US3180633A

US3180633A - Apparatus for producing ultraclean alloy steels

Info

Publication number: US3180633A
Application number: US210643A
Authority: US
Inventors: Kendrick C Taylor
Original assignee: Pennsalt Chemical Corp
Current assignee: Pennwalt Corp
Priority date: 1962-07-18
Filing date: 1962-07-18
Publication date: 1965-04-27
Anticipated expiration: 1982-04-27

Description

A ril 27, 1965 K. c. TAYLOR 3,180,633

APPARATUS FOR PRODUCING ULTRACLEAN ALLOY STEELS Filed July 18, 1962 2 Sheets-Sheet 1 F/Gi/ A 1 iii INVENTOR. KENDRIC'K C. TA VLOR ATTORNEY April 27, 1965 K. c. TAYLOR 3,180,633

APPARATUS FOR PRODUCING ULTRACLEAN ALLOY STEELS Filed July 18. 1962 2 Sheets-Sheet 2 142 55 7;: 1 h Z4 26 2a 2 id: 4 VP it X x INVENTOR KENDR/CK C. TA YL OR ATTORNEY United States Patent 3,180,633 APPARATUS FOR PRODUCING ULTRACLEAN ALLOY STEELS Kendrick C. Taylor, Oreland, Pa., assignor,.by mesne assignments, to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed July 18, 1962, Ser. No. 210,643 6 Claims. (Cl. 266-34) In general, this invention relates to new and improved methods and apparatus for producing ultraclean alloy steels. More particularly, it relates to the production of ultraclean alloy steels utilizing magnetic mixing in a vacuum chamber for better alloying and degassing.

In the production of various grades of steel manufactured from processes such as the open-hearth or electricarc furnaces, there is a need to produce ultraclean steel whose gas content approaches the very low levels obtained by consumable arc or induction melting. Additionally, there is a strong need for a dynamic mixing process which will insure greater shipped tonnage from the same melting output. Steel billets with these advantages must be capable of being produced in existing melting departments of steel mills from the equipment on hand such as large open-hearth or electric-arc furnaces.

At present, ultraclean steels whose gas content is at very low levels can be obtained only by consumable are or induction melting. For instance, the hydrogen level should be less than one part per million, and the oxygen level less than fifteen parts per million.

The present invention contemplates the addition to the present melting facilities in large steel mills of an inexpensive vacuum chamber capable of reducing the hydrogen content in the steel approximately 50 to 70 percent, the nitrogen content 7 to 15 percent, and the oxygen content by reduction 45 to 65 percent. This simple addition will enable the steel manufacturers to produce steel of greater ductility and cleanliness. These properties will produce a number of economies during subsequent hot Working of the resultant alloy. Fewer edge checks, tears, and cracks, a larger reduction per pass and less scrap due to scarfing and grinding the bloom before rolling are all advantages obtained by this process. This process will allow the production of 200 to 300 tons of ultraclean steel alloy in one operation from an open-hearth furnace as opposed to the normal maximum of 50 tons per operation in consumable arc and induction furnaces. Moreover, the dynamic mixing system of this invention enables more economical use of costly alloying additives such as titanium, chromium and cobalt.

This invention contemplates stream degassing as Well as area degassing. Area degassing is defined as degassing the surface area of molten metal in a ladle. By mixing the molten metal continuously, the surface area of the molten metal in the ladle changes and degassing is better effected. Moreover, with dynamic mixing in a vacuum chamber and area degassing of the molten metal, it is possible to eliminate a costly and inefiicient transfer from one ladle to another of molten metal from the furnace. Thus, super-heating problems created by the necessity of raising the temperature of the molten metal in the last ladle in order to compensate for temperature loss in transfer operations are avoided.

Additionally, the area degassing requires minimum material handling and minimum equipment cycling.

Therefore, it is the general object of this invention to provide a better method of producing ultraclean alloy steels.

Another object of this invention is to provide new and simpler apparatus for producing ultraclean alloy steels from existing melting departments in large quantities.

Another object of this invention is to provide a new and improved vacuum degassing process for molten metals utilizing magnetic stirring.

Another object of this invention is to provide a new and improved system for degassing metals wherein the metal is both stream degassed and area degassed.

Another object of this invention is to provide a better method of adding alloying agents to molten metal wherein more complete alloying is accomplished.

Another object of this invention is to provide simple and more economical apparatus for converting existing melting facilities to the production of ultraclean alloy steels.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in the drawings forms which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a partial cross sectional view of a preferred embodiment of the present invention.

