Patent Application
20190264304
The present disclosure relates to ductile iron alloys and particularly to ductile iron alloys that may be cast or made into thin-wall sections. It also relates to materials including a thin-wall layer of ductile iron which may include a low alloy content while maintaining desired mechanical properties and/or a controlled microstructure.
Ductile iron alloys contain carbon which may be present in the form of graphite nodules. The inclusion of nodules of graphite generally provides for more effective stress reduction than may be achieved when including dispersed graphite in other morphologies such as flakes in grey iron. For example, in ductile iron alloy materials, spheroidal shaped graphite may act to reduce risk of crack propagation and promote higher strength and increased fatigue resistance when compared to materials including graphite flakes.
In processes for making ductile iron alloys, a liquid melt may be prepared by mixing one or more component streams. Following mixing and generally the addition of one or more inoculating components, a melt may be cast and cooled to generate a ductile iron alloy composition. Preferably, the formed composition may include a tailored or controlled microstructure. Generally, control of a composition's microstructure is most readily achieved when the melt is cooled at sufficiently low rates. For example, if a melt is poured and cooled at too rapid of a rate, carbon may not have sufficient time to properly diffuse to graphite nodules, a condition that typically results in excessive amounts of carbide formation. Although some amount of carbides may be acceptable in some ductile iron alloys useful for some purposes, such as where very hard materials are needed, excessive growth of carbides may result in significantly reduced ductility.
Unfortunately, when forming thin-wall samples of ductile iron alloys it may be difficult to control and limit rates of cooling. Accordingly, it may be difficult to make a desired ductile iron alloy in thin samples with a desired microstructure. This aspect of making thin-wall samples or parts of ductile iron alloys has severely limited the use of ductile iron alloys in many applications, including those that would benefit from weight reductions associated with thin samples. Particularly, as cooling rates increase, it may be difficult to prevent excessive growth of carbides over nodular graphite. Accordingly, thin-walled samples of ductile iron alloys may tend to be too brittle for many applications.
There remains a need for low cost compositions of ductile iron alloys that may be produced in volume and that may be effectively cast in thin-wall samples while maintaining adequate properties of strength and ductility.
A cast iron alloy composition may include nodular or spheroidal graphite domains comprising an iron content of at least about 90% by weight; a remaining alloy content of less than about 10% by weight; about 0.65% to about 0.85% by weight copper; about 3.6% to about 4.2% by weight silicon; and about 3.4% to about 3.8% by weight carbon.
An article of manufacture may include a cast iron alloy composition including nodular or spheroidal graphite domains comprising an iron content of at least about 90% by weight; a remaining alloy content of less than about 10% by weight; about 0.65% to about 0.85% by weight copper; about 3.6% to about 4.2% by weight silicon; and about 3.4% to about 3.8% by weight carbon. The article may further include a thin-wall part including a thickness in at least one dimension of between about 1.5 mm and about 2.5 mm, wherein the thin-wall part may include a sum amount of ferrite domains and pearlite domains of greater than about 85% by volume with respect to the total volume of the part; and a ratio of said ferrite domains to said pearlite domains of about 0.75:1 to about 1.25:1.
The following terms as used herein should be understood to have the indicated meanings.
When an item is introduced by “a” or “an,” it should be understood to mean one or more of that item.
The term “alloy content” refers to an amount of all components in a metal alloy aside from the most prevalent or base component of the alloy. For example, the alloy content of an iron-based alloy includes all components present except for the base iron.
“Comprises” means includes but is not limited to.
“Comprising” means including but not limited to.
The term “substantially free” where referring to an amount of a component, unless explicitly defined by another amount, should be understood as meaning that the component may be present at no more than about 0.02% by weight.
Where a range of values is described, it should be understood that intervening values, unless the context clearly dictates otherwise, between and including the upper and lower limits of that range and any other stated or intervening value in other stated ranges, may be used within embodiments herein.
This disclosure is directed to ductile iron alloy compositions and articles made thereof which maintain desired mechanical properties and/or which maintain a desired or controlled microstructure even when cast to make thin-wall samples. For example, articles described herein may include one or more thin walls including a microstructure with a low carbide content. In some embodiments, thin-wall samples of ductile iron alloys may be made that include a low carbide content in interior regions of the thin-wall samples. For example, carbides, if present in a ductile iron sample, may be limited to the immediate surface of the sample. Particularly, a surface region of up to about 100 nm may sometimes include carbides which may be useful for wear resistance. Accordingly, loss in ductility, a common problem found when attempting to make thin-wall samples of ductile iron alloys using other iron alloys, may be minimized.
