US 3867133 A
High-Ni and/or high-Co, Mo-containing alloy steel is melted and peroxidized to convert Mo contained in the steel into molten Mo oxides. This peroxidized molten steel is treated with a molten slag forming agent comprising at least one basic oxide selected from the group consisting of alkali metal oxides and alkaline earth metal oxides and at least one acid oxide, to form double salts with the said Mo oxides and the said slag forming agent, and then discharging steel slag containing the said double salts.
Description (OCR text may contain errors)
Matted States Patent [1 1 Nagnro et at.
[ REFHNHNG PROCESS FOR REMOVING MO FROM HIGH-Nil AND/0R HIGH-CO, MiG-CONTAINING ALLOY STEELS  Inventors: Kazutalta Naguro; Taltao Seya, both of Tokyo, Japan  Assignee: Kawaguchi Seiko Kabushiki Kaisha, Kawaguchi, Japan  Filed: Sept. 17, 1973  Appl. No.: 398,157
 Foreign Application Priority Data Mar. 23, 1973 Japan 48-32736  U.S. Cl... 75/53, 75/54, 75/55,
7 75/129  Int. Cl. C2lc 7/04, C22c 33/00  Field of Search 75/53-60, 129
 1 References Cited UNITED STATES PATENTS r 3,309,196 3/1967 Kaneko 75/53 [4 Feb. 18, 1975 1/1966 Richter .[75/60 5/1967 Bowden ..75/53 Primary Examiner- Peter D. Rosenberg Attorney/432m, or FirmFlynn & Frishauf 5 7] ABSTRACT 5 Claims, N0 Drawings 1 REFINING PROCESS FOR REMOVING MO FROM HIGH-NI AND/OR HIGH-CO, MO CONTAINING ALLOY STEELS FIELD OF THE INVENTION This invention has to do with the refining of molybdenum-containingalloy steels to remove molybdenum (Mo) therefrom.
BACKGROUND OF THE INVENTION In the past, it has been very difficult to eliminate Mo from high-Ni and/or high-Co, Mo-containing alloy steels used particularly in jet engines and gas turbines. Mo has a considerably lower oxygen-affinity than has Fe. Mo oxides have less stability than FeO and larger dissociation constants than FeO, such that M is not practically oxidized in an oxidation refining in which undesirable elements are removed in the form of slag by oxidation.
In spite of these reasons, we have long carried out research on a method for facilitating the transfer of the Mo oxides into slag, based on our recognition that M0 is still present in molten steel in the form of Mo oxides in combination with oxygen, though in a slight quantity in molten steel in the peroxidized state, and the further recognition that the Mo oxides have a very low solubility and exhibit very slight transfer into slag in an ordinary oxidation refining. As a result, we have discovered that Mo oxides dissolved in molten steel can be transferred into slag by combination with a molten basic slag forming agent comprising at least one basic oxide se lected from the group consisting of alkali metal oxides and alkaline earth metal oxides and at least one acid oxide as principal constituents.
The object of this invention is to provide a refining process for effectively removing Mo from high-Ni, and- /or high-Co, Mo-containing alloy steels.
SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a process for subjecting a high-Ni, and/or high-Co, Mo-containing alloy steel to oxidation melting refining to form a peroxidized molten steel containing Mo oxides; contacting the peroxidized molten steel with a basic double oxide, comprising (i) at least one basic oxide selected from the group consisting of an alkali metal oxide and an alkaline earth metal oxide and (ii) at least one acid oxide, and with at least one oxidizer selected from the group consisting of a solid oxidizer, oxygen gas, an oxygen-enriched gas and a mixture thereof, toform a double salt of said double oxide and said Mo oxides; and discharging a slag containing said double salt.
DESCRIPTION OF THE PREFERRED EMBODIMENTS In a more detailed description of the present invention, a high-Ni and/or high-Co, Mo-containing alloy steel is melted, the said molten steel is subjected to oxidation refining by means of a solid oxidizer such as iron ore or a gaseous oxidizer such as oxygen gas, and substantial amounts of Cr, C, P, Mn, Si and other undesirable elements contained in the said molten steel are removed. When thisoxidation refining is excessive, the
said molten steel is partially peroxidized, thus resulting in the partial oxidation of the Mo constituent and transfer of Mo into slag. Because the amount of this transfer is very slight, and there is a considerable oxidation loss of Fe and other alloying elements, the Mo-removing refining, if conducted during this oxidation refining, would have only a limited effect. If most of the C, P, Mn and Si constituents were oxidized, it would be possible to cause the transfer of Mo in molten steel into slag even in the presence of a considerable amount of Cr. However, it has been revealed experimentally that the Mo-removing reactions proceeded fully only when the Cr content in'the molten steel is decreased to less than about 1 percent by weight, the contents of each of C, P, Mn and Si are decreased to less than about 0.1 percent by weight, respectively, and the oxidation r'efining is applied to a molten steel containing more than about 0.02 percent by weight of oxygen.
