US3603374A - Methods of producing large steel ingots - Google Patents

Abstract

A method of producing large steel ingots is provided combining the steps of pouring an ingot in the conventional manner, solidifying the same, removing an axial core lengthwise of said ingot to form a central cavity and filling the cavity with metal from an electrode by electroslag remelting.

Description

United States Patent l 72] Inventor Lloyd R. Cooper Pittsburgh, Pa. 1 21 Appl. No. 797,944 [22] Filed Feb. 10,1969 [45] Patented Sept. 7, 1971 [73 Assignee Heppenstall Company [54] METHODS OF PRODUCING LARGE STEEL INGOTS 3 Claims, 1 Drawing Fig.

[52] US. Cl 164/52, 29/5265 [51 Int. Cl 822d 27/02 [50] Field ofSearch 164/52, 50, 252, 53; 29/5264, 5265 [56] References Cited UNITED STATES PATENTS 1,207,572 12/1916 Law et a1. 164/252 2,230,296 2/1941 Hopkins 164/52 2,240,405 4/ l 941 Kinzel 164/52 2,248,628 7/1941 Hopkins 164/52 3,482,259 12/1969 Schwarz 164/52 X FOREIGN PATENTS 833,122 7/1938 France 164/52 107,798 6/1939 Australia 164/50 107,405 5/1939 Australia 164/52 503,716 4/1939 Great Britain 164/50 Primary Examiner-J. Spencer Overholser Assistant ExaminerV. Rising Att0rneyBuell, Blenko & Ziesenheim ABSTRACT: A method of producing large steel ingots is provided combining the steps of pouring; an ingot in the conventional manner, solidifying the same, removing an axial core lengthwise of said ingot to form a central cavity and filling the cavity with metal from an electrode by electroslag remelting.

PATENTEDSEP Han. 3503374 INVIEN'I Lloyd R. oper METHODS OF PRODUCING LARGE STEEL IllGOTS This invention relates to methods of producing large steel ingots and particularly to a method for producing ingots to provide a solid large ingot free of the central cavity or pipe which is a common problem in the casting of large ingots. This problem of piping in ingots is one which is well known to the steel industry but is of particularly great importance in casting large cross section ingots.

In the production of steel ingots for subsequent forging or rolling operations, the conventional method consists of teeming the liquid steel into chilled iron molds of the desired cross sectional area and height to contain the liquid steel, and to produce a solid steel ingot which can be heated and handled for the forging or rolling operation.

It is well established that steel which has been fully deoxidized (by such metal deoxidizers as silicon or aluminum or by carbon under conditions of low pressure) will occupy less volume after solidification than it did in the liquid form. Since the metal next to the sidewalls and bottom of the molds solidifies first, the liquid metal in the central portion of the ingot, which solidifies last, will shrink and occupy less final space with unacceptable shrinkage voids unless a satisfactory means is employed of providing additional liquid steel to overcome this final shrinkage mechanism. The use of refractory lined or exothermic sinkheads or hot tops is a well established practice in the art in the effort to assure sound ingot centers.

This method of producing sound ingots of killed steel is generally considered to be satisfactory for smaller ingot cross sections and weights, i.e. up to 20 inches to 30 inches diameter or thickness of ingot, weighing up to or tons total weight. On larger ingots, however, the time required for complete solidification of the ingot becomes increasingly longer as the ingot cross section increases, so that many hours elapse between the teeming of the liquid steel and the final total solidification of the steel at the ingot axis. As this elapsed time may exceed 10 hours or 20 hours or even hours, the reservoir of liquid steel in the sinkhead or hot top becomes ineffective to feed into the shrinkage cavities in the ingot body, and a central cavity or pipe results. It thus becomes increasingly difficult and impractical to guarantee sound ingot bodies when the ingot diameter or cross-sectional dimension exceeds 50 inches, and the total ingot weight exceeds 50 tons or more.

In recent years, the process of Electroslag Remelting" of steel ingots or electrodes has been developed for many chemical compositions of steel, high temperature alloys and other metals. In this remelting process, a solid steel electrode is melted progressively with the heat generated by the electrical resistance of a liquid slag to electric current passing through the steel electrode to the liquid slag, and thence to another electrode or to the resolidifying ingot and crucible or mold which contains the resolidifying ingot. The steel, which is progressively melted from the electrode, passes in liquid form through the liquid slag and collects in a pool of liquid steel below the liquid slag layer. The pool of liquid steel solidifies progressively so that at any one time of the remelting operation, it is a pool of liquid steel whiehrepresents only a small portion of the total weight of electrode(s) or steel ingot that is resolidified. In this process it has been well established that the large axial shrinkage voids of conventionally teemed ingots are avoided by the Electroslag Remelting and resolidification process.

The Electroslag Remelting process has been used for alloy steel ingots as large as 46 inches in diameter, and designs are being engineered for Electroslag Remelting of ingots larger than 100 inches in diameter of proportionate heavy weights. However, these extra large remelting facilities require power supplies and electrical systems for control of melting rate, which present an economic block to the practicality of the remelting system.

