US2582079A - Composition for addition to cast iron or steel - Google Patents

Description

Patented Jan. 8, 1,952

COIHPO SITION FOR- ADDITION TO CAST IRON OR- STEEL Jerome Strauss, New York, N. Y., and Daniel Leonard Edlund, Bethel, Pa., assiznors to Vanadium Corporation of America, New York, N. Y., a corporation of Delaware No Drawing. Application September 7, 1950, Serial No. 183,662

Claims. 1

This invention relates. to' a novel composition of matter for the control and improvement of the physical properties of cast iron and for other uses, such as the treatment of steel in the molten state.

Cast iron is a generic term which includes gray irons, white cast irons, chilled cast irons and malleable irons. metals depend in part upon chemical factors (principallythe percentages of carbon and silicon) and in part upon physical factors, both as influenced by conditions related to the manufacturing methods. This is so because cast iron is essentially the product of a process and the influence of the process details are observed in the qualities of the product. Alloying is employed to alter the properties of some cast irons;

also some iron castings both alloyed and not :alloyed are subjected to thermal treatments to produce desired results in castings for specific uses. The physical structure (i. e. the nature and distribution of the micro-constituents), and consequently the properties of the metal are The properties of these' influenced not only by these several factors but tion range.

The cast iron which is most used commercially for construction applications, however, is gray iron, but this term actually covers a wide range of compositions with corresponding widely varying properties. The composition of gray iron is usually confined within the limits .50 to 2.75% silicon and 2.70 to 3.60% total carbon. Within this range of composition the tensile strength may vary from 15,000 to 60,000 pounds per square inch and occasionally higher.

While a part of the carbon present in gray cast iron may be in the combined form as iron carbide, the greater amount is present in elemental form as graphite. The relative amounts of free carbon and combined carbon, as well as the shape, size and distribution of the particles are dependent upon the remaining chemical com-- position of the iron and the influences referred to above, namely, maximum temperature in the liquid state, rate of cooling during and after solidification, and types of heat treatment, if any, applied to a solidified casting.

Elements incidental to the production of cast iron may add or detract from its properties, such as strength. toughness and ductility. Sulphur, for example, is usually kept as low as possible because while it increases the strength of the iron to some degree, it very markedly reduces ductility. Control of sulphur depends, however, on raw materials and process and often it cannot be held to very low values because only highsulphur raw materials are available, the cost of electric furnace refining may not be permissible and chemical treatment may not be adequate or sufilciently uniform. Phosphorusoccasionally strengthens iron but in large amountsrenders it quite brittle.

Certain elements usually considered as alloying agents have been added to control the structure and properties of cast iron. In some cases the addition of such alloys results in one property being improved to the detriment of another, for example, strength may be improved but the toughness of the iron be reduced unless some adequate form of heat-treatment is provided to retain the toughness. In other cases improvement in strength is accompanied by reduction in the machinability of the iron; in some of these cases heat-treatment, such as annealing, may restore the machinability.

It is known that magnesium added to iron which would otherwise cast gray or nearly so contributes to this iron high strength and some ductility. The ductility has in some cases been found to be increased by an annealing treatment with relatively little sacrifice in this superior strength.

However, serious difficulties have beset attempts to make this magnesium practice one that would provide with assurance successive reproduction in continuous manufacturing operations of iron articles of high strength or high strength and good ductility. The boiling point of magnesium being considerably below both the melting temperatures of those metals with which it is preferably combined for making addition agents and below the temperatures at which cast iron is tapped and poured, causes extreme difficulty in controlling the overall recovery of magnesium from raw material to the finished cast iron product.

The boiling point of magnesium is about 2030 F., which results in very high losses due to vaporization of the magnesium when it is added to molten copper and molten nickel to produce such addition agents as 20% magnesium and 80% copper, and 20% magnesium and 80% nickel. Further difliculty is presented when it is attempted to introduce iron into these compositions. Iron is a very desirable carrier metal when magnesium is to be introduced into iron alloys, such as gray cast iron or steel. The introduction of iron into the copper or nickel base alloys mentioned above, however, only increase the already high losses of magnesium during manufacture.

