IL33334A - Steel making processes - Google Patents

Description

IMPROVEMENTS STEEL PROCESS ES ion relates to a process for making steel in induction crucible furnaces with intensive material and heat exchange between the metallic bath and the lover density also to an induction crucible furnace adapted to operating the said It is that electrical currents are induced in the metallic charge in induction crucible which have a cylindrical crucible surrounded by a cylindrical induction and that most o the electrical energy is converted heat and a smaller proportion into kinetio The heat liberated is responsible for the intended melting of the metallic while the kinetic energy is responsible for the bath agitation typical of induction crucible An upward current is set up on the crucible and the bath surface is heaped up into a shallow from which metal flows radially outwards to the crucible walls and then down the German Patent French Specification sufficient velocity of flow of the flowing the slag accummulating in the crucible will be Imparted a rotation contrary to the of motion of the The slag rises on the wall of the moves radially from all sides towards the centre and flows from the point where it reaches the down the wall of the This flow is designated as toroidal materials cannot be heated since no current can be induced in In the case of and assuming that the charge is not pure but contains alloying the characteristic feature is the reaction that takes place between the bath and low ivity slag is intended to absorb undesirable unwanted elements from the This is only possible provided that between the bath and the which has a lower density than the metal and therefore floats on intense of material and heat exchange are maintained so that the appropriate metallurgical reactions can take induction crucible furnaces hitherto usually operated the scope for metallurgical reactions has been since the slag be heated inductively and the exchange surfa e area between it and the bath is For this induction crucible furnaces are substantially reserved for the of highly pure charge for which the slaggin aspects the cycle are not icular difficulties in induotion furnace melting when it is desired to use sponge iron as a charge fo example in place of in Sponge iron is of course a relatively pure material with other known advantages for the It is however almost impossible to process sponge iron in induction since this material being o smaller weight than conventional its density being even lower than that of normal is only partially wetted by slags and its high porosity makes its conductivity If sponge iron is to be melted rapidly and economically it must be locally superheated as it enters the slag and this is impossible in the induction furnace as currently In other sponge iron is a highly unsuitable charge material for induction furnace It has however been proposed to overcome these which arise from the relatively low temperature and inertness of the by providing additional heating to compensate for the lack of induction heating in the slag it has for example been proposed German Patent Specification to heat the slag layer with a plasma torch playing on it from Apart from being this proposal entails providing an additional piece of which complicates the process and stands in the way of large scale The induction crucible furnace as normally and operated is equally incapable of maintaining an economical rate of metallurgical reaction involving intensive material and heat exchange between a metallic bath and a slag and of processing materials of low density and thermal such as sponge iron for The object of the invention is to facilitate the carrying out of reactions and processes of the type already described in an induction crucible with particular reference to the melting of charge of the sponge iron The relates to a process for malting steel in induction crucible furnaces having a cylindrical crucible surrounded by a cylindrical induction from charge materials which require metallurgical refining and have unfavourable melting The invention consists in that the ratio of the induction input to the crucible contents is high enough to form dome on the bath surrounded by a toroidal vortex of which absorbs the unwanted tramp elements from the bath during refining and drags the low density charge materials below the slag The inventio arises from the appreciation that the power input to the furnaoe coil and the corresponding power output induced in the crucible contents must bear a certain definite relationship to the weight of the if the motions induced in the bath and are to promote the desired metallurgical reactions and facilitate the melting down of low density charge The invention depends on the tion that the induction coil input must b sufficiently high to form a substantial dome on the bath surface surrounded by a toroidal vortex of if the latter is to bring about the specific notably the dragging down of low density materials below the slag If the oriiclble contents are assessed in tons of the specific power input required under the invention at a frequenc of is at least and preferably more than in order to attain the prescribed surface dome formation on the bath and secure the excitation of a toroidal At the condition for adequate metallurgical action can be as the quotient of the specific power input and the square root of the frequency must least The proposals of the invention lead to the formation of a much taller dome on the bath measured at the crucible than is usually above they lead to much higher flow velocities in the metal The surprising fact is that the slag round the sides of the it is displaced by the substantially circulates toroidally n the opposite direction to the under the drag of the The slag wells up along the crucible moves radially inwards from all sides on its exposed surface and on reaching the dome of sinks downwards and wards along the This is the flow pattern here referred to as a toroidal Between continuously circulating bath and new interfaces are continually presented