US3150966A - Deoxidizing compositions for steel - Google Patents

Description

p 29, 1964 w. N. ROSSBOROUGH 3,1503% DEOXIDIZING COMPOSITIONS FOR STEEL Filed May 4. 1961 A Q lo 20 so '40 x io -so 70 e0 PHASE DIAGRAM FOR THE SYSTEM CaOAl O SiO INVENTOR. WALTER N. ROSSBOROUGH ATTORNEYS United States Patent 3,150,956 DEOXHDIZENG COMPOSITEONS FOR STEEL Walter N. Rosshorough, North Olmsted, Ohio, assignor to Rosshorough Supply Company, Cleveland, Ohio, a corporation of Ohio Filed May 4, 1961, Ser. No. 107,690 2 illaims. (Cl. 75-434) This application, relating as indicated to deoxidizing agents and methods of producing rimmed, semi-killed and fully killed steels, is directed particularly to specific compositions of matter and to the use of these compositions of matter for the purpose of deoxidizing steel. Such a composition comprises a granular alloy or mixture of calcium, aluminum and silicon, or suitable compounds thereof.

More particularly, this deoxidizing agent contains from 19.1 to 28.2 percent aluminum and from 80.9 to 71.8 percent calcium silicide, i.e. CaSi by weight.

Additions of deoxidizing agents generally are required in the manufacture of most types of steels. Besides ferromanganese the most common deoxidizers used are ferrosilicon and/ or aluminum. The products of deoxidation with their use are silica, alumina, or aluminum silicate. It has long been known in the art of steel making that these products of deoxidation are refractory, that is, solid or very viscose at steel making temperatures. As a result, a very detrimental portion of these products of deoxidation remains in suspension in the steel until it is solidified in an ingot or casting form. These products of deoxidation can be seen as inclusions both in the microstructure and macrostructure of the solidified steel. These inclusions are very deleterious in castings, semi-finished and finished steel products. As these inclusions are not malleable when they appear near the surface of the semifinished products, such as slabs, blooms, billets, rods, or structural sections, they cause surface defects known as seams. On better grades of steel these seams are removed by automatic or hand scarfing, chipping or grinding. On specialty steels such expensive processes as electric are or induction furnaces are used, and, furthermore, these steels may be poured in vacuum, all in order to minimize the formation of these refractory inclusions. In addition various fluxing procedures have been used to aid in the removal of these inclusions with limited success.

It is an object of this invention to provide a deoxidizer composed of calcium, aluminum, and silicon, which composition is such that when reaction with the oxygen in solution in the liquid steel takes place, the products of deoxidation will have melting points between 2437 F. and 2910 F. These are illustrated in the accompanying drawing, showing the applicable portion of the ternary diagram of CaO--Al O SiO by Rankin, Wright, and

reig for refractories for furnace construction, p. 765, Basic Open Hearth Steelmaking, published by the American Institute of Mining and Metallurigcal Engineers, 1951. For the purpose of this invention, the composition of the pr oducts of deoxidation of the deoxidizer are outlined by the polygon ABCD in the drawing, the upper limit of the melting point of the oxides (2910'F.) being a temperature somewhat below the tapping temperature of most steels. In actual steelmaking practice, however, it must also he assumed that this ternary liquid slag phase will be contaminated by minor percentages of oxides of manganese, iron, chromium, titanium, and magnesium. Within limits normally experienced in steel making, these contaminants will not significantly change the melting point of the ternary phases of CaOAl O SiO for the purpose of this invention.

If the products of deoxidation have a composition lying between the 2437 F. and 2730 F. isotherms, they will be liquid at the solidification temperature of most commercial steels. Since they are liquid, there will be great and continuous tendency of these inclusions to coalesce into larger globules of slag, and, due to their much lower density, these will rise rapidly to the top surface or" the liquid steel and be incorporated into the ladle slag or ingot scum from the time the deoxidizer is added until the steel has solidified in ingot or casting form.

Other limitations that are important in connection with the deoxidizing agent are that it must not produce sufficient residual content of the added metals to cause deleterious conditions in the finished steel. For example under some conditions if the calcium silicide content is lower than 71.8%, as for example in the region AB of the diagram, the aluminum residual content may exceed 0.02%, which would be objectionable for some steel applications.

