CA1046285A

CA1046285A - Composite metal article containing additive agents and method of adding same to molten metal

Info

Publication number: CA1046285A
Application number: CA229,370A
Authority: CA
Inventors: John G. Frantzreb (Sr.); John R. Nieman
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1974-07-15
Filing date: 1975-06-16
Publication date: 1979-01-16
Also published as: US3921700A; DE2531573A1; DE2531573C2; IT1040888B; FR2278772A1; SE7508035L; JPS5132413A; FR2278772B1; GB1504979A

Abstract

COMPOSITE METAL ARTICLE CONTAINING ADDITIVE
AGENTS AND METHOD OF ADDING SAME TO MOLTEN METAL

A B S T R A C T

A composite wire-like structure for adding relatively volatile metallic agents such as magnesium to molten ferrous metal comprising an inner core of said metallic agent, an outer sheath of ferrous metal, and in insulating material disposed between said sheath and said core in surrounding relation to the core. A method is also provided for adding said agent to molten ferrous metal comprising the steps of continuously feeding the composite wire-like structure containing said agent at a controlled rate sufficient to provide a desired amount of said agent in the molten metal.

Description

104~285 Background of the Invention The present invention relates to a composite metal article containing additive agents and1method of adding same to molten metal. More particularly, the invention relates to a composite metal article for adding relatively volatile metallic agents to molten ferrous material as it is being cast.
The addition of alloying and treating agents into molten metal, such as steel, is well known in the art. The addition of such agents in wire~like form is also known and has been described in U. S. Patent No. 3,634,o75 issued January 11, 1972, to J. C. Hoff, and in the October 28, 1971, issue of "Iron Age." Thus, the use of wire-like structures for adding alloying and treating agents to molten metal provides an advantageous means of providing a final desired casting under excellent controlled conditions.
However, certain problems have been encountered where the agent to be added is relatively volatile because of the tendency of the material to be discharged or released prematurely ~hen fed into a ferrous melt. For example, where such treating agents are carried in a sheathed wire, materials such as magnesium melt at a temperature below the melting point of a ferrous melt, and thus become discharged or released before the wire is melted and absorbed into the molten bath.
Efforts have been made to provide a solution to the problem, and United States Patent 3,056,190 issued October 2, 1962 to D. S. Chisholm, et al discloses a method of combining magnesium with silicon to form magnesium silicide and carry the same within a ferrous metal envelope. However, even in th~æ ~orm, the magnesium tends to become dxscharged or released 30 prematurely. In United States Patent 3,741,753 issued ~une 26, 1973 to H. ~alz, et al,~ a method is taught for adding manganese 104~iZ85 to molten steel under vacuum conditions where the manganese is relatively volatile and presents a problem. In accordance with that patent, the manganese is first alloyed so as to reduce its volatility before being used.
Thus, it is seen that both of these patents require an additional alloying step in preparing the material for use as an additive to molten metal.
Summary of the Invention In accordance with one aspect of the invention there is provided a method of adding a relatively volatile metallic agent to molten ferrous metal comprising the steps of continuously feeding a composite wire-like structure containing said agent at a controlled rate sufficient to provide a desired amount of said agent within the molten ferrous metal, said composite wire-like structure comprising an inner core containing said relatively volatile metallic agent, an outer sheath of ferrous metal substantially concentrically disposed to said core, and a particulate insulating material having a melting or subliming point generally at least about equal to the melting point of said outer sheath disposed between said core and said sheath, said insulating material providing a heat barrier sufficient to protect said inner core from delivery prior to the melting of said outer sheath of ferrous metal.
In accordance with another aspect of the invention there is provided a composite wire-like structure for adding relatively volatile metallic agents to a molten metal, comprising an inner core of relatively volatile metallic agent, an outer sheath of non-volatile metal having a melting capability at the temperature of said molten metal, and a particulate insulating material with a melting or subliming point generally at least about equal to the melt-ing point of said outer sheath disposed between said sheath and said core in surrounding relation to said core, said insulating material providing a heat barrier sufficient to protect said core from delivery prior to the melting of said outer sheath.
As used herein, the term "relatively volatile" is intended to embrace substances that exert a substantial vapor pressure at the temperature of the molten metal to which the agent is to be added. The outer sheath will generally be of a metal similar in melting point to the molten metal being