for material and heat exchange so that the slag absorbs the elements undesirable in steel and kept the temperature of the steel in the Thus the vigorous agitation brought about in the bath and the slag by raising the power input as prescribed to more than based on the crucible compared with the conventional maximum of k promotes the required metallurgical activity in a simple The bath circulates so vigorously that particles of slag are entrained by and circulate with the This substantially increases the contact surface area between slag metal and further improves the material exchange The latter are so favourable that the reactions rapidly approach It is therefore essential to lay down special making notably with respect to phosphor If the latter is to be the carbon content of the bath must not exceed and is preferably limited to by Ways are of securing these conditions for example by adding oxygen blowing and so In the process of the invention must be so regulated that he carbon content of the bath is adjusted to the required depending on the charge materials either by oxidising with ore oxygen blowing or the like or by periodically adding carburising agents in the known In the process of the low density charge materials are fed on to the domed area of the bath optionally after removing slag It has in fact been found that by adding the lo density materials co ti at a rate matching the power input to the coil at the the said which may for example consist of iron in lumpy or finely granulated are not swallowed up by the slag layer but float either on the metal dome or the surrounding ring of slag until they are ungulfed at the junction of the slag and metal streams and dragged under the slag They are then trapped between metal and slag and surrounded by turbulent and quently highly reactive so that they melt into the bath without Feeding on to the dome of metal is possible so long as it remains from If the slag layer covers the the circulation slows down and the density lumps or granules on the slag surface are no longer dragged Before any more is charged the bath must be to expose the dome In this the process of the invention is characterised in that the oharge materials are added continuously at a rate matching the power input to the at the so that the heat required to melt down the form any fresh and support the corresponds exactly to the heat being generated inductively in the Continuous feeding at a rate matching the instantaneous power input to the furnace coil promotes the maintenance of constant bath temperature are facilitates the completion of metallurgical notably dephbsphorisa tlon prior to final provided the slag composition is suitably By maintaining the bath at a of max and preferably by and optionally by charging continuously with it possible to complete dephosphorisa tlon at The content of the bath can be held at the required level by using the appropriate e materials or by adopting means for oxidising the for example with ore oxygen blowing or the like or for g it in the known Another of the present Invention is induction crucible furnace adapted to carrying out the process of the invention particularly The induction crucible the invention is characterised in that the cylindrical induction coil is constructed to consume power at the rate of about 350 or based furnace ca at a frequency of or the corresponding rates indicated above at other working The sponge in granular or powder is fed continuously o to the exposed s dome of molten metal in the centre of the The feeding rate is regulated so that the heat to melt down the form any fresh slag and support the reactions corresponds exactly to the heat being generated inductively in are charged continuously along with the sponge By continuously adding carburising the residual oxides contained in the sponge iron are reduced and the carbon content of the bath kept at maximum and preferably If the slag covers the dome of molten some is Refining and dephosphorise tion accompany the down At final the refining process also After removing the refining the melt is carburised to the required final carbon content and to the tapping at the same time desulphurising it and optionally also degasifying it as described the previous example of from scrap It is again preferred for the same reasons as before to leave of its contents in crucible for the next tapping the the amount added in each As a modification to the procedures described above it may be preferable to keep the slag volume down by charging about of the total amoun of sponge iron before starting to charge the dephosphorising After removing the first phorisation be completed as the remainder of the sponge iro is by continuously adding basic oxides to form a suitable In this the quantities charged should be adjusted so that f sufficient slag is formed to absorb the phosphorus corresponding to leaving the steel with its specified minimum phosphorus The advantages attained by the invention reside therein that sponge a material of relatively low density can be used in steelmalcing in inductio cruoible Due to the motion of alag and bath controllable and predeterminable temperature conditions are attained which e of reaction and melting easy possibility of automotivation and flow of thus reaching better economy in The invention no be described more detail with reference to a drawing of an embodiment purely by way of The single Figure is a sohematlc view of the flow patterns at the bath surface in an induction crucible furnace carrying out the process of The current passing through the induction coil 1 induces electrical currents in the steel bath 3 in the rucible The radial pressure forces lead to the formation of a dome on bath surface the crucible The metal wells up in the direction of the arrows The drag causes the slag at the sides the dome to circulate in the direction of the arrows 7 form the toroidal The smal of material as sponge iron on to the dome are e trained by the mechanical forces set up by the metal and slag movements and dragged down below the insufficientOCRQuality

