US3197828A - Cast iron protection - Google Patents

Description

Aug. 3, 1965 CARTOUX ETAL CAST IRON PROTECTION Filed Jan. 2, 1962 Henri Carzoux Francis Dubrous INVENTORS United States Patent 3,197,823 CAST IRON PROTECTION Henri Cartoux and Francis Dubrons, both of Chedde, France, assignors to Pechiney, 'Compagnie de Produits Chimiques et Electrometallurgiques, Paris, France Filed Jan. 2, 1962, Scr. No. 165,711 Claims priority, application France, Jan. 3, 1961,

2 Claims. (Cl. 22-216.5)

The present invention deals with the protection of cast irons and more especially with ingot-moulds used in metallurgical smelting operations.

It is known that metals or alloys worked at temperatures higher than 1300 C. and cast at tempertures of at least 1300" C. and possibly above 1700 C., subject the cast iron ingot moulds (used for their casting) to severe corrosive action so that their ingoting proves uneconomical. This corrosion phenomenon occurs in the case of cast iron ingot moulds used in the casting of ordinary and special steels and proves very active when alloys such as cupro-chromiurn or other non-ferrous alloys are cast at temperatures of about 1700 C. The corrosion of the ingot mould cast iron brings about, moreover, impurities in the prepared ingot which becomes richer in iron and other impurities. This impurity is particularly troublesome when the alloys or metals cast do not contain iron.

Attempts have been made to reduce the magnitude of corrosion phenomena, as described above, by undertaking loaming of ingot moulds, and this is the usual practice in smelting works. This operation consists in coating the cast iron surface to protect it, by means of a carbon based preparation and of refractory products, such as talcum, alumina, etc. It has been determined however, that loaming cures only in a very insuflicient way the corrosion phenomena of ingot moulds. This is especially true when the cast temperature reaches high values of about 1700 C. In the latter case, the ingot mould lifetime is not increased markedly by loaming.

On the other hand, it is known that cast iron protection against chemical corrosion may be partially obtained by immersing cast-iron objects in a bath of molten aluminum, or of molten ferro-aluminum containing not more than 5% iron. It is known in general that the temperature of this bath of molten metallic substance is preferably under 800 C., that it is necessary to prepare the cast iron surface by mechanical and/or chemical means, that only one treatment is used, whose duration varies between a few seconds and a few minutes and that a tempering (quenching) effect is produced when the cast-iron object is withdrawn out of the molten metallic bath.

It is also known that structural investigations of cast iron surfaces thus treated generally show the existence of three layers. These layers comprise a superficial layer, whose composition is identical to the aluminum or alloy used for treatment, an intermediate layer composed chiefly of FeAl and a third layer of unchanged cast iron.

The object of the present invention is directed to a process for the protection of cast irons for greatly increasing the life-time of cast-iron ingot-moulds. The lifetime length may be increased from one to several tens of times, and even from one to 300 times and more, as in the case of the cupro-chromiurn smelting.

This life-time lengthening is also very greatly increased in the case of casting of ordinary and alloy steels, as well as of refractory cast irons. Moreover, the purity of the steel ingots as well as the appearance of these ingots, cast into ingot-molds according to the present invention are clearly improved as compared to ingot moulds as known until now. These unexpected results could be by no means foreseen.

Throughout the specification, ordinary steelis inice tended to mean a substance substantially composed of iron and of carbon in which the carbon proportion is not more than about 3% by weight.

Alloy steel is intended to mean a substance principally composed of iron and allied to metals such as chromium, molybdenum, manganese, tungsten, vanadium, titanium, zirconium, etc.

The other objects of the inventions will be set forth in the following description.

The cast iron protection process, according to the invention, comprises the protracted contacting of cast-iron ingot moulds withaluminum or an alloy based on aluminum at a temperature range at least about 50 C. higher than the melting point of said metal, and preferably from C. to about 300 C. and even higher than said melting point. The duration of the aforesaid contacting time is at least about 20 minutes, and can be an hour or more.

