A steel near-net-shape material having high fatigue strength and high tensile strength is provided. The steel near-net-shape material has a chemical composition containing, in mass %, C: 0.03 to 0.25%, Si: 0.02 to 0.50%, Mn: more than 0.70 to 2.50%, P: 0.035% or less, S: 0.050% or less, Al: 0.005 to 0.050%, V: more than 0.10 to 0.40%, and N: 0.003 to 0.030%. The steel near-net-shape material is composed of polygonal ferrite having an area fraction of 20 to 90% and a hard phase having an area fraction of 10 to 80%, and satisfies Formula (1). A diffusible hydrogen content of the steel near-net-shape material when charged with hydrogen by a cathodic hydrogen charging method is 0.10 ppm or more.

[V in precipitates]/[V]≥0.30  (1)

A steel near-net-shape material having high fatigue strength and high tensile strength is provided. The steel near-net-shape material has a chemical composition containing, in mass %, C: 0.03 to 0.25%, Si: 0.02 to 0.50%, Mn: more than 0.70 to 2.50%, P: 0.035% or less, S: 0.050% or less, Al: 0.005 to 0.050%, V: more than 0.10 to 0.40%, and N: 0.003 to 0.030%. The steel near-net-shape material is composed of polygonal ferrite having an area fraction of 20 to 90% and a hard phase having an area fraction of 10 to 80%, and satisfies Formula (1). A diffusible hydrogen content of the steel near-net-shape material when charged with hydrogen by a cathodic hydrogen charging method is 0.10 ppm or more.

[V in precipitates]/[V]≥0.30  (1)

A dual-phase stainless steel or dual-phase stainless steel seamless pipe has a certain composition, the dual-phase stainless steel or dual-phase stainless steel seamless pipe having a microstructure containing 20 to 70% austenitic phase and 30 to 80% ferritic phase by volume, the dual-phase stainless steel or dual-phase stainless steel seamless pipe having a yield strength, YS, of 448 MPa or more, and containing oxide inclusions of which oxide inclusions having an average particle diameter of 1 μm or more have a number density of 15/mm.sup.2 or less, and at most 50 mass % of the oxide inclusions having an average particle diameter of 1 μm or more are oxide inclusions containing aluminum.

An alloy material is provided which contains elements including, in mass %, C: 0.010 to 0.10%, Si: more than 0.10% to 0.50% or less, Mn:0.05 to 0.50%, Ni:34.5 to 37.0%, and Nb:0.001 to 1.0%, and which satisfies [T.sub.0≤T.sub.1-2], [C—Nb/7.7-Ta/15≤0.045], [Nb-7.7C≤0.30], and [Ta-15C≤0.30]. Where, each symbol of an element in the above formulas represents a content (mass %) of the corresponding element, T.sub.0 represents a Curie temperature (° C.) of the alloy material, and T.sub.1 represents a Curie temperature (° C.) of the alloy material after the alloy material is held at 900° C. for one minute and thereafter is cooled under conditions such that an average cooling rate in a temperature range from 600 to 300° C. is 0.2° C./s.

This steel sheet has a predetermined chemical composition, Ex. C that is obtained by Ex. C = (%C) - 12 ( (%Ti*)/48 + (%V)/51 + (%Nb)/93 + (%Mo)/96 + (%W)/184} is 0.020% or less, a microstructure at a ¼ depth position of a sheet thickness from a surface contains 60% or more of ferrite, 0% to 5% of MA and a total of 0% to 5% of pearlite and cementite with a remainder of bainite in terms of area fractions, in the microstructure, the average crystal grain diameter is 10.0 .Math.m or less, the average aspect ratio of crystal grains is 0.30 or more, the standard deviation of a Mn concentration is 0.60 mass% or less, a Ti-based carbide having a Baker-Nutting orientation relationship in the ferrite is precipitated in a semi-coherent state, and a tensile strength is 980 MPa or more.

This hot-rolled steel sheet has a predetermined chemical composition, in a microstructure, by area %, ferrite is less than 15.0%, residual austenite is less than 3.0%, L.sub.52/L.sub.7, which is a ratio of a length L.sub.52 of a grain boundary having a crystal orientation difference of 52° to a length L.sub.7 of a grain boundary having a crystal orientation difference of 7° about a <110> direction is 0.10 to 0.18, a standard deviation of a Mn concentration is 0.60 mass % or, less, and a tensile strength is 980 MPa or more.

After low-temperature finish rolling has been performed on a steel material having a certain chemical composition, cooling is performed at an average cooling rate of 10° C./s or higher to a temperature of 500° C., rapid cooling is further performed in a temperature range from a Ms temperature to a temperature of (Ms temperature - 200° C.), coiling is thereafter performed in a low temperature range of 250° C. or lower, and the coiled steel sheet is uncoiled and further subjected to rolling with a certain amount or more of rolling load per unit width and the like. Consequently, it is possible to obtain a high-strength hot-rolled steel sheet having a microstructure including, in terms of area fraction, 95% or more of a martensite phase at a position located at ¼ of the thickness of the steel sheet, in which an average aspect ratio of prior austenite grains is 3.0 or more.

This hot-rolled steel sheet has a predetermined chemical composition and predetermined metallographic structure, a ratio between a maximum depth of a region where, on one surface, a rotation angle between a normal line of the one surface and a (011) pole near the normal line of the one surface is 5° or less and a maximum depth of a region where, on the other surface, a rotation angle between a normal line of the other surface and a (011) pole near the normal line of the other surface is 5° or less is 1.00 to 1.20, and a tensile strength is 1150 MPa or more.

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.

A high-strength steel having a yield strength at a level of 800 MPa and a method of manufacturing the same, with the components and amounts thereof by weight percentage being: C:0.06-0.14%, Si: 0.1-0.30%, Mn: 0.8-1.60%, Cr: 0.2-0.70%, Mo: 0.1-0.40%, Ni: 0-0.30%, Nb: 0.01-0.030%, Ti: 0.01-0.030%, V: 0.01-0.05%, B: 0.0005-0.0030%, Al: 0.02-0.06%, Ca: 0.001-0.004%, N: 0.002-0.005%, P≦0.02%, S≦0.01%, O≦0.008%, the balance of Fe and unavoidable impurities; wherein the above elements meet the following relationships: 0.40%<Ceq<0.50%, Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15; 0.7%≦Mo+0.8Ni+0.4Cr+6V≦1.1%; 3.7≦Ti/N≦7.0; 1.0≦Ca/S≦3.0.