Claims (5)

WHAT IS CLAIMED IS j

1. Λ process for making steel in induction crucible furnaces having a cylindrical crucible surrounded by a cylindrical induction coil, from massive charge materials such as scrap or example which require metallurgical refining and also from low-density charge materials with unfavourable melting properties suoh as sponge iron for example wherein the ratio of the induction coil input to the crucible contents is high enough to form a dome on the bath surrounded by a toroidal vortex of slag, which absorbs the unwanted iron elements from the bath during refining and drags the low-density charge

materials below the slag surface, characterised in that the specific power input at a frequency of 50 o/seo is about 350 kw/ton or more , based on the furnace capacity, and tha at other frequencies the quotient of the specific power input and the square root of the frequency is at least ^9.5» and in that materials such as sponge iron in lump or granular form are charged on the slag-free dome of metal, optionally after dealagging the bath, and characterised in that the carbon content of the bath is regulated to within 0.1$ maximum and preferably 0*03 -0.07$.

2. A process as in Claim 1, characterised in that the charge materials are added continuously at a rate matching the power input to the coil at the time*, so that the heat

to .

required to melt down the additions , /form any fresh slag •to

and /support the reactions corresponds exactly to the heat being generated inductively in the bath.

3. A process as in Claims 1 or 2, characterised i that the carbon content of the bath is adjusted to the required level, depending on the charge materials used, either b y oxidising with ore additions, oxygen blowing or the like or by periodically adding oarburlsing agents in the known manner,

k, A process as in Claim 3, characterised in that when the melt is ready for tapping a residue of 50-60$ of the contents is left in the crucible, only ta ping the difference in each cycle*

5. A prooess as in any. of Claims 1 to k, characterised in that when sponge iron is used as the continuously added charge material it is, accompanied by the addition of slag-formers which promote dephosphorisetion, the melting down process being accompanied by refining, which is ompleted at meltdown.

6, A process as claimed in Claim 5 , characterised in that when sponge iron is used as the charge material, a proportio thereof (about 50$) is charged first without adding any dephosphorising slag-formers, the first slag is removed, and dephosphorisetion is completed as the remainder of the sponge iron is charged, by continuously addin basic oxides and adjusting the quantities charged so that Just sufficient slag is formed to absorb the phosphorous corresponding to leaving the steel with its specified minimum phosphorous content*

7· A crucible induction furnace adapted to carrying

Out the process of Claims 1 to j¾h¾ying a cy3:indrical crucible and a cylindrical induction coil, characterised in that the induction coil is constructed to consume 50 c/sec power at the rate of about 3 0 kw/ton or more, based on the furnace oa acity*

. . . . . . .. . *">

8, Process for making steel in induction crucible furnaces having a cylindrical pruoible surrounded by a cylindrical induction coil, from massive charge materials such as scrap and from low density charges such as sponge iron, substantially as hereinbefore described and with reference to the examples.

9<( Crucible induction furnaces for oarrying out a process as claimed in any of Claims 1 to 6, substantially as hereinbefore described and with reference to the enclosed drawings.

COHEN ZEDEK & SPfSBACH

P.O. BOX 33116

TEL AVIV, ISRAEL.

APPLICANT«S ATTORNEYS.