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%.

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 Iron60 at 75% Si, 1% Al, 1% Ca.

Description

BRIEF DESCRIPTION OF FIGURES

[0054] A complete and enabling description of the present invention, including its best mode, directed to a person commonly skilled in the art, is presented in the specifications, which makes reference to the attached figures, in which: [0055] FIG. 1a shows a chart of tensile strength and thermal conductivity for a state-of-the-art cast iron (Grade GJV 450 vermicular iron) at ambient temperatures (25 C.) and 400 C.;

[0056] FIG. 1b shows a chart of tensile strength and thermal conductivity for the high mechanical strength and high thermal conductivity vermicular cast iron alloy according to the present invention, at ambient temperatures (25 C.) and 400 C., and

[0057] FIG. 2 shows a comparative chart for thermal conductivity between a first state-of-the-art 1 cast iron (Grade GJV 450 vermicular iron), a second state-of-the-art 2 cast iron (Grade 350 gray cast iron), and the high mechanical strength and high thermal conductivity vermicular cast iron alloy according to the present invention, at temperatures of 20 C., 200 C., and 400 C.

DETAILED DESCRIPTION OF INVENTION

[0058] Now, we will refer in detail to the invention embodiments, one or more examples thereof being illustrated in the drawings. Each example is provided only to explain the invention, without limitation to it. Indeed, it will be apparent to people skilled in the art that various modifications and variations may be made to the present invention, without departing from the scope or spirit of invention. For example, functions illustrated or described as part of some embodiments may be used with another embodiment to produce yet another embodiment. Thus, the present invention must cover such modifications and variations as presented in the scope of the attached claims and their equivalents.

[0059] In general, the present invention describes a new vermicular cast iron alloy with special high mechanical strength and high thermal conductivity requirements. In addition to high thermal conductivity and guarantee of mechanical properties required for application in internal combustion engine blocks and heads, this alloy also stands out for having superior machinability compared to conventional Grade 450 vermicular cast irons.

[0060] Specifically, obtaining the new cast iron alloy with vermicular graphite of the present invention is possible by adding magnesium in a base metal for alloy production, by adding a magnesium alloy, for example, an Iron-Silicon-Magnesium (FeSiMg) alloy, during the alloy manufacturing process, which is the graphite modifying element, so that the final magnesium content in the alloy is between about 0.006% and 0.030% Mg. In addition to adding magnesium to the base metal, rare earths and inoculant are also added. The rare earths of the present alloy preferably consist of the element cerium, which plays a role similar to that of magnesium, that is, it modifies graphite, while the inoculant function is favoring graphite nucleation. The addition of rare earths, preferably cerium, shall correspond to about 2 to 3 times the sulfur amount by weight present in the base metal, falling within the 0.006%-0.020% Ce range in the alloy. The added inoculant amount is calculated based on the weight of molten metal bath poured into the casting molds. It is worth noting that the production capacity for the ladle used in the alloy manufacturing process can also influence the amount of elements (magnesium alloy, cerium, and inoculant) added to the alloy being produced, since the greater the ladle capacity, the greater the alloy production capacity and, consequently, higher the consumption of such elements.

[0061] In this way, adding magnesium alloy and rare earths to the base metal during the alloy manufacturing process enables precision in amounts of magnesium, rare earths, and silicon present in the alloy, which provide a graphite microstructure composed of up to 70% of vermicular particles and up to 30% of nodular particles for the high mechanical strength and high thermal conductivity vermicular cast iron alloy of the present invention.

[0062] Precisely, the magnesium alloy and rare earths can be added through cored wire during the alloy manufacturing process; the inoculant can be added through cored wire or ferroalloy. Other additives needed by the alloy can also be added via cored wire.

[0063] Cored wire is known in state-of-the-art to be a process in which a metal tube is filled with a powdered alloy that can contain different contents of, for example, magnesium, silicon, and/or at least one element of rare earths. During this process, the tube is introduced into the molten metal through a known injection station (GUESSER, L. G. et al Anlise comparativa entre processos de nodulizao. Seminrio Inoculao e Nodulizao de Ferros Fundidos So Paulo 1990).

