Provided are a high-strength steel sheet and a method for manufacturing the steel sheet. The high-strength steel sheet has a specified chemical composition with the balance being Fe and inevitable impurities, a microstructure including, in terms of area ratio, 30% or more of a ferrite phase, 40% to 65% of a bainite phase and/or a martensite phase, and 5% or less of cementite, in which, in a surface layer that is a region within 50 μm from the surface in the thickness direction, the area ratio of a ferrite phase is 40% to 55% and the total area ratio of a bainite phase having a grain diameter of more than 5 μm and/or a martensite phase having a grain diameter of more than 5 μm is 20% or less, and a tensile strength is 980 MPa or more.

A high-strength galvanized steel sheet that includes a chemical composition containing, by mass %, C: 0.15% or more and 0.25% or less, Si: 0.50% or more and 2.5% or less, Mn: 2.3% or more and 4.0% or less, P: 0.100% or less, S: 0.02% or less, Al: 0.01% or more and 2.5% or less, and Fe and inevitable impurities. The steel sheet having a microstructure containing, by an area percentage basis, a tempered martensite phase: 30% or more and 73% or less, a ferrite phase: 25% or more and 68% or less, a retained austenite phase: 2% or more and 20% or less, and other phases: 10% or less (including 0%), the other phases containing a martensite phase: 3% or less (including 0%) and a bainitic ferrite phase: less than 5% (including 0%).

Provided are a high-strength steel sheet and a method for manufacturing the steel sheet. The high-strength steel sheet has a specified chemical composition with the balance being Fe and inevitable impurities, a microstructure including, in terms of area ratio, 25% or less of a ferrite phase, 75% or more of a bainite phase and/or a martensite phase, and 5% or less of cementite, in which, in a surface layer that is a region within 50 μm from the surface in the thickness direction, the area ratio of a ferrite phase is 5% to 20%, and a tensile strength is 1180 MPa or more.

A high-strength plated steel sheet sequentially includes an internal oxidized layer, a soft layer containing the internal oxidized layer, and a hard layer including a structure having metallic structure which contains a low-temperature-transformation produced phase in a proportion of 20 to 85% by area of the whole of the metallic structure, polygonal ferrite in a proportion more than 10% by area, and 70% or less by area of the whole of the metallic structure, and-retained austenite in a proportion of 5% or more by volume of the whole of the metallic structure. The high-strength plated steel sheet satisfies the average depth D of the soft layer being 20 μm or more, the average depth d of the internal oxidized layer being 4 μm or more and less than D, and a tensile strength being 980 MPa or more.

When a non-oriented electrical steel sheet is produced by hot rolling a slab containing, by mass %, C: not more than 0.0050%, Si: 1.5-5.0%, Mn: 0.20-3.0%, sol. Al: not more than 0.0050%, P: not more than 0.2%, S: not more than 0.0050% and N: not more than 0.0040% to form a hot rolled sheet, cold rolling the hot rolled sheet without conducting a hot band annealing and then subjecting to a finish annealing, a compositional ratio of CaO in oxide-based inclusions existing in the slab defined by CaO/(SiO.sub.2+Al.sub.2O.sub.3+CaO) is set to not less than 0.4 and/or a compositional ratio of Al.sub.2O.sub.3 defined by Al.sub.2O.sub.3/(SiO.sub.2+Al.sub.2O.sub.3+CaO) is set to not less than 0.3, and a coiling temperature in the hot rolling is set to not lower than 650° C.

Disclosed herein is a high-strength plated steel sheet having a plated layer on the surface of a base steel sheet and containing predetermined steel components. The steel sheet includes, in the order from the interface of the base steel sheet and the plated layer towards the base steel sheet: a soft layer having a Vickers hardness that is 90% or less of the Vickers hardness at a portion t/4 of the base steel sheet, where t is a sheet thickness of the base steel sheet; and a hard layer consisting of a structure which is mainly composed of martensite and bainite and in which the average grain size of prior austenite is 20 μm or less. The average depth D of the soft layer is 20 μm or greater, and the average depth d of an internal oxide layer is 4 μm or greater and smaller than D.

A method for producing an RFeB system sintered magnet according to the present invention includes: a process (S1) of preparing a lump of HDDR-treated raw material alloy that contains a polycrystalline substance including crystal grains having an average grain size of 1 μm or less in terms of an equivalent circle diameter calculated from an electron micrograph image, by an HDDR treatment including steps of heating a lump of RFeB system alloy containing 26.5 to 29.5% by weight of the rare-earth element R, in a hydrogen atmosphere at a temperature between 700 and 1,000° C., and changing the atmosphere to vacuum while maintaining the temperature within a range from 750 to 900° C.; a process (S2) of preparing a lump of raw material alloy having a high rare-earth content by heating the lump of HDDR-treated raw material alloy at a temperature between 700 and 950° C. in a state where the HDDR-treated raw material alloy is in contact with a contact substance including a second alloy that contains the rare-earth element R at a higher content ratio than a content ratio of the rare-earth element R in the RFeB system alloy; a process (S3) of preparing raw material alloy powder by fine pulverization of the lump of raw material alloy having a high rare-earth content into powder having an average particle size of 1 μm or less; an orienting process (S4) including steps of placing the raw material alloy powder in a mold, and applying a magnetic field to the raw material alloy powder without conducting compression molding; and a sintering process (S5) including a step of heating the oriented raw material alloy powder at a temperature between 850 and 1,050° C.

Disclosed herein is a high-strength plated steel sheet containing an internal oxidized layer, a soft layer including the internal oxidized layer, and a hard layer including a structure having metallic structure containing a low-temperature-transformation produced phase in a proportion of 70% or more by area of the whole of the metallic structure, in which polygonal ferrite is in a proportion of 0% or more by area, and 10% or less by area of the same, and retained austenite is in a proportion of 5% or more by volume of the same. The high-strength plated steel sheet satisfies the average depth D of the soft layer is 20 μm or more, the average depth d of the internal oxidized layer is 4 μm or more and less than D, and a tensile strength of 980 MPa or more.

A metal powder for powder metallurgy contains Fe as a principal component, Ni in a proportion of 5 mass % or more and 20 mass % or less, Si in a proportion of 0.3 mass % or more and 5 mass % or less, and C in a proportion of 0.005 mass % or more and 0.3 mass % or less, and when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group and having a higher group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a higher period number in the periodic table than that of the first element is defined as a second element.

An inoculant for the manufacture of cast iron with spheroidal graphite is disclosed, the inoculant has a particulate ferrosilicon alloy having between 40 and 80% by weight of Si, 0.02-8% by weight of Ca; 0-5% by weight of Sr; 0-12% by weight of Ba; 0-10% by weight of rare earth metal; 0-5% by weight of Mg; 0.05-5% by weight of Al; 0-10% by weight of Mn; 0-10% by weight of Ti; 0-10% by weight of Zr; the balance being Fe and incidental impurities in the ordinary amount, wherein the inoculant additionally contains, by weight, based on the total weight of inoculant: 0.1 to 15% by weight of particulate rare earth metal oxide(s) and at least one of from 0.1 to 15% of particulate Bi.sub.2O.sub.3, and/or from 0.1 to 15% of particulate Bi.sub.2S.sub.3, and/or from 0.1 to 15% of particulate Sb.sub.2O.sub.3, and/or from 0.1 to 15% of particulate Sb.sub.2S.sub.3, and/or from 0.1 to 5% of one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or from 0.1 to 5% of one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, a method for producing such inoculant and use of such inoculant.