FIGURE 2 is a partial cross sectional of a second embodiment of the present invention.

In FIGURE 1, there is shown a vacuum chamber utilized in the present invention and generally designated by the numeral 10.

The vacuum chamber 10 consists of a bottom receiving pot 12 having a metal shell surrounding an interior refractory surface. The pot 12 has a cover 14 associated therewith. An annular flange 16 forms a lip on the pot to cooperate With an annular flange 18 on the top 14 to seal the vacuum chamber 10 when the top 14 is in place.

A non-magnetic stainless steel ladle receiving stand 20 is mounted on the iloor of the pot 12. The stand 20 has a ladle-shaped cavity 22 on the walls of which cavity are placed water-cooled

induction coils

24, 26 and 28.

The

induction coils

24, 26 and 28 are separate annular rings each connected through its own individual terminals (not shown) to a source of alternating current outside of the vacuum chamber 10. The

annular coils

24, 26 and 28 are held in place on the stand 20 by a removable retaining ring 42 of a non-magnetic material.

A ladle 30 containing molten metal to be degassed and alloyed is placed in the ladle cavity 22 with its trunnions 38 and journals 40 resting on the annular lip 42 of the stand 29. The ladle 30 has a non-magnetic outer surface such as stainless steel of the AISI 300 series or reinforced fiberglass such as Spiralloy, etc. A refractory liner 34 forms the interior surface of the ladle 30. The molten metal 36 is placed in the ladle 30 from the steel mill furnace.

When the top 14 of the vacuum furnace 10 is removed, the ladle 30 with its molten metal charge 36 is placed on the stand 20 by a suitable crane. It should be noted that for purposes of this invention, the molten metal charge 36 has a minimum layer of slag on the top thereof.

A conduit 44 extends to the interior of the pot 12 and is connected to a vacuum pump 46 for evacuating the chamber 10.

The cover 14 has a hopper 48 mounted over an opening St) in the center thereof. The hopper 48 is adapted to have an alloying material therein. Control of the feeding of the alloy material in the hopper 48 is effected by a trap chamber 51 located between two

adjacent valves

52 and 54. The trap chamber 51 is operated by first opening valve 52 to allow a predetermined amount of alloying material into the chamber 51. The valve 52 is then closed and the valve 54 opened to feed the alloy material to the molten metal in the ladle 39.

A conical battle 56 is supported by frames 58 is located immediately below the trap chamber 51. The baffle 56 is effective to insure the flow of alloy material to the greases side walls of the ladle fail for reasons which will be discussed below.

The operation of the vacuum chamber lit is-as follows: At the inception of the operation, the cover 14 is raised a few inches by an overhead crane (not shown) and moved to the side exposing the top of the pot 12. There is at this time no ladle in the support 20. The ladle 3t is filled from the furnace and transported by means of an overhead crane to the pot 12 and placed in the support 29 with its trunnions 33 resting on the lip 42. The lid 12 is then returned to place on the flanges lid.

The vacuum pump 46 then evacuates the chamber lit The

coils

24, 2d and 28 are then energized with alternat ing current whose frequency is between approximately .2 to 4 cycles per second. This low frequency is necessary in order not to induce any heating inthe molten metal charge 36. The magnetic field developed by the

coils

24, 26 and 23 passes almost exclusively through the molten metal charge 36 as it is the only ferromagnetic material adjacent to the coil. The varying magnetic fluxes in the

coils

2d, 26 and 28 set up magnetic forces causing lifting or depression of the molten steel adjacent to the ladle wall, depending upon the phase cycling of the coil.

The low frequency of the induced field and the considerable power supplied to it cause movement of the molten metal in the ladle in the direction of the induced currents. The molten steel can be made to move as much as 40 inches radially inwardly from the outer wall of theladle. that optimum magnetic stirring occurred between .55 and .7 cycle per second for 100 ton capacity ladles.

As the molten metal is moved from the outer walls toward the center or vice versa, the surface area of the metal is continuously moving. As the surface area of the molten metal changes, it is degassed by the vacuum in the chamber Id. The vacuum pump is able to more effectively degas the metal because of the magnetic stirring. In fact, it has been foundthat this type of area degassing is as effective as stream degassing. Approximately 50 to 70 percent of the hydrogen in the molten metal, to 65 percent of the oxygen, and 7 015 percent of the nitrogen can be removed by this type of degassing.