The said Mo-removing reactions are carried out through the addition of oxidizers and a basic double oxide into molten steel at the same time. The said oxidizers include such solid oxidizers as Fe O FeO and Fe O and such gaseous oxidizersinclude oxygen, air, and oxygen-enriched gases. The said basic double oxide, which has previously been melted and combined and exhibits basicity as a whole, is principally composed of one or more basic oxides selected from the group consisting of alkali metal oxides and alkaline earth metal oxides such as Na O, CaO, MgO, K 0, Li O, BeO, BaO, SrO, Cs O and mixtures of two or more thereof, and at least one acid oxide selected from SiO A1 0 and mixtures thereof. Thus, the basic double oxides are typified by: 2Na O.SiO 2CaO.SiO 3K O.Al O 3CaO.2Al O and 3MgO.SiO
Accordingly as the said Mo-removing reactions proceed, leading to a lower content of M0 in molten steel, the content of Mo oxides in slag formed by Moremoving refining becomes higher, and this makes further Mo-removing reactions difficult to take place under the effect of Mo equilibrium between slag and molten steel. It is therefore necessary to repeat Moremoving refining several times to exclude slag and to form new slag. The frequency of this Mo-removing refining varies with the level of Mo-removaland the degree of operational success; two or three cycles suffice when reducing the Mo content to less than 0.05 percent from molten steel containing 2 percent M0.
The said Mo-removing reactions depend upon the molten steel temperature, degree of peroxidation and the presence of alloy elements. Low temperatures have in general a desirable effect on such reactions, and the oxygen activity of alloy elements exerts an influence on these reactions. Mose of the alkali metals and alkaline earth metals have a very high affinity for oxygen as compared with that of Fe, Ni and Co, and are therefore hardly contained as alloy elements in molten steel by reduction, even when their oxides are added or injected into molten steel, but these alkali metal oxides and alkaline earth metal oxides are present in slag in a stable state in combination with Mo oxides. The said basic oxides include Na O, CaO, MgO, K 0, LiO BeO, BaO, SrO andCs O, and the said acid oxides include SiO and A1 0 As described above, by adding or directly injecting into peroxidized molten steel the previously melted and cooled double slag forming agent consisting principally of alkali metal oxides and/or alkaline earth metal oxides and acid oxides, the Mo constituent in the said molten steel is subjected to Mo-removing refining through its conversion into slag in the form of double salts in combination of the said molten double slag forming agent and Mo oxides.
The following examples will illustrate the practical application of the present invention. All percentages mentioned below are by weight unless otherwise indicated.
EXAMPLE 1 1. Melting-down:
2. Oxidation melting refining:
After slagging, 25kg of CaO and 200kg of iron ore were added into the said melt-down molten steel for a cycle, and Cr-removing oxidation refining was conducted while blowing oxygen into the resulting molten mixture. This cycle of oxidation melting operation involving adding CaO and iron ore while blowing oxygen and slagging, was repeated eight times. Consequently, a molten steel containing 0.1 percent Cr and 1.24 percent Mo was formed.
3. Mo-removing refining:
Then, Na 'O and SiO were mixed at a mol ratio of 2:1, melted,and after cooling, milled to a particle diameter of 1 -2mm, thus forming a slag forming agent comprising basic double oxides of the present invention. Mo-removing refining was performed by adding 80kg of this slag forming agent and 30kg of iron ore for every cycle into molten steel after the oxidation melting refining. During this Mo-removing refining, there were no fumes, and the Mo content in molten steel was decreased to 0.062 percent through four-cycles of this refining. The molten steel obtained had a chemical analysis of 22.9 percent Ni, 21.9 percent Co, 0.062 percent Mo, 0.012 percent C, 0.012 percent P, traces of each of Cr, Si and Mn, and the balance Fe.
