| abstract |
PROBLEM TO BE SOLVED: To provide a medium-high carbon steel excellent in cold forgeability and capable of securing strength even in a non-heat-treated state by controlling the structure of steel, not by adding a special alloy component. . SOLUTION: C: contains 0.40 to 1.0% by mass; eq (= C + Si / 24 + Mn / 6 + (Cr + Mo) / 5 + Ni / 40 + (Ti + Nb + V) / 5 + 5 × B) is 0.6 to 1.2% and the main structure is pearlite and / or pseudo pearlite, and ferrite, bainite, martensite, The volume fraction of the second phase comprising at least one kind of proeutectoid cementite is 7% or less, the size of proeutectoid ferrite precipitated on the prior austenite grains is 4 μm or less, the nodule diameter of the pearlite is 4.0 to 20 μm, and the lamella of the pearlite 120n spacing m and high carbon steel with excellent cold forgeability, characterized by being not more than m. |