2,408,305 Patented Sept. 24, 1946 UNITED STATES 'PATENT orrlcia‘..? , . „ Corhart Refractories Company, Louisville, Ky., ~ arcorporatîon of Delaware Application August 1, 1944, Serial No. 547,565v 6 Claims. (o1. 10s-59.) 1 of as much as V50% FeO.A120a to the good FeQCrzOa inthe syt'em disclosed in my U. S. Pat ent 2,271,365 promotes swelling of this also. It is very surprising therefore that my tests show f, that mixtures of al1 three spinels, FeO.Cr2Os, MgO.Cr2O3 and FeO.Al2O3 give a remarkably stable> refractory with a minimum of reaction This invention relates. to a novel heat cast chromite refractory, which is particularly suit able for use at high temperatures in contact With slags high in iron oxide. lBy heat cast is meant the complete melting as for example with the techiniques disclosed in U.; S. Patent #1,615,750 to Fulcher, and shaping .into the desired form by casting into molds and solidifying. ’ " The extensive use of electric furnaces for melt ing alloy steels~ has created new refractory prob ' with‘the slag." ' The inclusion of the FeO.Al2O3 decreases the Cr2O3 necessary and therefore low 10> ers cost. A solid solution of course results when a melt containing oxides in spinel proportions isl lems since the slags which arepreferred may cooled and the spinels do not have individual be quite diñerent from thel traditional high al existences inthe crystal phase. Nor is it essen kaline earth slags of the blast ‘furnace and the tial that the bivalentand trivalent oxides be open hearth. The slag in an electric furnace present in exactly equal molar quantities since 15 melting chrome steel commercially for examplel an’excess of as much as 20% of one or the analysed roughly 72% FeO, 16% A1202, 4% Cr203, other can apparently bev absorbed by the solid l 6% -Si02- and only 2% CaO and MgO, and such »solution In other words it is suflicient that the a slag has been used for test purposes on the moles of trivalent oxidev (A1202 and CrzOa) lie novel refractories disclosed below. In such a fur between 80 and 120% of the moles of bivalent nace, attack on the refractories is partly chem 20 oxide (FeG and MgO). Since both FeO and ical corrosion» and partly mechanical erosion. CrzOa are easily reduced during melting in the I have found that a heat cast refractory is par presence of carbon electrodes and since MgO ticularly advantageous where erosion Yis a factor volatilizes to som-e extent, the permissibility ofV since the crystals in forming on solidiñcation ap some variation is a distinct advantage. Since parently interlock and at anyrate give a strongly 25 excess FeO is harmful to resistance and since coherent body even whenj- reheated above the Cr2O3 is the most expensive ingredient, I prefer softening ltemperature of the amorphous matrix to calculate spinel proportions for the batch with associated with such refractories.` This matrixl the result that the product will err on the side replaces both the porosity and the ?luxing bond > of‘ higher A1203 and MgO- rather than higher of theburnt refractory and since it is in sub stantial equilibrium' with the crystals it is not FeO or CrzOs. To minimize the reduction to metallic iron I prefer -to add the iron oxide as appreciably corrosive on these crystals as` the Fe2Oa or'lï‘eaOiv While commercial chrome green temperature is increased and onthe’other Ahand u may ¿be used for Cr203 and a good grade of com by its substitution ~>for porosity> prevents ready , mercial magnesite for the MgO, the alumina be access of slags which` are corrosive into the body-V ing the chemically pure vgrade used'vfor metal ofthe refractory. ,_ - . - , » _ In my U. S. Patent 2,271,363 I have disclosed a heat cast refractory consisting of FeO.Cr2Os, to be made from pure materials since this was developed for use against commercial glasses Where the presence of SiO2 or MgO and A1203 together is harmful. V„l have found that pure FeQCrzOs> is excellent in chemical resistance to high FeO slags also but the high Cr2O3 content (68%) and the cost of pure