Cold drawn free-machining steel bar including bismuth

摘要

A cold drawn free-machining steel bar having a composition consisting essentially of, in weight percent, C up to 0.15; Mn 0.7 to 1.3; P 0.03 to 0.09; S 0.30 to 0.50; Bi 0.05 to 0.25; the sum of Ni, Cr, Mo and Cu up to 0.15 and the balance iron. The ratio % Mn / %S is from 1.7 to 3.0 and the %Mn-1.62x%S is from 0.05 to 0.40. The ratio %Bi /(%Ni+%Cu) is at least 2.0. The yield strength of the steel bar is further determined by the draft in cold drawing the bar from the hot rolled state and the cross section of the bar prior to draft.