For comparison, Mo-removing refining was carried out by adding 80kg of Na CO and 30kg of iron ore per cycle to molten steel after the said oxidation melting. White fumes were evolved. The fumes principally comprised decomposed CO gas and Na O evaporating at about 1,250C. Furthermore, in order to reduce the Mo content in molten steel to the above presented level of 0.062 percent, it was required to repeat the cycle six times, and the furnace wall was seriously damaged.
EXAMPLE 2 ple 1, principally consisting of 2CaO.SiO- in the form 6 of a double oxide powder was injected, with high pressure air as carrier gas, into the said peroxidized molten steel. This constituted the first cycle of Mo-removing refining. There was almost no white fume which might cause air pollution, during injection. After the completion of the said first cycle of injection, slag was discharged, and a second injection was conducted in the same manner. Upon the completion of a third similar injection, the Mo content in molten steel decreased to 0.052 percent, and the molten steel had a chemical analysis comprising 23.9 percent Ni, 22.3 percent Co, 0.05 percent Mo, 0.014 percent C, trace of Cr, and the balance substantially Fe.
For comparison, another Mo-removing operation was carried out under the same conditions as in the operation presented above, except for the use of lime (CaO) powder in place of 2CaO.SiO powder. White fumes were produced during the injection operation, and five cycles of injection and slagging were required for reducing the Mo content in molten steel to about 0.05 percent.
As is clearly shown in Examples 1 and 2, the slag forming agent showing the basici'ty in the present invention is formed by admixture and then melted. ln adding and injecting this slag forming agent into a molten steel, therefore, no toxic gas is produced, thus leading to no pollution nor damage to the furnace wall. Furthermore, as the slag forming agent of this invention is formed with a a previously melted and cooled double salt made from basic oxides and acid oxides, it is rapidly stabilized after its addition into molten steel in the form of a molten slag layer.
This invention is applicable vto all high-Ni and/or high-Co, Mo-containing alloy steels containing about 20 percent by weight or more Ni and/or Co in total.
Oxidation melting refining of high Ni and/or high- Co, Mo-containing alloy steel is repeated until, in the peroxidized molten steels thus obtained, the C content becomes less than about 1 percent by weight, the contents of each of C, P and Mn, less than about 0.1 percent by weight, and the 0 content, more than about 0.02 percent by weight.
In the oxidation melting refining of the' Mocontaining alloy steels, temperatures of from about 1,500 C. to about 1,650 C. are generally employed. The Mo-containing alloy steels are peroxidized to an oxygen content of from about 0.02 to about 0.3 percent by weight of oxygen. Thus, the peroxidized molten steel is at a temperature of from about 1,400 C. to about 1,550 C. when contacted with the basic double oxide and an oxidizer.
The quantity of basic double oxide employed can be varied considerably. Generally, from about 50 to about 60 kilograms of double oxide are used for each ton of Mo-containing alloysteel. Similarly, from about 0.5m to about 2m of oxygen as an oxidizer are used for each ton of Mo-containing alloy steel.
What is claimed is:
l. A refining process for removing Mo from a Mocontaining alloy steel having a high content of at least one of Ni and Co, which comprises:
subjecting said Mo-containing alloy steel to oxidation melting refining at a temperature of from about 1500".C. to about l650C. to form a peroxidized molten steel containing Mo oxides and having the following approximate elemental analysis in percent contacting said peroxidized molten steel at a temperature of from about l400C. to about 1550C. with a basic double oxide comprising (i) at least one basic oxide selected from-the group consisting of an alkali metal oxide and an alkaline earth metal oxide and (ii) at least one acid oxide, and with at least one oxidizer selected from the group consisting of a solid oxidizer, oxygen gas, an oxygen-enriched gas and a mixture thereof, to form a double salt of said double oxide and said Mo oxides, and
discharging a slag containing said double salt.
2. The process of claim 1 wherein said Mocontaining alloy steel contains at least about 20 percent by weight of a component selected from the group consisting of Ni, Co and a mixture thereof.
3. The process of claim 1, wherein the basic oxide is selected from the group consisting of Na O, CaO, MgO, K 0, Li O, BeO, BaO, SrO, C5 0 and mixtures of two or more thereof.
4. The process of claim 1, wherein the acid oxide is selected from the group consisting of SiO Al O and mixtures thereof. H
5. The process of claim 1, wherein said Mo-alloy steel contains at least about 20 percent by weight of a component selected from the group consisting of Ni, Co