US2033974A - Ferro-carbon-titanium alloy - Google Patents

Description

Patented Mar. 17, 1936 s PAT FEBRO-CARBON-TITANIUM ALLOY George F. to The Comstock, Niagara Falls, N. Y., assignor Titanium Alloy Manufacturing Company, New York, N. Y., a corporation of Maine No Drawing. Application June 20, 1935,

Serial No. 27,543 5 8 Claims.

application is a continuation in part of such as is used for sheets that must be very ductile, the ordinary low-carbon ferrotitanium alloys are not used to advantage, either on account of their high cost, or because of their high silicon or aluminum contents.

The reason for the objection to a high silicon content is that such steels or ingot-irons are best cast in the form of effervescing ingots, in which the evolution of gas on solidification causes the outer skin to solidify in an especially clean and pure state so that the highest ductility is attained; the presence of silicon in appreciable amounts in the steel interferes too much with the proper effervescence and structure of the ingots.

The reasons for the unsuitability of the other kind of low-carbon ferrotitanium alloy (of low silicon content), which has heretofore been available commercially for use in low-carbon steels, are chiefly that its cost is too high owing to the necessity for using considerable aluminum in its manufacture, and also in part because of the unavoidable presence in the alloy of an efiective amount of aluminum which has the same undesirable action on effervescing steel as that of silicon which I just described.

For efiervescing low-carbon steel, it has generally been found advantageous to use the highcarbon ferrotitanium, or ferro-carbon-titanium as it is known commercially, which can be made much cheaper than the aluminum-reduced lowcarbon alloy. It is added in rather small amounts to the molten steel a short time before pouring, and acts as a mild de'oxidizer and scavenger to control the efiervescence of gas on solidification of the steel and to produce ingots of the .best possible form, structure, and cleanness.

This commercial ferro-carbon-titanium, although suficiently free from silicon and aluminum to be satisfactory as an addition to effervescing steel, has suffered, up to the time of my present invention, from the disadvantage of too high a carbon content for use in the making of the present-day extremely low carbon steels.

The steels of this low-carbon type which are now made for rolling into sheets that must be formed cold into intricate shapes, such as automobile bodies, must have the lowest possible carbon content in order to permit the necessary distortion without cracking. After the addition of commercial high-carbon ferro-carbon-titanium to this steel, it is often found that the carbon content of the resulting steel is appreciably increased on account of the additional carbon added in the titanium alloy; hence an undesirable limit is imposed on the amount of titanium added so as not to get too much carbon in the steel.

The common high-carbon ferro-carbon-titanium alloyv heretofore in commercial use contains about to 18% titanium, 6 to 9% carbon, 2 to 3% silicon, and 1 to 2% aluminum.

In spite of statements published in the early years of the titanium alloy industry to the efi-ect that alloys of this nature contained free titanium and free carbon, it is now definitely established that the afiinity of titanium for carbon is so very strong that practically all the titanium in such an alloy combines with carbon, to form the carbide (T'lC) which contains 48 parts by weight of titanium to 12 parts by weight of carbon. Highcarbon ferro-carbon-titanium, therefore, consists structurally of titanium carbide in a matrix similar to gray cast iron, and also contains from 2 to 4% excess carbon, since the carbon content of the alloy is well over one-fourth of the titanium content. This excesscarbon, as shown by chemical analysis and by the dark fracture of the alloy, occurs largely in the form of graphite.

Several methods have been tried in the past to produce alloys similar to commercial ferro-carbon-titanium except with a lower carbon content, but the products of such methods invariably suffered from serious objections ,which rendered them unsuitable for use as sources of titanium for the treatment of low-carbon efiervescing steel. Methods involving the use of silicon or aluminum either to replace carbon as a reducing agent for the titanium ore, or to drive out the carbon from the molten alloy by-precipitation, gave products too high in those elements, and hence are unsatisfactory as hereinbefore explained.

The method of boiling out the carbon from the molten bath of alloy, after its reduction from the ore, by ore additions as commonly practiced in the refining of steel, has not been commercially successful, since when the carbon is really lowered in this way, the titanium is at the same time removed from the alloy either by oxidation or by precipitation of an infusible nitride in the furnace, so that the fluid low-carbon alloy thereby produced is of such a low titanium content as to be commercially worthless.

By the improved method which is hereinafter described for the production .of the alloy constituting the subject of my invention, I have succeeded in making regularly on a large scale and at a low cost a ferro-carbon-titanium with the desired titanium content between 1'7 and 23%, with carbon from 1.5 to 5%, and with not over 3% of silicon, aluminum, or other undesirable impurities. The carbon content is held below one-fourth of the titanium content so as to ensure the practical absence of graphite from the alloy, and this product has been found after industrial tests entirely suitable as a source of titanium for the treatment of efiervescing steels, similar to ingot iron, of the very lowest carbon content.