[0064] Additionally, the chemical composition of the new alloy presents another differential and distinctive character to existing vermicular iron alloys: strict control of elements that form segregating carbides, such as chromium, titanium, niobium, vanadium, and tungsten, the aforementioned control being performed through monitoring through chemical analysis of a molten metal bath sample. Such elements are contained in the filler material, such as steelscraps or cast iron, and are monitored via chemical analysis of a molten metal sample taken from the treatment ladle. Segregating carbides reduce the alloy mechanical properties and thermal conductivity. So the chromium content should be less than about 0.040%, the titanium content should be less than about 0.015%, the niobium content should be less than about 0.030%, the vanadium content should be less than about 0.030% and the tungsten content should be less than about 0.050%. In addition, other chemicals, such as phosphorus, sulfur, aluminum, and nickel, must also be kept at controlled trace amounts in order to reduce the occurrence of microstructure defects in the molten material that may either reduce properties or, for example, reduce the health of the parts. In this regard, the phosphorus content must be less than about 0.040% and the sulfur content must be less than about 0.020%, in order to avoid forming compounds that favor the formation of contraction cavities and form carbides and sulfides that reduce thermal conductivity. The aluminum content must be less than about 0.080% in order to avoid the formation of porosities and non-metallic inserts and the nickel content must be less than about 0.050% so as not to impair the material thermal conductivity.

[0065] It was found that the best alloy performance is obtained with a carbon content between about 3.500% and 3.900%, silicon content between about 1.40% and 1.70%, manganese content between about 0.200% and 0.400%, tin content between about 0.030% and 0.050%, copper content between about 0.300% and 0.600%, and molybdenum content less than about 0.350%. The chromium content favors the formation of carbides, which adds brittleness to the alloy. The tin, manganese, and copper contents favor pearlite formation, however, they reduce the material thermal conductivity. Therefore, the contents of these elements must be precisely controlled to combine good thermal conductivity with the pearlitic matrix formation. In view of this, the manganese, tin, and copper contents help to obtain a mostly pearlitic matrix for the alloy, resulting in a matrix in area up to about 80% pearlitic and up to about 20% ferritic. It is worth noting that the matrix ratio is calculated from microscopy images commonly known to a person skilled in the art. Precisely, the elements manganese, tin, copper, and molybdenum are added to the alloy via ferroalloy addition. The vermicular graphite and pearlite proportions can be calculated according to Annex B of international standard ISO16112.

[0066] The part final chemical composition, in addition to including such chemical elements as carbon, silicon, copper, tin, chromium, and manganese individually within their established ranges, must meet a Thermal Conductivity Factor ratio between 0.28 and 1.36, as described by the Thermal Conductivity Factor (TCF) equation:

[00001]$T\mathrm{CF}=\%C-\left(1.3\%\mathrm{Si}+\%\mathrm{Cu}+10\%\mathrm{Sn}+1.2\%\mathrm{Cr}+0.5\%\mathrm{Mn}\right).$

[0067] The Thermal Conductivity Factor (TCF) equation was derived from the copper equivalent formula, known in the state-of-the-art, that reflects the influence of each of these elements in the pearlite phase formation, with the addition of the silicon and carbon elements in the formula. The carbon and silicon percentage weights added to said formula were determined based on experiments and from the inventors' knowledge, in which the positive effect of carbon on thermal conductivity counterbalances the negative effects of the alloy elements Si, Cu, Sn, Cr, and Mn. Thus, it was found that the alloy of the present invention reaches tensile strength and yield strength values of 450 MPa and 320 MPa, respectively, and thermal conductivity of 39 W/mK, for a TCF between about 0.28 and about 1.36. It is worth noting that this TCF range maximum and minimum values are associated with the carbon content allowed in the present alloy, between about 3.500% and 3.900%.

[0068] Therefore, the purpose of the Thermal Conductivity Factor (TCF) is to combine the positive effect obtained through the addition of the elements Cu, Sn, Cr, and Mn in the alloy pearlite formation and mechanical strength with the content of each of these elements. The negative effect of such elements and that of silicon on thermal conductivity is counterbalanced by the positive effect of carbon.

[0069] Furthermore, the TCF equation is valid when individual contents of elements present in said equation are within the ranges of element contents indicated for the present alloy.

[0070] These microstructure and chemical composition parameters described for the alloy of the present invention ensure the combination of mechanical and physical properties at ambient temperature (25 C.) of limit of tensile strength equal to or greater than about 450 MPa, yield strength equal to or greater than about 320 MPa, and thermal conductivity equal to or greater than about 39 W/mK. At a temperature of 400 C., the alloy has a limit of tensile strength greater than about 350 MPa, a yield strength greater than about 265 MPa, and a thermal conductivity greater than about 38 W/mK.

