US2683661A - Fine grain iron and method of production - Google Patents

Description

Patenteol July 13, 1954 UHTED STATES ATENT OFFICE FINE GRAIN IRON AND METHOD OF PRODUCTION ration of Delaware No Drawing. Application October 31, 1951, Serial No. 254,191

10 Claims.

The invention relates to a method for the production of iron and steels and to the products obtained thereby, and includes correlated improvements and discoveries whereby the properties of iron and steel are decidedly improved.

Further, the procedure may be employed with killed steel of alloy or of carbon grades, and the steel may be manufactured by conventional methods.

Steels, in the course of their manufacture absorb certain undesirable gases and substances which may impart oor engineering properties and may make the material difficult to shape or work.

A principal object of the invention is to provide a method whereby the foregoing disadvantages may be substantially wholly obviated.

A further object of the invention is to provide a method in accordance with which an iron and steel may be produced as a fine grain product, and having distinctive corrosion and oxidation resistance and high impact values at room and at low temperatures.

Another object of the invention is to provide a process for the manufacture of a steel having a relatively lowered sulphur content, and with respect to which the nitrogen content has been eliminated or materially reduced.

A particular object of the invention is the provision of a method whereby the foregoing are achieved, and a product, namely an iron or a steel of enhanced properties, is obtained through the utilization of a composition containing a rare earth metal, preferably a plurality of rare earth metals with cerium being present'in a preponderant amount.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

For the production of a steel which is highly resistant to corrosion and oxidation, there are two generally accepted methods.

One method utilizes one or more of a number of commonly accepted alloys, and usually a minimum of 12% is employed. These alloys contain a member of the group consisting of molybdenum, chromium, nickel, cobalt, titanium, tantalum, columbium and zirconium with varying amounts of silicon, copper, aluminum and manganese.

The second method uses the minimum amount of those metals and produces a grain in which the interstitial spaces are reduced in size and, thus,

2 reduce the opportunity for corrosive and oxidation agents to attack the steel.

In view of the fact that the alloys which are usually employed in producing alloy and carbon grade steels are in great demand and as such are hard to obtain at all times, we decided to attempt to improve these types by producing a fine grain in the steel and to do this the molten steel has been treated with an alloy which is made up essentially of metals of the rare earth group.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the iron or steel possessing the features and properties, which are exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

In the practice of the invention, the properties of iron and steel, especially regular alloy and carbon grades, e. g, 4300; 2300 and 3100 a number of which are known as S. A. E. types, and other alloy-steel varieties designated as constructional steels, are decidedly improved by the addition of an appropriate amount of a composition containing a rare earth metal, either singly or in compatible combination, and suitably that which is now known in the trade, and which we designate herein as L-metal which contains a mixture of rare earth metals, and suitably containing a preponderant amount of cerium and of the following approximate percentage composition: cerium 50.00; lanthanum 30.00 and the balance various rare earth metals as praseodymium, samarium, neodymium, etc, and iron, to a melt, that is to the liquid iron or steel.

More especially, the procedure comprises preparing an iron containing melt, adding metallics, which may contain chromium, manganese, molybdenum, nickel, columbium, titanium, tantalum, cobalt, zirconium and silicon, thereto during furnacing, deoxidizing utilizing e. g. ierro silicon, calcium silicon, ferro manganese, and the like, and then adding the composition which, more particularly, contains a plurality of rare earth metals having cerium present in a preponderant amount.

While the addition of the rare earth metal may be eiiected at difierent phases of the melting and furnacing, a suitable procedure is to add it to the ladle either before or after deoxidizers havebeen added, and desirably before the ladle is onehalf full, that is while the ladle is less than one- 3 half full. However. another and somewhat preferred procedure is to place the material in the bottom of a ladle and cover over with a deoxidizer such as calcium silicide, or it may be placed in a thick walled pipe and the ends closed, and then placed in the bottom of the ladle where the liquid ferrous metal may be poured on top of it. Either method delays the action of the L-metal so that there will be suflicient liquid metal to allow a proper reaction therewith.

Further, we have found that when about 3 pounds of the L-metal, or its equivalent, have been added per ton of iron or steel a very fine grain structure results. However, depending on the pouring temperature, the size of the mold, and the analysis desired, an amount of about 1 pound of the L-metal to the ton has given beneficial results.

In the manufacture, the usual accepted good practice is employed and in addition to it, care is taken to see that the melt is properly deoxidized, that is, poured at a temperature which has been found to be lower than usual practice because of the fact that the treatment with the rare earth metal seemingly increases the fluidity of the treated metal.

Various quantities of rare earth metal have been tried and found to be effective. However, when excessive amounts of the metal have been added, the product has been found to be extremely dirty and as such offered low resistance to oxidation or corrosion. Our method makes eflicient use of the L-metal and at the same time utilizes only a very small amount. We have definitely found that not more than three pounds of L-metal per ton need be used provided that it is added to the melt as herein described and especially in the preferred manner.