My improved lower-carbon ferro-carbon-titanium alloy is preferably made in a single-phase carbon-lined electric furnace, similar to the furnace used for the regular high-carbon alloy, except that it is operated so that carbon is not absorbed from the furnace lining. The charge is composed of 350 pounds ilmenite, 250 pounds steel scrap, and 185 pounds anthracite coal. Current is supplied through a single electrode, at a potential of 50 volts, and regulated to use about 15,000 amperes. The absorption of carbon from the furnace is prevented by omitting a portion or all of the steep scrap from the first few charges so that the excess of ilmenite produces a furnace lining of a refractory titanium compound. By careful maintenance of this high-titanium lining, the furnace may be used for a very much larger number of heats without renewal of the crucible, than has heretofore been possible ordinarily in making the high-carbon alloy.

About half an hour before tapping a finished charge, an addition of 20 to 40 pounds of fine ilmenite ore may be advantageously made to the molten bath so as to produce a boil which assists in lowering the carbon content. This addition may be omitted, however, if the furnace is producing an alloy of sufficiently low carbon content without it, or if necessary the addition of ilmenite may be increased to as much as pounds.

The finished-product of this process is a homogeneous melt, and may be cast readily from the furnace. Such alloy solidifies in the form of a dense, solid, crystalline mass, free from the porosity that characterizes the common high-carbon ferro-carbon-titanium alloys. My new alloy is sufliciently hard and lacking in toughness to be crushed fairly readily to the size demanded for additions to molten steel, and when so crushed it exhibits on its surfaces a bright or light-gray fracture free from any black coloration such as is produced by the graphite in the high-carbon alloy. In my alloy the carbon content is substantially all in the combined form with any graphite below 0.2%.

An analysis of an average sample from a large number of casts of my improved lower-carbon ferro-carbon-titanium gave results as follows:-

' Per cent Titanium 19.75 Carbon 4.45 Silicon 2.56 Aluminum 1.30 Manganese 0.08 Chromium 7 0.073 Phosphorus 0.023

The balance of my new alloy is substantially iron, with unimportant traces of copper, nickel, zirconium, sulphur, nitrogen, etc. All components other than iron, carbon, and titanium are derived from impurities in the ore, scrap, or coal of the charge used in the furnace. and are not intentionally introduced, but must be controlled within reasonable limits.

By decreasing the proportions of iron and carbon in the charge, an alloy of still lower carbon content may be made, while preserving in other respects the characteristics of the alloy herein described. For example, alloys containing about 24% titanium and 1.84% carbon have been produced in the course of my experiments connected with the development of this new alloy. If the carbon is reduced too low, however, difliculties are encountered either from nitride formation, making the alloy too viscous and diflicult to tap from the furnace, or from solution of the hightitanium furnace-lining which results in preventing the production of low-carbon alloy in subsequent operations. For these reasons it has not been found practical as yet to produce regularly alloys with the proper titanium content 01' from 15 to 25% and less than about 2% carbon substantially iron. My preferred composition is 18 to 22% titanium, 3 to 4.5% carbon, 1 to 3% silicon and 0.5 to 1.5% aluminum, with the balance substantially iron, it being impractical to use sufficiently pure ore and coal to secure silicon and aluminum contents below these limits which I have given. They are low enough however to permit the alloy to be used in eflervescing or rimming steel without interfering with the proper evolution of gas in the molds.

The carbon content of my new ferro-carbontitanium alloy should be practically all in the combined form, with graphite below 0.2%, and to secure this result the total carbon is kept below one-fourth of the titanium content. As an illustration of the effectiveness of this relation, the following analyses are given as a result of my tests in the following table:

The graphic residue as stated in the above table was determined by dissolving an analytical sample of the alloy in nitric acid, filtering off the insoluble residue which includes all graphite, and then determining the amount of carbon in that residue by combustion in the standard manner.

Since the titanium content of my improved low-carbon-ferro-carbon-titanium alloy is over four times the carbon content, or more than suflicient to form titanium-carbide with all the carbon present in the alloy, it is obvious that it differs from the previous high-carbon ferrocarbon-titanium not only in containing practtically no graphite, but also in advantageously having an appreciable amount of titanium not combined with'carbon but occurring as a solid solution or compound with iron or other impurities. Therefore the titanium in my new alloy exists on the whole in a more free and effective form for acting on the steel in which the alloy is used, than in the old high-carbon alloy in which, on account of the excess of free carbon, all the titanium must necessarily be combined as carbide due to the recognized strong aifinity of titanium for carbon.

