Abstract: A steel for mechanical structures has a mixed texture which is composed of a hard phase comprising at least one texture selected from pearlite, bainite and martensite and a ferrite phase, wherein the average equivalent circle diameter of ferrite grains is 7 ?m or less and the (ferrite grain)-(ferrite grain) connection rate (X) which is expressed by formula (1) is 0.15 or less.

Abstract: The present invention provides a steel for a fracture splitting type connecting rod, in which: the steel contains C: 0.25-0.5% (in mass %, the same is applied hereunder), Si: 0.01-2.0%, Mn: 0.50-2.0%, P: 0.015-0.080%, S: 0.01-0.2%, V: 0.02-0.20%, Cr: 0.05-1.0%, Ti: 0.01-0.10%, and N: 0.01% or less; an f-value represented by the expression shown below is in the range of 0.003 to 0.04; and the average aspect ratio of sulfide system inclusions is 15 or less, f=[Ti]?[N]×48/14 (in the expression, [Ti] and [N] represent the contents (mass %) of Ti and N in a steel, respectively).