As an illustrative embodiment of a manner in which the method may be carried out, the following example is presented:

A heat of a manganese-molybdenum steel was made having the following analysis expressed as percentages:

Carbon 0.30 Manganese 1.80 Sulfur 0.024 Phosphorus 0020 Silicon 0.26 Molybdenum 0.47 Rare earth metal, the remainder iron 0.005

The charge consisted of:

Pounds Scrap 4,500 Pig iron 4,200

ter the melt had been formed and during furnacing, there were added:

Pounds Molybdenum oxide (M003) 75 Spar Scale 10 Ferro Silicon (75% FeSi) 60 Ferro Manganese (82% Mn) 190 To the ladle, prior to and during pouring, and suitably prior to the ladle being half full, there were added:

Pounds Ferro Manganese (85% Mn) 95 Alsifer 26 Grainal 17 Calcium Silicide 12 L-metal 8 Alsifer is a carbonless alloy of aluminum, silicon and iron having the following approximate composition: aluminum 20%; silicon 40%, and iron 40%. Grainal is an alloy containing aluminum, zirconium, titanium and boron of the following approximate percentage composition; aluminum 13.00; titanium 20.00; zirconium 4.00; manganese 8.00; boron 0.50; silicon 5.00; and the balance iron.

The slag was held back and the heat was tapped after a short interval, and. the pouring temperature was about 2690 F. The ingots were permitted to stand for about one hour after which they were stripped and placed in the soakin'g pits. After a period of 10 to 12 hours the ingots were cooled on a strip mill to billet size, and a thorough examination showed that the edges were not cracked.

Steels produced by the foregoing procedure may vary somewhat in the amounts of the various constituents, e. g. expressed as percentages: carbon 0.25-0.32; manganese 1.6-1.0; sulfur 0.04 maximum; phosphorus 0.04 maximum; silicon 0.2-0.3; molybdenum 0.4-0.5, and rare earth metal 0003-0009, the remainder being iron.

The method herein described for the production of iron and steel leads to the formation of a fine grain structure which enhances the resistance to corrosion. Since there is only a small amount of the L-metal remaining in the treated metal, it is believed that this condition is due to the small space between the grains which results from the reduction of the original dendritic structure and, hence, offers less interstitial space for attack.

The results show that there are several advantages which accrue to the user of L-metal when utilized in the manner described herein. Thus, one may use a standard material and obtain decided benefits due to its resistance to corrosion and oxidation. Further, the analysis may be varied so that less of a scarce and costly alloy will be employed to obtain the same results as the same untreated material with a larger amount of the alloy.

In the melting and casting of the iron and steel, certain precautions have been found to be beneficial and are recognized as being proper practice. For instance, a good pouring temperature would be about 2700 F. We have also found that the melt, after treatment in the ladle, should be poured immediately to insure quick freezing of the metal, and in some instances a thick walled ingot mold serves to effect the quick freezing. Due to the fact that slags cause reaction at the point of contact with the metal, it has been found that chilling the slag reduces such action, and this may be accomplished by the addition of slag making materials such as dolomite, burnt lime, and the like. Among the advantages attending the use of L-metal, are a reduction of the sulfur content and the obtention of a fine grain as cast. These occasion higher impact values at room and at low temperatures, and such values are especially valuable in those types of steel which must function properly and safely at low temperatures, e. g. those in the arctic and antarctic regions.

Further, when molten ferrous material has been treated with L-metal, or a metal made from a combination of rare earths, a fine grain results and later certain definite improved physi-'- cal and chemical characteristics are obtained. When steels are made in this way, it is highly desirable to make the steel so that this fine grain,

as cast, persists. This is accomplished by casting at a relatively low temperature, e. g. at temperatures from about 2710 F. to about 2780 F. and tapping or teeming as quickly as possible to solidify the material.

W e have observed that if, after treatment with a substance which will endow it with these fine grain properties, the metal is allowed to remain in a liquid state for a long period of time, the fine grain gradually disappears and the resultant metal compares in almost every way with untreated metal. Thus, when a melt is treated with L-metal and subsequently cast, as a sand casting, whose solidification rate is very slow, a very small reduction in the grain size is obtained which indicates that retention for a long time after treatment in a liquid state allows the force which produces the fine grain to be dissipated and, hence, the line grain qualities are not attained.

A distinctive characteristic of this treatment is that only a small amount of the rare earth metal is used, and this is such that analysis of the finished steel shows that the quantity added is no longer existent and that the quantity present is not greater than 0.018%, e. g. cerium. The rare earth metal content desirably may range from about 0.003% to about 0.009%, and suitably will be about 0.005%. This indicates that it is not the presence of an alloy which confers this fine grain property but rather an effect which is considered to induce nucleation.

Metallurgical examination of the results of the treatment or" liquid ferrous material with L- inetal leads to the belief either that the L metal is oxidized, or that it forms a compound with some of the non-metallics or with occluded gases which offer nuclei for crystallization similar to the result of adding titanium to aluminum, whereby a fine grain is obtained.

