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.

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.

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.

The disclosure discloses a NdFeB permanent magnet and a preparation method thereof. The magnet is composed of main phase I, a shell structure, a grain boundary phase adjacent to the shell structure, a main phase II, a Ga rich region and a Cu rich region. The magnet has high remanence, high coercivity, and high magnetic energy. In addition, this method can significantly reduce the production cost.

The disclosure discloses a NdFeB permanent magnet and a preparation method thereof. The magnet is composed of main phase I, a shell structure, a grain boundary phase adjacent to the shell structure, a main phase II, a Ga rich region and a Cu rich region. The magnet has high remanence, high coercivity, and high magnetic energy. In addition, this method can significantly reduce the production cost.

A high-strength cold-rolled steel sheet comprises: a chemical composition that contains C, Si, Mn, P, S, N, Al, Ti, Nb, and B with a balance consisting of Fe and inevitable impurities, and satisfies [mol % N]/[mol % Ti]<1; and a steel microstructure in which: an area fraction of ferrite is 30% or more and 60% or less; a total area fraction of tempered martensite and bainite is 35% or more and 65% or less; an area fraction of quenched martensite is 15% or less; an area fraction of retained austenite is 1% or more and 10% or less; an area fraction of low-Mn ferrite having a Mn concentration of 0.8×[% Mn] or less is 5% or more and 40% or less; a result of subtracting the area fraction of the low-Mn ferrite from the area fraction of the ferrite is 10% or more; an area fraction of a residual microstructure is less than 3%; and an average grain size of the low-Mn ferrite is 10 μm or less.

The present invention provides a rare-earth sintered magnet that is characterized in that: R (R indicates one or more elements selected from rare-earth elements, wherein Nd is essential), T (T indicates one or more elements selected from iron-group elements, wherein Fe is essential), X (X indicates one or two elements selected from B and C, wherein B is essential), M.sup.1 (M.sup.1 indicates one or more elements selected from Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, and Bi), 0.1 mass % or less of O, 0.05 mass % or less of N, and 0.07 mass % or less of C are contained; the average crystal grain size is 4.0 μm or less; and relational expression (1) 0.26×D+97≤Or≤0.26×D+99 is satisfied assuming that the degree of orientation is Or [%] and that the average crystal grain size is D [μm]. With this rare-earth sintered magnet, it is possible to achieve superior magnetic characteristics in which both high Br and high H.sub.cJ are achieved.

A hot-stamping formed body has a predetermined chemical composition and includes microstructure which includes residual austenite of which an area ratio is 10% or more and less than 20%, Among grain boundaries of crystal grains of bainite and tempered martensite a ratio of a length of a grain boundary having a rotation angle in a range of 55° to 75° to a total length of a grain boundary having a rotation angle in a range of 4° to 12°, a grain boundary having a rotation angle in a range of 49° to 54°, and the grain boundary having a rotation angle in, a range of 55° to 75° to the <011> direction as a rotation axis is 30% or more.

A hot-stamping formed body has a predetermined chemical composition and includes microstructure which includes residual austenite of which an area ratio is 10% or more and less than 20%, Among grain boundaries of crystal grains of bainite and tempered martensite a ratio of a length of a grain boundary having a rotation angle in a range of 55° to 75° to a total length of a grain boundary having a rotation angle in a range of 4° to 12°, a grain boundary having a rotation angle in a range of 49° to 54°, and the grain boundary having a rotation angle in, a range of 55° to 75° to the <011> direction as a rotation axis is 30% or more.

A hot-stamping formed body has a predetermined chemical composition and includes microstructure which includes residual austenite of which an area ratio is 5% or more and less than 10%. Among grain boundaries of crystal grains of bainite and tempered martensite in the microstructure, a ratio of a length of a grain boundary having a rotation angle in a range of 55° to 75° to a total length of a grain boundary having a rotation angle in a range of 4° to 12°, a grain boundary having a rotation angle in a range of 49° to 54°, and a grain boundary having a rotation angle in a range of 55° to 75° to the <011> direction as a rotation axis is 30% or more. The tensile strength of the hot-stamping formed body is 1500 MPa or more.