High mechanical strength and high thermal conductivity vermicular cast iron alloy, high mechanical strength and high thermal conductivity vermicular cast iron alloy manufacturing process, and internal combustion engine part

Abstract

This invention relates to a vermicular cast iron alloy with high mechanical strength and thermal conductivity requirements to replace the conventional gray and vermicular cast irons and introduces a manufacturing process for high mechanical strength and thermal conductivity vermicular cast iron alloy and internal combustion engine parts produced from said alloy. The alloy includes carbon, manganese, tin, copper, molybdenum, silicon, magnesium, rare earths, chromium, titanium, niobium, vanadium, tungsten, phosphorus, sulfur, aluminum, and nickel. The alloy has a graphite microstructure consisting of up to 70% of vermicular particles and up to 30% of nodular particles in area, with a matrix in area up to 80% pearlitic and up to 20% ferritic, with presence of segregating carbides of up to 1%.

In the claims: 
     
         1 . A high mechanical strength and high thermal conductivity vermicular cast iron alloy comprising:
 carbon from 3.500 to 3.900% by weight of the alloy;   silicon from 1.400 to 1.700% by weight of the alloy;   molybdenum in less than 0.350% by weight of the alloy;   copper from 0.300 to 0.600% by weight of the alloy;   manganese from 0.200 to 0.400% by weight of the alloy;   tin from 0.030 to 0.050% by weight of the alloy;   magnesium from 0.006 to 0.030% by weight of the alloy;   rare earths from 0.006 to 0.020% by weight of the alloy; and   trace amounts of aluminum, tungsten, nickel, chromium, phosphorus, niobium, vanadium, sulfur, and titanium, wherein the silicon, magnesium, and rare earths are added in a controlled manner, and the presence of aluminum, tungsten, nickel, chromium, phosphorus, niobium, vanadium, sulfur, and titanium, is controlled, and a chemical composition of chemical contents of said alloy are obtained from the Thermal Conductivity Factor (TCF) equation:
   TCF=% C−(1.3x% Si+%Cu+10x%Sn+1.2x%Cr+0.5x%Mn).
 
   
     
     
         2 . The cast iron alloy according to  claim 1 , wherein
 aluminum is less than 0.080% by weight of the alloy;   tungsten is less than 0.050% by weight of the alloy;   nickel is less than 0.050% by weight of the alloy;   chromium is less than 0.040% by weight of the alloy;   phosphorus is less than 0.040% by weight of the alloy;   niobium is less than 0.030% by weight of the alloy;   vanadium <0.030% by weight of the alloy;   sulfur is less than 0.020% by weight of the alloy; and   titanium is less than 0.015% by weight of the alloy.   
     
     
         3 . The cast iron alloy according to  claim 1 , wherein a content of magnesium present in the alloy is adjusted by adding a FeSiMg alloy. 
     
     
         4 . The cast iron alloy according to  claim 1 , wherein said rare earths comprises cerium. 
     
     
         5 . The cast iron alloy according to  claim 4 , wherein a content of cerium present in the alloy is from 2 to 3 times an amount by weight of sulfur present in a base metal used for producing the alloy. 
     
     
         6 . The cast iron alloy according to  claim 1 , wherein contents of chromium, titanium, niobium, vanadium, and tungsten in the alloy are controlled to prevent the formation of segregating carbides. 
     
     
         7 . The cast iron alloy according to  claim 1 , wherein manganese, tin, copper, and molybdenum are added via ferroalloys to avoid carbide formation and to obtain a mostly pearlitic matrix. 
     
     
         8 . The cast iron alloy according to  claim 1 , wherein said allow comprises a graphite microstructure comprising of up to 70% of vermicular particles and up to 30% of nodular particles in area, with a matrix in area up to about 80% pearlitic and up to about 20% ferritic, and with 
     
     
         9 . The cast iron alloy according to  claim 1 , wherein said alloy has a Thermal Conductivity Factor (TCF) from 0.28 to 1.36. 
     
     
         10 . The cast iron alloy according to  claim 1 , wherein said allow has a minimum limit of tensile strength of 450 MPa, a minimum yield strength of 320 MPa, and a minimum thermal conductivity of 39 W/mK, at ambient temperature (25° C.). 
     
     
         11 . The cast iron alloy according to  claim 1 , wherein said allow has a minimum limit of tensile strength of 350 MPa, a minimum yield strength of 265 MPa, and a minimum thermal conductivity of 38 W/mK at 400° C. 
     
     
         12 . A process for manufacturing the high mechanical strength and high thermal conductivity vermicular cast iron alloy according to  claim 1 , said method comprising the following steps:
 selecting cast raw materials based on an alloy composition of predetermined chemical element contents, the raw materials being at least one of base metals, ferroalloys, or filler material;   determining an amount of each cast raw material to be added to a molten metal treatment ladle based on the raw material selection and forming a molten metal bath;   monitoring chemical contents in the molten metal bath;   adding a magnesium alloy and at least one element of rare earths to the molten metal bath to form the alloy, said addition is made by one of: through a pan bottom of the molten metal treatment ladle before pouring the alloy into a casting mold to manufacture a part, or via cored wire into the molten metal treatment ladle during the alloy manufacturing process; and   adding inoculant while pouring the alloy into the casting mold to manufacture said part.   
     
     
         13 . The process according to  claim 12 , wherein said step of monitoring chemical contents in the molten metal bath is performed during the entire alloy manufacturing process through sequential molten metal bath sampling and chemical analysis of samples. 
     
     
         14 . The process according to  claim 13 , wherein said step of adding the magnesium alloy and at least one element of rare earths further comprises a step of adjusting the chemical contents in the molten metal bath, based on the chemical analysis of samples collected, to reach predetermined chemical contents. 
     
     
         15 . The process according to  claim 12 , wherein an added amount of said at least one element of rare earths corresponds to 2 to 3 times a sulfur amount by weight of said base metal. 
     
     
         16 . The process according to  claim 12 , wherein said step of adding inoculant is performed in the amount of 0.1% to 0.2% in relation to the weight of the molten metal poured during pouring the alloy into the casting mold. 
     
     
         17 . (canceled) 
     
     
         18 . The process according to  claim 12 , wherein a heating and treatment temperature for the molten metal bath is between 1,440° C. and 1,500° C. 
     
     
         19 .The process according to  claim 12 , wherein said filler material comprises scraps of steel, cast 
     
     
         20 . The process according to  claim 12 , wherein amounts of said magnesium alloy, said at least one element of rare earths, and said inoculant are determined using software. 
     
     
         21 . A high mechanical strength and high thermal conductivity vermicular cast iron alloy manufactured according to the process of  claim 12 . 
     
     
         22 . The process according to  claim 12 , wherein said magnesium alloy is an iron-silicon-magnesium (FeSiMg) alloy. 
     
     
         23 . The process according to  claim 12 , wherein said inoculant is a FeSi75 alloy. 
     
     
         24 . The process according to  claim 12 , wherein said at least one element of rare earths is cerium. 
     
     
         25 . An internal combustion engine part manufactured with the cast iron alloy according to  claim 1 . 
     
     
         26 . The internal combustion engine part according to  claim 25 , wherein said part is an engine block or an engine head. 
     
     
         27 . The internal combustion engine part according to  claim 25 , wherein said part does not require application of heat treatments after its solidification to reach high mechanical strength and high thermal conductivity. 
     
     
         28 . The process according to  claim 22 , wherein said FeSi75 alloy is Iron—60 at 75% Si, 1% Al, 1% Ca.