Disclosed is a steel composition including specified ranges of Ni; Mo; Co; Mo+Co+Si+Mn+Cu+W+V+Nb+Zr+Ta+Cr+C; Co+Mo; Ni+Co+Mo; and traces of Al; Ti; N; Si; Mn; C; S; P; B; H; O; Cr; Cu; W; Zr; Ca; Mg; Nb; V; and Ta in specified ranges; the remainder being iron and impurities. The inclusion population, as observed by image analysis over a polished surface measuring 650 mm.sup.2 if hot-formed or hot-rolled; and measuring 800 mm.sup.2 if cold-rolled, does not contain non-metallic inclusions of diameter >10 μm, and, in the case of a hot-rolled sheet, does not contain more than four non-metallic inclusions of diameter 5-10 μm over 100 mm.sup.2, the observation being performed by image analysis over a polished surface measuring 650 mm.sup.2.

A non-oriented electrical steel sheet according to an embodiment of the present invention includes, in wt %, C at 0.005% or less (excluding 0%), Si at 0.5 to 2.4%, Mn at 0.4 to 1.0%, S at 0.005% or less (excluding 0%), Al at 0.01% or less (excluding 0%), N at 0.005% or less (excluding 0%), Ti at 0.005% or less (excluding 0%), Cu at 0.001 to 0.02%, and the balance of Fe and inevitable impurities, and satisfies Formula 1 below, wherein a volume fraction of grains in which an angle formed by a {111} surface and a rolling surface of the steel sheet is 15° or less is 27% or more.

[Mn]/([Si]+150×[Al])≤0.35   [Formula 1]

(In Formula 1, [Mn], [Si], and [Al] are contents (wt %) of Mn, Si, and Al, respectively.)

The invention relates to a microstructure of an alloy for a tube for reformers, having an austenitic matrix structure, characterised in that: i) primary micrometric precipitates in the form of M.sub.23C.sub.6-type carbides, where M=Fe, Ni or Cr, and/or M(C,N)-type carbides, where M==Nb or Ti, are formed during the solidification of the alloy; ii) secondary nanometric precipitates in the form of M.sub.23C.sub.6-type carbides, where M=Fe, Ni or Cr and/or M(C,N)-type carbides, where M==Nb or Ti, are formed during the activation of the tube; and iii) between 0.1 and 0.3% of Ni.sub.16Si7Nb.sub.6-type intermetallic precipitates is formed during the use of the tube.

The invention relates to a microstructure of an alloy for a tube for reformers, having an austenitic matrix structure, characterised in that: i) primary micrometric precipitates in the form of M.sub.23C.sub.6-type carbides, where M=Fe, Ni or Cr, and/or M(C,N)-type carbides, where M==Nb or Ti, are formed during the solidification of the alloy; ii) secondary nanometric precipitates in the form of M.sub.23C.sub.6-type carbides, where M=Fe, Ni or Cr and/or M(C,N)-type carbides, where M==Nb or Ti, are formed during the activation of the tube; and iii) between 0.1 and 0.3% of Ni.sub.16Si7Nb.sub.6-type intermetallic precipitates is formed during the use of the tube.

There is provided a precipitation-strengthened stainless steel plate having a chemical composition: by mass %, C: 0.01 to 0.10%; Si: 0.02 to 3.0%; Mn: 0.02 to 2.0%; Ni: 20 to 30%, Cr: 14 to 25.0%; Mo: 1.0 to 4.0%; Cu: 0.01 to 2.0%; Co: 0.01 to 0.5%©; V: 0.1 to 1.0%; B: 0.001 to 0.01%; N: 0.02% or less; Ti: 2.0 to 5.0%; Al: 0.002 to 5.0%; Ti+Al: 3.3 to 6.0%; and the balance being Fe and impurities, the precipitation-strengthened stainless steel plate having a Vickers hardness Hv of 300 or higher, wherein the number density γ′: Ni.sub.3(Al, Ti), which is an intermetallic compound, is 0 to 5/μm.sup.2. As a heat resistant component material, the precipitation-strengthened stainless steel plate is less expensive than conventional Ni-based alloys such as NCF625 and NCF718, and more excellent in high temperature properties than a precipitation-strengthened heat-resistant stainless steel such as SUH660.

