US2013877A - Molybdenum-titanium ferro-alloys - Google Patents

Description

Patented Sept. 10, 1 935 MOLYBDENUM TITANIUM FERRO-ALLOYS I George F. Comstock, Niagara Falls, N. Y., assign'or to The Titanium Alloy Manufacturing Company,-New York, N. Y., a corporation ofrMaine Application March 23, 1934, Serial No. 717,073

No Drawing.

4 Claims. (01. 75-1) 5 acter for treating iron and steel to remove therefrom gaseous and other impurities that have ,in-

jurious effects, and also to modify the properties of such ferro-metals by incorporating therewith proper amounts of molybdenum and titanium that combine advantageously with the molten ferrometals in forming the finished product/which,

from an industrial and commercial viewpoint, is both economical and satisfactory.

The advantages of small additions of molybdenum, generally under 1%, to cast iron are wellrecognized, whereby an increase in strength, a slight increase in ductility and resistance to shock, a reduction in the size of the graphite flakes, and a slight increase in hardness and chilling tendency are beneficially effected.

The usual commercial varieties of ferro-molybdenum as used in steel are not well suited for additions 'to cast iron, since their melting point is too high, and their solution in the iron at ordinary foundry temperatures is too slow. Thus ferromolybdenum intended for use in cast iron is made with a very low carbon content and with considerable silicon so as. to lower its m'elting point to meet the industrial conditions.

.30 The advantages of small additions of titanium to cast iron were discovered many years ago, and this use of titanium has attracted considerable attention recently with the development of a ferro-titanium alloy that is low in carbon and high in silicon, so as to have a low melting point and rapid solubility in cast iron, such alloy being described in U. S. Letters Patent No. 1,946,670 issued to me February 13, 1934.

The effects of titanium comprise a marked de crease in size of the graphite flakes, an increase in graphitization, a slight increase in strength, and a retardation of the chilling tendency. The addition of titanium is therefore very useful in connection with a hardening element, such as molybdenum or chromium, since such titanium counteracts the chilling tendency of the latter elements, and supplements the increase in strength by a much more marked refinement of 50 the graphite flakes.

The use of titanium and molybdenum together in cast iron, while desirable for the reasons mentioned above, is rather difiicult in ordinary foundry p'ractice, especially when the iron is melted '55 in a cupola, and also when other alloys, such as chromium or :nickel, must be added simultaneously after the iron is tapped from the furnace.

This diliiculty is due to the fact thatthe addition of too much cold material to the iron at that time may decrease its fluidity so that it will not 5 flow well into the molds. It may be impossible to superheat the iron sufficiently in the cupola totake care'of this difliculty, and preheating the alloy additions not only makes handling them inconvenient, but also in case a highly reactive 10 alloy is used, such as term-titanium, it may impair the value of the alloy by oxidizing the surface.

The objects of this invention are, among other things, to combine the titanium and molybdenum which it may be desired to add to cast iron into 15 a single alloy so that the advantages of both elements may be obtained in the iron, without adding more cold material than wouldbe involved by the addition of a single alloy.

For example, if it should be desired to add 0.6% 20 molybdenum and 0.2% titanium to a cast iron, the addition of about 1.3% of a ferro-molybdenumtitanium alloy such as I have produced and will hereinafter. describe containing approximately 15% titanium and molybdenum, would be 25 sufilcient, and would require only 13 pounds of cold alloy to be melted by and dissolved in 1000 pounds of cupola iron; On the other hand, if the same addition were made by means .of the previously known ferro-alloys containing respec- 30 tively about 60% molybdenum and 20% titanium,

the incorporation of 20 pounds of cold alloy to the 1000 pounds of the molten iron would be necessary, or more than in excess of that involved with the use of my new combined molyb- 35 denum-titanium ferro-alloy. Furthermore the .melting point of the latter would naturally be a cleaner and more sound molybdenum alloy steel 45 may be produced by using this improved combined alloy as a source of molybdenum instead of the ordinary ferro-molybdenum, and the advantages of deoxidation and purification by titanium are likewise obtained in that way without the 50 necessity for making any further additions of solid alloys to the finished molten steel.