materials is a draw back to general commercial use. Also expen sive and even higher in Cr2O3 content (79%) is pure MgO.Cr2O3 as disclosed in my U. S. Patent 2,271,362 but this refractory also has limitations> in its tendency to swell and disrupt undermoxi dizing conditions. Even the Vcombination of as` much as 50% FeO.Cr2Os with MgO.Cr2O3 in the system `disclosed in my U. S. Patent 2,271,364 did not entirely prevent this swelling in contact With the high FeO slag. On the otherV hand addition production _by electrolysis. Specimen batches which I have heat cast and tested against the high FeO slag are illustrated in Table I below. The analyses are calculated into approximate spinel proportions as shown in Table II and test results,-- with the high F‘eO- slag are indicated. l TABLE I Batch composition, in per cent by weight CrzOs Feed: Mg() A120: , 2,408,305 3 TABLE' II Calculated proportions in mol percent Slag tests were made by mixing 25% byxvolume slag with the powdered refractory and vfiring for 71/2 hours at 1500° C. The shrinkage and de-` crease in apparent porosity was taken as an indi-v cation of the extent of interaction, while oxida- y refractory. With complete melting it is also pos sible to adjust the composition to minimize non spinel crystallization. In Table IlI are listed batches with chrome ore as an ingredient which have all given good tests against the high FeO, tion was indicated by swelling. >With pure mate low alkaline earth slag. ,„ rials it was found that equally good results were 20 obtained with melt H which has 17% less Cr203 TABLE III than melt A and subsequent service tests with brick of this composition have given outstand C2203 FeO MgO A1203 m . . O » CaO ing performance where commercial burnt refrac tories failed rapidly. 25 I have also discovered that unlike the results in tests against commercial bottle glass, a certain amount of Si02 can be tolerated without ruining the resistance to slag despite high FeO content. Good results were obtained when as much as 8% aoQ SiOz was added to ferrous chromite. The possibility of including SiO2 as well as MgO and A1203 permits the substitution of chrome ore for at least part of the chrome green with a distinct saving in costs. Tests with chrome ore included in the batch have shown however that the S102 should still be kept as low as possible. For this reason as well as to permit maximum These batches were made by using the maxi mum amount of the above chrome ore, adding to it necessary amounts of chrome green, alumina, magnesite or Fe304 (and in one case kyam'te) to give the indicated analysis. At the lower Cr203 substitution of the chromev ore for chrome green ~ it is desirable to use a high grade, chemical typev 40. level the resistance to slag clearly decreased as MgO replaced FeO contrary to the usual teach of chrome ore. One which I have found suitable ings for burnt chrome refractorles for use against high alkaline earth slags. This effect is so pro nounced in fact that substantially equivalent re analysed 52.55% Cr2O3, 14.56% (total Fe as) FeO, 15.72% MgO, 11.72% A1203, 1.57% CaO, and 3.31% S102. ` ' ' As it occurs in nature, the primary component 45 sults were obtained on the test for melt VJ with 20% Cr203 and melt O with 38.6% C1203, the of chrome ore is usually considered to be former being high in FeO and the latter in MgO. With FeO maintained high however, resistance increased as Cr203 increased. Even the 1% -of Si02 in melt Q in comparison with melt H showed but considerable of the FeO is replaced with MgO and considerable of the Cr203 is replaced by 50 a measurable effect on resistance and in general A1203 while of even greater» importance to its characteristics as a refractory, a gangue is also l present in which the following magnesium sil icates have been identified in various ores: Si02 should be kept below 5% to gain the full advantage of such batches. Fig. 1 is the conventional representation by an equilateral tetrahedron of all compositions on a 55 weight per cent basis which