Case hardened steel excellent in the prevention of coarsening of particles during carburizing thereof, method of manufacturing the same, and raw shaped material for carburized parts

A method of producing a case hardening steel having good grain coarsening prevention properties during carburization, characterized in that said method comprises preparing a steel comprising, by mass,

• 0.1 to 0.4% C,
• 0.02 to 1.3% Si,
• 0.3 to 1.8% Mn,
• 0.001 to 0.15% S,
• 0.030 to 0.04% Al,
• 0.022 to 0.04% Nb,
• 0.006 to 0.0186% N,
• one, two or more selected from
• 0.4 to 1.8% Cr,
• 0.02 to 1.0% Mo,
• 0.1 to 3.5% Ni,
• 0.03 to 0.5% V,
• and in which
• P is limited to not more than 0.025%,
• Ti is limited to not more than 0.010%, and
• O is limited to not more than 0.0025%,
• with the balance being iron and unavoidable impurities, heating the steel to a temperature of not less than 1150° C., maintaining the steel at that temperature for not less than 10 minutes, and hot rolling the steel to form wire or bar steel, the steel, following completion of hot rolling, having a Nb(CN) precipitation amount of not less than 0.005% and an AlN precipitation amount that is limited to not more than 0.005%.

A hot forged steel blank material for catburized parts in its final hot rolled condition, having good grain coarsening prevention properties during carburization, characterized in that said blank material comprises, by mass,

• 0.1 to 0.40% C,
• 0.02 to 1.3% Si,
• 0.3 to 1.8% Mn,
• 0.001 to 0.15% S,
• 0.030 to 0.04% Al,
• 0.022 to 0.04% Nb,
• 0.006 to 0.0186% N,
• one, two or more selected from
• 0.4 to 1.8% Cr,
• 0.02 to 1.0% Mo,
• 0.1 to 3.5% Ni,
• 0.03 to 0.5% V,
• and in which P is limited to not more than 0.025%,
• Ti is limited to not more than 0.010%, and
• O is limited to not more than 0.0025%,
• with the balance being iron and unavoidable impurities, the steel blank material having a Nb(CN) precipitation amount of not less than 0.005% and an AlN precipitation amount that is limited to not more than 0.005%.