It may be added, somewhat by way of recapitulation, that a steel having a tendency ordinarily to solidify in large dendrites, has a much smaller grain size as cast than the untreated metal. This finer grain size increases resistance to corrosion, and. gives a relatively high impact value at room and at low temperatures.

Furthermore, the addition, as above indicated, of a rare earth metal either singly or in compatible admixture effects a reduction in the sulfur content, and such reduction results in enhanced physical properties and distinctive cleanliness in the product.

Since certain changes in carrying out the above process, and certain modifications in the product which embody the invention may be made without departing from its scope, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

l. A method for the production of iron and which comprises preparing an iron containing melt, adding metallics thereto during furnacing, deoxidizing, incorporating a composition containing a rare earth metal, in an amount not more than three pounds per ton, pouring and quick freezing.

2. A method for the production of iron and steel which comprises preparing an iron containing melt, adding metallics thereto during furnacing, deoxidizing with the addition, and in conjunction therewith, of a composition containing a rare earth metal, in an amount not more than three pounds per ton, pouring and quick freezing.

3. A method for the production of iron and steel which comprises preparing an iron containing melt, adding metallics thereto during furnacing, deoxidizing, incorporating a composition containing a plurality of rare earth metals, in an amount not more than three pounds per ton, pouring and quick freezing.

4. A method for the production of iron and steel which comprises preparing an iron containing melt, adding metallics thereto during furnacing, deoxidizing with the addition, and in conjunction therewith, of a composition containing a plurality of rare earth metals, said composition containing cerium in a preponderant amount, in an amount not more than three pounds per ton, pouring and quick freezing.

5. A method for the production of iron and steel which comprises preparing an iron containing melt, adding metallics thereto during furnacing, deoxidizing substantially completely, then adding a composition containing a plurality of rare earth metals, said composition containing cerium in a preponderant amount, and being added in an amount not more than three pounds per ton, pouring and quick freezing.

6. A method for the production of iron and steel which comprises preparing an iron containing melt, adding metallics including a member of the group consisting of chromium, molybdenum, manganese, nickel, columbium, titanium, tantalum, cobalt, zirconium and silicon thereto during furnacing, deoxidizing, adding a composition containing a rare earth metal to the ladle in an amount not more than three pounds per ton, pouring and quick freezing.

7. A method for the production of iron and steel which comprises preparing an iron containing melt, adding metallics including a member of the group consisting of chromium, molybdenum, manganese, nickel, columbium, titanium, tantalum, cobalt, zirconium and silicon thereto during furnacing, deoxidizing, adding a composition containing a rare earth metal to the ladle during pouring, and while the ladle is less than one-half full, in an amount not more than three pounds per ton, pouring and quick freezing.

8. An art cle of manufacture, a steel characterized by a fine grain structure, substantial freedom from dendrites, resistance to corrosion, a relatively high impact value at low temperatures, capable of being directly rolled to billet size and having the following approximate composition expressed as percentages: carbon 0.25- 0.32; manganese 1.6-1.9; sulfur 0.04 maximum; phosphorus 0.04 maximum; silicon 0.2-0.3; molybdenum 0.4-0.5; and rare earth metal 0.003- 0009, the remainder iron, said steel being produced by the method defined in claim 1.

9. An article of manufacture, a steel characterized by a fine grain structure, substantial freedom from dendrites, resistance to corrosion, a relatively high impact value at low temperatures, capable of being directly rolled to billet size and having the following approximate composition expressed as percentages: carbon 0.25- 0.32; manganese 1.6-1.9; sulfur 0.04 maximum; phosphorus 0.04 maximum; silicon 0.2-0.3;

mee'smei 7 molybdenum 0.4-0.5; and rare e'arth met-a1 0.005, Number the remainder iron, said steel being produced by 1,892,044 the method defined 'in claim 7. 2,360,717

10. As an article of manufacture, a steel as defined in claim 8, said -steel being produced by 5 the method defined in claim 3. 2 3:; 8

References Cited in the file of this patent UNITED STATES PATENTS Number 3 Name Date Eldred et a1. e Dec. 27, 1932 Phelps Oct. 17, 1944 FOREIGN PATENTS Country Date France Dec. 27, 1943 OTHER REFERENCES 10 Making, Shaping and Treating of Stee1, 6th edition, page 575. Published in 1951 by the U. S. Steel Co., Pittsburgh, Pa.

Claims (1)

1. A METHOD FOR THE PRODUCTION OF IRON AND STEEL WHICH COMPRISES PREPARING AN IRON CONTAINING MELT, ADDING METALLICS THERETO DURING FURNACING, DEOXIDIZING, INCORPORATING A COMPOSITION CONTAINING A RARE EARTH METAL, IN AN AMOUNT NOT MORE THAN THREE POUNDS PER TON, POURING AND QUICK FREEZING.