Alloy cast iron and manufacturing method of rolling piston using the same

Abstract

An alloy cast iron, and a method of manufacturing a rolling piston for a rotary compressor includes, by weight, 3.0˜3.5% carbon (C), 2.2˜2.4% silicon (Si), 0.5˜1.0% manganese (Mn), 0.1˜0.3% phosphorus (P), 0.06˜0.08% sulfur (S), 0.7˜1.0% chrome (Cr), 0.6˜1.0% copper (Cu), and a residue formed of Fe and inevitable impurities, wherein 3˜8 vol % steadite structure is formed.

1 . An alloy cast iron comprising, by weight:
 3.0˜3.5% carbon (C);   2.2˜2.4% silicon (Si);   0.5˜1.0% manganese (Mn);   0.1˜0.3% phosphorus (P);   0.06˜0.08% sulfur (S);   0.7˜1.0% chrome (Cr);   0.6˜1.0% copper (Cu); and   a residue formed of Fe and inevitable impurities,   wherein 3˜8 vol % steadite structure is formed.   
     
     
         2 . The alloy cast iron of  claim 1 , wherein the alloy cast iron undergoes a thermal processing including quenching and tempering. 
     
     
         3 . The alloy cast iron of  claim 2 , wherein the quenching is performed by maintaining the alloy cast iron at 900±10° C. for 90˜150 minutes, then by oil-cooling the alloy cast iron to 50˜90° C., and then by maintaining the alloy cast iron at 50˜90° C. for 5˜7 hours. 
     
     
         4 . The alloy cast iron of  claim 3 , wherein the tempering is performed by maintaining the alloy cast iron at 250±10° C. for 150˜210 minutes, and then by cooling the alloy cast iron to room temperature in air. 
     
     
         5 . The alloy cast iron of  claim 4 , wherein the tempered alloy cast iron has a Rockwell hardness of 45˜55. 
     
     
         6 . A method of manufacturing a rolling piston for a rotary compressor, the method comprising:
 a melting step of preparing a molten metal comprising, by weight, 3.0˜3.5% carbon (C), 2.2˜2.4% silicon (Si), 0.5˜1.0% manganese (Mn), 0.1˜0.3% phosphorus (P), 0.06˜0.08% sulfur (S), 0.7˜1.0% chrome (Cr), 0.6˜1.0% copper (Cu), and a residue formed of Fe and inevitable impurities;   a casting step of pouring the molten metal in a mold and cooling thereby preparing a semi-product in which 3˜8 vol % steadite structure is formed;   a grinding step of grinding the cooled semi-product to a prescribed shape; and   a thermal-processing step of thermally-processing the ground semi-product for a Rockwell hardness of 45˜55.   
     
     
         7 . The method of  claim 6 , wherein the thermal-processing step includes quenching and tempering. 
     
     
         8 . The method of  claim 7 , wherein the quenching is performed by maintaining the alloy cast iron at 900±10° C. for 90˜150 minutes, then by oil-cooling the alloy cast iron to 50˜90° C., and then by maintaining the alloy cast iron at 50˜90° C. for 5˜7 hours. 
     
     
         9 . The method of  claim 7 , wherein the tempering is performed by maintaining the alloy cast iron at 250±10° C. for 150˜210 minutes, and then by cooling the alloy cast iron to room temperature in air.