US2141671A - Manufacture of wrought iron - Google Patents

Description

Patented Dec. 27, 1938 UNITED STATES MANUFACTURE OF WROUGHT IRON Edward B. Story, Library, Edgeworth, Pa., assignors and Evard P. Best, to A. M. Byers Company, Pittsburgh, Pa, a corporation of Pennsylvania No Drawing. Application May 26, 1937, Serial No. 144,920

4 Claims.

The present invention relates to the manufacture of wrought iron, and more particularly to an improvement in the Aston process in which a previously formed molten refined iron is mixed '5 in comminuted form with a previously formed molten slag to form a wrought iron ball, which is then handled in the usual way to expel the surplus slag and produce the product known as Wrought iron. We have found that the addition of an efiective amount of aluminum to the refined metal, prior to the incorporation of the slag, produces a marked improvement in the process, particularly in the control of the slag content and its distribution in the finished product. The wrought iron also has an increased tensile strength and a lessened susceptibility to aging.

The invention will be described with particular reference to its embodiment in the'present commercial practice of making wrought iron in accordanoe with the Aston process. In such commercial practice, the iron is first blown in a Bessemer converter, the blowing being continued at a relatively high temperature until the iron is full-blown. The blown metal from the Bessemer converter is poured into a transfer ladle, from which it is in turn poured into the ladles of the shotting machines, which serve topour the molten refined iron into receptacles containing molten iron-silicate slag, known as processing slag. Through a combination of physicochemical reactions involving metal solidification and relative gas solubilities of the metal in the molten and solid conditions, the molten refined metal is disintegrated into a comminuted form to form a spongy mass of iron and slag, which collects at the bottom of the slag receptacle. This ball or mass of commingled iron and slag is removed and squeezed to expel the surplus slag. It is then subjected to the usual rolling operations to produce products such as bars and plates which have the well known fibrous structure characteristic of Wrought iron.

It has been recognized that in the best Wrought iron the slag fibres should be thin and uniformly distributed. In the commercial manufacture of wrought iron, as heretofore carried out, it has been difiicult to uniformly secure the desired fineness and uniform distribution of the slag fibres, and it is frequently necessary to roll the iron to bar form and repile and reroll in order to secure a fine textured slag distribution. Notwithstanding all these precautions the wrought iron has often displayed undesirably large individual slag pockets.

We have found that if an efiectiveamount of aluminum is added to the refined iron before it is dispersed in the processing slag, a finer textured and more uniform distribution of the slag is secured, and that the tendency to form large slag pockets order to be effective, the aluminum should be added in an amount of at least two pounds per ton of the Bessemer metal, but not exceeding fifteen pounds per ton, as aluminum in such high ranges adversely affects the Weldability of the Wrought iron. The aluminum is added preferably from two to six pounds per ton, usually about four pounds per ton of the Bessemer metal.

In applying the invention to the usual com mercial operation of the Aston process, the iron is first fully blown in a Bessemer converter in the usual way and then poured into the transfer ladle. The iron is then poured from the transfer ladle into the ladles of the shotting machines. During such pouring the aluminum is added, preferably being thrown into the stream of metal. The aluminum is preferably added in the form of a 50% ferro-aluminum because of its greater specific gravity, the necessary aluminum addition being figured on the basis of 50% aluminum in the term-aluminum. The refined metal to which the aluminum thus added is then poured into the receptacles containing the separately formed molten iron-silicate slag, as described for example in the Wille Patents Nos. 1,890,660 and l,933,5'l7.' As the stream of molten iron enters the slag, it is disintegrated and the iron in comminuted form is dispersed in the processing slag and settles through the slag to the bottom of the receptacle forming a spongy mass. of iron and slag or ball, which is removed, squeezed to expel the surplus slag and to weld the iron particles together to form a bloom which is then rolled in the usual Way.

Since the full-blown iron is highly oxidized, the aluminum is undoubtedly substantially all converted into aluminum oxide. As is well known, the alumina inclusions formed in steel when aluminum is used as a deoxidizer are in a relatively fine state of dispersion. The alumina particles are highly iniusible and do not display a tendency to combine with neighboring particles to form masses large enough to rise up and clear themselves of the metal. If the metal from the Bessemer converter, to which the aluminum has been added in relatively large amounts required in our process, were to be cast in ingot form, the amount of alumina inclusions would undoubtedly be so great as to detrimentally affect, if not completely spoil, the metal. However, we have found that under the peculiar conditions obtaining in the Aston process in which the refined metal is mixed in comminuted form with the processing slag, such alumina inclusions are substantially eliminated from the iron. The iron solidifies in the form of tiny individual particles, which present a very large aggregate surface between the iron and the slag, so that the finely dispersed alumina particles are eliminated or is substantially eliminated. In I washed from the metal by the slag and the metal itself shows little if any evidence of alumina inclusions. Since the metal is highly oxidized, the aluminum is substantially completely oxidized and eliminated from the iron, the analysis of the iron showing at most but a trace of aluminum,

' when the preferred amount of about two to six pounds per ton of aluminum is used.