Other conditions necessary in connection with the deoxidizing agent are careful control of the quantity of calcium silicide. This is important in order not to exceed 0.05% silicon residuals in the steel.

As is well known to those skilled in the art of steelmaking, the deoxidation procedure described is only a theoretical possibility which does not take place to a satis factory extent in actual practice as carried out up to now because it is the practice to add ferromanganese, ferrosilicon, aluminum and sometimes calcium silicon alloy in 2" x 5", or 5" by down lump size. Further, each is added separately and conventionally in the order of deoxidizing power; that is, ferromanganese first and aluminum last. As each of these deoxidizers is added to the liquid steel and reacts with the dissolved oxygen, the respective oxides, cg. manganese oxide, silica, alumina, or aluminum silicate, are formed of these, manganese oxide is the only material liquid at steel-making temperatures, but since it is the weakest deoxidizer it does not prevent the formation of the other oxides. Even when all thre or all four lump deoxidizers are added simultaneously, the refractory type of inclusions form.

The object of this invention, namely, the formation of the low melting point ternary CaO-Al O SiO deoxidation product is achieved, it was discovered, when a granular, e.g. 8 mesh by down, alloy or mixture of constituent deoxidizers is added, in an amount only sufiicient to fix all the available oxygen stoichiometrically, as a mixture chiefly of these three metals Whose oxides must be such as to be within the polygon A-BCD.

The available oxygen alluded to is the amount which is dissolved in the liquid steel tapped or poured, plus the oxygen absorbed during liquid transfer in air, e.g., tapping or teeming, minus the oxygen which is in equilibrium with .005-0.10 percent Al and .01.O5 percent Si. At this low level of deoxidizer concentration, the steel was found to be semi-killed.

In connection with the drawing, the principal area of these ingredients falls within the polygon AB-C-D. These generally are within the temperature ranges mentioned earlier for the ternary oxides formed from the metals silicon, calcium, and aluminum, which when oxidized fall within this diagram. This diagram encloses the complete area of the deoxidizers of this invention. In particular examples, references are made to X, X"R, X"SK, X"K, and XF, in which R represents rimmed steel, SK represents semi-killed steel, K represents killed steel, and F represents a fully killed steel. It will be noted that the line AD is substantially tangent to the 2910 F. isotherm and the line B--C falls within the 2910 F. isotherm, with the projection to falling on the base line of the ternary diagram at about the 2910 F. isotherm.

The preferred composition of the deoxidizer, which is referred to generally hereinafter under the name Kleendoxsil is Ca23%, Al24%, Si4-8%, the balance being non-pertinent incidental elements. When this deoxidizer is completely oxidized, the resulting slag will have a composition of CaO17.8%, Al O -25.1%, SiO 57.1%, represented in the ternary diagram CaOAl O -SiO by the point X which falls on the M-N line in the upper portion of the diagram. This is one extreme limit of the possible slags obtained from the oxidation of a very small amount, i.e. one pound, in a very large mass, i.e. 2,000 pounds, of a highly oxidized rimmed steel.

For another example, generally outside the preferred range but illustrating the range'of this invention, would be the extreme limit of the possible slag conditions obtainable, which would be GIG-32.2%, Al O 4-5.3%, SiO --0.0%, and which is represented by the point X on the drawing. This is a condition where only calcium and aluminum are completelyoxidized. in actual practice, the resulting slag compositions will lie between these two extreme positions.

For a further example, if .87 pound of Kleendoxsil per ton of steel is added to a carbon .05 rimmed steel, various small portions of the three el ments go into solution instead of being oxidized, and the silicon being the weakest of the three deoxidizer elements forms the highest residual element of the three. Consequently, the SiO content in the resulting slag will be relatively lower, for example CaO-20.4%, AlO 27.4-%, SiO 52.2%, which is represented by the point XR on the drawing.

The residual amounts will be determined by the amount of oxygen in the steel in equilibrium with each deoxidizer element. This will depend on the type of steel desired.

In a further example of a semi-killed steel, if 1.4 pounds of Kleendoxsil per ton of steel are added, considerably higher residuals of the three elements will result. The slag formed in this case will have a composition of CaO29.3%, Al O -38.7%, and SiO 32%, represented by the point X"SK on the drawing.

