US2765225A - Treatment of cast iron - Google Patents

Description

nited States Patent TREATMENT OF CAST IRON Sam F. Carter, Jr., Charles K. Donoho, and Ray A. Dyke, Jr., Birmingham, Ala., assignors to American Cast Iron Pipe Company, Birmingham, Ala., a corporation of Georgia No Drawing. Application October 14, 1953, Serial No. 386,108

Claims. (Cl. 75-27) This invention relates to the production of gray cast iron of improved properties by treatment of molten iron in the ladle with an exothermic flux.

During the course of experiments in the treatment of molten cast iron, it has been found that when calcium compounds, such as the commercial calcium-silicon alloy containing approximately 32% calcium and 63% silicon, also known as calcium silicide, are added to molten iron at abnormally high temperatures of 3000 F. or greater, certain desirable effects are obtained which do not result when the addition is made to iron at a lower temperature, such as those normally found in the ladle. Among the desirable effects thus produced is a compacting of the graphite form which changes the graphite in the solidified iron from flake form to at least partially nodular or spherulitic form.

It has also been found that the improved properties desired in the cast iron are enhanced when a small percentage of rare earth oxides, such as a mixture of the oxides of cerium, lanthanum, etc., used to produce misch metal, is added to the molten iron with the calciumsilicon alloy.

However, in most gray iron foundry operations it is impractical to maintain the required temperature of about 3000 F., because to produce molten iron at that temperature consistently requires electric furnace melting and obviates the use of the conventional cupola favored by the majority of gray iron manufacturers.

It is therefore the principal object of the present invention to provide a new procedure for the production of gray cast iron by treatment in the ladle at normal ladle temperatures which Willresult in substantially the same desirable characteristics in the iron as cast as those obtained by the addition of calcium-silicon alloy to molten iron at the impractically high temperature of 3000 F.

silicon alloy not oxidized by the exothermic reaction to approximately 3000 F. The addition of this exothermic mixture to molten iron at normal ladle temperatures produces substantially the same desirable effects in the iron as those obtained when a similar mixture omitting the sodium nitrate is added to iron at a temperature of approximately 3000 F.

A mixture containing from to by weight of calcium-silicon alloy, from 8% to 25% of sodium nitrate, and from 2% to 34% of rare earth oxides, has been found most effective in improving the quality of gray cast iron, as evidenced by the properties of the solidified iron hereinafter set forth. It has also been found to be important that, within the above recited limits, there should always be an excess of calcium metal above that required to react with the sodium nitrate according to the following reaction:

The combining weights of the calcium and sodium nitrate in this reaction being 80 and 85, respectively, it follows that the ratio of calcium metal to sodium nitrate should be approximately equal to or greater than unity in order to provide the required excess of calcium. A mixture containing the lower limit of 50% of calcium-silicon alloy would normally be expected to yield 32% of 50%, or 16%, of calcium metal. Accordingly, when a mixture containing 50% of calcium-silicon is used, it is preferable to include not over 16% of sodium nitrate.

The nature of the invention will be readily understood from the following illustrative example wherein, as elsewhere in the description and claims, all percentages are by weight.

A base iron of the following average composition was melted in a basic lined induction furnace having a 500 pound capacity:

Percent Total carbon 4.00 Silicon 1.50 Sulfur .02 Manganese .30 Phosphorus r .04 Iron Remainder This base iron was held at a controlled temperature of 2650 F. and poured into several 70 lb. shank ladles to which various additions were made. The following tabulation shows the ladle additions made for three ladles, the

chemical content in per cent of the pertinent elements, and the results of tensile strength and hardness tests on r more. 50 1" diameter test bars cast in dry sand molds.

Tensile Brinell Ladle No. Ladle Addition St S Ca Ce Strength, Hardness p. s. l.

3% Exothermle flux( 2. 63 013 .0018 015 65,200 179 2% Exothermle fluxfi) 2. 36 .015 0007 015 57, 900 2% Cast 2. 49 016 0004 None 7 20, 900 111 b By spectrograph.

This object, and others which will be apparent from the following description, may be achieved in accordance with the present invention by treating molten cast iron in the ladle, at normal ladle temperatures, with a mechanical mixture of finely granular calcium-silicon alloy, rare earth oxides and sodium nitrate.

We have found that mechanical mixture of an oxidizing agent, such as commercial sodium nitrate, with calciumsilicon alloy and rare earth oxides produces an exothermic flux which, upon addition to molten iron at ordinary ladle temperatures of 2400 F. to 2700 F., evolves suflicient heat to raise the temperature of the excess of calcium- In the experiment represented by the above tabulation, ladle No. 7 was the control ladle wherein an addition of straight calcium-silicon alloy was made to bring the silicon content of the iron into the same range as that produced by addition of the exothermic flux mixture of the present invention. It will be noted that in the case of ladle No. 7 (a) sulfur reduction was less effective, (b) calcium recovery was not as great, (0) no cerium was found in the iron, and (d) tensile strength and hardness were both very significantly lower than in the metal from ladles Nos. 3 and 5 which were treated with our flux mixture containing 78.1% of calcium-silicon alloy, 15.7% of sodium nitrate and-6.2 of rare earth oxides.

Castings have also been made of small pipe fittings from iron obtained by treating eight2000 lb. ladles of molten iron from a 36" cupola with a 2 /2% addition of an exothermic flux mixture of the character above described. These castings had an average tensile strength of about 60,000 p. s. i. and a Brinell hardness of about 130. Similar results and eifects have been obtained by treating other 'cupola melted base irons, as Well as 'electric arc'melted irons.