In addition to providing significant weight reduction, the ductile iron alloys described herein may be less expensive than other iron alloys, including, for example, other iron alloys that may include high alloy content and which may include significant amounts of molybdenum, aluminum, niobium, or other alloying components that may increase cost. Accordingly, compositions and/or articles may be provided which include a thin-wall layer of a ductile iron alloy and which yield a significant reduction in weight at a significantly reduced cost.
In some embodiments, compositions and articles described herein may comprise or consist of a ductile iron alloy. For example, articles may include one or more parts or components that may be cast or made entirely or in part of a ductile iron alloy. One or more parts of an article cast or made of a ductile iron alloy may include at least one dimension that may be thin. For example, in some embodiments, a sample or part of an article cast or made of a ductile iron alloy may include a dimension that is less than about 6 mm, less than about 4 mm, or less than about 2 mm. Moreover, a thin-wall part of an article may maintain suitable mechanical properties such as hardness and ductility. For example, the thin-wall sample may include a hardness and ductility that are at least comparable to the hardness and ductility that may be achieved for a thicker sample.
In some embodiments, a liquid melt may be cast and made into an object that includes one or more dimensions that is thin or limited in thickness. In some embodiments, a cast object may be subject to one or more polishing operations, machining operations, or other operations after a melt is cooled or solidified. Generally, it is desirable that any changes in shape and thickness in an object that occur after an object is cast are minimized. Herein, where reference is made to a thickness of a thin-wall part of a material, composition, or article, the referenced thickness may include the thickness as cast as well as the thickness after common machining operations. Where reference to a thickness is specifically intended to denote the thickness of an article after machining, polishing, or other operations that may modify the thickness of the article, the term “machined thickness” will be used. Similarly, where reference to a thickness is specifically intended to denote the thickness of an article following cooling, the term “as-cast thickness” will be used.
In some embodiments, a composition may be made from a liquid melt that is configured to solidify and produce a ductile iron alloy that maintains suitable hardness and ductility even if the same melt is used to form different parts of an article that may vary over a considerable range of thicknesses. For example, in some embodiments, an article may include a first sample or part including a ductile iron alloy that is relatively thick and also include a thinner second sample or part of a ductile iron alloy. A thinner part of an article may maintain a hardness and ductility that is comparable to the hardness and ductility in a thicker part of the article. In some embodiments, mechanical properties in thinner parts of an article may even be improved over thicker parts of the article.
In some embodiments, ductile iron alloys may include, in addition to a majority portion of iron, silicon in an amount of about 3.6% to about 4.2% by weight, copper in an amount of about 0.65% to about 0.85% by weight, and carbon in an amount of about 3.2% to about 3.8% by weight. In some embodiments, ductile iron alloys may further include one or more of manganese in an amount of between about 0.1% to about 0.5% by weight and magnesium in an amount of between about 0.03% to about 0.06% by weight. Other components, generally present in amounts of less than about 0.04% by weight, may include, by way of nonlimiting example, cerium, chromium, molybdenum, nitrogen, nickel, phosphorus, sulfur, antimony, and tin. For example, in some embodiments, ductile iron alloys may include aluminum in an amount of less than about 0.8% by weight and/or molybdenum in an amount of less than about 0.04% by weight.
In some embodiments, ductile iron alloys may include, in addition to a majority portion of iron, an alloy content of less than about 10.5%, less than about 10.0%, less than about 9.5%, or less than about 9.0% by weight. In some embodiments, ductile iron alloys described herein may be substantially free of components which may be used in more expensive ductile iron alloys, such as aluminum, molybdenum, boron, niobium, or other materials and combinations thereof.
In some embodiments, ductile iron alloys may be cast or made into articles which include a thickness in at least one dimension in a range of about 1.0 mm to about 6.0 mm. In some embodiments, within the aforementioned range, an upper thickness boundary may be about 5.0 mm, 4.5 mm, 4.0 mm, 3.5 mm, 3.0 mm, 2.5 mm, 2.0 mm, or 1.75 mm. In some embodiments, within the above range, a lower thickness boundary may be about 1.25 mm, 1.5 mm, 1.75 mm, or 2.0 mm. For example, in some embodiments, ductile iron alloys may be cast into articles which include a thickness in at least one dimension of about 2.0 mm to about 4.0 mm.