Since the temperature of cast'iron flowing from the cupola is normally in the range of 2300 to 2800 F., it is obvious that additional losses will be encountered through vaporization when magnesium alloys are added to iron. When pure metallic magnesium is added to cast iron at such uring temperatures, its volatilization can be e plosive in character. Magnesium continues to v porize as long as the iron remains molten and the time element combined with the initial violent reaction results in variable losses and properties that vary beyond the limits of satisfactory commercial control. The use of alloy addition agents, such as the 20% magnesium and 80% copper, and 20% magnesium and 80% nickel compositions previously mentioned, does not satisfactorily overcome these difliculties. For example, if the cast iron to which such alloys are added is on the high side of the above temperature range, a violent reaction will occur with high losses of magnesium through volatilization as well as loss of metal and danger to the operators through spattering of the molten cast iron. If, on the other hand, the temperature of the iron is low, -incomplete solution may occur, re-

' sulting in segregation and in variation in both structure and properties throughout the product.

We have discovered in the course of extended experiments directed toward the development of a commercially satisfactory practice for producing magnesium-containing cast iron of predictable and reproducible properties that certain combinations, preferably in alloy form, of magnesium, silicon, manganese and iron aflord an unexpected means of simplification of these problems. Primarily, our discovery consists in a certain critical combination in the proportions of magnesium, silicon, manganese and iron, which substantially increases the recovery of magnesium in manufacture of the addition a ent as well as when this agent is added to' molten cast iron. This combination of effects results in a substantial cost saving. More significant, however, is the tact that, when using aloys of compositions within the limits of our invention, the desired improvements in the finished cast iron are obtainable more readily and with much greater regularity. While cast iron in which substantially all of the carbon is in the form of spheroids has been produced frequently, it has been diilicult to obtain structurally perfect castings under production conditions with a variety of designs, melting equipment, raw materials and other foundry conditions. An infinitely closer approach to perfection can be attained in the use of the alloy herein described. The mechanism of the behavior of this magnesium-silicon-manganeseiron composition within the critical ranges hereinafter set forth has not been fully explained but the results have been obtained with such regularity both in production of the alloy and in its use with gray cast iron over a substantial amount of production and a large number of different foundries-that a distinct advance in the art through its use has been established.

The ranges of composition which have produced the advantages described are 5 to 25% magnesium, 20 to silicon, 2 to 12% manganese, the balance substantially all but not less than 20% or more than iron, except for customary impurities and minor elements, such as carbon, sulphur, phosphorus, etc., which generally do not exceed a total of 4%. Nickel is not included among these minor elements; it is present today in some pig irons and in most iron and steel scrap and hence may be present in these alloys up to about 2% and is not detrimental to the functioning of the alloys. In our compositions, aluminum is a detrimental element. It should be kept below 1% and preferably below 0.6%. Within the ranges of composition already cited, we prefer to restrict the relationship of the several elementssothat the ratio of silicon to magnesium is not less than about 1:1 and not greater than about 6:1, and the ratio of magnesium to manganese is not less than 1 :1 and not greater han 6:1. Following are four examples of co ositions within these critical ranges and posse ing the preferred ratio of elements which were anufactured and used successfully:

The definite advantages obtained with an iron content between 20% and 60% are twofold: the iron increases the specific gravity of the alloy, aiding it to penetrate the molten metal, and it raises the melting point, thus slowing down the rate of solution in the molten cast iron, eil'ecting more uniform distribution throughout the mass. In addition to melting too rapidly in the absence of iron, the cost of production becomes excessive if the iron is held below about 20%. If the iron content is permitted to exceed 60%, then the magnesium losses during manufacture of the alloy become excessive and very costly, and the rate 'of solution of such alloys in molten cast ironis too slow and their effectiveness is greatly impaired.

By use of alloys having compositions within the described limits, superior results have been achieved in respect to formation of nodules of graphite in cast iron and reduction of shrinkage of cast iron, over and above what had been previously attained by the best known and most widely used alloy, namely, 80% nickel and 20% magnesium, together with the development of maximum amounts of tensile strength.