[0071] These mechanical and physical properties are achieved with the material in its molten raw state, without the need to use heat treatments after the component solidification. Thus, the alloy of the present invention is obtained with a matrix in area up to about 80% pearlitic and up to about 20% ferritic, with a segregating carbide level of up to about 1%.

[0072] The improvement of the alloy of the present invention can be easily seen in FIGS. 1a and 1b.

[0073] To be exact, FIG. 1a shows a chart of limits of mechanical strength (MPa) and thermal conductivity (W/mK) for a state-of-the-art alloy: conventional Grade 450 vermicular cast iron, at ambient temperatures (25 C.) and 400 C. The state-of-the-art alloy has a TCF of 1.6, thermal conductivity of about 35 W/mK, and a limit of mechanical strength of about 480 MPa at room temperature (25 C.). At a temperature of 400 C., the alloy has a thermal conductivity of about 36 W/mK and a limit of mechanical strength of about 410 MPa. Since these are values obtained through experimental testing, the thermal conductivity values may have a small variation in relation to the value listed in the table found in ISO16112 standard.

[0074] FIG. 1b shows a chart of limits of mechanical strength (MPa) and thermal conductivity (W/mK) for the vermicular iron alloy of the present invention, with a TCF of 0.8, at ambient temperature (25 C.) and 400 C. At ambient temperature, said alloy has thermal conductivity and limit of tensile strength of about 39 W/mK and 500 MPa, respectively; at a temperature of 400 C., the present alloy exhibits thermal conductivity and limit of tensile strength of about 38 W/mK and 420 MPa, respectively.

[0075] FIG. 2 shows a comparative chart of thermal conductivity at temperatures of 20 C., 200 C., and 400 C. between the alloy of the present invention, a state-of-the-art 1 cast iron alloy (Grade 450 vermicular cast iron alloy) and a state-of-the-art 2 cast iron alloy (Grade 350 gray cast iron alloy). The present alloy has a TCF of 0.8; the state-of-the-art 1 alloy, a TCF of 1.6; and the state-of-the-art 2 alloy, a TCF of 2. At a temperature of 20 C., the thermal conductivity values for the alloy of the present invention are 39 W/mK; for the state-of-the-art 1 cast iron, 35.2 W/mK; and for the state-of-the-art 2 cast iron, 45.7 W/mK. At a temperature of 200 C., the thermal conductivity values for the alloy of the present invention are 40 W/mK; for the state-of-the-art 1 cast iron, 37.1 W/mK; and for the state-of-the-art 2 cast iron, 42.1 W/mK. At a temperature of 400 C., the thermal conductivity values for the alloy of the present invention are about 38.4 W/mK; for the state-of-the-art 1 cast iron, 36 W/mK; and for the state-of-the-art 2 cast iron, 38.9 W/mK.

[0076] Thus, based on FIGS. 1a, 1b and 2, it is noted that the thermal conductivity values for the alloy of the present invention are close to the thermal conductivity values for the state-of-the-art 2 cast iron alloy (gray cast iron alloy) and considerably higher than the thermal conductivity values for the state-of-the-art 1 cast iron alloy (Grade 450 vermicular cast iron alloy). At the same time, the alloy of the present invention has higher mechanical strength than both state-of-the-art 1 and 2 alloys. Thus, the alloy of the present invention combines the high thermal conductivity of gray cast iron alloy with a mechanical strength greater than that of Grade 450 vermicular cast iron alloy.

[0077] Additionally, the present invention describes a manufacturing process for high mechanical strength and high thermal conductivity vermicular cast iron alloy. The process herein disclosed comprises the following steps: [0078] selecting cast raw materials based on an alloy composition of predetermined chemical element contents, the raw materials being base metal, ferroalloys, and/or charge material; [0079] determining the 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; [0080] monitoring the chemical contents in the molten metal bath; [0081] adding magnesium alloy and at least one element of rare earths to the molten metal bath to form the alloy in one of the following ways: through the bottom of molten metal treatment laddle before pouring the alloy into a mold to manufacture a part or via cored wire into the molten metal treatment ladle during the alloy manufacturing process; [0082] adding inoculant while pouring the alloy into a casting mold to manufacture a part (i.e., pouring the alloy into a mold to fill it and form a part).

