US2853768A - Overhead conductor - Google Patents

Description

Sept. 30, 1-958 v. c. BOUCEK OVERHEAD CONDUCTOR Filed Feb. 2a, 1956 INVENTOR. V/NC'E/VT 6. BOUCEK,

dOmLaZL his Attorney."

United States Patent OVERHEAD coNDUcroR Vincent C. Boucek, Pittsburgh, Pa., assignor to United States Steel Corporation, a corporation of New Jersey Application February 28, 1956, Serial No.- 570,656

3 Claims. (Cl. 29-494) This invention relates generally to steel -manufacture and, in particular, to a conductor of rimmed steel with a high carbon content.

This is in part a continuation of my application, Serial No. 511,438, filed May 26, 1955, for High-Carbon Rimmed Steel and Method of Making It.

Rimmed steel has peculiar, well known advantages for certain uses. to make rimmed steel having only a medium or low content of carbon, the maximum carbon content being .28 or 30% (TheMaking, Shaping and Treating of Steel, 6th ed., p. 573). In certain applications where rimmed steel is desirable, a higher carbon contcntwould .be advantageous and it is accordingly the object of my invention to produce such steel anda novel conductor made therefrom.

A more specific object is to. provide a novel overhead galvanized conductor wire. of rimmed steel, having a sufficiently high strength after galvanizing to permit a greater spacing between vthesupports than has been possible heretofore, and the low A. C. resistivity necessary in such product.

The single figure of the accompanying drawing is a cross section of a conductor wire according to the invention.

My invention is concerned first with the production of steels having a carbon content of over 35% and up to 1.10%, and the manufacture of conductor wire therefrom. Briefly stated, the invention comprises adding'to such steel, when it has been teemed into molds and while it is still liquid, an exothermic rimmingagent of novel composition. Preferably the rimming agent is added to each mold while steel is being teemed thereinto and, specifically, before the mold is half filled. The rimming agent is composed of iron'oxide and sodium fluoride, but includes also an exothermic-reaction mixture of granular aluminum and a compound affording a source of oxygen for combination therewith, such as sodium nitrate. The amount of the rimming agent used is from one to four pounds per ton of ingot weight. The following ranges "are satisfactory for the several ingredients of the rimming agent:

Table 1 Percent by weight Iron oxide 40-80 Granular aluminum 2.5-17 Sodium nitrate -34 Sodium fluoride 5-20 The amount of sodium nitrate should be double the amount of aluminum. The ingredients should be in such a state of subdivision as to pass through an S-mesh screen and should be thoroughly mixed before use.

The iron oxide acts to promote rimming action in the liquid steel by furnishing oxygen for combination with It has been possible heretofore, however,

2,853,768 Patented Sept. 30, 1958 some of the carbon present therein. The sodium nitrate furnishes oxygen for combination with the aluminum. This reaction results in the evolution of alarge amount of heat serving to fuse theiiron oxide'andsodium fluoride Without causing localized cooling of the ingot. The sodium fluoride acts as a flux to sweep upward "the alumina resulting from the oxidation of the aluminum. The overall result of the addition of the fimming agent, therefore, is to putfused'iron oxide and sodiumfiuoride into the liquid 'steel as it is being-teemed into'the mold so that, on standing thereafter, rimming will proceed vigorously for such period as necessary ;to form a case of the desired thickness. After the .iron oxide of the rimming agent'has reacted, a sodium-aluminate scum remains which acts -as a flux and scavenger 'for any refractory'inclusions such as silicates.

The rimmed high-carbon steel containing less than .04% Si, which I am able to'produce makes possible a novel overhead conductor wire of high strength after galvanizingand low A. C. resistivity in the bare or uncoated state. For this product,the steel'when processed and galvanized by conventional manufacturing practice, gives a wire having a strength of from 150,000 to275,000 p. s. i., depending on the carbon content, an elongation in 10 of 4-8%, and an effective A. C. resistivity in B. W. G. #12, in the. bare state with 'zinc.coating removed, of from 7.5 to 8.5 ohms per 1000"to*alternating currents of 5 milliamperes at .1000 cycles per second.

As a typical example of the practiceiof the invention, I make a heat of steel by conventional basic open-hearth practice except that I do not add any deoxidizer such as ferrosilicon, aluminum or 'ferrotitan'rum and magnesium, either to the bath in'the furnace or to the'ladle after tapping the furnace. The carbon content of the heat is brought down progressively'in'the furnace to approximately the desired final value, e. g., 0.65%, and ferromanganese is added as required in the furnace or in the ladle. This may be as little as a half 'pound 'per' ton in one case and as much as 25 pounds per tonin another. After tapping, the steel is teemed into big-end-down, bottle-top ingot molds, i. e., without hot tops, with the addition of about 2.5 pounds per ton of ingot weight, of a rimming agent composed of 68% globular iron oxide in the'form of deseamer dust, 17% sodium fluoride, 10% sodium nitrate and 5% granular aluminum. After :a predetermined time for rimming, depending onthethicknessof case desired, i. e.,from 15 seconds 'to 5 minutes, the rimming action is substantially arrested by chemically precapping, viz., the addition of about 2 oz. perton of ingot weight, of a suitable deoxidizer such. as aluminum or calcium-silicon'alloy, after which the molds are mechanically capped.