exist in the four- component system CrzOs-MgO-FeO-AlgOs. The six binary systems, i. e., FeO-CrzOa, MgO-Cr20s, A1203-CI‘203, For use in burnt refractories an attempt to sta bilize and distribute this gangue is often made by heating the ore to recrystallization temperatures FGO-A1203, FeO-MgO and MgO-AlzOa, are represented' by compositions 60 along the edges of the tetrahedron. The four ternary systems, i. e., FeO-MgO-CrzOs, CrzOs MgO-AlzOs, Al2O2-FeO-Cr2O3 and FeO-MgO A1203, are represented by compositions on the before compounding. Complete recrystallization 65 triangular faces of the tetrahedron. All composi tions of four oxides are represented by points through fusion has been tried-»but it was found Within the tetrahedron. Four of the binary sys that the secondary component was generally tems are between a bivalent oxide and a trivalent poorer from the refractory standpoint than when the same ore was recrystallized at a temperature below the fusion point. " When the refractory compositions are com-._ pletely melted and cast to shape however these oxide and these form spinels l(FeO.Cr2O3, MgO.Cr2O3, FeO.Al2O3 and Mg0.Al2Os) at the 70 points indicated on the edges of the tetrahedron. A11 four ternary systems have solid solutions be tween two spinels (FeO.Cr20a-MgO.Cr2O3, considerations are unimportant because the re MgO.Cr203-MgO.Al2O3, MgO.A12O3-FeO.Al2Oa and fractory is held together by interlocking crystalsv thev compositions of which rather than by the fluxing matrix as in the burnt 75 Fe0.Al2O3-FeO.'Cr2O3), are represented by points on theV straight lines 2,408,305 ,5 l FeO.Fe203 and.-ll'llîgo?xllezO3` as >components 'with the? other .fóur' spirielsï" ln burnt refractories this lî‘e203` is preservedfand. in fact 'some additional Fe203 may. be formed during burning by oxida tionzof :part'oïf the'lì‘eO.y In manufacture» of the which connect' the two spinel's on the: triangular faces of the tetrahedron'; All compositions of four oxides in whichv the moles oflbivalent oxide 4are equal ‘to theinoles of trivalent oxide fall on the shaded ’plane of Fig. 1 which passes‘thrïougn the four spinel compositions. All compositions which heat cast refractory »in thek .presence of carbon electrodes however, conditions are reducing and the .oxide> must be in equilibrium with metallic iron being formed, so'that k1ï‘e20'3 originally pres entjis substantially all converted to FeO, keeping the system'. quaternary.V Since FeO‘Jï‘ezOa is not Ihave found resistant to- high FeO, low alkaline earth'slag are on, or yclose to, this plane in conr position. ` . l . Because only three points' are required‘toiix a 10 plane but four spinels are located on this plane n very refractory. this 'is another advantage of the it follows that compositions on the plane can be vheat cast refractory over a burnt refractory. expressed in more than one way in terms of the While the burnt refractory art teaches that Fe0.Cr203 is unstable at elevated temperatures and that it is advantageous to add MgO to con vert to Mg0.Cr203 and FeO, I have not found heat cast refractories high in FeO.Cr203 especially sus lation however and for that reason I express my ceptible to oxidation. I attribute this to the lack compositions in terms of individual spinels. All of porosity which confines any oxidation attack 20 compositions in the shaded plane of Fig. 1 are to the surface alone. shown on a magnified scale as a spinel tetra In Table V below I give the mol values of the hedron in Fig. 2. According to my discoveries it four major constituents of melts'G to T inclusive is advantageous to select for a high FeO, low of the above Tables I and III: alkaline earth slag, a spinel composition with ap» preciable percentages of Fe0.Cr203 and FeO.A1203 TABLE V _ spinels present.