The invention described here makes use of a combination of conventional ingot teeming with the Electroslag Remelting system for assuring the production of the largest forging ingots with the center soundness characteristics of Electroslag Re melted ingots at a much lower cost for capital equipment and operating expense.

In this invention, a conventional large forging ingot is teemed into a mold with refractory lined or exothermic sinkhead, according to present practices. After this steel solidifies, an axial cavity is formed throughout the full length of the solidified ingot. The diameter of this cavity will be in order of 20 percent to 35 percent of the outside diameter of the ingot, and may be formed by trepan boring cold, trepan punching under a press, or drift punching under a press.

In the case of trepan boring or trepan punching, it is intended that the core, thus removed, would be forged to a smaller diameter to furnish electrodes for Electroslag Remelt' ing within the cavity formed by removal of the core.

In the case of the drift punching operation, it is realized that the majority of the center material of the ingot will be dis placed laterally to the location adjacent to the inside surface of the punched hole. In this case, the metal for the electrode to be used in Electroslag Rcmelting will be furnished from another ingot from the same melt or from another melt of the same nominal composition as the large ingot.

The inside surface of the cavity in the bored or punched ingot will be prepared by shot blasting or machining to assure freedom from excessive oxide. The electrode will be similarly prepared by casting, forging and/or sh-ot blasting, or machining. The electrodes may be in several lengths of sufficient weight to completely fill the axial ingot cavity as well as starting pool and hot topping volume.

The ingot is set up in the remelting station. as shown in the accompanying Figure, showing a vertical section of an ingot according to the invention with the remelting operation partially completed. The original ingot 10 is prepared by coring or punching an axial hole 11 through the full length. In the illustration, the original ingot sinkhead is shown as being integrally cored or punched with the ingot body. In practice this sinkhead may also be removed, and another more symmetrical block be used for the electroslag hot topping. The hollow ingot l0, preheated to the proper temperature range, is positioned on the preheated starting block 12, and the prepared electroslag 13 is added (powdered or liquid condition). The electrode 14 is lowered into position, and the power turned on. The electrically heated liquid slag melts the end of the electrode as well as an adjacent zone of the ingot metal, as indicated by the depth of penetration" 17. In the partially completed cycle shown in the Figure, the liquid slag 13 has melted steel from the end of the electrode (at 15), forming the shallow pool of liquid steel 16 containing steel from the electrode and from the adjacent portion of the ingot. The depth of penetration 17 of the liquid (and resolidified) steel, is controlled by the power input and the preheat temperature range of the ingot body. The diameter of total remelted metal normally represents one-third to one-half of the diameter of the original ingot cross section, although greater or smaller ratios may be obtained by controlling the power input, and preheating parameters.

The economics of this invention become readily apparent when it is realized that the power requirement for melting the inner core equal to one-third of the total ingot diameter is only slightly more than 10 percent of that required for electroslag remelting the entire ingot at the large overall diameter.

This application of the combination of conventional teeming and Electroslag Remelting produces large cross section ingots completely free from the central porosities or cavities, as well as the excessive chemical segregation found in conventionally teemed ingots. It brings the practice of Electroslag Remelting within ready economic consideration, as compared with the complete remelting of exceptionally large and heavy forging ingots.

This invention is also readily applied to the production of large composite ingots of different chemical compositions between the inner core" and the outer shell" of the composite ingot. In this application, the penetration or mixing. of the steel from the electrode composition into the steel of the initial ingot composition, is kept to a minimum by a lesser preheating temperature range for the starting block and ingot, and a corresponding control of the power input and melting rate of the electrode material.

While I have illustrated and described a presently preferred practice of my invention in the foregoing specification, it will be understood that this invention may be otherwise embodied within the scope of the following claims.

I claim:

I. The method of producing large steel ingots comprising the steps of:

a. casting a steel ingot to the final desired size,

b. removing an axial core lengthwise of said cast ingot to form a central cavity,

c. melting a steel electrode formed from the core removed from the ingot within said central cavity under a fused slag by passing an electrical current through said electrode within the cavity to the ingot, and

d. solidifying the melted electrode metal within the cavity to form a solid ingot mass.

2. The method of claim I wherein the axial core is removed by punching said core from said ingot.

3. The method of claim 1 wherein the axial core is removed by trepanning said core from the ingot.

Claims (3)

1. The method of producing large steel ingots comprising the steps of: a. casting a steel ingot to the final desired size, b. removing an axial core lengthwise of said cast ingot to form a central cavity, c. melting a steel electrode formed from the core removed from the ingot within said central cavity under a fused slag by passing an electrical current through said electrode within the cavity to the ingot, and d. solidifying the melted electrode metal within the cavity to form a solid ingot mass.

2. The method of claim 1 wherein the axial core is removed by punching said core from said ingot.

3. The method of claim 1 wherein the axial core is removed by trepanning said core from the ingot.

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