An R—Fe—B base sintered magnet is provided consisting essentially of R (which is at least two rare earth elements and essentially contains Nd and Pr), M.sub.1 which is at least two of Si, Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi, M.sub.2 which is at least one of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W, boron, and the balance of Fe, and containing an intermetallic compound R.sub.2(Fe,(Co)).sub.14B as a main phase. The magnet contains an R—Fe(Co)-M.sub.1 phase as a grain boundary phase, the R—Fe(Co)-M.sub.1 phase contains A phase which is crystalline with crystallites of at least 10 nm formed at grain boundary triple junctions, and B phase which is amorphous and/or nanocrystalline with crystallites of less than 10 nm formed at intergranular grain boundaries and optionally grain boundary triple junctions.

The present invention relates to a grain oriented electrical steel sheet having excellent core loss and to a method for manufacturing same. The electrical steel sheet according to one aspect of the present invention may have a composition comprising, by weight %, Si: 1.0 to 4.0%, Al: 0.1 to 4.0%, and a rare earth element: 0.0001 to 0.5% by the total content of the whole rare earth element.

Free-cutting steel that has the same or better machinability compared to low-carbon sulfur-lead composite free-cutting steel, despite of no-addition of Pb, is provided. Free-cutting steel contains, in mass %, C: 0.08% or less, Mn: 0.50 to 1.50%, P: 0.100% or less, S: 0.250 to 0.500%, N: 0.0050 to 0.0150%, O: more than 0.0100% and 0.0500% or less, Cr: 0.50 to 1.50%, at least one of Si, Al, or Ti: 0.050 to 0.500% in total, with the balance being Fe and inevitable impurities, with an A value defined by formula (1) satisfying 0.40 to 2.00, and with a B value defined by formula (2) satisfying 1.10×10.sup.−3 to 1.50×10.sup.−2; and a steel microstructure with distributed 3000 or more sulfide particles with an equivalent circular diameter of 5 μm or less per mm.sup.2.

Provided is steel for nitrocarburizing with excellent surface fatigue strength. The steel has a nitride compound layer with a thickness of 5.0 μm to 30.0 μm and a hardened layer in an order from a steel surface to steel inside, where a thickness of a porous layer on an outermost surface of the compound layer is 3.0 μm or less and 40.0% or less of a compound layer's thickness, the hardened layer has hardness of HV600 or more, HV400 or more and HV250 or more at 50 μm inward from the steel surface, from the steel surface to the steel inside of 400 μm, and from the steel surface to the steel inside of 600 μm, respectively, an unhardened portion excluding the compound and hardened layers has a predetermined chemical composition, and the hardened layer has a chemical composition with a higher N content than the unhardened portion.

In a steel sheet according to the present embodiment, a Ti content and a N content satisfy Ti−3.5×N≥0.003, at a sheet thickness ¼ position, a metallographic structure includes 90% or more of martensite in terms of volume fraction, at the sheet thickness ¼ position, a number density of TiC having a circle equivalent diameter of 1 to 500 nm is 3.5×10.sup.4 particles/mm.sup.2 or more, at the sheet, thickness ¼ position, a value of a median value of a Mn concentration+3σ is 5.00% or less, and a hardness measured at the sheet thickness ¼ position is 1.30 times or more a hardness measured at a position 50 μm deep from a surface of the steel sheet.

A medium carbon steel sheet for cold working that has a hardness of 500 HV to 900 HV when subjected to high-frequency quenching and a quick cooling to a room temperature is carried out. The medium carbon steel sheet includes, by mass %, C: 0.30 to 0.60%, Si: 0.06 to 0.30%, Mn: 0.3 to 2.0%, P: 0.03% or less, S: 0.0075% or less, Al: 0.005 to 0.10%, N: 0.001 to 0.01%, and Cr: 0.001 to 0.10%, the balance composed of Fe and inevitable impurities. An average diameter d of a carbide is 0.6 μm or less, a spheroidizing ratio p of the carbide is equal to or more than 70% and less than 90%, and the average diameter d (μm) of the carbide and the spheroidizing ratio p % of the carbide satisfy the expression d≦0.04×p−2.6.

A hot-rolled steel sheet includes a specific chemical composition, and includes a microstructure represented by, in vol %: retained austenite: 2% to 30%; ferrite: 20% to 85%; bainite: 10% to 60%; pearlite: 5% or less; and martensite: 10% or less. A proportion of grains having an intragranular misorientation of 5° to 14° in all grains is 5% to 50% by area ratio, the grain being defined as an area which is surrounded by a boundary having a misorientation of 15° or more and has a circle-equivalent diameter of 0.3 μm or more.

Provided is a steel sheet having a predetermined chemical composition, wherein precipitates having a diameter of less than 0.1 μm are present in a number density of 10 to 200/μm.sup.2 in a depth region of 1 to 10 μm from a surface, an amount of dissolved C in a depth region of 10 to 60 μm from the surface is less than 0.20 mass %, and a tensile strength is 1200 MPa or more. Further, provided is a method for producing a steel sheet comprising a step of hot rolling a steel slab having a predetermined chemical composition, then coiling it at 580° C. or less, a step of pickling the hot rolled steel sheet to remove oxide scale and remove the surface layer of the hot rolled steel sheet down to at least 5 μm, and a step of cold rolling the hot rolled steel sheet, then holding it in an atmosphere of a dew point of −20 to 20° C. at a temperature region of 200 to 400° C. for 20 to 180 seconds and holding it at a temperature region of 740 to 900° C. for 40 to 300 seconds.

Provided is a steel sheet having a predetermined chemical composition and microstructure, wherein a block size in a first depth region of 1 to 10 μm from the surface is 5.0 μm or less, a block size in a second depth region of 10 to 60 μm from the surface is 6.0 to 20.0 μm, and a block size in a third depth region of 60 μm to 1/4 thickness from the surface is less than 6.0 μm. Further, provided is a method for producing a steel sheet comprising a step of hot rolling a steel slab having a predetermined chemical composition, then coiling it at 500° C. or more, a step of pickling the hot rolled steel sheet to remove oxide scale, wherein an amount of removal of the surface layer of the hot rolled steel sheet is less than 5.00 μm, a step of cold rolling by a rolling reduction of 30 to 90%, and an annealing step of holding in an atmosphere of a dew point of −20 to 20° C. at a temperature region of 740 to 900° C. for 40 to 300 seconds.

An alloy pipe and a method for producing the same are disclosed. The alloy pipe of the present invention contains, as a component composition, in terms of % by mass, Cr: 11.5-35.0%, Ni: 23.0-60.0%, and Mo: 0.5-17.0%, has an austenitic phase as a microstructure, has a Mo concentration (% by mass) in a grain boundary of the austenitic phase that is 4.0 times or less than a Mo concentration (% by mass) within grains of the austenitic phase, and has a tensile yield strength in a pipe axial direction of 689 MPa or more and a ratio (compressive yield strength in a pipe axial direction)/(tensile yield strength in a pipe axial direction) of 0.85 to 1.15.