A nitrided steel member including an iron nitride compound layer formed on a surface of a steel member having predetermined components, wherein: in X-ray diffraction peak intensity IFe.sub.4N (111) of a (111) crystal plane of Fe.sub.4N and X-ray diffraction peak intensity IFe.sub.3N (111) of a (111) crystal plane of Fe.sub.3N, which are measured on a surface of the nitrided steel member by X-ray diffraction, an intensity ratio expressed by IFe.sub.4N (111)/{IFe.sub.4N (111)+IFe.sub.3N (111)} is 0.5 or more; Vickers hardness of the iron nitride compound layer is 900 or less, Vickers hardness of a base metal immediately under the iron nitride compound layer is 700 or more, and a difference between the Vickers hardness of the iron nitride compound layer and the Vickers hardness of the base metal is 150 or less; and a thickness of the iron nitride compound layer is 2 to 17 μm.

A nitrided steel member including an iron nitride compound layer formed on a surface of a steel member having predetermined components, wherein: in X-ray diffraction peak intensity IFe.sub.4N (111) of a (111) crystal plane of Fe.sub.4N and X-ray diffraction peak intensity IFe.sub.3N (111) of a (111) crystal plane of Fe.sub.3N, which are measured on a surface of the nitrided steel member by X-ray diffraction, an intensity ratio expressed by IFe.sub.4N (111)/{IFe.sub.4N (111)+IFe.sub.3N (111)} is 0.5 or more; Vickers hardness of the iron nitride compound layer is 900 or less, Vickers hardness of a base metal immediately under the iron nitride compound layer is 700 or more, and a difference between the Vickers hardness of the iron nitride compound layer and the Vickers hardness of the base metal is 150 or less; and a thickness of the iron nitride compound layer is 2 to 17 μm.

A method of manufacturing an austenitic stainless steel, being dissolved and refined, by providing Si from 0.2 to 2.0% by mass, Mn from 0.3 to 5.0% by mass, S at 0.007% by mass or less, Ni from 7.0 to 15.0% by mass, Cr from 15.0 to 20.0% by mass, Al at 0.005% by mass or less, Ca at 0.002% by mass or less, Mg at 0.001% by mass or less, and 0 from 0.002 to 0.0065% by mass and setting a ratio, during refining, of CaO/SiO.sub.2 in a slag between 1.0 and 2.5. The remainder comprises Fe and unavoidable impurities, and a mass ratio indicated by (Mn+Si)/Al among Mn, Si, and Al is 200 or more. An oxide-based nonmetallic inclusion comprises MnO—SiO.sub.2—Al.sub.2O.sub.3—CaO, where Al.sub.2O.sub.3 is 30% by mass or less, Cr.sub.2O.sub.3 is 5% by mass or less, and MgO is 10% by mass or less, and a sulfide-based nonmetallic inclusion is CaS whose maximum area is 100 μm.sup.2 or less.

A hollow screw and related process of making is provided, wherein the hollow screw is formed from a generally circular corrosion resistant stainless steel disk cut from flat roll stock. The hollow screw includes a head and an elongated and hollow shaft having a wall thickness between about 0.2 to about 0.7 millimeters extending therefrom and defining a shank portion and a threaded portion having a plurality of threads thereon with a rotational drive mechanism configured to facilitate tightening via the threads. The process involves annealing to soften the stamped hollow screw, followed by thread rolling, and then age hardening the hollow screw. As such, the resultant hollow screw is relatively lightweight, about 50% the mass of a solid core screw made from the same material, with a sufficient thread strength to meet most aerospace applications and contributes to important aircraft fuel economy.

A hollow screw and related process of making is provided, wherein the hollow screw is formed from a generally circular corrosion resistant stainless steel disk cut from flat roll stock. The hollow screw includes a head and an elongated and hollow shaft having a wall thickness between about 0.2 to about 0.7 millimeters extending therefrom and defining a shank portion and a threaded portion having a plurality of threads thereon with a rotational drive mechanism configured to facilitate tightening via the threads. The process involves annealing to soften the stamped hollow screw, followed by thread rolling, and then age hardening the hollow screw. As such, the resultant hollow screw is relatively lightweight, about 50% the mass of a solid core screw made from the same material, with a sufficient thread strength to meet most aerospace applications and contributes to important aircraft fuel economy.