Provided are thick hot-rolled composite-phase steel having excellent durability and a manufacturing method therefor. The thick composite-phase steel having excellent durability according to the present invention comprises, by wt %, C: 0.05 to 0.15%, Si: 0.01 to 1.0%, Mn: 1.0 to 2.3%, Al: 0.01 to 0.1%, Cr: 0.005 to 1.0%, P: 0.001 to 0.05%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, Nb: 0.005 to 0.07%, Ti: 0.005 to 0.11%, Fe, and inevitable impurities, and has a mixed phase of ferrite and bainite as a base structure, wherein, in the base structure, the area fraction of each of a pearlite phase and a martensite and austenite (MA) phase is less than 5%, and the area fraction of a martensite phase is less than 10%.

A hot stamped body with high strength, good bendability and crack propagation resistance, consisting of: in mass %, C: 0.06% or more to less than 0.20%, Si: 0.010-1.00%, Mn: 0.80-2.00%, P: 0.100% or less, S: 0.010% or less, Al: 0.010-0.500%, N: 0.010% or less, Nb: more than 0.020% to 0.10% or less, Ti: 0-0.10%, V: 0-0.10%, Cr: 0-0.50%, Mo: 0-1.00%, B: 0-0.0100%, Ni: 0-0.50%, REM: 0-0.0100%, Mg: 0-0.010%, Ca: 0-0.0100%, and Co: 0-2.0%, with the balance: Fe and impurities, wherein a microstructure includes, in area fraction, ferrite: 5-50%, and martensite: 50-95%, a proportion of regions in the martensite where GAIQ values are 35000 or more to less than 45000 is 30 area % or more, and a maximum bending angle α (deg) is 90 or more.

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.

press hardening method includes the following steps: A. the provision of a steel sheet for heat-treatment, precoated with a zinc- or aluminum-based pre-coating, B. the deposition of a hydrogen barrier pre-coating over a thickness from 10 to 550 nm, and comprising at least one element chosen from among: nickel, chromium, magnesium, aluminum and yttrium, C. batch annealing of the precoated steel sheet to obtain a pre-alloyed steel sheet, the cooling after the batch annealing being performed at a speed of 29.0° C.h.sup.−1 or less, D. the cutting of the pre-alloyed steel sheet to obtain blank, E. thermal treatment of the blank to obtain a fully austenitic microstructure in the steel, F. the transfer of the blank into a press tool, G. the hot-forming of the blank to obtain a part, H. the cooling of the part obtained at step G).

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 is a ferritic stainless steel having improved magnetization including, in percent by weight (wt %), 0.01% or less (excluding 0) of C) 0.003% or less (excluding 0) of N, 15 to 18% of Cr, 0.3 to 1.0% of Mn, 0.2 to 0.3% of Si, 0.005% or less (excluding 0) of Al, 0.005% or less (excluding 0) of Ti, and the balance of Fe and inevitable impurities, and satisfying the following equation,

(Ti+Al+8*(C+N)/Mn)≤0.3  Equation (1)

(wherein Ti, Al, C, N, and Mn denote amounts (wt %) of the respective elements).

An additively manufactured object formed by depositing weld bead layers, each of the weld bead layers being obtained by melting and solidifying a filler metal made of a mild steel, the additively manufactured object includes a plurality of the weld bead layers having a ferrite phase with an average grain diameter of 11 μm or less in a part except for a surface oxide film.

Disclosed are a Nb microalloyed high strength high hole expansion steel and a production method therefor. The chemical ingredients of the steel in percentages by weight are as follows: 0.01-0.05% of C, 0.2-0.6% of Si, 0.8-1.5% of Mn, ≤0.02% of P, ≤0.005% of S, ≤0.008% of N, <0.001% of Als, ≤0.0050% of Ca, 0.01-0.08% of Nb, and optionally one or both of 0.1-0.6% of Cu and 0.005-0.04% of Sn, wherein Mn/S>250, total oxygen [O].sub.T is 0.007-0.020%, and the balance is Fe and inevitable impurities. In the present invention, microalloy elements such as Nb are selectively added, and the basicity of slag, the type and melting point of the inclusion in steel, the content of free oxygen in molten steel, and the content of acid-soluble aluminum Als during the smelting process are controlled, and then, a strip is cast by means of twin-roll thin strip continuous casting, and the strip directly enters a lower closed chamber in a non-oxidizing atmosphere and enters an online rolling mill for hot rolling in closed conditions, and after rolling, the strip steel is cooled by air atomization cooling, and finally, the produced steel coil can be used directly as a hot rolled plate or can be used after acid pickling and leveling.