One example of steel made in accordance with the .in-

vention gave the following-analyses:

Table II Per- Per- Per- Per- Per- Percent cent cent cent; cent cent 0 Mn P S Si Al Ladle Analysis 67 22 015 024 02 Recheck Analysis of Billets: Entire Cross Section- Top of Ing0t .66 20 015 025 .01 .006 Bottom of Iugot .62 19 Surface of Billet-Top 0t Ingot 45 .20 .010 015 Center Drillings on 2" x 2" Billet-Top of Ingot .95 23 .019 .069 01 006 The cross-section of ingots of high-carbon steel produced according to my invention is characterized by an outer zone or rim area of a predetermined thickness, and this area persists in the billets rolled from the ingots and in wire rod and wire made from the billets. The drawing shows the section of such a wire 10 which has a circumferential outer zone 12. In this area, the carbon and sulphur contents are approximately two-thirds of the average concentration (ladle analysis) and there is an almost complete freedom from inclusions, giving the steel exceptionally good drawing properties and high electrical conductivity when made into wire. The carbon and sulphur contents in the central area 11 of the cross-section are 1.5 or more times the average concentration.

Ingots of steel made by my method may be hot-rolled into blooms and billets as well as conventional low-carbon rimmed steel (i. e., steel containing .12% carbon and 50% manganese) and exhibit freedom from pipe giving a higher yield, and also good surface condition. Segregation in the ingots is well controlled and may easily be kept below the limits established for many applications. The case or rim is cleaner and freer of inclusions than normal killed steeland this condition persists even at the top center of the ingots. The carbon gradient from surface to center gives desirable hardening properties. The steel when rolled into wire rod draws well into fine wire and is also easy to'cold-roll into strip. The low silicon and aluminum and freedom from inclusions improve the electrical conductivity, making the steel particularly desirable for the production of the high-strength Wire used in communication lines.

A novel rimmed-steel overhead conductor wire results from processing steel made as explained above and containing from .35 to .85% carbon and from .15 to .75% manganese, according to known practices, because the low silicon (less than 04%) which, of necessity, means that the steel will be rimmed in the absence of other deoxidizer, keeps the A. C. resistivity to a satisfactorily low value. As a typical example, I roll wire rod from billets of rimmed steel, made as described above, containing about .65% C, about .40% Mn, less than .02% P, less After pickling and liming, the patented rod is drawn to size, i. e., #12 size B. W. G. As drawn, it has a tensile strength of betwen 200,000 and 275,000 p. s. i. The hard-drawn wire is then galvanized by the conventional hot-dip process, i. e., by passing it first through a bath of molten lead at about 950 F., then through an acid pickling bath, a water rinse, a flux bath and then through a bath of molten zinc at about 820.F. The zinc coatinglayer is indicated at 13 in the drawing.

When galvanized, the finished Wire will have a tensile strength of from 190,000 to 275,000 p. s. i. and an elongation in 10" of from 4 to 8%. The #12 size 13. W. G. wire in the bare state, with the zinc coating removed, will exhibit a resistivity between 7.5 and 8.5 ohms per 1000' to a current of 5 milliamperes at a frequency of 1000 cycles per second, measured at 80 F.

I have found that resistivity values such as those given above cannot be achieved if the steel is killed as it would be with silicon contents in excess of .05 as taught by Fowle et al. Patent No. 2,327,256. The low resistivity values, furthermore, result from the rimmed character of the steel and specifically the fact that the case or exterior rim is substantially lower in metalloids than the average for the entire section.

Although I have disclosed herein the preferred practice and embodiment of my invention, I intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention.

I claim:

1. A galvanized overhead conductor wire of rimmed steel containing from .35 to .85% carbon, from .01 to 04% silicon, and from .15 to .75 manganese, said conductor having a tensile strength between 150,000 and 275,000 p. s. i., the cross-section thereof being characterized by a circumferential outer zone of substantial thickness having a lower carbon content than the central area and said wire having a resistivity in #12 size B. W. G. and the bare or uncoated state, of about 8 ohms per thousand feet to an alternating current of 5 milliamperes and a frequency of 1000 cycles per second, measured at 80 F.

2. A conductor wire asdefined by claim 1, characterized by the carbon content in said zone being about twothirds the average carbon content of the wire.

3. A conductor wire as defined by claim 2, characterized by the carbon content of the wire apart from said zone being at least 1.5 times the average carbon content of the wire.

References Cited in the file of this patent UNITED STATES PATENTS 383,192 Seaman May 22, 1888 791,096 Hoopes -a May 30, 1905 2,191,189 Wade Feb. 20, 1940 2,297,357 Kelley Sept. 29, 1942 2,356,450 Epstein Aug. 22, 1944 2,514,793 Pietsch July 11, 1950 2,610,911 Udy Sept. 16, 1952 2,628,898 Hiltz Feb. 17, 1953 2,737,696 Shields Mar. 13, 1956

Claims (1)

1. A GALVANIZED OVERHEAD CONDUCTOR WIRE OF RIMMED STEEL CONTAINIG FROM .35 TO .85% CARBON, FROM .01 TO .04% SILICON, AND FROM .15 TO .75% MANGANESE, SAID CONDUCTOR HAVING A TENSILE STRENGTH BETWEEN 150,000 AND 270,000 P.S.I., THE CROSS-SECITON THEREOF BEING CHARACTERIZED BY CIRCUMFERENTIAL OUTER ZONE OF SUBSTANTIAL THICKNESS HAVING A LOWER CARBON CONTENT THAN THE CENTRAL AREA AND SAID WIRE HAVING A RESTIVITY IN #12 SIZE B. W. G. AND THE BARE OR UNCOATED STATE, OF ABOUT 8 OHMS PER

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