Sintered steel alloy for wear resistance at high temperatures and fabrication method of valve-seat using the same

Abstract

Disclosed is a sintered steel alloy for wear resistance at high temperatures, which is applied to a valve seat of an internal combustion engine including an automobile. The sintered steel alloy includes: 10.0 to 14.0 parts by weight of cobalt powder; 5.0 to 9.0 parts by weight of molybdenum powder; 1.5 to 4.1 parts by weight of chromium powder; 0.7 to 1.3 parts by weight of carbon powder; 1.0 to 1.8 parts by weight of manganese powder; 0.4 to 1.2 parts by weight of silicon powder; 0.2 to 0.8 parts by weight of sulfur powder; and 0.1 to 0.7 parts by weight of vanadium powder, based on 100 parts by weight of iron powder, and thus a service life of the valve seat is extended.

What is claimed is: 
     
         1 . A sintered steel alloy for wear resistance at high temperatures, comprising: 10.0 to 14.0 parts by weight of cobalt powder; 5.0 to 9.0 parts by weight of molybdenum powder; 1.5 to 4.1 parts by weight of chromium powder; 0.7 to 1.3 parts by weight of carbon powder; 1.0 to 1.8 parts by weight of manganese powder; 0.4 to 1.2 parts by weight of silicon powder; 0.2 to 0.8 parts by weight of sulfur powder; and 0.1 to 0.7 parts by weight of vanadium powder, based on 100 parts by weight of iron powder. 
     
     
         2 . The sintered steel alloy of  claim 1 , wherein 10.0 to 20.0 parts by weight of copper powder based on 100 parts by weight of the iron powder is further added as an infiltrate into a composition of the sintered steel alloy. 
     
     
         3 . A method of manufacturing a valve seat using a sintered steel alloy for wear resistance at high temperatures, the method comprising:
 a mixing operation of evenly mixing the sintered steel alloy described in  claim 1 ;   a pressurizing operation of pressurizing a resulting mixture formed in the mixing operation at a set pressure;   a sintering operation of sintering a resulting molded body formed in the pressurizing operation along with the infiltrate described in  claim 2  to infiltrate copper into the molded body;   a low temperature treatment operation of treating a resulting sintered body formed in the sintering operation at low temperatures to change residual austenite into martensite; and   a heat treatment operation of tempering a resulting low temperature treated body formed in the low temperature treatment operation to remove a residual stress therefrom.   
     
     
         4 . The method of  claim 3 , wherein the pressurizing operation includes pressurizing the composition of the valve seat at a surface pressure of 6 to 10 tons/cm 3 . 
     
     
         5 . The method of  claim 3 , wherein a final product after the heat treatment operation has a hardness (HRA) of 71 to 81. 
     
     
         6 . The method of  claim 3 , wherein a final product after the heat treatment operation has a density (g/cm 3 ) of 7.4 to 8.1. 
     
     
         7 . The method of  claim 3 , wherein the molded body is sintered and copper-infiltrated in a temperature range of 1120±20° C. for 30±10 minutes in the sintering operation. 
     
     
         8 . The method of  claim 3 , wherein the low temperature treatment operation includes cooling a sintered body formed in the sintering operation in a temperature range of −120±10° C. for 20±5 minutes. 
     
     
         9 . The method of  claim 3 , wherein the heat treatment operation includes heating a low temperature heated body formed in the low temperature treatment operation in a temperature range of 600±20° C. for 120±10 minutes.