In some embodiments, ductile iron alloys may include a desired or controlled microstructure even when cast or made into thin-wall samples or parts of a composition or article. Description of the microstructure of a ductile iron alloy composition may include analysis of one or more sections of a sample and a determination of an amount of a particular chemical form of a component in a sample or part of a sample. Except where otherwise noted, where an analysis of one or more sections or parts of a sample is described, analysis values may be representative of the overall composition of the sample or part of a sample. In some embodiments, the microstructure of a ductile iron alloy may be characterized based on one or more area coverage percentage values occupied by regions or domains of a certain chemical form identified in one or more microscopic sections of a sample. The aforementioned area coverage percentage values may also be used to determine one or more percentages of the volume of a sample occupied by one or more microstructure domains or regions. For example, in some embodiments, a percentage of the volume of a sample that may be occupied by regions or domains indicative of one or more chemical forms including graphite, ferrite, pearlite, carbide, and combinations of the chemical forms thereof may be given.
In some embodiments, the microstructure of a ductile iron alloy may include graphite domains present in an amount of about 5% to about 12% by volume with respect to the total volume of a ductile iron alloy. In some embodiments, the microstructure of a ductile iron alloy may include graphite domains present in an amount of greater than about 5% by volume with respect to the total volume of a ductile iron alloy. Graphite domains may be substantially spheroidal or nodular in shape. For example, graphite domains may be substantially free of flakes such as may typically be found in grey iron.
In some embodiments, the microstructure of a ductile iron alloy may include ferrite domains present in an amount of about 40% to about 70% by volume with respect to the total volume of a ductile iron alloy or volume of a thin-wall part of a ductile iron alloy composition. Ferrite, which may also be referred to as a-iron, includes iron atoms in a body-centered cubic geometry. In some embodiments, within the above range, an upper volume percentage boundary for ferrite may be about 65%, about 60%, about 55%, or about 50%. In some embodiments, within the above range, a lower volume percentage boundary for ferrite may be about 45% or about 50%, about 55% or about 60%. For example, in some embodiments, a percentage of ferrite domains may be about 40% to about 50% by volume with respect to the total volume of a ductile iron alloy or volume of a thin-wall part of a composition or article including a ductile iron alloy.
In some embodiments, the microstructure of a ductile iron alloy may include pearlite domains present in an amount of about 15% to about 50% by volume with respect to the total volume of a ductile iron alloy or volume of a thin-wall part of a ductile iron alloy composition. Pearlite refers to a layered structure including alternating layers of ferrite and iron carbide. In some embodiments, within the above range, an upper volume percentage boundary for pearlite may be about 45%, about 40%, or about 35%. In some embodiments, within the above range, a lower volume percentage boundary for pearlite may be about 20%, about 25%, about 30%, about 35%, or about 40%. For example, in some embodiments, a percentage of pearlite domains may be about 40% to about 50% by volume with respect to the total volume of a ductile iron alloy or volume of a thin-wall part of a ductile iron alloy composition or article including a ductile iron alloy.
In some embodiments, the microstructure of a ductile iron alloy may be characterized based on the total amount or sum of ferrite and pearlite in a sample of the ductile iron alloy. For example, in some embodiments, a sum amount of ferrite and pearlite domains may be greater than about 85% by volume or greater than about 90% by volume with respect to the total volume of a ductile iron alloy or volume of a thin-wall part of a ductile iron alloy composition. In some embodiments, the microstructure of a ductile iron alloy may include an increasing amount of pearlite or increasing ratio of pearlite with respect to ferrite for samples of decreasing wall thickness.
In some embodiments, the microstructure of a ductile iron alloy may include carbide domains present in an amount of no more than about 2%, about 1.5% or about 1.0% by volume with respect to the total volume of a ductile iron alloy or part of a ductile iron alloy.
