Carburized bearing steel component and steel bar for carburized bearing steel component

Abstract

A carburized bearing steel part has a predetermined chemical composition, and, in the carburized bearing steel part, the number density of oxide particles having an equivalent circle diameter of 5 μm or more, and containing CaO, Al2O3 and SiO2, such that the content ratio of Al2O3 with respect to the total mass of CaO, Al2O3, and SiO2 is 50% by mass or more, is 3.0/cm2 or less in an arbitrary cross section of the part, the Vickers hardness at a depth of 50 μm from a rolling surface is 750 or more, and the compressive residual stress at the rolling surface is 900 MPa or more. Also provided is a steel bar for a carburized bearing steel part that is suitable for obtaining the foregoing carburized bearing steel part.

1 . A carburized bearing steel part, comprising an interior portion at a depth of at least 2.00 mm from a surface of the carburized bearing steel part, the interior portion having a chemical composition comprising, in terms of % by mass:
 C: 0.15 to 0.25%,   Si: 0.70 to 1.50%,   Mn: 0.40 to 1.50%,   Cr: 0.15 to 1.50%,   Mo: 0.001 to 0.150%,   S: 0.001 to 0.030%,   N: 0.004 to 0.020%,   Ca: 0.0002 to 0.0100%,   Al: 0.001 to 0.010%,   O: 0 to 0.005%,   P: 0 to 0.030%,   Ni: 0 to 3.00%,   Cu: 0 to 1.00%,   Co: 0 to 3.00%,   W: 0 to 1.00%,   V: 0 to 0.30%,   Ti: 0 to 0.300%,   Nb: 0 to 0.300%,   B: 0 to 0.0050%   Pb: 0 to 0.50%,   Bi: 0 to 0.50%,   Mg: 0 to 0.0100%,   Zr: 0 to 0.0500%,   Te: 0 to 0.1000%,   rare earth elements: 0 to 0.0050%,   Sn: 0 to 2.0%,   In: 0 to 0.50%, and   a balance consisting of Fe and impurities,   wherein a number density of oxide particles, which have an equivalent circle diameter of 5 μm or more, and comprise CaO, Al 2 O 3  and SiO 2 , such that a content ratio of Al 2 O 3  with respect to a total mass of CaO, Al 2 O 3 , and SiO 2  is 50% by mass or more, is 3.0/cm 2  or less in an arbitrary cross-section of the carburized bearing steel part,   wherein a Vickers hardness at a depth of 50 μm from a rolling surface is 750 or more, and   wherein a compressive residual stress at the rolling surface is 900 MPa or more.   
     
     
         2 . The carburized bearing steel part according to  claim 1 , wherein the interior portion at a depth of at least 2.00 mm from the surface of the carburized bearing steel part has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:
 Ni: 0.01 to 3.00%,   Cu: 0.01 to 1.00%,   Co: 0.01 to 3.00%,   W: 0.01 to 1.00%,   V: 0.01 to 0.30%,   Ti: 0.001 to 0.300%,   Nb: 0.001 to 0.300%, and   B: 0.0001 to 0.0050%.   
     
     
         3 . The carburized bearing steel part according to  claim 1 , wherein the interior portion at a depth of at least 2.0 mm from the surface of the carburized bearing steel part has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:
 Pb: 0.01 to 0.50%,   Bi: 0.01 to 0.50%,   Mg: 0.0001 to 0.0100%,   Zr: 0.0001 to 0.0500%,   Te: 0.0001 to 0.1000%, and   rare earth elements: 0.0001 to 0.0050%.   
     
     
         4 . The carburized bearing steel part according to  claim 1 , wherein a C content of a carburized layer in a rolling surface is from 0.60 to 1.10% by mass. 
     
     
         5 . A steel bar for a carburized bearing steel part, the steel bar comprising an interior portion at a depth of at least 2.00 mm from a surface of the steel bar, the interior portion having a chemical composition comprising, in terms of % by mass:
 C: 0.15 to 0.25%,   Si: 0.70 to 1.50%,   Mn: 0.40 to 1.50%,   Cr: 0.15 to 1.50%,   Mo: 0.001 to 0.150%,   S: 0.001 to 0.030%,   N: 0.004 to 0.020%,   Ca: 0.0002 to 0.0100%,   Al: 0.001 to 0.010%,   O: 0 to 0.005%,   P: 0 to 0.030%,   Ni: 0 to 3.00%,   Cu: 0 to 1.00%,   Co: 0 to 3.00%,   W: 0 to 1.00%,   V: 0 to 0.30%,   Ti: 0 to 0.300%,   Nb: 0 to 0.300%,   B: 0 to 0.0050%   Pb: 0 to 0.50%,   Bi: 0 to 0.50%,   Mg: 0 to 0.0100%,   Zr: 0 to 0.0500%,   Te: 0 to 0.1000%,   rare earth elements: 0 to 0.0050%,   Sn: 0 to 2.0%,   In: 0 to 0.50%, and   a balance consisting of Fe and impurities,   wherein a number density of oxide particles, which have an equivalent circle diameter of 5 μm or more, and comprise CaO, Al 2 O 3  and SiO 2 , such that a content ratio of Al 2 O 3  with respect to a total mass of CaO, Al 2 O 3 , and SiO 2  is 50% by mass or more, is 3.0/cm 2  or less in an arbitrary cross-section of the steel bar.   
     
