Acero de forja, forjado y cigüeñal

摘要

A forging steel is excellent in fatigue strength and hydrogen cracking resistance. The forging steel contains: 0.15 to 0.75% by mass C, 0.1 to 0.6% by mass Si, 0.3 to 1.4% by mass Mn, 0.1 to 2% by mass Ni, 0.5 to 2.5% by mass Cr, 0.1 to 0.5% by mass Mo, 0.01 to 0.2% by mass V, 0.015 to 0.04% by mass Al, 0.002% by mass or below and above 0% by mass S, 0.003% by mass or below and above 0% by mass Ti, and the balance of Fe and inevitable impurities. The respective number densities of S-containing inclusion particles having a S content of 20% by mass or above, and Ti-containing inclusion particles having a Ti content of 50% by mass or above among inclusion particles above 5 µm in length present in an observation area in a cross section of the forging steel are 100 particles/cm 2 or below, and 30 particles/cm 2 or below, respectively.