The cast irons, dealt with by the invention, are ordinary or refractory cast irons, and in particular cast irons called hematites i.e. containing at most 0.1% phosphorus by weight.

The aluminum alloys employed are preferably ferroaluminums, such as industrial ferro-aluminum containing 30 to 40% aluminum by weight. I

According to a preferential means of achieving the results of this invention, the cast irons are contacted several times with aluminum or aluminum alloy. One treatment only provides a great improvement of the behaviour of cast irons, especially by using ferro-aluminums containing 30 to 40% aluminum by weight. But, in most cases, the effect of protection becomes excellent only after several treatments, the number of these lying generally between 2 and 15 depending on the aluminum or aluminum alloy used, and according to the casting temperature of said aluminum or aluminum alloy. The number may decrease, for instance when the temperature increases, and it is preferably comprised between 3 and 5 for ferroaluminum containing 30 to 40% aluminum by weight, and between 5 and 15 for aluminum.

The objects of the invention are advantageously achieved when the cast irons to protect are at a temperature of the order of several hundreds of degrees, and, for instance, lying between 250 C. and 400 C., when contacting the metal or treatment alloy. This operating mode avoids high thermal stresses which are harmful to the integrity of the cast-iron objects (ingot moulds, for example) thus prepared.

After contacting the cooling of cast irons thus treated is preferably carried out slowly to achieve tempering effects.

According to a preferential form of application of the invention, cast irons are used which have undergone no surface preparation, neither by a mechanical means, nor by chemical pickling, or even by loaming. The surface of these cast irons presents then, before being submitted to the protecting actions, an oxydation state corresponding to that of raw cast irons as produced by smelting works.

According to a preferential form of execution of the invention, the first treatments are carried out with naked cast irons, i.e. raw 'cast iron as produced by smelting works, as described above, while the following treatments are preferably effected in loamed cast irons.

A physico-chemical study of the cast-iron surface based chiefly on the examination of micrometallography, diffraction by X rays and emission spectrography, has allowed the applicants, in a general but non-restrictive Way, to bring to light, at the surface of the aforesaid cast irons, the succession of four layers, having very different aspects and structures.

The accompanying drawing comprises a diagrammatic illustration of a photomicrograph of the surface layers which characterize cast iron treated in accordance with this invention. These layers are enumerated as follows from the exterior to the interior:

(I) A layerl, based on iron oxide, often accompanied by fayalite i.e. ferrous silicate Fe SiO A very weak proportion of aluminum, of the order of 1% by weight, is also seen.

(II) A layer 2, which, in polarized light, reveals a very fine aggregate of black, white and grey interspersed areas. This layer has an exceptional micro-hardness and a. remarkable chemical inertia, with respect to acid and diluted bases.

(III) A layer 3, containing flake graphite 5, surrounded by a geometric paving of very fine crystalline structure, which would result from partial carburization of cast-iron perlite. The total thickness of layers 1, 2 and 3, together, varying in terms of the treatment according to the invention, is of the order-of several tenths of millimeters.

(IV) Below the layer 3, is found proper cast iron 4, whose structure is unchanged.

The treated cast irons, presenting at their surface the four layers, defined above and more especially the layer 2, constitute one of the objects of the invention.

The cast irons treated, according to the invention, a large number of times, for instance many tens of times, show a characteristic surface entirely wrinkled, these wrinkles being normally visible, and their amplitude being of the order of some tenths of a millimetre. This phenomenon is the more outstanding, the higher the number of treatments. This wrinkled surface is' clearly seen when the ingot-moulds have been used for ingoting aluminum, the temperature of casting being of the order of 750 C. about; the aforesaid ingoting being repeated a hundred or several hundreds of times; and the ingotmoulds being, in virtue'of said repeated ingoting, auto- Example 1 I Ingot moulds made of cast iron of the following composition:

