METHOD FOR REFINING METAL MELTS OR SLAGS

Abstract

The present invention concerns the field of refining metal melts or slags and provides in particular a reactive material based on calcium aluminate and carbon, its process of preparation and various methods for refining metal melts using the same.

Claims

1. A method for refining a metal melt or slag comprising contacting said material comprising a substrate wherein said substrate comprises: from 50 to 90% (in weight) of calcium aluminate in the form of powder; and from 10 to 50% (in weight) of carbon in the form of powder and optionally one or more additives, metals, or mixtures thereof with said metal melt or slag by anyone of the following steps: by applying said active material to the metal melt as a covering powder so as to form an aggregate; by applying said active material as granules, powder, or spheres into the melt such as through porous plugs of the vessel containing the slag or melt; by applying said active material as a lining of the vessel containing the slag or melt; or by filtering the metal melt or slag with a filter for metal melts or slags comprising a ceramic comprising said material or a coating comprising said material.

2. The method according to claim 1 wherein in said material: The calcium aluminate powder has a particle size of less than 100 m; The carbon has a particle size ranging from 20 to 50 m.

3. The method according to claim 1 wherein in contact of metal melts or slags: calcium aluminate reacts with the carbon and forms calcium aluminate suboxides at a temperature of at least 1000 C. calcium and/or aluminum are deposited on the at least partially decarburized calcium aluminate zone in contact with the metal melt; and a. thin solid calcium aluminate layer is formed in situ due to the reaction of these suboxides with the oxygen of the metal melt; whereby forming an activated collector material.

4. The method according to claim 3 wherein the activated collector material comprises a coating layer on said substrate, said coating layer comprising a calcium aluminate layer.

5. The method according to claim 4 wherein the coating layer has a thickness comprised between 200 nm and 10 m.

6. The method according to claim 1 wherein said filter has a structure chosen from the group consisting in open-cell honeycomb geometry, spaghetti filter geometry, perforated filter geometry, mashed fibers structure, fibrous tissue structure, sphere structure.

7. The method of claim 1, wherein the substrate further comprises one or more additives, metals, or mixtures thereof.

8. The method of claim 1, wherein the step of applying said active material as granules, powder, or spheres into the melt is performed through porous plugs of the vessel containing the slag or melt.

Description

DESCRIPTION OF THE FIGURES

[0098] FIG. 1: Carbon bonded alumina substrate coated with a CA2/C-functional coating.

[0099] FIG. 2: Evolution of temperature and oxygen of the steel melt.

[0100] FIG. 3: Prismatic filter sample after the dipping test in steel melt at 1650 C. approx.

[0101] FIG. 4: In situ formed thin calcium aluminatelayer contributing as collector for inclusions.

[0102] FIG. 5: In situ formed thin calcium aluminatelayer and its roughness.

[0103] FIG. 6: The thin calcium aluminate layer contributing as functional collector of alumina inclusions.

[0104] The following examples are given for illustrative and non-limitative purpose of the present invention.

EXAMPLE I

[0105] a) A water based spraying slurry containing solids of 64 mass. % of CA2 calcium aluminate, 30 mass. % Carbores P (synthetic pitch), 2.7 carbon black and 3.3 graphite has been prepared. The solid content of the spraying slurry was 65 mass. % and boric acid, citric acid, castamend VP 95 L, contrapum K 1012 and ammoniumlignisulfonate have been used as additives. An already pre-pyrolised 10 pore per inch carbon bonded alumina foam filter has been coated with the spraying slurry, dried and afterwards pyrolysed at 800 C. in a coke bed. In FIG. 1 the carbon bonded alumina substrate with the CA2/carbon coating after the pyrolisis is shown. Similar coatings have been achived with materials comprising 95% calcium aluminates and 5% carbon.

[0106] b) A prismatic filter as coated above (FIG. 3) has been dipped in a 42CrMo steel melt (in a special melting device with full controlled atmosphere, Ar blowing, 0 ppm oxygen in the atmosphere above the melted bath) that has been oxidised with the aid of iron oxide and deoxidised with the aid of Al. In FIG. 2 the evolution of the temperature and the oxygen of the steel are plotted. After deoxidising of the steel melt the prismatic filter sample has been dipped in the steel for 30 sec and has been rotated with 30 rpm at approx. 1650 C. After dipping the filter sample has been taken out and has been cooled down in a Argon champer before shifted out of the melting device.

[0107] FIG. 4 demonstrates the formation of an in situ thin reactive layer on the surface of the CA2/carboncoating which is functionalised. On the top of this in situ layer, alumina inclusions have been detected.

[0108] In FIG. 5 this thin layer on the CA2-coating is demonstrated; the thin layer takes the shape of the substrate beneath (FIG. 5, right). A reactive layer with high roughness as an effective collector is generated.