The exact mechanism whereby the aluminum insures a more uniform and finer textured slag distribution isnot at present fully understood. While the aluminum undoubtedly deoxidizes the metal to a large extent, deoxidation alone does not apparently account for the improved properties, since if the metal is deoxidized with the usual deoxidizers, silicon or manganese, the wrought iron is detrimentally affected. It may be that the presence of the aluminum in the iron,

or the presence of the alumina which is expelled from the iron particles as they solidify, affects the wetting action of the slag upon the iron. Whatever may be the reason, the slag appears to be more easily expelled from the ball in the press and exists in the form of finer and more uniformly distributed fibres in the rolled product.

Tests have shown that if a refined heat of iron from the Bessemer converter is divided into two portions, one of which is treated in accordance with our process and the other untreated, and both portions processed, pressed, rolled and otherwise handled in an identical manner, the wrought iron from that portion which was treated with aluminum will display a substantial difierence in character from that produced from the untreated metaL'in that the fibrousness of the untreated metal will be considerably more coarse in texture than that of the treated metal, and the slag fibres will be larger and willnot have the fine and uniform distribution obtained in the 1 aluminum-treated metal. Also, the metal treated with aluminum will have an increased tensile strength; for example, if the untreated metal has a tensile strength of about 48,000 pounds per square inch, the treated metal will have a tensile strength of about 51,000pounds per square inch. The treated metal also has a lower susceptibility to aging either by strain aging or quench aging.

While the addition of the aluminum is particularly advantageous to metal refined in a Bessemer converter, the metal for making the wrought iron may be otherwise refined, as in an open-hearth or electric furnace, in which case smaller amounts of aluminum may be required as the metal is .less oxidized.

While the amount of aluminum added is considerably greater than that employed in usual steel making practice to kill the steel in the ingot molds, the amount of aluminum used is preferably less than that theoretically required to completely deoxidize the Bessemer metal. For example, it would require about eight pounds of aluminum per ton to completely deoxidize the full-blown metal from the converter, whereas we find that about four pounds of aluminum per ton is sufficient to give the desired control of the slag distribution. When the hotter metal is poured into the cooler slag as in the Aston process, the solidification of the metal causes release of in cluded gas which results in a dispersion of the metal into the slag in a finely comminuted form. As the finely comminuted iron particles become solidified, the solubility of the iron oxide is greatly decreased and the iron oxide is expelled is fully efiective during the solidification of the iron and the formation'of the spongy mass or ball of iron and slag, since the iron is not subjected to any continued or substantial oxidation between the time of the aluminum addition and the solidification of the iron in comminuted form upon its incorporation into the slag. The aluminum addition would be ineffective for the purpose of the present invention, if the Bessemer metal to which the aluminum is added were to be puddled in an iron-oxide-containing slag, since such pud-dling would result in a reoxidation of the metal and the dissipation of the deoxidizing effect of the aluminum before the iron could come to nature and form a puddle ball. While we prefer to form the ball by pouring the metal into a receptacle filled with molten slag, as described for example in said Wille patents, the iron may be otherwise incorporated into the molten slag so long as the iron is not subjected to oxidizing treatment which would neutralize the efiect of the aluminumaddition.

While we have specifically described the preferred embodiment of our invention, it is to be understood that the invention may be otherwise embodied and'practiced within the scope of the 7 following claims.

We claim:

1. The process of controlling the slag content and distribution in the manufacture of wrought iron, which comprises refining iron by blowing in a Bessemer converter, adding aluminum to the blown molten iron in the proportion of about two to six pounds of aluminum to 'a ton of iron, mixing the ironrin comminuted form with a separately formed molten slag to form aspongy mass of iron and slag, and expelling the surplus slag from such mass. a

2. The process of controlling the slag content and distribution in the manufacture of wrought iron, which comprises refining iron by blowing in a Bessemer converter, adding aluminum to the blown molten iron in the proportion of about two V proportion of about two to six pounds of aluminum to one ton of iron, mixing the molten iron in comminuted form with a separately formed molten slag to form a'spongy mass ofiron and slag, and expelling the surplus. slag from such mass.

4. The process of controlling the slag content and distribution in the manufacture of wrought iron, which comprises forming a molten refined iron, adding aluminum to the molten iron in the proportion of about two to fifteen pounds of aluminum to one ton of iron, mixing the molten iron in comminuted form with a separately formed molten'slag to form a spongy mass of iron and slag, and expelling the surplus slag from such mass. 1

' EDWARD B. STORY.

EVARD P. BEST.