Vermicular Cast Iron Alloy, Combustion Engine Block and Head

Abstract

The present invention refers to a vermicular cast iron alloy specially designed for blocks and heads of internal combustion engines that have special requirements for mechanical strength and machinability; said vermicular alloy has a microstructure that results in high values of mechanical properties, such as a minimum strength limit of 500 Mpa, a minimum yield limit of 350 MPa, along with good machinability; also, wherein the ferritization factor must be such that it is between 3.88 and 5.48. This set of properties makes it possible to design new engine blocks and heads with complex geometry, high mechanical properties, without compromising machinability, making it attractive both from a technical and economic point of view.

Claims

1. Vermicular cast iron alloy comprising carbon contents in the range of 2.6% to 3.2%, manganese values between 0.1% to 0.3%, maximum phosphorus of 0.05%, chromium less than 0.06%, tin less than 0.03% and copper less than 0.20%; the alloy characterized by presenting a microstructure with a ferritic matrix comprising at least 90% of ferrite and at least 70% of vermicular graphite; said alloy comprising silicon in the range of 4.60% to 5.70%; and wherein the Ferritization Factor (F.F.) calculated as F.F.=% Si−% Cu−10×% Sn−1.2×% Mn−0.5×% Mn is between 3.88 to 5.48.

2. Vermicular cast iron alloy, according to claim 1 characterized in that it presents graphite nodules in up to 30% of the microstructure.

3. Vermicular cast iron alloy, according to claim 1 characterized in that it has a minimum strength limit of at least 500 MPa and a minimum yield limit of at least 350 Mpa.

4. Internal combustion engine head, characterized in that it is manufactured in vermicular cast iron alloy, as defined in claim 1.

5. Internal combustion engine block, characterized in that it is manufactured in vermicular cast iron alloy, as defined in claim 1.

Description

BRIEF DESCRIPTION OF FIGURES

[0034] Preferred embodiment of the present invention is described in detail based on the listed figures, which are exemplary and not limiting.

[0035] FIG. 1—Typical microstructure of a class 250 gray cast iron, (A1) without attack and (A2) with attack, showing the predominantly pearlitic matrix; typical microstructure of a class 450 vermicular cast iron, (B1) without attack, evidencing the shape of the graphite particles and (B2) with attack, evidencing the predominantly pearlitic matrix; typical microstructure of a class 400 nodular cast iron, (C1) without attack, evidencing the shape of the graphite particles and (C2) with attack, evidencing the matrix constituted by similar fractions of ferrite and pearlite; typical microstructure of a class 600 nodular cast iron, (D1) without attack, evidencing the shape of the graphite particles and (D2) with attack, evidencing the predominantly pearlitic matrix.

[0036] FIG. 2—(a) part of an engine block with 50% nodularity and high porosity index, (b) part of an engine block with 10% nodularity and free of porosity, (c) part of a block engine with 20% nodularity and low porosity index.

[0037] FIG. 3—Relationship between the amount of inoculant used as a function of the silicon content.

[0038] FIG. 4—Ferrite proportion according to the ferritization factor of a vermicular cast iron.

[0039] FIG. 5—Impact Resistance of a high silicon vermicular cast iron according to the Ferritization Factor. Data obtained from U-notch specimens.

[0040] FIG. 6—Micrographs of the ferritic matrix vermicular cast iron object of the present invention: a) optical microscopy, magnification of 100×, with attack; b) optical microscopy, magnification of 500×, with attack.

[0041] FIG. 7—strength limit results for the ferritic vermicular cast iron object of the present invention. The comparative example is for class 450 vermicular cast iron. The average strength limit is 587 MPa for the present material.

[0042] FIG. 8—Yield limit results for the ferritic vermicular cast iron object of the present invention. The comparative example is for class 450 vermicular cast iron. The average yield limit is 523 MPa for the high silicon vermicular cast iron in this document.

[0043] FIG. 9—Elongation results for the ferritic vermicular cast iron object of the present invention. The comparative example is for class 450 vermicular cast iron. The average elongation is 1.86% for the vermicular cast iron of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0044] The present invention relates to vermicular cast iron alloy, especially defined by having a microstructure with a ferritic matrix comprising at least 90% ferrite and at least 70% vermicular graphite, said alloy comprising silicon in the range of 4.80% to 5,70% and wherein the Ferritization Factor is calculated as F.F.=% Si−% Cu−10×% Sn−1.2×% Mn−0.5×% Mn is between 3.88 to 5.48.

[0045] The proposal of the present patent arises to produce a vermicular cast iron with a ferritic matrix with high Si content and a maximum nodularity of 30% for the manufacture of engine blocks and heads, which tensile strength limit is greater than 500 MPa.

[0046] The feasibility of producing vermicular cast iron with a strength limit greater than 500 MPa and good machinability creates new opportunities for the automotive sector. The mechanical properties provided by this alloy allow the manufacture of engine blocks and heads with greater geometric complexity and greater power and performance.