The amount of alloy added to molten cast iron to be cast into gray iron castings varies with the nature of the iron (as influenced by the raw materials used and the conditions of processing during melting), the maximum temperature attained by the molten iron, the temperature at which the addition is made, the sulphur content of the iron and perhaps other factors. In general, the addition approximates 0.12% to 0.20% of contained magnesium plus an amount of contained magnesium equal to 1% times the su1- compositlon, ofthe alloy being used as well as the various-.factorsinfluencing the character ofthe molten cast iron, as-pointed out'above, and

the method of adding the alloy to the molten iron. It is, however, a good starting. point in establishing the practice in a specific foundry while on a, particular melting practice so that a limited-amount of experimentation varying the addition upward and downward'readily establishes the optimum-addition required. In general, the amount of alloy added should be suchtas to' leave-in the solidified cast. iron a total magnesium content of'0.04 to 0.10%, preferably 005 to Another-advantage possessed by these alloy ade ditiorl magnesium during both the manufacturing process and during use in the treatment of gray iron. Alloys within these ranges of composition have the peculiar characteristic of being dissolved sumciently easily in cast iron that they may be effectively used at the lowest customary pouring temperatures which characterizemodem commercial foundry practice. On the other hand, solution is sumciently-slow that the alloy and its components will be uniformly distributed throughout the melt and the magnesium will not be lost so rapidly as to prevent it from exerting its influence throughout the entire mass of cast iron. No additional care and no modifica-.

tions' of prior practice are required. the. addition of the alloy to iron that would otherwise cast gray, and of low to moderate strength, being the sole requisite. The reason or reasons why these alloys melt at suchcrictical rates so as to be usable at full effectiveness over such a wide range of casting temperatures, but still melt slowly enough so that all ingredients, and particularly the magnesium are distributed uniformly throughout the cast iron have not been clariagents isthat of increased recovery offled but the observations have been sufilciently numerous to be conclusive.

When alloys within composition ranges of the present invention are added to cast iron, increases in strength are secured ranging from about to well over 100%, and the brittle iron becomes ductfle, with greatly increased resistance to shock and sudden impact. In improving the mechanical properties to such high de rees the alloys covered by this invention regulate the microstructure of the gray iron so as to produce nodular-graphite in the required amounig usuallyto the extent of complete conversion of the carbon to this-form.

The presence of manganese in these alloys gives rise to two outstanding and unpredictable effects. The first is the contribution toward the recovery of magnesium in the preparation of the addition alloys. The second is the part played by manganese as a component of these alloys and their effects upon the cast iron being treated. In this second case the contribution by 6 sample 1 An outstanding, example of the effects or; the

alloys. of: this. invention upon cast iron wasobtain'ed' when a; particularly weak iron, 1. e. low intensile strength and hardness, was treated with: an alloycontaining: 21.25% magnesium, 34.42% silicon, 4.09% manganese and the balance iron. Analysesof'the untreated and treated compositions were as follows:

I,C, vMn Bi 5 P Mg,

Untreated 3150 0.50 2.70 0.000 0.084 .1.... MgTreated.......... 2.73 0.53 3.31 0.010 0.085 0.096

The tensile strength and hardness of two bars each of treated and untreated portions of the melt, are given below:

Example 2 An addition alloy according to the invention and containing 21% magnesium, 34% silicon, 4% manganese and the balance iron was added to agray iron containing- Per cent- Total carbon 3.39

Silicon i.. 2.27

Manganese .26 Phosphorus .024 Sulphur .01

An amount of the addition alloy was used to calculate to an addition of 315% magnesium based on the weight of the iron to which it was added.

The physical. properties of the treated cast iron were:

Tensile strength lbs. per sq. in.-- 62,400 Yield strength. lbs. per sq. in.-- 36,300 Elongation per cent 10 Reduction of area do- 7.1

Brinell hardness 163 Example 3 The addition alloy used in this example contained 24.30% magnesium, 37.79% silicon and 4.06%manganese; the balance being iron. Various quantities of this addition alloy were added to an electric furnace iron having the analysis:

Per cent Total carbon 3.73 Silicon 2.61 Sulphur .04 Phosphorus .15 Manganese .86

In all cases where the addition of the alloy exceeded 1.50%, the iron was practically all nodular. Tensile tests showed results ranging from 61,450 to 77,100 pounds per square inch. In each case the sulphur was reduced to practically 01%.

