Abstract: As a burring processed member able to suppress the formation of fatigue cracks in a burring part, one having a structure satisfying the following relations (1) to (3) is disclosed: 3?Ra?100 . . . (1), 3.0<h . . . (2), 24+r?[TS/(40+0.28×Ra)]<h . . . (3), where, “Ra” is an arithmetic mean roughness (?m) of the burring end face, “h” is a height (mm) from the first surface to the burring end face, “r” is a radius of curvature (mm) of the curved wall part, and “TS” is the tensile strength (MPa) of the sheet-shaped part.

Abstract: Provided is a hot rolled steel sheet having a predetermined chemical composition and a microstructure comprising, by area ratio, pearlite: 90 to 100% and pro-eutectoid ferrite: 0 to 10%, wherein the pearlite has an average lamellar spacing of 0.08 to 0.30 ?m, and the percentage of cementite in the pearlite having a major axis length of more than 0.3 ?m and an aspect ratio of less than 3.0 is less than 15%.

Abstract: Hot-rolled steel sheet having a chemical composition including, in mass %, C: 0.02 to 0.20%, Si: 0.01 to 1.50%, Mn: 0.10 to 3.00%, P: 0.10% or less, S: 0.010% or less, Al: 0.005 to 0.100%, Ti: 0.02 to 0.20%, N: 0.001 to 0.010%, Cu: 0 to 0.50%, Ni: 0 to 0.50%, Cr: 0 to 1.00%, Mo: 0 to 0.40%, Nb: 0 to 0.060%, V: 0 to 1.00%, B: 0 to 0.0100%, Ca: 0 to 0.0050%, O: 0.0100% or less, and the balance: Fe and impurities; in which: a steel micro-structure includes, in area %, ferrite: 60 to 80%, and a total of ferrite and bainite: 90% or more; an average of the crystal grain size of ferrite and bainite is 7.0 ?m or less, a standard deviation of the crystal grain size is 2.0 or less; and a standard deviation of a diameter of Ti carbo-nitrides is 10 nm or less.

Abstract: 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 ?m or less, and the pearlite has an average pearlite block size of 20.0 ?m 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.