Abstract: This hot-rolled steel sheet has a desired chemical composition, a microstructure contains, in area %, ferrite: 10 to 30%, bainite: 40 to 85%, retained austenite: 5 to 30%, fresh martensite: 5% or less, and pearlite: 5% or less, the ferrite has an average particle size of 5.00 ?m or less, a difference between an average nanoindentation hardness of the ferrite and an average nanoindentation hardness of the bainite is 1,000 MPa or less, and the tensile strength is 980 MPa or more.

Abstract: This hot-rolled steel sheet has a predetermined chemical composition, the number % of crystal grains of bainite that are in contact with both tempered martensite and residual austenite is 80% or more of all crystal grains of the bainite, a C concentration in the residual austenite is 0.80 mass % or more, an average crystal grain size of the residual austenite is 0.70 ?m or less, and a standard deviation of Vickers hardness is 25 HV0.01 or less.

Abstract: 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%, L52/L7, which is a ratio of a length L52 of a grain boundary having a crystal orientation difference of 52° to a length L7 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.

Abstract: This hot-rolled steel sheet has a predetermined chemical composition, in which in a case where the thickness is denoted by t, a metallographic structure at a t/4 position from the surface includes, by area fraction, 77.0% to 97.0% of bainite or tempered martensite, 0% to 5.0% of ferrite, 0% to 5.0% of pearlite, 3.0% or more of residual austenite, and 0% to 10.0% of martensite, in the metallographic structure, the average grain size excluding the residual austenite is 7.0 ?m or less, the average number density of iron-based carbides having a diameter of 20 nm or more is 1.0×106 carbides/mm2 or more, a tensile strength is 980 MPa or more, and an average Ni concentration on the surface is 7.0% or more.

Abstract: This hot rolled steel sheet is a hot rolled steel sheet including a base steel sheet and a scale formed on a surface of the base steel sheet, in which the base steel sheet has a predetermined chemical composition, the scale has a layer structure composed of wustite, magnetite, and hematite in order from the base steel sheet side or a layer structure composed of the wustite and the magnetite in order from the base steel sheet side, and, when a thickness of the scale is represented by s, a thickness of the hematite is represented by h, and a thickness of the magnetite is represented by m, the s, the h, and the m satisfy formula (1) and formula (2). (h+m)/s<0.

Abstract: This hot-rolled steel sheet has a predetermined chemical composition, and in a case where the thickness is denoted by t, the metallographic structure at a t/4 position from the surface contains one or both of tempered martensite and lower bainite at a volume percentage of 90% or more, the tensile strength is 980 MPa or more, and the average Ni concentration on the surface is 7.0% or more.

Abstract: This hot-rolled steel sheet has a predetermined chemical composition, in which in a case where the thickness is denoted by t, a metallographic structure at a t/4 position from the surface includes, by area fraction, 77.0% to 97.0% of bainite or tempered martensite, 0% to 5.0% of ferrite, 0% to 5.0% of pearlite, 3.0% or more of residual austenite, and 0% to 10.0% of martensite, in the metallographic structure, the average grain size excluding the residual austenite is 7.0 ?m or less, the average number density of iron-based carbides having a diameter of 20 nm or more is 1.0×106 carbides/mm2 or more, a tensile strength is 980 MPa or more, and an average Ni concentration on the surface is 7.0% or more.

Abstract: A hot press-formed part according to an aspect of the present invention contains a predetermined chemical composition; in which a microstructure in a thickness ¼ portion includes, by unit vol %, tempered martensite: 20% to 90%, bainite: 5% to 75%, and residual austenite: 5% to 25%, and ferrite is limited to 10% or less; and a pole density of an orientation {211}<011> in the thickness ¼ portion is 3.0 or higher.

Abstract: A hot press-formed part according to an aspect of the present invention contains a predetermined chemical composition; in which a microstructure in a thickness ¼ portion includes, by unit vol %, tempered martensite: 20% to 90%, bainite: 5% to 75%, and residual austenite: 5% to 25%, and ferrite is limited to 10% or less; and a pole density of an orientation {211}<011> in the thickness ¼ portion is 3.0 or higher.

Abstract: A steel sheet according to an aspect of the present invention includes a predetermined chemical composition; in which a metallographic structure in a ¼ t portion contains residual austenite of 4 volume % to 70 volume %; [Mn]?/[Mn]ave>1.5 is satisfied in the ¼ t portion; f?s/f??0.30 and [C]×[Mn]?0.15 are satisfied in the ¼ t portion.

Abstract: A hot-rolled steel sheet according to the present embodiment has a chemical composition containing, in mass %: C: 0.07 to 0.30%, Si: more than 1.0 to 2.8%, Mn: 2.0 to 3.5%, P: 0.030% or less, S: 0.010% or less, Al: 0.01 to less than 1.0%, N: 0.01% or less, O: 0.01% or less, and one or more types selected from the group consisting of Sb, Sn and Te in a total amount of 0.03 to 0.30%, with a balance being Fe and impurities, and satisfying Formula (1). The micro-structure of the hot-rolled steel sheet includes ferrite and pearlite in a total amount of 50 area % or more. The tensile strength of the hot-rolled steel sheet is 900 MPa or less. Si+Mn?3.20??(1) Where, a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1).