Percent by weight were treated in accordance with this invention. Industrial ferro-aluminum of usual quality, containing about 35% aluminum by Weight, and having a solidification point of about 1350 C. was used for treatment. The ingot moulds used are new raw-ingot moulds, such as produced by smelting Works, that have been stocked in sheltered shops. Their useful surface has undergone no preparation, neither by mechanical means, nor by chemical pickling. The first four ferro-aluminum casts are effected in naked ingot-moulds, i.e. with no loaming. By loaming, will be understood coating the internal surface of the cast iron mould with a particulate refractory product. These ingot-moulds are previously heated at about 300 C. to 400 C. The ferro-aluminurn is cast in the ingot-moulds, the casting temperature lying between 1450 C. and 1500 C. The castings are undertaken at intervals of about two hours. After having unmoulded the ingots, the ingot moulds are hot, with a temperature of the order of about 300 C. to 400 C. Before the fifth and later treatments are carried out, the ingot moulds are loamed by means of a talcum based preparation. Once the treatments are over, the slanted sections taken on the treated surface of cast irons, as well as the physico- Kg./mm. Layer 1 340 Layer 2 860 Layer'3 245 Layer 4 315 Once the treatment is over, the ingot-moulds are put into service and loamed before each cupro-chromium casting, with the help of a talcum-based preparation. We use these ingot-moulds for the ingot-moulding of cuprochromium containing 10% by weight of chromium, whose melting point is of the order of 1250 C. and whose casting temperature is about 1700 C. We ascertain that these ingot-moulds support normally at least 1000 cuprochromium castings and that the cast cupro-chromium conserves its original purity.

By way of comparison, we take ingot-moulds identical to those described at the beginning of this example, but we put them into service as such, without subjecting them, previously, to the treatments according to the invention. These non-treated ingot-moulds, fully loamed before each cupro-chromium casting, do not allow more than about 10 castings and the cast cupro-chromium is found to be soiled by iron and other impurities, when in contact with the ingot-mould cast irons.

Example 2 The chief differences with respect to Example 1 are the following: aluminum is used instead of ferro-aluminum and is cast at 900 C. to 950 C., the casting intervals lying between one and two hours. Fifteen successive treatments are carried out by each ingot-mould. On and after the fifth treatment, the ingot-moulds are loamed. Once the treatments are over, the ingot-moulds present the same results as those already described in Example 1.

The process of surface treatment of cast irons according to the invention is not limited to the cast-iron objects (casting) presently the form of an ingot-mould, but comprises also cast-iron objects of all possible forms. The aforesaid objects can be treated by immersion in the metal or cast alloy, under the same conditions of surface states, durations, temperatures, nature of treatment metals or alloys, as those described above for ingot-moulds and with the same results. There should be considered as lying in the scope of the present invention every castiron presenting at its surface the physico-chemical characteristics set forth above, particularly cast iron obtained by application of the process, which is the object of the invention.

The aforesaid products comprise, among other-s, the cast-iron ingot-moulds destined for the ingoting of metals or non-ferrous alloys, cast at temperatures of at least 1300 C., said ingot-moulds having been subjected to the treatment according to the invention, before being put into service.

They also comprise the cast-iron ingot-moulds for ingoting of refractory cast irons, ordinary and alloy steels; these ingot-moulds permitting, because of the treatment, according to the invention, ingoting under much indre economical conditions than previously.

They comprise also the cast-iron equipment castings and the cast-iron apparatus castings, exposed to chemical corrosion and subjected, before entering upon service, to the treatment according to the invention, said cast-iron equipment castings and cast-iron apparatus castings exhibiting, thanks to this treatment, an amazing increase in resistance to that corrosion, among others to sulfhydric and/or", sulfurous gasesat high temperatures, for instance above 500 C., as well as to saline mists.

They comprise also any cast-iron equipment castings and cast-iron apparatus castings exposed to sharp and considerable temperature difierences, of the order of several hundreds of degrees, and having been subjected, before entering into service, to the treatment according to the invention. These castings exhibit, thanks to the aforesaid treatment, a remarkable improvement of their dimensional stability.