In a still further example, 2.26 pounds of Kleendoxsil per ton of steel are added; and much higher residuals would be required to be in equilibrium with the necessarily low oxygen content in a killed steel. The slag formed in a particular example of this would have a composition of CaO-37.5%, Al O 4-6.0%, SiO -16.5%, which is indicated by the point XK on the drawing.

As a special illustration of this killed steel, we might cite another example in which 1.05 pounds per ton of Kleendoxsil are added in cylinder form and quickly submerged until an extremely low oxygen concentration is obtained. This produces still higher residuals of the metals in question but the slag formed as the result of the addition of the'cylinder of Kleendoxsil will produce a composition of about 48.3% CaO, 51.7% A1 indicated by the point XF on the drawing.

The melting points ofthe various types of slags described above can be approximated by interpolating the isothermal lines crossing the curve through X, XR, X"SK, X"K, and X"F. The line X'K when extended upward passes through the 100% silicon apex of the ternary diagram. Point X represents the slag composition resulting from the complete oxidation of the calcium and aluminum in the Kleendoxsil, but none of the silicon. The shift of the slag composition from X to X? in the final example is due to the large aluminum residuals associated with the'extremely low oxygen concentration in the steel in this example.

With the above materials, it is fully understood that ferromanganese addition, if any, and before any strong deoxidizers, such as ferrosilicon, aluminum or calcium silicide are added in sufficient amount to fix the available oxygen as indicated in the following tables. Table I shows the amount of material added for rimmed steel, Table II for semi-killed and fully killed steel.

Table l 7 Lbs. Kleendoxsil Percent C in steel: (ton steel) Table II Percent C in steel:

It is to be realized, of course, that these deoxidizers may be used at any carbon level in the steel, i.e. from 0.2% to 2.00% carbon, by extrapolation and interpolation of the amounts indicated in the tables. The accuracy of the degree of dcoxidation achieved is determined by the accuracy of the carbon determination.

The pulverulent deoxidizer is added preferably in 20 pound increments packed in combustible bags. If added loose, e.g. by shovel, obviously much of pulverulent deoxidizer would be carried away by the updraft of hot gases from the liquid steel. The combustible bags burst on striking the liquid steel and the pulverulent deoxidizer is scattered, minimizing any local high concentration of deoxidizer in the liquid steel. This promotes the complete oxidation of the deoxidizer particles and the formation of the liquid phase of oxides. The Kleendoxsil is added uniformly, one bag at a time, during the time the ladle is six-tenths to eight-tenths full, the object being to get as much of the steel in the ladle as possible, allowing as much as possible of the dissolved oxygen to escape in the form of carbon monoxide, thenadding the deoxidizer uniformly without any excessive local concentrations of deoxidizer in the liquid steel, and finally adding the ferrosilicon or aluminum before any furnace slag begins to flow from the furnace near the end of the tap.

This invention is not to be construed as limited to the aforesaid procedure. The Kleendoxsil can be added lowor during the ladle filling to accentuate the benefits of the exothermic reaction on any possible ladle skull formation. However, if it is added in this manner, a slightly larger amount will be required because the C+O=CO reaction in the ladle will be minimized. In addition, more of the liquid slag phase will form. More oxygen will be adsorbed during ladle filling, and the products of deoxidation will have a longer distance to rise to the top of the metal in the ladle.

Mechanized chutes for ladle additions are preferred in the eiecution of this invention, since the addition of ferrosilicon and/or aluminum required to meet steel chemistry specifications can be delayed. With such provision at least two-thirds of the heat of steel can be allowed to tap into the ladle before adding manually in paper bags about three-quarters of the required Kleerb doxsil. After about a fifteen second pause to allow the Kleendoxsil to react, the ferrosilicon and/or aluminum addition is chuted in. The remaining one-quarter of the required Kleendoxsil is added in the tap stream, preferably uniformly in the steel runner or into the tap stream as it falls into the ladle.

Under some conditions the pulverulent may be agglomerated or pelletized.

The deoxidizers of this invention are not limited to ladle additions but may be used for bath deoxidation when compressed or cast into star or cylinder form or con tainers. Such shapes may be fastened to steel bars and submerged into the steel bath just prior to tapping.