In some embodiments, one or more microstructure domains or parts of a ductile iron alloy may be substantially independent of thickness or a microstructure may be varied in a controlled manner between parts of a ductile iron alloy that differ in thickness. For example, in some embodiments, an article may include a ductile iron alloy where the microstructure of the alloy changes in transitioning between thicker and thinner parts of the ductile iron alloy. For example, in some embodiments, thicker parts of a ductile iron alloy, such as parts greater than about 6 mm, may include a ferrite to pearlite ratio of at least about 4.5:1 or at least about 5:1. However, thinner parts of a ductile iron alloy may include increased amounts of pearlite and a decreased ratio of ferrite to pearlite regions. For example, in some embodiments, thin-wall parts including a thickness of about 1.5 mm to about 2.5 mm may include a ferrite to pearlite ratio of about 0.75:1 to about 1.25:1. In some embodiments, including embodiments suitable for casting or making thin-wall parts including a thickness ranging between about 1.5 mm and about 2.5 mm, both ferrite domains and pearlite domains may be present in an amount of about 40% to about 50% by volume with respect to the total volume of a part of a ductile iron alloy.
In some embodiments, one or more tests may be used to provide information regarding the properties of materials described herein. For example, the materials herein may be characterized to obtain a measure of ductility. A measurement of a material's ductility may be used to indicate an amount to which the material may be deformed or stretched when placed under tensile stress without fracture. For example, a ductile material may produce a significant elongation in tests where a material is placed under tensile stress including tests defined as in ASTM E-8. Ductility may commonly be expressed as a percentage value expressing the percentage increase in length of a test piece subjected to a tensile force with respect to the original length.
In some embodiments, a ductile iron alloy may be characterized by a ductility of greater than about 1.5%, greater than about 2.0%, or greater than about 2.5%. In some embodiments, ductility may be maintained even when a ductile iron alloy is cast or made as a thin-walled sample. For example, in some embodiments, the ductility of a sample may be greater than about 2.0% even when the sample is made from a mold suitable to prepare a sample within a thickness range of about 2 mm to about 4 mm. The ductility of a thin-walled sample as described above should not be confused with a sample prepared in bulk, where cooling may be more easily controlled, and which may then be cut to a piece or gauge of certain thickness.
In some embodiments, the materials herein may be characterized to obtain a measure of a material's hardness. For example, the hardness of a material may be measured in a test such as the Brinell hardness test described in ASTM E-10-15a. The Brinell hardness test is an indentation test where a steel ball may be forced into a sample at a certain pressure and then measuring the surface area of a resultant indentation. In some embodiments herein, the Brinell hardness (commonly expressed as the Brinell hardness number or BHN) of a ductile iron alloy composition may be between about 250 BHN and about 340 BHN. In some embodiments, hardness may be maintained even when a ductile iron alloy is cast or made as a thin-walled sample. In some embodiments, the Brinell hardness of samples may show a relatively consistent hardness for samples that is nearly independent of sample thickness.
Additional information related to the compositions described herein may be understood in connection with the examples provided below.
In one example, molds were made and used to produce rectangular-solid samples or “finger” castings of different thicknesses. Particularly, a mold was made to create finger castings with various thicknesses ranging from about 2 mm to about 6 mm. Another mold was also prepared to create finger castings in thicknesses of about 2 mm, about 2.5 mm, about 3 mm, about 3.5 mm, about 4 mm, and about 6 mm.
Prepared samples were characterized for hardness using a Brinell hardness test. In addition, sections of the prepared samples were prepared for microscopic analysis. The result of Brinell hardness testing of samples prepared in this Example 1 is shown in
In this Example 2, simulations were run to examine various properties associated with solidification and cooling of a liquid melt during the formation of a ductile iron alloy. The simulations were executed using the MAGMASOFT™ simulation software to predict cooling rates and solidification of metal in some of the embodiments herein. MAGMASOFT™ is a simulation tool supplied by MAGMA GieBereitechnologie GmbH. As shown in
Using the information in
Although the compositions and methods described herein and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition, or matter, means, methods and steps described in the specification. Use of the word “include,” for example, should be interpreted as the word “comprising” would be, i.e., as open-ended. As one will readily appreciate from the disclosure, processes, machines, manufactures, compositions of matter, means, methods, or steps presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufactures, compositions of matter, means, methods or steps.
This application claims the benefit of U.S. provisional application No. 62/424,215, filed 18 Nov. 2016, which is hereby incorporated by reference as though fully set forth herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/061791 | 11/15/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62424215 | Nov 2016 | US |