My improved molybdenum-titanium, ferro-alley herein described may be produced in a number of ways, and my invention is not confined to '55 any one method of manufacture, nor to any one composition of alloy product.

As an example of one method which has been used to form the desired combined alloy product, the following procedure is given:

A mixture of 251 grams of rutile, containing 78% TiOz, 2% silica and 20% iron oxide;

1'79 grams of roasted molybdenite containing 81% M003, 12% silica, 4% iron oxide, about 1% sulphur, and 2% other miscellaneous impurities;

144 grams of finely divided aluminum metal;

and

36 grams of cryolite (sodium-aluminum fluo ride, of commercial purity) as a flux (totaling 610 grams) were milled together in a ball mill for 15 hours, and the resulting powderwas then placed ina graphite crucible. Such mixture was then ignited by an electric arc resulting in a vigorous alumino-thermic reaction thev duration of which was about 45 seconds.

The contents of the crucible were taken out when cold, and a metal button of the following analysis was easily separated from the slag:-

, Per cent Molybdenum 47.52 Titanium 15.06

Iron 29.40 Aluminum n 2.81 Silicon (by difference) 5.21

Production on a larger scale would result in an alloy of lower residual aluminum content, and the relative amounts of the various constituents may be controlled by changing the mix used for the charge. A somewhat higher silicon content may often be desired for promoting easy fusibility and rapid solution of the alloy when used.

. The proportions of ingredients in the mixture used for the alumino-thermic reaction may be varied within wide limits, depending on the composition of metallic product desired. For example a similar reaction was started with the following proportions of the same ingredients as described in the above-example:

Per cent Alloys of similar character may be made in the electric furnace, by smelting ores of molybdenum and titanium in the same operation. Since the production of ferromolybdenum in the electric furnace requires a limeslag for'best results, and

since titanium cannot be reduced readily into a ferro-alloy out of a lime slag, it is advisable for making the combined alloy in an electric furnace either to reduce the molybdenum first, pour off the lime slag, and then reduce the titanium from another slag; or to make the ferromolybdenum the scraplast. This charge wassmelted for about separately and then add it, in place of scrap iron, to the bath from which titanium is reduced.

As examples of these two methods the following procedures were followed:

Example 3.-In a single-phase two-electrode 5 furnace lined with magnesite, a charge conslst-. ing of t was smelted for about 2 hours, using 2000 to 2500 amperes at 60 volts.

The slag was then poured off, leaving the alloy in the furnace, and a new charge composed of 20 was added the aluminum being melted first, and

2 hours, using 2500 to 3000 amperes at 60 volts, and finally both slag and alloy were poured out of the furnace. The alloy produced was found to contain Per cent 85 Titanium 13.10 Molybdenum 43.10 Silicon 1.67 Aluminum 3.57 o Carbon -2 0.09

' Iron plus impurities 38.47,

Example 4.--The other electric-fumace method may be illustrated by the followingF-The same furnace as above described was used, and a charge consisting of Per cent Aluminum 21.8 50 Ferromolybdenum (64% molybdenum) 21.6 Rutile (97% T102) "T54 Cryolite 2.8

was added, the aluminum being melted first and followed by the ferromolybdenum. The charge was smelted for 1 hours, using about 3000 amperes and volts, and the alloy produced con 00 tained f Per cent Titanium 19.09 Molybdenum A 51.38 Silicon 2.20 85 Aluminum 3.37

Carbon 0.09 Iron plus impurities 23.87

' In the production of these improved molybdenum-titanium ferro-alloys, it is advantageous if the contents of silicon and aluminum are fairly high, for instance up to -10 or 15%, as the presence of these elements lowers the melting points of the alloys and increases their fluidity, so that they separate more completely from the. slag formed when the alloys are made.