The deoxidizers of this invention also may be used to deoxidize steel in the ingot mold during teeming or after teeming, but before the ingot has crusted over.

The polygon encompassing the slag compositions resulting from the complete oxidation of the deoxidizer taught in this invention may be described by the following four points:

Percent Percent Percent CaO A1203 SiOz I Percent Ca Percent Al Percent Si In general it will be appreciated that the composition of the material will be as indicated within the diagram ABCD. In addition to this from 19.1 to 28.2 percent aluminum is included in this pulverized deoxidizing agent. It is also understood that other compositons may be used, incorporating a greater amount of calcium and a greater amount of aluminum, that will produce upon full oxidation or partial oxidation, as was seen in connection with this application, a slag composition within the polygon ABCD of the drawing. Various figures have been given for certain points on the boundary line of the polygon and within the polygon, such as the points M and N. It will be appreciated, however, that substantially the preferred composition will be that in the upper portion of the diagram as represented by the compositions along the line MXN, and as was covered in the above statement. It will be understood, of course, that various other materials have been lmown in connection with the fiuxing art and some of these include patents such as Chandler 2,767,484, Strauss 2,819,256, Kjellman 2,727,815, and Perrin 2,228,836, but it also will be understood that there are particular advantages to the t3 compositions disclosed herein and these include the following: That it is a more economical deoxidizer than others that may have been employed in this prior art.

It is understood also that it is possible to make semikilled steels with lower residual silicon than with other known deoxidizers, and under test data it already has been shown that the surface qualities of steel deoxidized with this material is far superior to the conventional deoxidizers, including ferrosilicon, silicon manganese, aluminum, etc. It also is realized that this is a compact ladle addition comparable to the endothermic 50 percent ferrosilicon alloys and it requires a very modest amount, if any, of rather expensive calcium material and, therefore, is a more economical deoxidizer than that taught in the Chandler and Strauss patents.

Although the present invention has been described in connection with several embodiments thereof, variations and modifications may be resorted to by those skilled in the art without departing from the principles of this invention. All of these variations and modifications are considered to be within the scope or" the present invention as disclosed in the foregoing description and defined by the appended claims.

I claim:

1. A deoxi-dizing composition consisting essentially of approximately 23 percent by weight of calcium, 24 percent by Weight of aluminum, and 48 percent by Weight of silicon, the balance being non-pertinent incidental elements, said composition having a particle size of approximately 8 mesh and upon oxidation in molten steel forms slag having melting points within the range of 2437" F. to 2910 F., and the relative proportion of the oxides being Within the polygon ABCD of the CaO-Al O SiO ternary diagram.

2. A pulverized deoxidizing composition for steel consisting essentially of 19.1 to 28.2 percent by Weight of aluminum and 71.8 to 80.9 percent by Weight of calcium silicide, said composition upon oxidation in molten steel forming slag having a melting point in the range of 2437 F. to 2910 F., and the relative proportions of the oxides being within the polygon A-B-CD of the ternary diagram.

References Cited in the file of this patent UNITED STATES PATENTS 2,079,901 Davidson May 11, 1937 2,120,740 Faust et al. June 14, 1938 2,727,815 Kjellman Dec. 20, 1955 2,767,084 Chandler Oct. 16, 1956 2,832,682 Reygagne Apr. 29, 1958 OTHER REFERENCES Basic Open Hearth Steelmaking, 1951, page 765.

Claims (1)

1. A DEOXIDIZING COMPOSITION CONSISTING ESSENTIALLY OF APPROXIMATELY 23 PERCENT BY WEIGHT OF CALCIUM, 24 PERCENT BY WEIGHT OF ALUMINUM, AND 48 PERCENT BY WEIGHT OF SILICON, THE BALANCE BEING NON-PERTINENT INCIDENTAL ELEMENTS, SAID COMPOSITON HAVING A PARTICLE SIZE OF APPROXIMATELY 8 MESH AND UPON OXIDATION IN MOLTEN STEEL FORMS SLAG HAVING MELTING POINTS WITHIN THE RANGE OF 2437*F. TO 2910*F., AND THE RELATIVE PROPORTION OF THE OXIDES BEING WITHIN THE POLYGON A-B-C-D OF THE

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