In the above examples, additions of theexothermic flux mixture in amounts of from 2% to 3 of the total weight of the molten iron were found highly effective for producing the desired results. With base irons of other compositions the amount of the mixture added may vary betWeen'0.5% and 5.0% for maximum eifectiveness. Variation of the composition of the mixture Within the preferred range of from 50% to 90% of calcium-silicon alloy,

from 8% to 25% of sodium nitrate, and from 2% to 34% of rare earth oxides, may also necessitate the use i of a mixture addition either greater or less than the 2% to 3% amounts found effective in the foregoing examples. For-best results, it has been found that the separate ingredients of the flux mixture should be pulverulent or finely granular, such as 8 mesh or finer, in order to allow thorough mixing and intimate contact of the diiferent constituents.

The proportions of the ingredients of the flux mixture may be varied to suit difierent base iron analyses, iron temperatures and mechanics of introduction, and still provide the same improvement in characteristics of the cast iron. Although, for economic reasons, the commercially available calcium-silicon alloy is used as the preferred source of calcium in the flux mixture of the present invention, calcium metal, or other metallic alloys high in calcium content, may be used instead with substantially the same results. If calcium metal is used in place of the calcium-silicon alloy, an additional inoculant, such as ferro-silicon, should be included in the mixture. It will also be understood that other'oxidizing agents equivalent in oxidizing effect to sodium nitrate, such as potassium nitrate and potassium chlorate, may be substituted for the sodium nitrate presently preferred as the .oxident of ounfiux mixture.

What is claimed is:

1'1. An exothermic flux for the treatment of molten cast iron containing calcium, rare earth oxides and an oxidizing agent, wherein the amount of calcium is in excess of that required to react 'exothermica'lly with the oxidizing agent.

2. An 'exothermic flux for the treatment of molten cast iron containing a major proportion of calcium silicide and minor proportions of an oxidizing agent and rare earth oxides. 3. .An-exotherm-ic flux for the treatment of molten cast iron containing from about 8% to about 25% of an oxiiron containing from about 8% to about of sodium nitrate, from about 2% to about 34% of rare earth oxides, and an amount of calcium metal in excess of that required to react with the sodium nitrate according to the reaction 5. An exothermic flux for the treatment of molten cast iron consisting of a finely granular mechanical mixture of calcium-silicon alloy, sodium nitrate and rare earth oxides.

6. An exothermic flux for the treatment of molten cast iron consisting of from about 50% to about 90% of calciur'n-silicon alloy, from about 8% to about 25 .of sodium nitrate, and from about 2% to about 34% of rare earth oxides.

7. An exothermic flux for the treatment of molten cast iron consisting of approximately 78% calcium-silicon alloy, approximately 16% sodium nitrate, and approxima-tely'6% rare earth oxides.

8. An-exotherinic fiux for the treatment of molten cast iron consisting of a finely granular mechanical mixture of sodium nitrate, rare earth oxides, and a calciumcompound where-in the amount of calcium metal is in excess of that required to react with the sodium nitrate according to the reaction 7 which includes the step of adding to molten iron'an exdizing agent, tromabout 2% to about 34% of rare earth oxides, and the remainder a calcium compound wherein the amount of calcium metal'is in excess of that required to react exothermic-ally with the oxidizing agent;

4. An exothermic flux for the treatment of molten cast othermic tlux mixture containing calcium, rare earth oxides, and an oxidizing agent, the amount of calcium in said mixture being in excess of that required to react exothermicallywith the oxidizing agent. a

10. A process according to claim 9 wherein'the temperature of the molten iron is not more than about'2700 F.

11. .A process according to claim 9 wherein the amount of fiuxmixture added is from about 0.5% to about 5.0% of the total weight of the *molten iron.

12. A process'according to claim 9 wherein the amount of :flux mixture added is from about 2% to about 3% of the total weight of "the molten iron.

'13. .Aprocess for improving the properties of cast iron which includes the step of adding to molten iron a finely granular exothermic flux :mixture containing from about 50% to about 9 0% of calcium-silicon alloy, from about 8% .to'a'bout'25% of sodium nitrate, and from about 2% to about 34% of rare earth oxides.

I 14. A' :process according to claim 13 wherein the temperature of the molten iron is from about 2400 F. to about 12700 F.

15. Ap'rocess according to claim 13 wherein the amount of. flux mixture added is 'fromlabout 2% to about 3% of the total weight of the molten iron.

References Cited in the file of this patent UNITED STATES PATENTS 2,249,336 Udy July 15, 1941 2,488,511 Morrogh Nov. 15, 1949 2,643,949 Tisdale June 30, 1953 2,662,820 Crome Dec. 15, 1953

Claims (1)

1. 3. AN EXOEHERMIC FLUX FOR THE TREATMENT OF MOLETEN CAST IRON CONTAINING FROM ABOUT 8% TO ABOUT 25% OF AN OXIDIZING AGENT, FROM ABOUT 2% TO ABOUT 34% OF RARE EARTH OXIDES, AND THE REMAINDER A CALCIUM COMPOUND WHEREIN THE AMOUNT OF CALCIUM METAL IS IN EXCESS OF THAT REQUIRED TO REACT EXOTHERMICALLY WITH THE OXIDIZING AGENT.