High-strength carburized part and a method of the same

Abstract

A high-strength carburized part comprising a core having a chemical composition of C: 0.15 to 0.30% by weight, Si: 0.25 to 1.10% by weight, Mn: 0.3 to 1.20% by weight, Cr; 1.25 to 2.0% by weight and a balance including unavoidable impurities and Fe, a vacuum-carburized surface having a carbon ratio ranging from 1.0 to 1.5%, a region extending from the surface to a depth of 50 μm and having a grain boundary oxide layer with a depth of 1 μm or less, wherein a area ratio of carbides of said surface is from 5 to 15% and at least 90% of carbides have a grain size of 5 μm or less, wherein the core comprises an interior region which cannot be carburized.

What is claimed is:  
     
         1 . A high-strength carburized part comprising: 
 a core having a chemical composition of, 
 C: 0.15 to 0.30% by weight,  
 Si: 0.25 to 1.10% by weight,  
 Mn: 0.3 to 1.20% by weight,  
 Cr: 1.25 to 2.0% by weight and  
 a balance including unavoidable impurities and Fe;  
   a vacuum-carburized surface having a carbon ratio ranging from 1.0 to 1.5%;    a region extending from the surface to a depth of 50 μm and having a grain boundary oxide layer with a depth of 1 μm or less, wherein a area ratio of carbides of said surface is from 5 to 15% and at least 90% of carbides have a grain size of 5 μm or less , and    wherein the core comprises an interior region which cannot be carburized.    
     
     
         2 . The high-strength carburized part as set forth in  claim 1 , wherein the core further comprises B and Ti in an amount of from 0.0005 to 0.0050% by weight and from 0.02 to 0.06% by weight, respectively.  
     
     
         3 . The high-strength carburized part as set forth in  claim 1 , wherein the core further comprises Nb in an amount of from 0.02 to 0.12% by weight.  
     
     
         4 . The high-strength carburized part as set forth in  claim 2 , wherein the core further comprises Nb in an amount of from 0.02 to 0.12% by weight.  
     
     
         5 . The high-strength carburized part as set forth in  claim 1 , wherein the core further comprises at least one of: Pb ranging from 0.01 to 0.20% by weight, Bi ranging from 0.01 to 0.10% by weight, Ca ranging from 0.0005 to 0.0050% by weight and S ranging from 0.005 to 0.100% by weight.  
     
     
         6 . The high-strength carburized part as set forth in  claim 2 , wherein the core further comprises at least one of: Pb ranging from 0.01 to 0.20% by weight, Bi ranging from 0.01 to 0.10% by weight, Ca ranging from 0.0005 to 0.0050% by weight and S ranging from 0.005 to 0.100% by weight.  
     
     
         7 . The high-strength carburized part as set forth in  claim 3 , wherein the core further comprises at least one of: Pb ranging from 0.01 to 0.20% by weight, Bi ranging from 0.01 to 0.10% by weight, Ca ranging from 0.0005 to 0.0050% by weight and S ranging from 0.005 to 0.100% by weight.  
     
     
         8 . The high-strength carburized part as set forth in claim  4 , wherein the core further comprises at least one of: Pb ranging from 0.01 to 0.20% by weight, Bi ranging from 0.01 to 0.10% by weight, Ca ranging from 0.0005 to 0.0050% by weight and S ranging from 0.005 to 0.100% by weight.  
     
     
         9 . The high-strength carburized part as set forth in  claim 1 , wherein the chemical composition of Si is 0.60% by weight or less.  
     
     
         10 . The high-strength carburized part as set forth in  claim 1 , wherein the chemical composition of Mn is 0.60% by weight or less.  
     
     
         11 . The high-strength carburized part as set forth in  claim 1 , wherein the core further includes at least one of: Cu in an amount of 0.30% by weight or less, Ni in an amount of 0.30% by weight or less and Mo in an amount of 0.05% by weight or less.  
     
