Case hardening steel and carburized part using same

Abstract

A case hardening steel high in impact strength, consists essentially of carbon in an amount of from 0.1 to 0.3% by weight, silicon in an amount of from more than 0.3 to 1.0% by weight, manganese in an amount of from 0.3 to 1.7% by weight, phosphorus in an amount of not more than 0.03% by weight, sulfur in an amount of not more than 0.03% by weight, molybdenum in an amount of not more than 1.0% by weight, aluminum in an amount of not more than 0.04% by weight, nitrogen in an amount of not more than 0.03% by weight, and balance being iron and inevitable impurities. The case hardening steel meets an equation of [C %]+5([P %]+[S %])≦([Mn %]+[Mo %]+1.8)/8.

What is claimed is:  
     
         1 . A case hardening steel consisting essentially of carbon in an amount of from 0.1 to 0.3% by weight, silicon in an amount of from more than 0.3 to 1.0% by weight, manganese in an amount of from 0.3 to 1.7% by weight, phosphorus in an amount of not more than 0.03% by weight, sulfur in an amount of not more than 0.03% by weight, molybdenum in an amount of not more than 1.0% by weight, aluminum in an amount of not more than 0.04% by weight, nitrogen in an amount of not more than 0.03% by weight, and balance being iron and inevitable impurities, 
 wherein said case hardening steel meets the following equation:    [C %]+5([P %]+[S %])≦([Mn %]+[Mo %]+1.8)/8  Eq. (1).    
     
     
         2 . A case hardening steel as claimed in  claim 1 , further consisting essentially of boron in an amount of from 0.001 to 0.005% by weight, and at lease one of niobium in an amount of from 0.01 to 0.10% by weight and titanium in an amount of from 0.01 to 0.10% by weight.  
     
     
         3 . A case hardening steel as claimed in  claim 1 , wherein said case hardening steel has an elemental composition to meet the following equation:  
       [C %]+5.2([P %]+[S %])≦([Mn %]+[Mo %]+3.8)/22+96[B %]+[austenite grain size number according to JIS G 0551]/111  Eq. (3)  
     
     
         4 . A case hardening steel as claimed in  claim 1 , further consisting essentially of at least one selected from the group consisting of lead in an amount of not more than 0.3% by weight, bismuth in an amount of not more than 0.15% by weight and calcium in an amount of not more than 0.1% by weight.  
     
     
         5 . A case hardening steel consisting essentially of carbon in an amount of from 0.1 to 0.3% by weight, silicon in an amount of from more than 0.3 to 1.0% by weight, manganese in an amount of from 0.3 to 1.7% by weight, phosphorus in an amount of not more than 0.03% by weight, sulfur in an amount of not more than 0.03% by weight, aluminum in an amount of not more than 0.04% by weight, nitrogen in an amount of not more than 0.03% by weight, chromium in an amount of from more than 0 to 1.6% by weight, and balance being iron (Fe) and inevitable impurities, 
 wherein the case hardening steel meets the following equation:    [C %]+5([P %]+[S %])≦([Mn %]+1.8)/8  Eq. (2).    
     
     
         6 . A case hardening steel consisting essentially of carbon in an amount of from 0.1 to 0.3% by weight, silicon in an amount of not more than 0.3% by weight, manganese in an amount of from 0.3 to 1.7% by weight, phosphorus in an amount of not more than 0.03% by weight, sulfur in an amount of not more than 0.03% by weight, molybdenum in an amount of not more than 1.0% by weight, aluminum in an amount of not more than 0.04% by weight, nitrogen in an amount of not more than 0.03% by weight, and balance being iron and inevitable impurities, 
 wherein said case hardening steel meets the following equation:    [C %]+5([P %]+[S %])≦([Mn %]+[Mo %]+1.8)/8  Eq. (1).    
     
     
         7 . A case hardening steel as claimed in  claim 6 , further consisting essentially of chromium in an amount of from more than 0 to 1.6% by weight.  
     
     
         8 . A case hardening steel as claimed in  claim 6 , wherein said case hardening steel has an elemental composition to meet the following equation:  
       80[Si %]+24[Mn %]+33[Mo %]+13≦40  Eq. (4)  
     
     
         9 . A case hardening steel consisting essentially of carbon in an amount of from 0.1 to 0.3% by weight, silicon in an amount of not more than 0.3% by weight, manganese in an amount of from 0.3 to 1.7% by weight, phosphorus in an amount of not more than 0.03% by weight, sulfur in an amount of not more than 0.03% by weight, aluminum in an amount of not more than 0.04% by weight, nitrogen in an amount of not more than 0.03% by weight, and balance being iron and inevitable impurities, 
 wherein the case hardening steel meets the following equation:    [C %]+5([P %]+[S %])≦([Mn %]+1.8)/8  Eq. (2).    
     
     
         10 . A carburized part formed of a case hardening steel which consists essentially of carbon in an amount of from 0.1 to 0.3% by weight, silicon in an amount of from more than 0.3 to 1.0% by weight, manganese in an amount of from 0.3 to 1.7% by weight, phosphorus in an amount of not more than 0.03% by weight, sulfur in an amount of not more than 0.03% by weight, molybdenum in an amount of not more than 1.0% by weight, aluminum in an amount of not more than 0.04% by weight, nitrogen in an amount of not more than 0.03% by weight, and balance being iron and inevitable impurities, wherein said case hardening steel meets the following equation:  
       [C %]+5([P %]+[S %])≦([Mn %]+[Mo %]+1.8)/8  Eq. (1),  wherein said carburized part has a hardened layer of carburized case including fine austenite whose austenite grain size number according to JIS G 0551 is not smaller than 7.