To solve a problem about warpage of a steel sheet due to a difference in temperature raising rate between an overlapped part and a one-sheet part. This manufacturing method includes: a step of heating an overlapped blank; a step of transferring the heated overlapped blank; and a step of performing presswork on the heated overlapped blank by using a die, in which in the heating step, when sheet thicknesses of the first and second steel sheets are set to t1 and t2, respectively, and an average heating rate at a sheet temperature from 20 to 800° C. of a portion with a total sheet thickness (t1+t2) of an overlapped portion, and that of a non-overlapped portion are set to V and v1, respectively, the total sheet thickness (t1+t2) is 2.5 to 5.0 mm, a maximum length L of the overlapped portion is 100 to 1100 mm, an area S1 of the first steel sheet, an area S2 of a portion, of the second steel sheet, which is overlapped with the first steel sheet, and the average heating rates V and v1 satisfy Expressions (1) to (3), and the heating is performed at a heating temperature and for a heating time within a specific range on a plane of coordinates defined by the heating time and the heating temperature.

A cold-rolled and heat-treated steel sheet having a microstructure of, in surface fraction: between 10% and 30% of retained austenite, said retained austenite being present as films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of such Martensite Austenite islands having a size above 0.5 μm, at most 10% of fresh martensite and
recovered martensite containing precipitates of at least one element chosen among niobium, titanium and vanadium. A manufacturing method thereof is also provided.

A cold-rolled and heat-treated steel sheet having a microstructure consisting of, in surface fraction: between 10% and 30% of retained austenite, the retained austenite being present as films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of the Martensite Austenite islands having a size above 0.5 μm, at most 1% of fresh martensite, at most 50% of tempered martensite, and recovered martensite containing precipitates of at least one element chosen among niobium, titanium and vanadium. A method for manufacturing the cold-rolled and heat-treated steel sheet is also described.

The present invention relates to a grain-oriented electrical steel sheet including 2.0 to 6.0 wt % of Si, 0.01 wt % or less (excluding 0 wt %) of C, 0.01 wt % or less (excluding 0 wt %) of N, and 0.005 to 0.1 wt % of Co, and including a balance of Fe and other inevitable impurities.

Fe-Al-based plated hot-stamped member exhibiting excellent formed part corrosion resistance and post-coating corrosion resistance and manufacturing method. The hot-stamping member includes Fe-Al-based plated layer on one or both surfaces of a base material, the base material has a predetermined steel component, Fe-Al-based plated layer has a thickness of 10 μm or more and 60 μm or less, formed by A, B, C and D layers sequentially from a surface toward the base material, and each of the four layers is a Fe-Al-based intermetallic compound containing Al, Fe, Si, Mn and Cr for predetermined contents with the balance made up of impurities, the D layer further contains Kirkendall voids each of which cross-sectional area is 3 μm.sup.2-30 μm.sup.2 for 10 pieces/6000 μm.sup.2 or more and 40 pieces/6000 μm.sup.2 or less.

A high-strength galvanized steel sheet includes a steel sheet containing a predetermined component element, a mass ratio of a content amount of Si to a content amount of Mn in the steel (Si/Mn) being 0.2 or more, and a steel structure in which an average grain size of inclusions existing in an area extending from a surface to a position of ⅓ of a sheet thickness is 50 μm or less, and an average nearest distance between ones of the inclusions is 20 μm or more; and a galvanized layer provided on a surface of the steel sheet, in which an amount of diffusible hydrogen contained in the steel is less than 0.25 mass ppm, oxides containing predetermined elements in an outer layer portion of the steel sheet account for 0.010 g/m.sup.2 or more per one surface, and a tensile strength is 1100 MPa or more.

A low-carbon iron-chromium-molybdenum alloy comprises, in weight percent: carbon from about 0.1 to about 0.8 percent; manganese from about 0.1 to about 4 percent; silicon from about 0.1 to about 0.5 percent; chromium from 14 to about 16 percent; nickel up to about 8 percent; vanadium up to about 0.1 percent; molybdenum from 14 to about 16 percent; tungsten up to about 6 percent; niobium from about 0.1 to about 0.8 percent; cobalt up to about 0.2 percent; boron up to 0.1 percent; nitrogen up to about 0.1 percent; copper up to about 1.5 percent; sulfur up to about 0.05 percent; phosphorus up to about 0.05 percent; balance iron from about 50 to about 65 percent; and incidental impurities wherein the alloy contains a ratio of Cr/Mo of about 0.9 to about 1.1. The alloy can be used as a valve seat insert for combustion engines.

Provided is a high strength steel sheet that has a predetermined chemical composition and is manufactured under optimum conditions, the high strength steel sheet having a steel microstructure including, by area, ferrite: 30% or more and 80% or less, tempered martensite: 3.0% or more and 35% or less, and retained austenite: 8% or more, wherein the quotient of the area fraction of grains of the retained austenite, the grains having an aspect ratio of 2.0 or more and a minor axis length of 1 μm or less, divided by the total area fraction of the retained austenite is 0.3 or more, wherein the quotient of the average Mn content (mass %) in the retained austenite divided by the average Mn content (mass %) in the ferrite is 1.5 or more.

Provided is a high strength steel sheet that has a predetermined chemical composition and is manufactured under optimum conditions, the high strength steel sheet having a steel microstructure including, by area, ferrite: 30% or more and 80% or less, martensite: 5% or more and 35% or less, and retained austenite: 8% or more, wherein the quotient of the area fraction of grains of the retained austenite, the grains having an aspect ratio of 2.0 or more and a minor axis length of 1 μm or less, divided by the total area fraction of the retained austenite is 0.3 or more, wherein the quotient of the average Mn content (mass %) in the retained austenite divided by the average Mn content (mass %) in the ferrite is 1.5 or more.

Disclosed are a non-oriented electrical steel sheet and a manufacturing method therefore, the sheet ensuring excellent magnetic characteristics by having increased texture intensity of surface (100) through strict control of the content ratio of Si, Al and the like and through final annealing heat treatment in an inert gas atmosphere.