2 -lO~Z~5 treated, and advantageously will be of a similar composition. In other words, the outer sheath will generally not materially affect the composition of the molten metal, but it will be understood that non-volatile alloying agents or other additives could be included in the outer sheath, if desired. The insu-lating material may be any material capable of retaining the core material below its boiling point or the point at which the vapor pressure becomes excessive prior to the melting of the sheath material. Preferably, the core material is also kept below its melting point. In this way, delivery of the core material will occur simultaneously with the melting of the sheath material.
The insulating material should also be a substance which is compat-ible with the molten melt desired, i.e., it should not add any unwanted materials. Thus, a preferred form of insulating material is a particulate substance of either an agent desired to be added, or of a composition sub-stantially similar to the melt, or a combination of both. The invention has been particularly valuable in adding alloying or treating agents to molten ferrous metal, where the temperature of the melt will be of the order of around 2600F. or higher, and where a number of the desired additives are volatile.
For example, it is well known to add magnesium to cast iron or steel in order to provide modular treatement thereof. However, magnesium has a boil-ing point of about 2025F. Accordingly, additions of magnesium have been some-what troublesome in the area now under discussion. Similarly, zinc has a rather low boiling point and where it is desired to add zinc to a molten metal, volatility problems are likely to occur. In addition, certain casting processes are carried out in a vacuum, and in such a case metals such as aluminum and manganese are also sufficiently volatile to cause problems. Thus, these and any other materials, which may be sufficiently volatile to cause a problem, may be advantageously added by using the present invention.

t 104~S

Brief Description of the Drawings A preferred form of the invention is illustrated in the accompanying drawings forming a part of this description, in which:
Figure 1 is an isometric view partly in section of a composite wire-like structure fabricated in accordance with the invention; and ~ igure 2 is a sectional view of the structure shown ln ~igure 1 taken substantially in the plane of line 2-2 of ~igure 1.
~ hile only the preferred form of the invention is shown, it should be understood that various changes or modifi-cations may be made within the scope of the claims attached hereto without departing from the spirit of the invention.
Detailed Description of the Preferred Embodiment Referring now more particularly to the drawings, there is shown in ~igure 1 a composite wire-like structure 11 comprising an inner core 12 of relatively volatile agent, an outer sheath 13 of relatively non-volatile metal, and an insulating material 14 disposed bet~een said sheath and said core in surrounding relation to the core.
Preferably, the structure is used for adding an agent to molten ferrous metal comprising the step of continuously feeding the wire-like structure at a controlled rate sufficient to provide a desired amount of agent in the molten ferrous metal.
In the preferred form, the tubular sheath 13 is also generally composed of ferrous metal with or without an alloying agent, and the insulating material 14 is preferably composed of particulate ferrous material such as iron or steel.
B30 rhe ~ire-like treating agent is used to add alloying agents or treating materials or both by any of the available 10~85 processes for adding wire-like treating agents to molten metal.
~or a more detailed description of such process, the citations given a~ove may be consulted.
In order to better illustrate the in~ention, the ~ollo~ing examples of composite articles are g~ven, and it should ~e understood that these examples are gi~en for illus-trative purposes and are not to be construed as limiting the invention. In the examples, the ~ire core 12 has a diameter of .125 inch and the tubular sheath 13 has a nominal diameter of .375 inch and a wall thickness of O.15 inch.
Example 1.
In this example, the protective ~lanket consists o~
powdered iron, the sheath is steel, and the core is magnesium.
The protective blanket is particularly suitable due to its high specific heat C0.11 ~tu~lb. degree ~ and relatively slow thermal conductivity.