However, in the use of these alloys for additions to molten steel or cast iron, the presence of aluminum is not desirable because it may result in the formation of alumina in the steel or cast iron so treated with the'alloy. Alumina in steel or iron is very apt to cause dirtiness from the presence of non-metallic inclusions, or may form a tough skin on the surface of the molten metal so as to interfere with the smooth flow of the metal into the molds in which it is cast. Probably the efiect of about 3 to 4% of aluminum in the molybdenum-titanium ferro-alloys would not be noticeably objectionable, but larger amounts of aluminum should be avoided, for it is desirable to keep the aluminum content as low as possible. Hence aluminum should not be used to lower the melting point and increase the fluidity of these alloys. r Silicon, on the other hand, may-be incorpo ratedin my improved alloys to advantage as it improves production in the same way as aluminum does, and does not have the same detri-' mental effect as aluminum on steel or iron in which the alloys may be used. The presence of silicon to the extent of about 5 to 10% of the alloy is not only permissible, but definitely advantageous, especially in the alumino-thermic method of production, where it increases the.

yield by making the alloy more fluid and more easily separated from the slag in a clean form; and silicon is likewise advantageous in the use of the alloys in cast iron, where the lower melting point due to silicon is helpful in promoting the solution of the alloy, and the rapid diffusion in the iron of the more difilcultly fusible elements, such as titanium and molybdenum.

As a suitable source of silicon'in these improved molybdenum-titanium ferro-alloys made by the alumino-thermic method, I have found that calcium silicide as an addition to the mix offers several pronounced advantages.

It not only furnishes the desired silicon, but constitutes a comparatively cheap source of calcium. Calcium has almost as strong an ailinity for oxygen as aluminum, and is therefore an excellent reducing agent. By using calcium to replace some of the aluminum in the mixtures for alumino-thermic reactions, the total amount of heat generated in the mixture is not reduced, yet the'amount of aluminum is reduced so that there ;is less danger of. aluminum remaining in the metallic form in the resulting alloy. Calcium silicide in the mix therefore serves to give the advantages of a silicon content in the product, and at the same time provides a way to avoid the disadvantages of using too much aluminum.

For some purposes it may be desirable to have a higher titanium content than 20% in my improved molybdenum-titanium ferro-alloys, and this may beattained through the use of calcium silicide in the mix without too much sacrifice of economy or yield. When the mix for the alumino-thermic reaction as described, containing only rutile, roasted molybdenite, aluminum, and cryolite, was modified by using either more rutile or a higher-grade rutile so as to increase the proportion of TiO: to M00: in the mix so as to increase the titanium content of the alloy produced, the result of the reaction was that only a negligible amount of alloy was obtained in a clean solid button, since the slag and most of the alloy were too refractory to separate well.

Either a higher temperature, or an additional flux was required for good production.

Increasing the cryolite flux was not efiective, as it consumed more heat in melting. The use of sodium chlorate and more aluminum produced more heat, but titanium as well as aluminum were oxidized by the-chlorate, so that the aluminum content of the product came high; also the formation of additional alumina did not improve the fluidity of the slag.

The use of some magnesium in the mix with the chlorate helped in providing additional heat, but much magnesium could not be used because it reacted too explosively and blew the charge out of the crucible, and its oxide, like alumina, in-

creased the viscosity of the slag.

I found that calcium silicide, however, with some magnesium and sodium chlorate in themix, gave better results, permitting higher titanium contents to be obtained in the metallic products, without toohigh aluminum, and with reasonably high yields. The silicon improved the fluidity of the higher-titanium metal, and the calcium provided more heat in oxidizing; the calcium oxide also improved the fluidity of the slag, thereby promoting the separation of clean metal.

As examples of the efiects of the hereinbefore described variations, in the mix used for the production of molybdenum-titanium ferro-alloys by the alumino-thermic method, the following data are presented. The mixtures were prepared in amounts of 876 to 970 grams each, and were milled for 15 to 16 hours in an iron ball mill, and ignited by means of an electric arc in a graphite crucible. 4

Designation of examples A comparison of Example A with the Examples 1 and 2 first described will show how a simple increase in the titanium content of the same mix, 'even with increased aluminum, resulted in the separation or too small an amount of alloy, from the slag, for an analysis. Comparing these Examples 1 and 2 with Examples ,3, C, and D however, it will be noted that'alloys or higher titanium content were produced by proper proportioning of the mixtures containing calcium silicide.