[0109] In FIG. 6 the capturing of alumina inclusions on the in situ formed thin CA2-layer is demonstrated. The carbon in the EDX analysis comes from the sputtering with carbon of the sample for generating the SEM-micrographs.

[0110] Inclusions areas numbered 1, 2 and 3 in FIG. 6 were analyzed. The element analysis of these inclusions was determined and is detailed below:

[0111] #1:

TABLE-US-00001 Element Wt % At % CK 07.19 11.60 OK 49.47 59.93 AlK 32.34 23.23 CaK 10.36 05.01 FeK 00.64 00.22

[0112] #2:

TABLE-US-00002 Element Wt % At % CK 07.88 12.25 OK 51.50 60.17 MgK 00.70 00.54 AlK 37.81 26.19 CaK 01.04 00.49 MnK 00.21 00.07 FeK 00.85 00.29

[0113] #3:

TABLE-US-00003 Element Wt % At % CK 09.40 14.26 OK 53.19 60.58 MgK 00.23 00.17 AlK 36.72 24.80 CaK 00.30 00.14 FeK 00.14 00.05

EXAMPLE II

[0114] An impregnation slurry based on solids of 66 mass. % of CA6/calcium aluminate, 30 mass. % Carbores P (synthetic pitch), 2.7 carbon black and 3.3 graphite has been prepared. The solid content of the slurry was 77 mass. % and boric acid, citric acid, castamend VP 95 L, contrapum K 1012 and ammonium lignisulfonate have been used as additives. In the impregnation slurry a polyurethane (PE) foam of 10 pore per inch has been dipped, the coated PE foam has been treated with air to open the functional macro pores and after drying a spraying slurry with 65 mass. % solids has been applied. After second drying, the filter has been pyrolysed at 800 C. in a coke bed.

[0115] This example shows that a coating made of the material of the invention can be achieved on a skeleton (here plastic) of different composition.

[0116] The filter as coated above may then be used for refining a metal melt by conducting step b) as in Example I above.

EXAMPLE III

[0117] Carbon/Calcium aluminate composite beads/aggregates have been prepared using a gel-casting process by alginate gelation as disclosed by Oppelt et al. in Metallurgical and Materials Transactions B, 2000, 45B, 2014, 2000-2008.

[0118] This method is based on the gelation of sodium alginate in direct contact with calcium ions in an aqueous solution as solidifying agent. Controllable casting is possible through the use of sodium alginate, stabilizer, and plasticizer. Sodium alginate serves as a gelation reagent, which can be dissolved in deionized water at room temperature. It is a polysaccharide, which consists of mannuronic and guluronic acids that are combined in sequential block structures.

[0119] During the dropping process, sodium alginate and calcium ions react by attracting each other's molecular chains and form a three-dimensional network which then lead to the formation of beads/aggregates with diameters between 0.5 mm up to 5 mm. 64 g calcium aluminate and 36 g carbon (in the form of synthetic pitch like Carbores from Rutgers Germany; graphite and soot) powders were mixed (64 mass. % of CA2 calcium aluminate, 30 mass. % Carbores P, 2.7 carbon black and 3.3 graphite).

[0120] The powder mixture and 29 ml water with 1 g additive mixture based on 0.4 g the gelifying agent (sodium alginate) and 0.6 gr. Darvan C (Vanderbilt company) as plasticizer, were homogenized for 15 minutes and finally milled for 3 hours in a polypropylene chamber with zirconia milling media. The powder to water ratio was 70:30.

[0121] The composite suspension was added dropwise into the liquid with 99.2 ml water with a solidifying agent of 0.8 g calcium chloride, and precipitation occurred. The wet green beads were removed from the water with the aid of a sieve and subsequently dried for 24 hours at 313.15 K. Afterwards the beads/aggregates were pyrolysed at 800 C.

[0122] These beads/aggregated can be incorporated with Argon gas via the porous plug to a metal melt in steel ladle or in a steel treatment ladle or in the converter.

EXAMPLE IV

[0123] A 42CrMo4 steel having an amount of sulphur 0.035% has been refined with the filter of Example II.

[0124] Inclusions were characterized in the metal melt before (i) and after (ii) refining, with an automatic SEM: [0125] (i) Pretreated steel below 10 ppm O after the Al addition without any filter immersion (reference): [0126] Total inclusions: 3917 [0127] Main groups: [0128] Alumina based inclusion: 940 [0129] Galaxite based inclusions: 62 [0130] MnO/MnS inclusions: 2335 [0131] + other inclusions [0132] (ii) Pretreated steel below 10 ppm O after the Al addition with a calcium [0133] aluminate/carbon filter immersion for 10 sec: [0134] Total inclusions: 680 [0135] Alumina based inclusions: 350 [0136] Galaxite based inclusions: 10 [0137] MnO/MnS inclusions: 10 [0138] + other inclusions

[0139] The about results provide evidence that the metal melt has been purified in that substantially all inclusions have been successfully removed.