FORGED CRANKSHAFT AND METHOD FOR MANUFACTURING THE FORGED CRANKSHAFT

摘要

A forged crankshaft (1) includes a carbon steel containing S, wherein in a portion corresponding to a machined outer circumferential surface of a shaft part such as journals (J), crank pins (P), a front part (Fr), and a flange (Fl), a ratio x/y of an area rate x of sulfide in a position (X) corresponding to a parting surface of a die for finish forging to an area rate y of sulfide in a position (Y) corresponding to a bottom of a die impression of the die for finish forging is equal to or lower than 1.5. The forged crankshaft (1) can avoid an occurrence of machined surface cracks on the journals (J) and the crank pins (P) after the outer circumferential surface is machined.