A comparison of the mixtures in Examples Proportions of mix used A B C D I Per- Per- Per- Perce'nt cent cent cent Rutile (78% TiO 23 20' 20 8 Rutile (97% T102) 23 .22. 3 22. 3 23. 7 Roasted molybdenite (93% M00 23 Roasted molybdenite (81% M00 22. 3 20 12.4 Finely divided aluminum. 25. 3 18. 9 17.8 18. 6 Finely divided magnesium- 3. 3 3. 3 4. 1 Calcium silicide 4. 4 6. 7 5. 1 Sodium chlorate 4. 4 5. 5 6. 2 Cryolite 5. 7 4. 4 4. 4 4. 1

Analysis of alloy produced Per- Per- Per cent cant cent Titanium Not enough' 23.28 22.28 32. 4o for analysis.

Molybdenum "do... 37. 86 34. 30 21. 15 Silicon 14. 35 ll. 35 Aluminum. l. 98 7. 09 Iron plus impurities 27. 09 28. 01

a longer time.

um i'erro-alloys on a larger scale, better results in regard to recoveries and lower aluminum content of the alloy may be expected, because, owing to the smaller ratio of radiating surface of the larger crucible to the bulk of its contents,

there isa smaller proportion of heat lost by radiation in larger scale operation, and the charge thereiore reaches a higher temperature during the reaction and holds its hightemperature for This results in a more complete reaction, so that more of the aluminum is oxidized, and more of the other metals reduced from the slag.-

As an illustration of this eflect, Example E is now given which was made exactly similar to the first mentioned example; but using a charge oi. 12,750 grams instead of 610 grams.' The proportions of the mix used were the same, namely,

less aluminum and slightly higher molybdenum and titanium contents than the product of the small-scale reaction which I have first described in the first example. The alloy button obtained from the small charge weighed 125 grams, representing a recovery of 47% of the metallic elements' (other than aluminum) introduced, while the product of the larger charge weighed 3390 indicating a recovery of 61% of the same elem . I have also used calcium 'silicide eflectively inmaking ierroetitanium alloys as well as nickeltitanium alloys. lily-invention is not to be coniined to any particular method production, although the use oi calcium silicide as'an aid in producing alloys of high titanium content and low aluminum by the alumino-thermic method is considered a part of my invention. My invention is also not limited to any particular composition of the improved molybdenum-titanium g ierro-alioys, but covers these *compounds as a broad group oriamily oi alloys. For most purposes however, it is believed that the alloys would be most useful especially in cast iron, if the molybdenum content were about three times the titanium content, and with aluminum as low as possible, and iron not' over 30%. The preferred specification or contents for a standard grade of molybdenum-titanium ierro-alioy would.there- Iron plus impurities to 30% (24% average) 20 For treating certain grades of alloy steels, a higher proportion of titanium to molybdenum might be desirable in theierro-alloy, and a composition similar to that stated for Example D" 25 above would then be called for.

By the term balance substantially iron occurring in the claims, I mean that the alloys called for may also contain small amounts of additional metals totaling from a trace to not more than 5%, such as manganese, copper, chromium and zirconium, as well as the addition of a trace to, about 4% of one-or more of the elements, carbon, phosphorus, sulphur, nitrogen, oxygen, etc.: these additions being insuilicient in quantity to change substantially the characteristic properties of the said alloys.

I claim as my invention:

1. A rerro-alloy having a low melting point and freely flowing for treatingl'ilynolten cast iron 40 or steel containing substantia 25 to 75% oi molybdenum, substantially 5 to of titanium, and the balance principally iron.

2. A term-alloy having a low melting pointand treely'iiowing for treating molten cast iron 45 or steel containing molybdenum 25-75%. titanium 545%, silicon trace to 25% and aluminum trace to 15% withthe balance substantially iron.

8. A .ierro-alloy having a low melting point and freely flowing for treating molten cast iron 60 or steel containing molybdenum 41-55%, titanium 12-20%. silicon 8-121, aluminum trace to 4%, and the balance substantially iron.-

4. A ierro-slloy having a low melting point 5 and freely ilowing for treating molten cast iron or steel containing molybdenum about 48%, tita num about 16%, silicon about 10%, aluminum about 2%, and the balance substantially iron.

GEORGE I". COMBTOCK.