Methods of sampling and analysis currently in use show after the addition of the alloys of this invention that the carbon content and the sulphur content of the untreated irons have been reduced by the treatment. The reduction in 7' the sulphur content is no doubt due to the combination of magnesium with at least part .of the sulphur and its removal as a slag or a slag forming consituent. The reason for the change in the carbon content is not so obvious and it may be that the change is apparent rather than real due to the diiference in the form and the distribution of the carbon and creating a necessity for difierent methods of sampling and analysis than those commonly in use. Completely satisi'actory procedures have not yet been devised or discovered. I

It has heretofore been an absolute requiremen in the production of cast iron having all or nearly all of its carbon in the form of spheroids gang gm be added following the addition of the m esium alloy a second addition rich in silicon, such as ferrosilicon, the amount in most cases be-v ing substantial. In the use of the alloys of this invention such final addition of ferrosilicon is not a necessity and -may be dispensed with in many cases. The amount of silicon represented by the addition of the alloys according to our invention is very much less than that which would be added according to prior art methods subsequent to the incorporation of the magnesium alloy. Even in those instances where a final addition of silicon-rich alloy is made, the total silicon content represented by this addition plus the silicon content added by means of the magneslum-silicon-manganese-iron alloy is distinctly less than the silicon added as a late ferrosilicon addition according to prior art methods. When the late i'errosilicon addition is actually employed in conjunction with the alloys of this invention, the maximum amount of ferrite in the microstructure may be attained with a minimum silicon addition, leaving not more than a very small amount of pearlitic structure in the matrix and through this means advantage in respect of machinability and reduction in the wear on tools used formachining will result. Production of an iron with minimum pearlite also results in maximum ductility of the iron composition. While fairly satisfactory results can be obtained in some instances in the treatment of cast iron with compositions of matter within the ranges previously specified, not in the form of alloys but in the form of mechanical mixtures, much better results are obtained by the use of these compositions in alloy form.

Alloys of this invention have also been added to molten steel for lowering the sulphur content oi the steel. For example, steels have had their 8 sulphur content decreased from about .030 to about .020% by the use of these alloys.

The invention is not limited to the preferred embodiment but may be. otherwise embodied or practiced within the scope oi. the following claims.

We claim: l. A composition of matter for addition to iron or steel, said composition comprising about to magnesium, about 20 to 45% silicon and about 2 to 12% manganese, the balance being substantially all iron, the iron being in an amount between about 20 and 60%.

2. An alloy for addition to iron or steel, said alloy comprising about 5 to 25% magnesium, about 20 to 45% silicon and about 2 to 12% man ganese, the balance being substantially all iron, the iron being in an amount between about 20 and 60%. 3. A composition of matter for addition to iron or steel, said composition comprising about 5 to 25% magnesium, about 20 to 45% silicon and about 2 to 12% manganese, the ratio of silicon to magnesium being between about 1:1 and 6:1, the balance being substantially all iron, the iron being in an amount between about 20 and 1 4. A composition of matter for" addition to iron or steel, said composition comprising about 5 to 25% magnesium, about 20 to 45% silicon and about 2 to 12% manganese, the ratio of magnesium to manganese being between about 1:1 and 6:1, the balance being substantially all iron, the iarm being in'an'amount between about 20 and 4. 5. A composition of matter for addition to iron or steel, said composition comprising about 5 to 25% magnesium, about 20 to 45% silicon and about 2 to 12% manganese, the ratio of silicon to magnesium being between about 1:1 and 6:1, the ratio of magnesium to manganese being between about 1:1 and 6:1, the balance being sub stantially all iron, the iron being in an amount between about 20 and 60%.

. JEROME STRAUSS.

DANIEL LEONARD EDLUND.

REFERENCES C ITED The following references are of record in th file of this patent:

Claims (1)

1. A COMPOSTION OF MATTER FOR ADDITION TO IRON OR STEEL; SAID COMPOSITION COMPRISING ABOUT 5 TO 25% MAGNESIUM, ABOUT 20 TO 45% SILICON AND ABOUT 2 TO 12% MANGANESE, THE BALACNE BEING SUBSTANTIALLY ALL IRON, THE IRON BEING IN AN AMOUNT BETWEEN ABOUT 20 AND 60%.