     
         6 . The steel bar for a carburized bearing steel part according to  claim 5 , wherein the interior portion at a depth of at least 2.00 mm from the surface of the steel bar has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:
 Ni: 0.01 to 3.00%,   Cu: 0.01 to 1.00%,   Co: 0.01 to 3.00%,   W: 0.01 to 1.00%,   V: 0.01 to 0.30%,   Ti: 0.001 to 0.300%,   Nb: 0.001 to 0.300%, and   B: 0.0001 to 0.0050%.   
     
     
         7 . The steel bar for a carburized bearing steel part according to  claim 5 , wherein the interior portion at a depth of at least 2.00 mm from the surface of the steel bar has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:
 Pb: 0.01 to 0.50%,   Bi: 0.01 to 0.50%,   Mg: 0.0001 to 0.0100%,   Zr: 0.0001 to 0.0500%,   Te: 0.0001 to 0.1000%, and   rare earth elements: 0.0001 to 0.0050%.   
     
     
         8 . The carburized bearing steel part according to  claim 1 , wherein the interior portion at a depth of at least 2.00 mm from the surface of the carburized bearing steel part has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:
 Ni: 0.01 to 3.00%,   Cu: 0.01 to 1.00%,   Co: 0.01 to 3.00%,   W: 0.01 to 1.00%,   V: 0.01 to 0.30%,   Ti: 0.001 to 0.300%,   Nb: 0.001 to 0.300%, and   B: 0.0001 to 0.0050%, and   wherein the interior portion at a depth of at least 2.0 mm from the surface of the carburized bearing steel part has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:   Pb: 0.01 to 0.50%,   Bi: 0.01 to 0.50%,   Mg: 0.0001 to 0.0100%,   Zr: 0.0001 to 0.0500%,   Te: 0.0001 to 0.1000%, and   rare earth elements: 0.0001 to 0.0050%.   
     
     
         9 . The carburized bearing steel part according to  claim 1 , wherein the interior portion at a depth of at least 2.00 mm from the surface of the carburized bearing steel part has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:
 Ni: 0.01 to 3.00%,   Cu: 0.01 to 1.00%,   Co: 0.01 to 3.00%,   W: 0.01 to 1.00%,   V: 0.01 to 0.30%,   Ti: 0.001 to 0.300%,   Nb: 0.001 to 0.300%, and   B: 0.0001 to 0.0050%, and   wherein a C content of a carburized layer in a rolling surface is from 0.60 to 1.10% by mass.   
     
     
         10 . The carburized bearing steel part according to  claim 1 , wherein the interior portion at a depth of at least 2.0 mm from the surface of the carburized bearing steel part has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:
 Pb: 0.01 to 0.50%,   Bi: 0.01 to 0.50%,   Mg: 0.0001 to 0.0100%,   Zr: 0.0001 to 0.0500%,   Te: 0.0001 to 0.1000%, and   rare earth elements: 0.0001 to 0.0050%, and   wherein a C content of a carburized layer in a rolling surface is from 0.60 to 1.10% by mass.   
     
     
         11 . The carburized bearing steel part according to  claim 1 , wherein the interior portion at a depth of at least 2.00 mm from the surface of the carburized bearing steel part has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:
 Ni: 0.01 to 3.00%,   Cu: 0.01 to 1.00%,   Co: 0.01 to 3.00%,   W: 0.01 to 1.00%,   V: 0.01 to 0.30%,   Ti: 0.001 to 0.300%,   Nb: 0.001 to 0.300%, and   B: 0.0001 to 0.0050%, and   wherein the interior portion at a depth of at least 2.0 mm from the surface of the carburized bearing steel part has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:   Pb: 0.01 to 0.50%,   Bi: 0.01 to 0.50%,   Mg: 0.0001 to 0.0100%,   Zr: 0.0001 to 0.0500%,   Te: 0.0001 to 0.1000%, and   rare earth elements: 0.0001 to 0.0050%, and   wherein a C content of a carburized layer in a rolling surface is from 0.60 to 1.10% by mass.   
     
     
         12 . The steel bar for a carburized bearing steel part according to  claim 5 , wherein the interior portion at a depth of at least 2.00 mm from the surface of the steel bar has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:
 Ni: 0.01 to 3.00%,   Cu: 0.01 to 1.00%,   Co: 0.01 to 3.00%,   W: 0.01 to 1.00%,   V: 0.01 to 0.30%,   Ti: 0.001 to 0.300%,   Nb: 0.001 to 0.300%, and   B: 0.0001 to 0.0050%, and   wherein the interior portion at a depth of at least 2.00 mm from the surface of the steel bar has a chemical composition comprising, in terms of % by mass, one or two or more elements selected from:   Pb: 0.01 to 0.50%,   Bi: 0.01 to 0.50%,   Mg: 0.0001 to 0.0100%,   Zr: 0.0001 to 0.0500%,   Te: 0.0001 to 0.1000%, and   rare earth elements: 0.0001 to 0.0050%.