The following parameters setting forth the composition ~ r~
more clearly ~5 given in Table I belo-~:
Table I
~OLUME~100 Ft. C%~ DENSITYWEIGHT (%~
Sheath408.89 cc C 18.8~ x 7.82 a 3~197.5 gms. C 33.3 ~e Powder1~521.67 cc C 70.1~ x 3.92 = 5~964.9 gms ( 62.2 Mg Core241.32 cc ( 11.1~ x 1.80 = 434.4 gms. ( 4.5 Total2~171.88 cc (100.0~ x 4.42 = 9~596.8 gms. (100.0 ~xample 2.
In this example~ the protecti~e blanket consists of a blend of lron powder and graphite, while the sheath is steel and t~e core is magnesium. It is well known that carbon suppresses 30 the reaction of magnesium vapor, and is therefore included to ~o~zf~s control the degree of the reaction. ~t will also be appreciated that the addition of carbon can be tolerated in certain desired ferrous allo~s by starting with a melt capable of utilizing such addition, Moreover, the amount of carbon added by this example is rather small The physical parameters given in Table II
below have been established for the article of this example:
Table II
~LU~E~100 Ft. {~ DENSITY ~EIGHT C~i Shea~h408.89 cc C 18.8~ x 7.82 =3,197.5 gms. ( 37.92 ~e Po~der1,141.25 cc C 52.52 x 3.92 =4,473.7 gms. ( 53.0 Graphite (C~ 380.42 cc ( 17.62 x 0.8~ = 338.6 gms. ( 4.0~
~g, Core241.32 cc ( 11.12 x 1.80 =434.4 gms. C 5.12 Total2,171.88 cc (100.02 x 3.89 =8,444.2 gms. (100.0 ~xample 3 In this example, the protective blanket consists of po~dered magnesium and coke. This is a commercial product produced by the American Cast Iron Pipe Company of Birmingham, Alabama, and contains magnesium and carbon. The product, which is foundry coke filled with approximately 45~ by weight ~ith magnesium, provides a timed release of magnesium vapor in addition to the magnesium contained in the solid core. In Table III
below, the physical parameters of this exa~ple are given;
Table III
~OLU~100 ~t. C~2 D~N~ITY ~ErGHT C~2 Sheath 408,89 cc C 18.82 x 7,82 = 3,197,5 gms. C 65.5 ~ag-Coke Powder 1,521.67 cc ( 70,12 x 0.82 = 1,247.8 gms. C 25.6~
Mg Core 241,32 cc C 11.1~ x 1.80 = 434.4 gms. C 8.92 . . . . . . .
Total 2,171.88 cc C100.02 x 2.25 = 4,879,7 gms. Clob~

