Hot mold steel for long life cycle die casting having high thermal conductivity and method for preparing the same

Abstract

According to an embodiment, the described hot mold steel may be excellent in high thermal conductivity to decrease the temperature difference in materials at high temperature, thereby making heat-checking properties excellent. When the hot mold steel according to the present disclosure is used for die casting, the cooling rate of the product produced using the die casting is quick, thereby improving the physical properties of the produced product and shortening the cooling time to improve productivity. Furthermore, the hot mold steel may have excellent high temperature durability, such that the die casting produced using the hot mold steel may have characteristics of a long life cycle.

What is claimed is: 
     
         1 . A hot mold steel, comprising:
 0.35 to 0.45% by weight of carbon;   0.20 to 0.30% by weight of silicon;   0.30 to 0.40% by weight of manganese;   0.50 to 1.20% by weight of nickel;   1.5 to 2.2% by weight of chromium;   2.0 to 2.6% by weight of molybdenum;   0.0001 to 1.0% by weight of tungsten;   0 to 0.40% by weight of titanium;   0.30 to 0.50% by weight of vanadium;   0.0001 to 0.003% by weight of boron;   0.005 to 0.02% by weight of copper; and   iron.   
     
     
         2 . The hot mold steel of  claim 1 , further comprising 0.02 to 0.08% by weight of aluminum. 
     
     
         3 . The hot mold steel of  claim 1 , further comprising 0.005 to 0.06% by weight of nitrogen. 
     
     
         4 . The hot mold steel of  claim 1 , further comprising 0.001 to 0.006% by weight of phosphorus and 0.0001 to 0.002% by weight of sulfur. 
     
     
         5 . The hot mold steel of  claim 1 , wherein:
   F(1)=F(C)×F(Si)×F(Mn)×F(Cr)×F(Mo)×F(Ni)
     F(C)=0.37−0.39×(0.12̂% by weight of carbon)
     F(Si)=0.7×% by weight of silicon+1
     F(Mn)=3.35×% by weight of manganese+1
     F(Cr)=2.16×% by weight of chromium+1
     F(Ni)=0.36×% by weight of nickel+1
     F(Mo)=3×% by weight of molybdenum+1
     and F(1) is equal to or greater than 25.   
     
     
         6 . The hot mold steel of  claim 5 , wherein F(1) is equal to or greater than 30. 
     
     
         7 . The hot mold steel of  claim 1 , wherein
   F(2)=% by weight of molybdenum+0.5×% by weight of tungsten
   and F(2) is in the range of 2 to 3.   
     
     
         8 . The hot mold steel of  claim 1 , wherein
   F(3)=% by weight of titanium+% by weight of vanadium   and F(3) is in the range of 0.4 to 0.5.   
     
     
         9 . The hot mold steel of  claim 1 , wherein
   F(4)=% by weight of chromium+3.3×(% by weight of molybdenum+0.5×% by weight of tungsten)
   and F(4) is equal to 9 or more.   
     
     
         10 . A method of die casting, comprising die casting with the hot mold steel of  claim 1 . 
     
     
         11 . A method for preparing hot mold steel, comprising:
 preparing an steel ingot that contains 0.35 to 0.45% by weight of carbon, 0.20 to 0.30% by weight of silicon, 0.30 to 0.40% by weight of manganese, 0.50 to 1.20% by weight of nickel, 1.5 to 2.2% by weight of chromium, 2.0 to 2.6% by weight of molybdenum, 0.0001 to 1.0% by weight of tungsten, 0.30 to 0.50% by weight of vanadium, 0.0001 to 0.003% by weight of boron, and 0.005 to 0.02% by weight of copper, and iron;   preparing a mold material by forging the steel ingot;   quenching the mold material; and   tempering the mold material after the quenching.   
     
     
         12 . The method of  claim 11 , further comprising performing an electro-slag remelting (ESR) process prior to forging the steel ingot. 
     
     
         13 . The method of  claim 12 , wherein the ESR process is performed under an argon gas atmosphere. 
     
     
         14 . The method of  claim 11 , further comprising performing a preliminary heat treatment on the steel ingot at a temperature of 800 to 1300° C. prior to the forging of the steel ingot. 
     
     
         15 . The method of  claim 11 , wherein the forging is performed at a forging ratio of 5 S or more. 
     
     
         16 . The method of  claim 11 , wherein the forging is performed at a temperature of 850 to 1300° C. 
     
     
         17 . The method of  claim 11 , wherein the quenching is performed at a temperature of 900 to 1030° C. 
     
     
         18 . The method of  claim 11 , wherein the tempering is performed at a temperature of 500 to 630° C. 
     
     
         19 . The method of  claim 11 , wherein the tempering includes
 performing primary tempering at a primary temperature of 580 to 600° C., and   performing secondary tempering at a secondary temperature of 550 to 590° C.   
     
     
         20 . The method of  claim 19 , further comprising:
 performing tertiary tempering at a tertiary temperature of 610 to 630° C. after performing the secondary tempering.