After the molten metal charge 36 has been degassed, the alloying material in the trap chamber 51 is fed into the ladle 3%. Since the alloying material is forced to flow down the conical baffle 5s toward the outer Walls ofthe ladle 3% it does not flow toward the center ofthe molten charge 36. The magnetic stirring of the molten metal being from the outer walls toward the center carries that alloying material which falls to the outer walls of the ladle in toward the center with the resultant effect of excellent alloy homogeneity due to the magnetic stirring. V

Since only one ladle was necessary in the operation, only one temperature drop occurred, the drop in temperature when themolten metal was poured from the furnace into the ladle. This temperature drop is approximately to 70 F. Such a temperature drop is permissible and there is minimum need for reheating or preheating the molten metal so as to give rise to superheating problems. After the steel alloy has been produced by this process, the lid 14 is raised and moved to the side.

Then a crane removes the ladle 39 before the start of another operation.-

The second embodiment of the present invention is shown in FIGURE 2. In this operation, the lid' 14 of FIGURE 1 has been replaced by a lid 60 having an annular flange 62 to cooperate with the lip 16 on the pot I2. A ladle 6 is mounted on the lid ed in a man-' ner to be discussed below. The ladle (54 has trunnions 66 and 6%, and is adapted to receive molten metal from the open-hearth or other furnace. At the bottom of the ladle 64 there is a nozzle opening 70 controlled by the In a practical embodiment, it was found vertically movable stopper rod '72. is filled, the stopper rod 72 is of course in its lowermost position sealing off tle nozzle opening 7%. Thus, the ladle 6 5 has a molten metal charge '74, such as steel, aluminum, etc., therein. The nozzle 76 extends from the bottom of the ladle 64 toward the interior of the chamber 10. It should be noted that the ladle 3% is empty and is adapted to receive the molten'metal charge 74 from the ladle 6d.

'The nozzle 76 is connected to an annular flange 73 which cooperates with an annular flange 3%) on the lid to hold a rupture disc 82 in place.

of the chamber ll) so that the evacuation could be effected.

Whenthe molten metal ruptured the disc 82 and flowed through the sleeve 84, it was stream degassed by the vacuum in the chamber Til. Additionally, if it is desired to react a gas with the molten metal, a conduit 94 can be placed on the lid 6d. The conduit 94 would have a suitable source of reacting gas attached thereto. The

reacting gas would be directed toward the stream of molten metal. One-such reacting gas could be chlorine which would act as a reducing agentto combine with impurities and gases in molten metal such as aluminum, which would subsequently be removed as a gaseous by-product by the vacuum pump as. V

The ladle 64 is generally supported on a standard 36 mounted on the lid 6t). When the stopper rod 72 is returned to its closed position after the molten metal in the ladle 64 has flowed into the ladle 3d, the evacuation of the chamber it? may be continued.

An alloy material hopper 88 is also mounted on the lid '69. The alloy material hopper 38 has a trap chamber 91 formed by two

valves

94 and 92. The hopper S3 directs alloying material into the molten metal in the ladle 3d where it is homogeneously combined with the molten metal due to the magnetic stirring therein. 7

The system shown in FIGURE 2 has the advantage of utilizing stream degassing with further area degassing if desired. However, it does require the use of two ladles and two transfer of molten metal. The first transfer is from the furnace to the ladle s4 and the second from the ladle 64 to the ladle 30. This causes a drop in the temperature of the molten metal of about to F. as opposed to only 50 to 70 F. in the embodiment shown in FIGURE 1. Additionally, it is difficult to utilize the baffle principle of placing the alloy materialon the edges of the interior of the ladle 30 as was shown in FIGURE 1.

The processes shown in FIGURES 1 and2 may be applied to a wide variety of steel grades. These include tool steels, bearing steels, deep drawing steels, hot rolled strip for cutlery and similar purposes, and specialized electrical grades. These are all ultraclean alloy steels. As shown, this vacuum steel making process can be applied to existing open-hearth and other furnace units so as to' achieve the low levels of gas content obtained ble to an overhead crane which could lift them out of place. a

Because of the extremely homogeneous melt achieved by the magnetic stirring, the process shown in FIGURES When the ladle 64' 1 and 2 means more economical use of costly alloy materials such as titanium, chromium and cobalt.

The present inventon may be embodied in other specific forms Without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

I claim:

1. Molten steel handling apparatus comprising a chamber, vacuum means for evacuating said chamber, a nonmagnetic ladle in said chamber for receiving molten metal, said ladle including a cup-shaped fiberglass shell, and inductive means in said chamber for inducing low frequency electro-magnetic force currents in molten metal in said ladle to continuously move molten metal up to the surface level thereof while said ladle is in said chamber.