The thermal protection afforded by the blanket 14 is determined b~ the ther~al conductivity and particle size of the blanket material. ~04~Z85 Thus, it is seen that the preferred insulating material is a partic-ulate form of one or more of the substances to be added and has a melting or subliming point (temperature) at least about equal to the melting point of the outer metallic sheath. Thus, as illustrated in the preceding examples, iron has a melting point substantially equal to the melting point of the steel sheath while graphite and coke sublime well above the melting point of the sheath. These particles may vary from small powder form to large granular form. Since correspondingly smaller particles present a greater number of non-homogeneous heat transfer surfaces, and'therefore reduced thermal conduc-tivity, the protection provided by any of the above blanket compositions may be varied by an appropriate change in the size of the particles incorporated in the blanket. It has been determined that a wire having the aforementioned dimensions in a composition as described in Example 1 will melt in a 2500F.
bath at a rate of approximately 6 to 7 inches per second. For these condi-tions, the iron powder protective blanket of Example 1 comprising particles lE2 prD r~' d ~s ILP between 40 and 140 mesh ro~i~L~ adequate thermal protection to prevent pre-mature melting and vaporization of the magnesium core. In the event that it is found desirable to increase the thermal protection provided by the 40 to 140 mesh particles, smaller particles could be used. In this way, a slower feed rate could be used.
For large castings that may require wire feed rates about 6 to 7 inch per second melting rate provide4 t~e instant wire, two or more wires may be fed simultaneously into the molten metal bath. Alternatively, the wire may be heated to increase the melting rate. In general, any suitable heating method may be used such as passing the wire through a heated zone or utilizing resistance heating of the sheath.
If resistance heating of the sheath is desired, the blanket and/or the core should be electrically isolated to prevent resistant heating of these components. For this purpose, lO~Z85 electrically non-conductive materials may be selected ~or the blanket or electrically conductive materials may be processed such as by coating to render them non-conductive. Also a non-conductive coating could be provided on the inner surface of the sheath or on the outer surface of the core.
~ rom the above examples, it is seen that the wire-like structure made according to the invention is suitable for use in any of the methods cited above, and may be utilized either with or without additional heating. It is also seen that the composite wire-like structure is capable of protecting the inner core of volatile material from premature release in a reliable manner .
A further benefit is provided by the present invention by virtue of the fact that as the ~ire is melted, the granular or particulate blanket material is absorbed into the molten stream. This absor~tion reduces the temperature of the stream at a small zone contiguous to the end of the wire where the inner core is ~eing deli~ered. This reduced temperature zone permitS cores such as magnesium to be absorbed into the stream in a less volatile manner since the severity of the magnesium reaction 1~ temperature dependent.
In addition, the use of an outer core of a material having a melting point similar to that of the molten metal ~eing treated causes the delivery and reactions such as the magnesium reaction to occur while ~elow the surface of the molten material This further reduces the severity of the reaction.
From the foregoing description, it is seen that an improved composite metal article containing additive agents a~e provided for use in a method of adding alloying or treating 3Q agents to molten metal, It is also seen that an article is provided ~hlch is particularly advantageous for adding volatile additives such as magnesium to molten ferrous metal and the like.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of adding a relatively volatile metallic agent to molten ferrous metal comprising the steps of continuously feeding a composite wire-like structure containing said agent at a controlled rate sufficient to provide a desired amount of said agent within the molten ferrous metal, said composite wire-like structure comprising an inner core containing said relatively volatile metallic agent, an outer sheath of ferrous metal sub-stantially concentrically disposed to said core, and a particulate insulating material having a melting or subliming point generally at least about equal to the melting point of said outer sheath disposed between said core and said sheath, said insulating material providing a heat barrier sufficient to protect said inner core from delivery prior to the melting of said outer sheath of ferrous metal.

2. A method of adding an agent to ferrous metal as defined in claim 1, in which the composite wire-like structure is preheated prior to feeding same into the molten ferrous metal.

3. A method as in claim 1, wherein said relatively volative metallic agent is delivered below the surface of the molten ferrous metal.

4. A composite wire-like structure for adding relatively volatile metallic agents to a molten metal, comprising an inner core of relatively volatile metallic agent, an outer sheath of non-volatile metal having a melt-ing capability at the temperature of said molten metal, and a particulate insulating material with a melting or subliming point generally at least about equal to the melting point of said outer sheath disposed between said sheath and said core in surrounding relation to said core, said insulating material providing a heat barrier sufficient to protect said core from delivery prior to the melting of said outer sheath.

5. A composite wire-like structure as defined in claim 4, in which the insulating material also comprises additional additive agents.

6. A composite wire-like structure as defined in claim 4, in which the sheath is of a metal having a chemistry substantially similar to the chemistry of the molten metal.

7. A composite wire-like structure for adding relatively volatile metallic agents to a molten ferrous metal, comprising an inner core of rela-tively volatile metallic material, an outer sheath of ferrous metal having a melting capability at the temperature of said molten ferrous metal to which the structure is to be added substantially concentrically disposed to said core, and a particulate insulating material having a melting or subliming point generally at least about equal to the melting point of said outer sheath disposed between said core and said sheath providing a heat barrier sufficient to protect said core from delivery prior to the melting of said outer sheath.

8. A composite wire-like structure as defined in claim 7, in which the inner core comprises a nodularizing agent.

9. A composite wire-llke structure as defined in claim 8, in which the nodularizing agent is magnesium.

10. A composite wire-like structure as defined in claim 7, in which the particulate material is iron.

11. A composite wire-like structure as defined in claim 7, in which the particulate insulating material is an alloy of iron.

12. A composite wire-like structure as defined in claim 7, wherein the particulate material is magnesium coke.