> Actually, since a solid solution occurs between these spinel oxides, description in terms of individual spinels is artificial anyway. Such description has advantages in batch calcu as well as MgO.Cr2O3 and Mg0.Al203. f A single Mzllzmols in 100 grams of batch composition of FeO, MgO, Cr203> and A1203 can in general be represented by a line in the spinel tetrahedron with its ends in two different faces of the tetrahedron; that is, as long as the moles of bivalent oxide equal the moles of trivalent oxide Melt C1203 375 355 132 132 132 255 254 254 34e 357 38o 332 445 the Quaternary composition can be represented by points in two ternary spinel planes or «by those Quaternary spinel compositions along a line con necting in the tetrahedron the two ternary com positions. Thus in Table IV are given the two calculated ‘terminal ternary Ispinel compositions for such composition lines for the batches in Table III. The calculations ignore the» S102 and CaO im purities and therefore add up to 100% for visualizing their location in Fig. 2. With the normal amount of annealing given a heat cast refractory, p Fe() 233 337 355 132 235 459 253 111 203 337 42o 111 122 MgO 24s 124 20s. 431 30o 4o 283 456 339 124 4o 409 394 A1203 147 147 432 47o 443 236 276 302 115 145 76 13o 49 In the following claims I meanby “principally” over 90% of the total composition of the re the composition does not crystallize completely fractory. and the Si02 remains as an amorphous matrix What I claim is: 1. A heat cast refractory composed principally of Cr203, FeO, A1203 and MgO in which the moles of Cr2013 plus Al203 lie between 80% and 120% of the moles of FeO plus MgO and in which the FeO is not less than 8%, the MgO not less than containing any impurities and residual amounts of spinel forming oxides. ` 1.5%, the C`r203 not less than 11% and the A1203 not over 50% by weight by chemical analysis and in which the ratio of the mols of MgCl to the'mols of FeO lies between 0.1 and 4. 55 2. A heat cast refractory composed principally of Cr203, FeO, A1203 and MgO in which the moles of Cr203 plus A1203 lie between 80% and 120% of the moles of FeO plus MgO and in which the ' FeO lies between 8% and 38%, the MgO lies be 60 tween 1.5% and 21%, the Cr203 lies between y11% and 80% and the A1203 lies >between 5% and 50% by weight by chemical analysis and in which the ratio of the mols of MgO to the mols of FeO lies ' between 0.1 and 4. It is characteristic of these novel compositions that appreciable percentages are in the propor tions of Fe0.Cr2O3 and F‘e0.Al203 and that all four spinel forming oxides are present. ì In natural chrome ores, varying amounts of the iron oxide are present as Fe203 and such ores should be considered in a sexenary system with . ‘ 3. A heat cast refractory composed principally of Cr203, FeO, A1203 and MgO substantially in the proportions of their spinels in which the pro portion of Fe0.Cr203 liesbetween 40% and 60%, the proportion of Mg0.Cr203 lies between 20% and 40% and the pro-portion of Fe0.Al20_3 lies between 20% and 40% by weight and in which `theiron oxide is in excess of 20%` by weight. 4. A heat cast refractory composed principally of Cr203, FeO, A1203, MgO and S102 in which the >moles of C1203 plus A1203 lie between 80% and 7 2,408,305 120% of the moles of FeOplus MgO vand in which the FeO is not less than 8%, the MgO is not less than 1.5%, the'CrzOs is not less than 11%, the A1203 is not over-50% and the SîOz is not over 8% 'by weight by chemical analysis and in which the ratio of the mols of MgO to the mols of FeO lies between 0.1 and 4. 5. A heat cast refractory composed principally of 8-38% Feo, 1.5-21% Mgo, 11-80% Crzoa, 5-50% A1203 and 0-8% SiOz by weight and in which the moles of 01'203 plus A1203 lie between 80% and 120% of the moles of FeO plus MgO and in which the ratio of the mols of Mg0 to the mols of FeO lies between 0.1 and 4. 6. A heat cast refractory composed principally of 1-5% S102 and of CrzOa, FeO, A1203 and MgO substantially the proportions of their spinels and in which the proportion of Fe0.Cr203 lies be tween 40% and 60 %, the proportion of Mg0.Cr20a lies between 20% and 40% and the proportion of FeO.Al2O3 lies between 20% and 40% by Weight and in which the iron oxide is in excess of 20% by weight. THEODORE E. FIELD.