Production method for a crankshaft

摘要

A crankshaft is formed by hot forging and subsequent cooling and has a metallic structure including a bainite at not less than 70 % by area ratio. Moreover, Kf is greater than 3.80, Hf is less than 19.5, and Hg is greater than 18.8 in the following first to third formulas: Kf = 5 C % - 0.168 Si % + 1.8 Mn % + 0.4 Cr % + 2.5 Mo % + 1.5 V % - 1 Hf = 24.96 × C % - 1 / 18 �¢ Si % + 1 / 12 �¢ Mn % + 1 / 6 �¢ Cr % + 0.01 + 1 / 7 �¢ Mo % + 4 / 5 �¢ V % Hg = 32.16 × C % + 3 / 13 �¢ Si % + 1 / 22 �¢ Mn % + 1 / 18 �¢ Cr % + 3 / 10 �¢ Mo % + 5 / 7 �¢ V % .