The alloy with less than 5% total carbon and less than 0.2% graphite has been found not to increase appreciably the carbon content of steel to which it is added as a deoxidizer, whereas 'an alloy containing free carbon or graphite has been found to carburize in an undesirable way the steel in which it is incorporated.

Hence by the use of this improved low-carbon ferro-carbon-titanium, steel manufacturers are now enabled to take advantage of the purifying and other beneficial efiect's of titanium in soft steel containing less than 0.07% carbon without the danger of raising the carbon too high as is likely to occur when using the regular ferrocarbon-titanium of 6 to 9% carbon content.

Until the development of my improved alloy, producers of soft steel containing less than about 0.07% carbon were unable to obtain the advantages of titanium treatment of their steel in order to produce better rolling quality and greater cleanness, because they found that the regular ferro-carbon-titanium containing 6 to 9% carbon, a large proportion of which is in the free or graphitic state, gave too high a carbon content in the finished steel. As I have hereinbefore stated, the previously known low-carbon ferrotitaniums were too high in silicon or aluminum to be practical for use in this kind of steel.

However, with my new ferro-carbon-titanium alloy containing less than 0.2% free carbon, low in silicon and aluminum, and having a close dense structure, the titanium treatment of very low-carbon steel may be accomplished successfully, with resulting benefits to the cleanness, rolling quality, and surface of the steel, and without the absorption by the steel of appreciably more carbon than it would have without any final addition of a deoxidizing or scavenging alloy.

The dense structure and lack of porosity of my new alloy have been found not to interfere with its solubility in molten steel, provided the titanium content is not over 25% and the carbon content is not below 1.5% or over 5%, and these characteristics constitute an industrial advantage in that they tend to cause the readily.crushable particles of alloy to sink into the steel bath to which they are added, instead of remaining on the surface as porous particles of the older high-carbon alloy tend to float, soihat my new alloy is more effectively incorporated in the steel and is not so readily lost by burning in the air at the surface of the bath.

I claim as my invention:-

1. An alloy capable of being cast from an electric furnace and soluble in molten steel, said alloy containing 15 to 25% titanium, 1.5 to 5% carbon and less than one-fourth the titanium content, not over 0.2% graphite, not over 3.5%

silicon and not over 3% aluminum, with the balance substantially iron.

2. An alloy capable of being cast from an electric furnace and soluble in molten steel, said alloy containing 15 to 25% titanium, 1.5 to 5% carbon substantially all in the combined form,

not over 3.5% silicon, and not over 3% aluminum, with the balance substantially iron.

3. An alloy capable of being cast from an electric furnace and soluble in molten steel, said alloy containing 1.5 to 5% carbon substantially all in the combined form, 15 to 25% always in excess of four times the carbon content and partly free from combination with carbon, not over 3.5% silicon, and not over 3% aluminum, with the balance substantially iron.

4. An alloy capable of being cast from an electric furnace and soluble in molten steel, said alloy containing 18 to 22% titanium, 3 to 4.5% carbon, with the titanium content partly free from combination with the carbon, 1 to 3% silicon, and 0.5 to 1.5% aluminum with the balance substantially iron.

5. In the manufacture of ferro-carbon-titanium alloys containing from 15 to 25% titanium and less than 5% carbon by carbon reduction in a carbon-lined electric furnace, the step which consists in forming an inner lining of a refractory titanium compound on the carbon lining of said furnace by melting therein a charge containing titanium ore and carbon, said ore being in an amount in excess of that required to produce a completely fusible mass, whereby a lining of a refractory titanium compound is superposed on said carbon furnace lining.

6. In the manufacture of ferro-carbon-tita nium alloys containing from 15 to 25% titanium by carbon reduction in a carbon-lined electric furnace, the step which consists in melting therein a charge of ilmenite and carbon, said ilmenite being in excess of the amount required for said alloy, to form from the molten mass a lining of a refractory titanium compound superposed on said carbon furnace lining.

7. In the manufacture of ferro-carbon-tita nium alloys containing from 15 to 25% titanium by carbon reduction in a carbon-lined electric furnace, the step which consists in melting therein a charge of ilmenite, carbon and steel scrap, said ilmenite being in excess of the amount required for said alloy, to form from the molten mass a lining of a refractorytitanium compound superposed on said carbon furnace lining.

8. The method of treating eifervescing low carbon steel with titanium without increasing its carbon content which consists in incorporating in the molten steel 9. ferro-carbon-titanium alloy containing 15 to 25% titanium, 1.5 to 5% carbon and less than one-fourth the titanium content, and not over 0.2% phite, not over 3.5% silicon and not over 3% aluminum, said alloy being soluble in the molten steel and not appreciably increasing the carbon content of the efiervescing steel so treated.

GEORGE F. COMS'IOCK.

titanium and