2. Molten steel handling apparatus comprising a chamber, vacuum means for evacuating said chamber, a nonmagnetic ladle in said chamber for receiving molten metal, inductive means in said chamber for inducing low frequency electro-magnetic force currents in molten metal in said ladle to continuously move metal up to the surface level thereof while said ladle is in said chamber, a hollow stand in said chamber for receiving and removably supporting said ladle, said stand supporting said inductive means, and said inductive means including a coil concentric with said ladle.

3. Apparatus in accordance with claim 2 wherein said stand includes a removable flange for supporting said ladle, said flange being additionally adapted to hold said coil in place whereby said coil may be easily lifted out of said stand when said ladle and flange are removed.

4. Molten steel handling apparatus comprising a chamber, vacuum means for evacuating said chamber, a nonmagnetic ladle in said chamber for receiving molten metal, said ladle including a stainless steel cup-shaped shell, a supporting stand in said chamber removably supporting said ladle, and inductive means supported by said stand for inducing low frequency electro-magnetic force currents at a frequency of between .2 and .8 cycles per second in molten metal in said ladle to continuously move metal up to the surface level thereof while said ladle is in said chamber.

5. Molten steel handling apparatus comprising a chamber, vacuum means for evacuating said chamber, a nonmagnetic ladle in said chamber for receiving molten metal, inductive means in said chamber for inducing low frequency electro-magnetic force currents in molten metal in said ladle to continuously move metal up to the surface level thereof while the ladle is in said chamber, a hollow stand in said chamber removably supporting said ladle by a surface adjacent the upper end of said stand cooperating with a portion of the ladle axially spaced from the bottom of the ladle, said stand supporting said inductive means, and said inductive means including a coil concentric with said ladle.

6. Molten steel handling apparatus comprising a chamber, vacuum means for evacuating said chamber, a nonmagnetic ladle in said chamber for receiving molten metal, inductive means in said chamber for inducing low frequency electro-magnetic force currents in molten metal in said ladle to continuously move metal up to the surface level thereof while said ladle is in said chamber, said chamber including a removable cover supporting an alloy material hopper thereon, an alloy material directing means associated with said hopper, said alloy material directing means including a conical refractory member supported by said lid and positioned to direct the alloy material toward the side walls of said ladle.

References Cited by the Examiner UNITED STATES PATENTS 2,071,942 2/ 37 Rohn 49 2,513,082 6/50 Dreyfus 13-26 2,686,823 8/54 Jones 13-26 2,837,790 6/5 8 Rozian 7549 2,848,317 8/58 Coupette 7549 FOREIGN PATENTS 339,579 12/ 30 Great Britain. 702,225 l/ 5 4 Great Britain.

OTHER REFERENCES Metal Industry, Sept. 20, 1957, pp. 234235.

Tix, A.: Vacuum Treatment of Steel by the Bochimer Stream Degassing Process, J. Iron and Steel Institute, Mar-ch 1959, pp. 260-265.

Byrne, J. W.: Worlds Largest Vacuum Induction Furnace, Metal Progress, April 1960, pp. 83-86.

Parsons, D. E.: Vacuum Degassing of Steel, The Canadian Mining and Metallurgical Bulletin, vol. 54, No. 86, February 1961, pp. 163-169.

DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

Claims

2. MOLTEN STEEL HANDLING APPARATUS COMPRISING A CHAMBER, VACUUM MEANS FOR EVACUATING SAID CHAMBER, A NONMAGNETIC, LADLE IN SAID CHAMBER FOR RECEIVING MOLTEN METAL, INDUCTIVE MEANS IN SAID CHAMBER FOR INDUCING LOW FREQUENCY ELECTRO-MAGNETIC FORCE CURRENTS IN MOLTEN METAL IN SAID LADLE TO CONTINUOUSLY MOVE METAL UP TO THE SURFACE LEVEL THEREOF WHILE SAID LADLE IS IN SAID CHAMBER, A HOLLOW STAND IN SAID CHAMBER FOR RECEIVING AND REMOVABLY SUPPORTING SAID LADLE, SAID STAND SUPPORTING SAID INDUCTIVE MEANS, AND SAID INDUCTIVE MEANS INCLUDING A COIL CONCENTRIC WITH SAID LADLE.