US Patent 7967921 Carburized component and manufacturing method thereof

A carburized component with a base metal containing 0.10% to 0.40% C, 0.05% to 0.8% Si, 0.35% to 1.2% Mn, 2.0% to 5.0% Cr, remnant including Fe and inevitable impurities, a carburized layer formed on a surface layer portion, a grain boundary oxidized layer depth of 1 μm or less on a surface thereof and an average C concentration of 1.5% to 4.0% at 25 μm deep from the surface, and adjusted so as to satisfy 1.76 SC−1.06<WCr<1.76 SC+0.94, wherein said carburized layer also has a carbide area ratio of 15% to 60% at 25 μm deep from the surface, a fine carbide area ratio, a dimension of 0.5 μm to 10 μm, and constitutes 80% or more of the total and 70% by volume or more of said fine carbide is M3C type.