[0047] Therefore, the present invention meets the demand of the industry by combining sustainability with this production, as new projects with this alloy allow the manufacture of engines with lower pollutant emissions.

[0048] Obtaining cast iron with graphite in vermicular form is possible through controlled additions of magnesium, which is the graphite modifier element, so that the final magnesium content is between 0.008-0.030% Mg.

[0049] In addition to the controlled addition of magnesium through the addition of Fe—SiMg alloy, the addition of cerium and inoculant (FeSi75) is also controlled. Cerium, also known as rare earths, plays a role similar to magnesium, while the inoculant has the function of favoring the nucleation of graphite. The addition of cerium must correspond to 2-3 times the amount of sulfur present in the base metal.

[0050] The amount of inoculant added depends on the Si content in the alloy and the capacity of the pan used. This relationship is shown in FIG. 3.

[0051] The chemical composition of the new alloy differs from the composition of conventional class 450 vermicular cast iron mainly by its low C content (2.6-3.2%), high Si content (4.6-5.7%) and residual values of perlitizing elements.

[0052] To ensure the formation of ferrite associated with high mechanical properties, a Ferritization Factor between 3.88 and 5.48 must be defined as:

Ferritization Factor=% Si−% Cu−10×% Sn−1.2×% Cr−0.5×% Cr.

[0053] For values lower than 3.88, pearlite is formed, with a consequent increase in hardness and a drop in machinability, as shown in the graph in FIG. 4. Above these values, the material becomes extremely fragile, making its application impossible.

[0054] The graph in FIG. 5 shows the evolution of impact energy absorption values according to the Ferritization Factor.

[0055] Typical levels of elements for the material claimed by this document compared to conventional class 450 vermicular cast iron are shown in table 1.

TABLE-US-00001 High Si Vermicular Iron, Element class 500 Class 450 Vermicular Iron Carbon 3.2-3.8%  2.6-3.2% Silicon 2.0-2.5%  4.6-5.7% Sulfur <0.030%  <0.015% Manganese <0.5% 0.1-0.3% Copper <1.0%  <0.06% Tin <0.1%  <0.01% Magnesium 0.005-0.030%    0.005-0.030%   Cerium 0.005-0.030%    0.005-0.030%  

[0056] From the chemical composition described in Table 1 and complying the Ferritization Factor range between 3.88 and 5.48, the material in this document reaches high values of tensile strength limit, above 500 MPa combined with the minimum yield limit of 350 MPa with a ferritic matrix. This microstructure can be seen in FIG. 6.

[0057] In a preferred embodiment, the silicon Si content in the alloy can range between 4.8-5.7%.

[0058] Thus, to obtain the present material within these ranges of chemical composition, the base metal must be prepared in the furnace with a high silicon content between 4.4 and 4.7% and a sulfur content not exceeding 0.020%.

[0059] Then the base metal must be transferred from the furnace to a leaking or treatment pan. The metal is then treated with pre-calculated amounts of magnesium and cerium as shown. Next, the inoculant is added in the appropriate amount, following the proportions described in the graph in FIG. 2 and, finally, the liquid metal is poured into convenient molds.

[0060] In addition to accurately calculating all additions made to the pan, process temperatures must also be well controlled. For the furnace, the approximate temperature of 1550° C. is indicated and the leaking must take place at temperatures from 1370 to 1450° C.

[0061] The result is to obtain a high silicon vermicular cast iron, with a predominantly ferritic matrix. The graphite format is predominantly vermicular (form III of the ISO 945/1975 standard [9])—above 70%, and there is also the presence of graphite in nodules (form VI of the ISO 945/1975 standard [9]) at a maximum of 30%.

[0062] The main factor that favors the higher strength limit, without machinability drop, of this new type of vermicular cast iron is the combination of chemical elements that comply with the Ferritization Factor between 3.88 and 5.48, responsible for the hardening by solid solution of the ferritic matrix.

[0063] FIGS. 7, 8 and 9 show results of strength limit, yield limit and elongation limit of the ferritic vermicular cast iron of the present invention, with Ferritization Factor between 3.88 and 5.48 and nodularity less than 30%.

[0064] Thus, the material claimed has high mechanical properties, especially high tensile strength, due to the ferritic matrix hardened by solid solution, combined with good machinability and also, without presenting the brittleness typical of cast irons with a high silicon content. These properties are important in the manufacture of engine blocks and heads with superior performance.

[0065] Thus, the new alloy can be used in the production of high-power density engines, which are susceptible to high levels of mechanical demand.

[0066] In this sense, the present invention also refers to an internal combustion engine head and block, manufactured in gray cast iron alloy, as defined above.

[0067] It is important to emphasize that the above description has the sole purpose of describing, by way of example, the particular embodiment of the invention in question. Therefore, it becomes clear that modifications, variations and constructive combinations of elements that perform the same function in substantially the same way to achieve the same results, remain within the scope of protection delimited by the appended claims.