Gray cast iron alloy, and internal combustion engine head

Abstract

The present invention refers to a gray cast iron alloy with chemical composition especially developed to promote high hot mechanical strength and good thermal conductivity, with antimony and nitrogen contents, wherein the antimony content ranges from 0.05 to 0, 12% by weight, and the nitrogen content ranges from 0.008 to 0.013% by weight, based on the total weight of the gray cast iron alloy.

Claims

1. A gray cast iron alloy presenting a chemical composition with antimony and nitrogen contents, further comprising contents of at least one of the following elements: carbon; phosphorus; silicon; manganese; sulfur; chromium from 0.05 to 0.25% by weight, based on the total weight of the gray cast iron alloy; copper from 0.01 to 0.95% by weight; tin from 0.01 to 0.12% by weight; molybdenum from 0.03 to 0.30% by weight; and iron, where the antimony content ranges from 0.05 to 0.12% by weight and the nitrogen content ranges from 0.008 to 0.013% by weight; wherein at least the iron and the carbon form a pearlitic matrix with graphite veins; and wherein the antimony and the nitrogen are bound with the iron to stabilize the pearlitic matrix.

2. An internal combustion engine head, characterized in that it is made of gray cast iron alloy, as defined in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The preferred embodiment of the invention in question is described in detail based on the listed figures, which have a character merely illustrative and non-limiting, since adaptations and modifications may be made without thereby departing from the scope of the claimed protection.

(2) FIG. 1 is a diagram illustrating the relations required to obtain good hot strength values in gray cast irons.

(3) FIG. 2 illustrates a graph relating the drop of Hardness (HB) and Tensile Strength Limit (LR) with exposure of gray iron alloys for 96 h at 705° C.

DETAILED DESCRIPTION OF THE INVENTION

(4) As described above, the present invention refers to a gray cast iron alloy with chemical composition especially developed to promote high hot mechanical strength and good thermal conductivity.

(5) The gray cast iron alloy of the present invention exhibits a chemical composition with antimony and nitrogen contents, which distances itself from the traditional compositions of the state of the art.

(6) More specifically, the antimony content ranges from 0.05 to 0.12% by weight, and the nitrogen content ranges from 0.008 to 0.013% by weight, based on the total weight of the gray cast iron alloy.

(7) Preferably, the iron alloy further comprises contents of at least one of the following elements: carbon, phosphorus, silicon, manganese, sulfur, chromium, copper, tin, molybdenum and iron.

(8) If present, the chromium contents range from 0.05 to 0.25% by weight, the copper contents range from 0.01 to 0.95% by weight, the tin contents range from 0.01 to 0.12% by weight, and the molybdenum contents range from 0.03 to 0.30% by weight, based on the total weight of the gray cast iron alloy.

(9) FIG. 1 shows the relations required to obtain good values of hot strength in gray cast irons. A pearlitic matrix is required, the presence of graphite particles (veins) of small size and with suitable shape. In addition, the pearlitic matrix must be thermodynamically or kinetically stabilized, otherwise decomposition of pearlite carbide occurs, with consequent decrease in mechanical strength.

(10) The contribution of each element of the chemical composition of the gray cast iron alloy of the present invention to this hot property is indicated in FIG. 1.

(11) More specifically, the amount of nitrogen is related to the form of graphite with low notch, the amounts of chromium and antimony relate to the stability of pearlite carbides, and the amounts of copper, chromium, tin and antimony relate to the matrix of pearlite.

(12) The three characteristics together affect the hot strength of the gray cast iron alloy. This is achieved, in the present invention, with low contents of alloying elements, which maximizes the thermal conductivity of the gray iron.

(13) The present invention refers to a new gray cast iron alloy with a combination of traditional alloying elements such as carbon, manganese, sulfur, silicon, phosphorus, chromium, tin, copper and molybdenum, and controlled contents of antimony and nitrogen in combination such that it allows obtaining high levels of hot mechanical properties, good stability of the hot microstructure, and good thermal conductivity values.

(14) This combination of alloying elements allows obtaining a gray cast iron with levels of tensile strength limit of from 250 to 350 MPa at room temperature, and tensile strength limit of from 180 to 280 MPa at 400° C., depending on thickness of the section wherein such property is referred. With these mechanical strength levels, it is not necessary to employ vermicular cast irons for a number of applications, which results in products that are more economical and with higher thermal conductivity.

(15) The gray cast iron bound to nitrogen and antimony, object of the present invention, also has an extremely important property, which is the thermal stability of the microstructure, so that the strength does not suffer marked decreases in hot work, a typical condition of some components of internal combustion engines. FIG. 2 illustrates this behavior, verifying that increasing contents of nitrogen and antimony decrease the hardness and strength drop by exposure to high working temperatures.

(16) In addition, the combination of the alloying elements enables a good machinability matrix to be obtained, which for internal combustion engine heads is a critical factor, given the large amount of machining these components need to suffer in their production, in particular in milling and drilling operations.

(17) In order to obtain this set of properties, the combination of contents of chemical element is such that the antimony content is between 0.05 to 0.12% by weight, and the nitrogen content between 0.008 to 0.013% by weight, in relation to the total weight of the gray cast iron alloy. Such concentrations are higher than those found in the state of the art.

(18) Thus, the present invention of cast irons bound to antimony and nitrogen, especially at specific concentrations, allows the development of superior performance engine heads, suitable for high engine operating temperatures.

(19) In this regard, the present invention also refers to an internal combustion engine head, made of gray cast iron alloy, as defined above.

(20) It is important to highlight that the above description is for the sole purpose of describing in an exemplifying manner the particular embodiment of the invention in question. It is therefore clear that modifications, variations and constructive combinations of the elements performing the same function in substantially the same manner to achieve the same results, remain within the scope of protection delimited by the appended claims.