactor to form a silicon carbide film on a surface of the second substrate.

A steel sheet includes, as a chemical composition, by mass %: C: 0.05-0.30%; Si: 0.2-2.0%; Mn: 2.0-4.0%; Al: 0.001-2.000%; P: 0.100% or less; S: 0.010% or less; N: 0.010% or less; Ti: 0-0.100%; Nb: 0-0.100%; V: 0-0.100%; Cu: 0-1.00%; Ni: 0-1.00%; Mo: 0-1.00%; Cr: 0-1.00%; W: 0-0.005%; Ca: 0-0.005%; Mg: 0-0.005%; a rare earth element (REM): 0-0.010%; B: 0-0.0030%; and a remainder of Fe and impurities, in which a metallographic structure contains, by area ratio, 95% or more of a hard structure and 0-5% of residual austenite, by mass % in a cross section in a thickness direction, C1/C2 which is a ratio of an upper limit C1 of a Mn content to a lower limit C2 of the Mn content is 1.5 or less, and a bake-hardening amount BH is 150 MPa or less.

The invention relates to a method for producing a high strength coated steel sheet having a yield stress YS>550 MPa, a tensile strength TS>980 MPa, and improved formability and ductility. The steel contains: 0.15%≦C≦0.25%, 1.2%≦Si≦1.8%, 2%≦Mn≦2.4%, 0.1%≦Cr≦0.25%, Al≦0.5%, the balance being Fe and unavoidable impurities. The sheet is annealed at a temperature between TA1=Ac3−0.45*(Ms−QT) and TA2=830° C. for at least 30s then quenched by cooling it to a quenching temperature QT between 180° C. and 300° C., then heated to a partitioning temperature PT between 380° C. and 480° C. and maintained at this temperature for a partitioning time Pt between 0 sec and 300 sec, then either hot dip coated and cooled to the room temperature with a cooling rate of at least 25° C./s below 300° C., or directly cooled to the room temperature with a cooling rate of at least 25° C./s and further electro-galvanized, or cooled to the room temperature with a cooling rate of at least 25° C./s without coating. The steel according to the invention contains 5% to 25% of intercritical ferrite, at least 50% of partitioned martensite, at least 10% of residual austenite, less than 10% of fresh martensite, and bainite, the sum of partitioned martensite and bainite being at least 60%. It also relates to the obtained coated or non coated sheet.

A method for manufacturing a steel product, is provided. A heated steel starting product at a temperature between 380° C. and 700° C., having a metastable fully austenitic structure, with a composition including, in percent by weight: 0.15%≦C≦0.40%, 1.5%≦Mn≦4.0%, 0.5%≦Si≦2.5%, 0.005%≦Al≦1.5%, with 0.8%≦Si+Al≦2.5%, S≦0.05%, P≦0.1%, at least one element chosen among Cr and Mo, such that: 0%≦Cr≦4.0%, 0%≦Mo≦0.5%, and 2.7%≦Mn+Cr+3 Mo≦5.7% is provided. Then the starting product is hot formed at a temperature between 700° C. and 380° C., with a cumulated strain ε.sub.b between 0.1 and 0.7, in at least one location of the heated steel starting product, to obtain a fully austenitic hot-formed steel product; quenched by cooling the product down, at a cooling rate VR.sub.2 superior to the critical martensitic cooling rate, to a quenching temperature QT lower than Ms in order to obtain a structure containing between 40% and 90% of martensite, the rest of the structure being austenite; then maintained at, or reheated up to a holding temperature PT between QT and 470° C. and holding the product at the temperature PT for a duration Pt between 5 s and 600 s

A gradient steel material with a high plastic surface layer and a high strength inner layer, and a manufacturing method are provided. Weight percentages of the components of the gradient steel material are: C≤0.15%, Si≤1%, Mn≤1.5%, and the balance of Fe and inevitable impurities, the surface layer of the steel material being ferrite, and the inner layer being ferrite+bainite. The manufacturing method therefor comprises: smelting, casting, rolling, and a heat treatment, wherein in the heat treatment step, a steel material is heated to an austenite temperature Ac3 or more and kept at said temperature for more than 3 min; thereafter, the material is cooled to a temperature range between Ar3 and Ar1 in a two-phase zone at a cooling rate of less than 0.5° C./s, and is then cooled to room temperature at a cooling rate of greater than 5° C./s. The present steel material does not need to be obtained by means of the compound preparation of different materials as only a single material is processed. At the same time, the composition of the steel material is simple. Although the internal and external microstructures are different, the difference is a gradual process, and the strength at the interface is good.

A soft magnetic material that is sheet-shaped or foil-shaped and has a high saturation magnetic flux density, contains iron, carbon, and nitrogen, and includes a martensite containing carbon and nitrogen, and γ-Fe, wherein the γ-Fe includes a nitrogen-containing phase. The soft magnetic material is produced by steps of heating an iron-based material that is sheet-shaped or foil-shaped, carburizing the iron-based material with a carburizing gas, dispersing a granular carbide in α-Fe in the iron-based material at a temperature equal to or lower than a eutectoid temperature, transforming the α-Fe into γ-Fe at a temperature higher than the eutectoid temperature, diffusing nitrogen into the γ-Fe using a nitrogen supply gas to form γ-Fe—N—C, and rapidly heating and then rapidly cooling the γ-Fe—N—C to transform the γ-Fe—N—C into a martensite. The result is a thermally stable soft magnetic material having a saturation magnetic flux density higher than that of pure iron.