The soft magnetic low carbon steel and its manufacturing method, and the manufacturing method null mass of the soft magnetic low carbon steel part which uses the said steel are superior in machinability and

摘要

PROBLEM TO BE SOLVED: To produce soft magnetic steel which can be worked in a high yield even in the case of steel parts having a complicated shape by imparting excellent cold heading properties and machinability thereto, and to provide a method for producing soft magnetic steel parts which have excellent magnetic properties by using the soft magnetic steel. SOLUTION: The soft magnetic low carbon steel having excellent machinability and magnetic properties consists of steel having a composition containing, by mass, =0.05% C, =0.1% Si, 0.10 to 0.50% Mn, =0.030% P, 0.010 to 0.15% S, =0.01% Al, =0.005% N and =0.02% O, and the balance substantially Fe, and in which Mn/S (mass ratio) satisfies =3.0. The steel has a structure in which ferrite crystal grain sizes are =100 μm, MnS precipitates having grain sizes of =0.2 μm are present by 0.02 to 0.5 pieces/μm2 in the ferrite crystal grains, and further, the average grain sizes of the MnS precipitates are 0.05 to 4 μm.