The new applications of the process discovered by the applicant lie also in the scope of the invention.

The aforesaid applications comprise among others, the ope-rations of ingoting of ferrous metals such as refractory cast irons, ordinary and alloy steels, non-ferrous metals such as cupro-alloys, cast at temperatures of at least about 1300" (3., into cast-iron ingot-moulds previously treated according to the invention. The applications also involve the protection against chemical corrosion against considerable differences of temperature of every cast-iron material, previously treated according to the invention.

What we claim is:

1. A process for casting molten metalliferous materials other than aluminum and aluminum base allows into protected cast iron ingot moulds, said molds being initially characterized by a raw cast iron surface, said process comprising the steps of casting into said molds at least one metal selected from the group consisting of aluminum and a ferroaluminum containing from 30 to 40 percent aluminum, holding the metal in said mold for at least about 20 minutes at a temperature range from at least about 50 C. higher than the melting point of said metal, withdrawing after solidification the metal cast into said mold, repeating the process of casting said metal into said mold for from three to 15 times, and thereafter casting a metal or alloy other than an aluminum base metalliferous material into the moulds thus protected.

2. A process for casting molten metalliferous materials other than aluminum and aluminum base alloys into pro- 0 tected cast iron ingot moulds, said molds being initially characterized by a raw cast iron surface, said process comprising the steps of casting, into said molds at least one metal selected from the group consisting of aluminum and a ferroaluminum containing from 30 to percent aluminum, holding the metal in said mold for at least about 20 minutes at a temperature range from at least about C. higher than the melting point of said metal, withdrawing after solidification the metal cast into said mold and loaming the surfaces of the mold after a casting step, at least one casting step being conducted before a loaming step with loaming and casting steps being thereafter alternately repeated, said casting steps being conducted for from three to 15 times, and thereafter casting a metal or alloy other than an aluminum base metalliferous material into the moulds thus protected.

References Cited by the Examiner UNITED STATES PATENTS 2,090,408 8/37 Vance 117-53 2,197,660 4/40 Glunz et al. 22-2165 2,304,067 12/42 Anderson 117-53 2,396,730 3/46 Whitfield 22-204 2,455,457 12/ 48 Whitfield 22-204 2,618,530 11/52 Gardner 117-53 2,620,530 12/52 Sulprizio 22-204 OTHER REFERENCES Non-Ferrous Foundry Metallurgy, Murphy, A. 1., pp. 232249, Ingot Casting Practice, Pergamon Press Ltd, London, 1954, pp. 232, 233, 235238 and 245 particularly relied on. J. SPENCER OVERHOLSER, Primary Examiner. MARCUS U. LYONS, MICHAEL V. BRINDISI,

Examiners.

Claims (1)

1. A PROCESS FOR CASTING MOLTEN METALLIFEROUS MATERIALS OTHER THAN ALUMINUM AND ALUMINUM BASE ALLOWS INTO PROTECTED CAST IRON INGOT MOULDS, SAID MOLDS BEING INITIALLY CHARACTERIZED BY A RAW CAST IRON SURFACE, SAID PROCESS COMPRISING THE STEPS OF CASTING INTO SAID MOLDS AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM AND A FERROALUMINUM CONTAINING FROM 30 TO 40 PERCENT ALUMINUM, HOLDING THE METAL IN SAID MOLD FOR AT LEAST ABOUT 20 MINUTES AT A TEMPERATURE RANGE FROM AT LEAST ABOUT 50*C. HIGHER THAN THE MELTING POINT OF SAID METAL, WITHDRAWING AFTER SOLIDIFICATION THE METAL CAST INTO SAID MOLD FOR FROM THREE TO 15 TIMES, AND THEREAFTER CASTING A METAL OR ALLOY OTHER THAN AN ALUMINUM BASE METALLIFEROUS MATERIAL INTO THE MOULDS THUS PROTECTED.

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