The seamless steel pipe according to the present disclosure includes a chemical composition consisting of, in mass %, C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, Al: 0.001 to 0.100%, N: 0.0500% or less, O: 0.050% or less, Ni: 3.00 to 6.50%, Cr: more than 10.00 to 13.40%, Mo: 0.50 to 4.00%, V: 0.01 to 1.00%, Ti: 0.010 to 0.300%, and Co: 0.010 to 0.300%, with the balance being Fe and impurities, and satisfying Formula (1), and a microstructure containing, in volume ratio, 80.0% or more of martensite, wherein a depassivation pH of an inner surface is 3.50 or less.

Cr+2.0Mo+0.5Ni+0.5Co≥16.0  (1)

Provided is a hot rolled steel sheet comprising a predetermined chemical composition, and a metallic structure comprising, by area ratio, pearlite: 90 to 100%, pseudo pearlite: 0 to 10%, and pro-eutectoid ferrite: 0 to 1%, wherein the pearlite has an average lamellar spacing of 0.20 μm or less, and the pearlite has an average pearlite block size of 20.0 μm or less. Provided is a method for producing a hot rolled steel sheet comprising heating a slab to 1100° C. or more, hot rolling where an exit side temperature of finishing rolling is 820 to 920° C., primary cooling the steel sheet down to an Ae1 point by an average cooling rate of 40 to 80° C./s, then secondary cooling the steel sheet from the Ae1 point down to a coiling temperature by an average cooling rate of less than 20° C./s, and coiling the steel sheet at a coiling temperature of 540 to 700° C.

Provided is a method for producing a rail, with which the sweep in the height direction of a rail before straightening can be suppressed when producing standard rails specified in JIS E 1101. The method includes subjecting a bloom having a chemical composition containing, in mass %, C: 0.60% or more and 0.85% or less, Si: 0.10% or more and 1.00% or less, and Mn: 0.10% or more and 1.30% or less, with the balance being Fe and inevitable impurities, to hot rolling to obtain a rail, subjecting the rail to accelerated cooling under conditions where a cooling start temperature T1 of rail head is 750° C. or higher and 850° C. or lower, a cooling stop temperature T2 of rail head is higher than 700 ° C., and T1−T2 is 20 ° C. or more, and then allowing the rail to be naturally cooled.

Provided is a method for producing a rail, with which the sweep in the height direction of a rail before straightening can be suppressed when producing standard rails specified in JIS E 1101. The method includes subjecting a bloom having a chemical composition containing, in mass %, C: 0.60% or more and 0.85% or less, Si: 0.10% or more and 1.00% or less, and Mn: 0.10% or more and 1.30% or less, with the balance being Fe and inevitable impurities, to hot rolling to obtain a rail, subjecting the rail to accelerated cooling under conditions where a cooling start temperature T1 of rail head is 750° C. or higher and 850° C. or lower, a cooling stop temperature T2 of rail head is higher than 700 ° C., and T1−T2 is 20 ° C. or more, and then allowing the rail to be naturally cooled.

A steel sheet having a tensile strength of 1100 MPa or more and excellent in crash resistance, having a micro-structure containing tempered martensite: 95 vol. % or more, wherein in a cross section parallel to a sheet-thickness direction of the steel sheet, when a sheet thickness is denoted by t, in a 300-μm-square region centered about a t/2 point, a standard deviation of Vickers hardnesses that are measured under a load of 9.8 N at 30 points is 30 or less, wherein when a 100-μm-square region centered about a t/2 point is divided into 10×10, 100 subregions, and at a center of each of the subregions, a nano hardness is measured under a maximum load of 1 mN, out of the subregions, the number of subregions each of which makes a difference in nano hardness of 3 GPa or more from any one of eight surrounding subregions is 10 or less.

The present invention relates to a method for manufacturing a component of austenitic TWIP or TRIP/TWIP steel. A flat product (1) is deformed by achieving at least one indentation (16) on at least one surface of the flat product (1) in order to have in the deformed product (5) areas of a high strength steel embedded in a matrix of a ductile material. The invention also relates to the use of the component where areas of a high strength steel embedded in a matrix of a ductile material are required in the same component.

The present invention relates to a method for manufacturing a component of austenitic TWIP or TRIP/TWIP steel. A flat product (1) is deformed by achieving at least one indentation (16) on at least one surface of the flat product (1) in order to have in the deformed product (5) areas of a high strength steel embedded in a matrix of a ductile material. The invention also relates to the use of the component where areas of a high strength steel embedded in a matrix of a ductile material are required in the same component.

The present invention provides a heat treatment method of turnout track comprising performing an accelerated cooling on the turnout track to be treated having a railhead tread with a temperature of 650-900° C. so as to obtain the turnout track with full pearlite metallographic structure, wherein the accelerated cooling velocity performed on the working side of railhead of the turnout track is higher than that performed on the non-working side of the railhead of the turnout track. The present invention provides a turnout track obtained with a heat treatment process as depicted therein. The turnout track in present invention has good straightness; both the hardness and tensile strength of the working side of railhead are higher than that of the non-working side of railhead.

The present invention provides a heat treatment method of turnout track comprising performing an accelerated cooling on the turnout track to be treated having a railhead tread with a temperature of 650-900° C. so as to obtain the turnout track with full pearlite metallographic structure, wherein the accelerated cooling velocity performed on the working side of railhead of the turnout track is higher than that performed on the non-working side of the railhead of the turnout track. The present invention provides a turnout track obtained with a heat treatment process as depicted therein. The turnout track in present invention has good straightness; both the hardness and tensile strength of the working side of railhead are higher than that of the non-working side of railhead.

The present invention relates to a structural steel sheet suitable for ships or steel structures and, more particularly, to a high-strength steel sheet having excellent ductility and low-temperature toughness and a method for manufacturing same.