     
         12 . The high-strength carburized part as set forth in  claim 1 , wherein the core further comprises at least one of the following: 
 B and Ti in an amount of from 0.0005 to 0.0050% by weight and from 0.02 to 0.06% by weight, respectively; and    Nb in an amount of from 0.02 to 0.12% by weight; and    Pb ranging from 0.01 to 0.20% by weight, Bi ranging from 0.01 to 0.10% by weight, Ca ranging from 0.0005 to 0.0050% by weight and S ranging from 0.005 to 0.100% by weight, wherein at least one of the following is true: 
 the chemical composition of Si is 0.60% by weight or less,  
   the chemical composition of Mn is 0.60% by weight or less or    Cu in an amount of 0.30% by weight or less, Ni in an amount of 0.30% by weight or less and Mo in an amount of 0.05% by weight or less.    
     
     
         13 . A method of manufacturing a carburized part, comprising steps of; 
 working an alloy that includes 0.15 to 0.30% C by weight, 0.25 to 1.10% Si by weight, 0.3 to 1.20% Mn by weight, 1.25 to 2.0% Cr by weight and a remaining balance including unavoidable impurities and Fe into a shape of the carburized part;    vacuum-carburizing said alloy such that a C content on a surface of said alloy is from 1.0 to 1.5%.    
     
     
         14 . The method of  claim 13 , wherein in a region extending from a surface of the carburized part to a depth of 50 μm, 
 an area ratio of carbides is ranging 5 to 15%, and at least 90% of carbides have a grain size of 5 μm or less and a grain boundary oxide layer with a depth of 1 μm or less.  
 
     
     
         15 . The method of  claim 13 , wherein said alloy further comprises B and Ti in an amount of from 0.0005 to 0.0050% by weight and from 0.02 to 0.06% by weight, respectively.  
     
     
         16 . The method of  claim 13 , wherein said alloy further comprises Nb in an amount of from 0.02 to 0.12% by weight.  
     
     
         17 . The method of  claim 15 , wherein said alloy further comprises Nb in an amount of from 0.02 to 0.12% by weight.  
     
     
         18 . The method of  claim 13 , wherein said alloy further comprises at least one of: Pb ranging from 0.01 to 0.20% by weight, Bi ranging from 0.01 to 0.10% by weight, Ca ranging from 0.0005 to 0.0050% by weight and S ranging from 0.005 to 0.100% by weight.  
     
     
         19 . The method of  claim 15 , wherein said alloy further comprising at least one of: 
 Pb ranging from 0.01 to 0.20% by weight;    Bi ranging from 0.01 to 0.10% by weight;    Ca ranging from 0.0005 to 0.0050% by weight or    S ranging from 0.005 to 0.100% by weight.    
     
     
         20 . The method of  claim 16 , wherein said alloy further comprising at least one of: 
 Pb ranging from 0.01 to 0.20% by weight;    Bi ranging from 0.01 to 0.10% by weight;    Ca ranging from 0.0005 to 0.0050% by weight or    S ranging from 0.005 to 0.100% by weight.    
     
     
         21 . The method of  claim 17 , wherein said alloy further comprising at least one of: 
 Pb ranging from 0.01 to 0.20% by weight;    Si ranging from 0.01 to 0.10% by weight;    Ca ranging from 0.0005 to 0.0050% by weight or.    S ranging from 0.005 to 0.100% by weight.    
     
     
         22 . The method of  claim 13 , wherein said alloy meets at least one of the following conditions: the chemical composition of Si is 0.60% by weight or less; and the chemical composition of Mn is 0.60% by weight or less; Cu is in an amount of 0.30% by weight or less, Ni is in an amount of 0.30% by weight or less and Mo is in an amount of 0.05% by weight or less.  
     
     
         23 . A gear for use in a power transmission, said gear being made of a material comprising: 
 a core having a chemical composition of 
 C: 0.15 to 0.30% by weight,  
 Si: 0.25 to 1.10% by weight,  
 Mn: 0.3 to 1.20% by weight,  
 Cr: 1.25 to 2.0% by weight and  
 a balance including unavoidable impurities and Fe;  
   a vacuum-carburized surface having a carbon ratio ranging from 1.0 to 1.5%;    a region extending from the surface to a depth of 50 μm and having a grain boundary oxide layer with a depth of 1 μm or less, wherein a area ratio of carbides of said surface is from 5 to 15% and at least 90% of carbides have a grain size of 5 μm or less, and    wherein the core comprises an interior region which cannot be carburized.