STEEL FOR MECHANICAL STRUCTURE FOR COLD WORKING, AND METHOD FOR MANUFACTURING SAME

摘要

Provided are a steel for a mechanical structure for cold working, and a method for manufacturing the same, whereby softening and variations in hardness can be reduced even when a conventional spheroidizing annealing process is performed. A steel having a predetermined chemical composition, the total area ratio of pearlite and pro-eutectoid ferrite being at least 90 area% with respect to the total metallographic structure of the steel, the area ratio (A) of pro-eutectoid ferrite satisfying the relationship A > Ae with an Ae value expressed by a predetermined relational expression, the average equivalent circular diameter of bcc-Fe crystal grains being 15-35 µm, and the average of the maximum grain diameter and the second largest grain diameter of the bcc-Fe crystal grains being 50 µm or less in terms of equivalent circular diameter.