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|1. (WO2017033773) MECHANICAL STRUCTURE STEEL FOR COLD-WORKING AND MANUFACTURING METHOD THEREFOR|
|Applicants:||KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL, LTD.)
|Title:||MECHANICAL STRUCTURE STEEL FOR COLD-WORKING AND MANUFACTURING METHOD THEREFOR|
Provided are: mechanical structure steel for cold-working capable of achieving spheroidization equal to or greater than in the past and capable of greater softening than in the past even when spheroidizing annealing time is shortened more than usual; and a manufacturing method therefor. The present disclosure is mechanical structure steel for cold-working that is characterized in: comprising C, Si, Mn, P, S, Al and N; the steel metal structure containing pro-eutectoid ferrite and pearlite; the total area ratio of the pro-eutectoid ferrite and pearlite with respect to the total structure being at least 90% and the area ratio Af of the pro-eutectoid ferrite satisfying the relationship Af ≥ A in relation to value A represented in formula (1); the mean circle equivalent diameter of bcc-Fe crystal grains being 15-30 µm; and the pearlite lamellar spacing being 0.20 µm or less on average. A = (103−128×[C(%)]) × 0.80 (%) ... (1) In formula (1), [C(%)] represents C content in mass%.