[0083] Alternatively, the monitoring step for 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. Additionally, the addition step for magnesium alloy and at least one element of rare earths also comprises an adjustment step for chemical contents in the molten metal bath, based on the chemical analysis of samples collected, to reach the predetermined chemical contents.

[0084] In an alternative mode, the added amount of at least one rare earth element corresponds to 2 to 3 times the sulfur amount by weight of base metal.

[0085] Also alternatively, the inoculant addition step to the alloy is performed in the amount of 0.1% to 0.2% in relation to the weight of the molten metal poured into the casting molds.

[0086] In an alternative mode, the alloy composition comprises approximately the following predetermined chemical contents:

TABLE-US-00004 Carbon from 3.500 to 3.900; Silicon from 1.400 to 1.700; Molybdenum <0.350; Copper from 0.300 to 0.600; Manganese from 0.200 to 0.400; Tin from 0.030 to 0.050; Magnesium from 0.006 to 0.030; Rare earths from 0.006 to 0.020; Aluminum Trace amounts; Tungsten Trace amounts; Nickel Trace amounts; Chromium Trace amounts; Phosphorus Trace amounts; Niobium Trace amounts; Vanadium Trace amounts; Sulfur Trace amounts; Titanium Trace amounts

[0087] In another alternative mode, the heating and treatment temperature for the molten metal bath is between about 1,440 C. and about 1,500 C.

[0088] Alternatively, the charge material is one of, but not limited to, scraps of steel or cast iron and ferroalloys.

[0089] In another alternative mode, the determination steps for the amount of magnesium alloy, rare earths, and inoculant are performed through an operating system of specific and commercially-available software.

[0090] Alternatively, the alloy produced can be the new vermicular cast iron alloy with special high mechanical strength and high thermal conductivity requirements, as above mentioned.

[0091] Alternatively, the magnesium alloy can be an Iron-Silicon-Magnesium alloy (FeSiMg).

[0092] Alternatively, the inoculant is, e.g., a FeSi75 alloy (preferably, Iron60 at 75% Si, 1% Al, 1% Ca).

[0093] In another alternative mode, at least one rare earth element shall comprise mostly the element cerium.

[0094] The addition of magnesium alloy (e.g., FeSiMg) and rare earths to the base metal adjusts the magnesium, rare earths, and silicon contents in the alloy, respectively. The elements magnesium, rare earths, and silicon act in graphite modification and nucleation for the alloy. The chromium, titanium, niobium, vanadium, and tungsten contents are strictly controlled, since these elements form segregating carbides, which decrease the alloy mechanical properties. The phosphorus, sulfur, aluminum, and nickel contents are controlled in the base metal to remain also as trace amounts in the alloy. The alloy obtained through this process does not require the application of heat treatments after its solidification to reach high mechanical strength and high thermal conductivity.

[0095] In particular, the maximum chromium, titanium, niobium, vanadium, and tungsten contents are controlled as via raw material selection and thus are not added separately in the base metal.

[0096] The present invention also introduces a new internal combustion engine part manufactured with the high mechanical strength and high thermal conductivity vermicular cast iron alloy of the present invention.

[0097] In an alternative mode, the part may be either an engine block or an engine head. Additionally, the part does not require the application of heat treatments after its solidification to reach high mechanical strength and high thermal conductivity.

[0098] The new high mechanical strength and high thermal conductivity vermicular cast iron alloy is designed for internal combustion engine blocks and heads and has a combination of advantages from two other different alloys (values referring to ambient temperature (25 C.), alloy properties described in ISO16112 standard): [0099] high tensile strength, equal to or greater than about 450 MPa, high yield strength equal to or greater than about 320 MPa, typical values of Grade GJV 450 alloys; [0100] high thermal conductivity, equal to or greater than about 39 W/mK, equivalent to higher grade gray cast irons at high temperatures including, for example, combustion engine working temperatures; and [0101] superior machinability than conventional Grade GJV 450 vermicular cast irons.

[0102] Therefore, the present invention describes a new vermicular cast iron alloy with special high mechanical strength and high thermal conductivity requirements and a new manufacturing process for the new vermicular cast iron alloy, which allows the development of higher performance engine blocks and heads, suitable for high power density engines, involving high levels of mechanical stress and thermal conductivity.

[0103] This written description uses examples to describe the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The invention patentable scope is determined by the claims and may include other examples occurring to those skilled in the art. Such other examples are intended to be covered by the scope of claims, if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with non-substantial differences from the literal language of the claims.