US3536122A - Method of producing steel bars by continuous casting - Google Patents

Description

United States Patent Inventors Fritz Willim Kloten, and Ferdinand Fiala, Thalwil, Switzerland Appl. No. 669,378 Filed Sept. 21, 1967 Patented Oct. 27, 1970 Assignee Concast A G Zurich, Switzerland, a Swiss company Priority Sept. 23, 1966 Switzerland 13,777/66 METHOD OF PRODUCING STEEL BARS BY CONTINUOUS CASTING 17 Claims, 1 Drawing Fig.

[56] References Cited UNITED STATES PATENTS 2,128,941 9/1938 Hudson 164/96X 2,840,872 7/1958 Bidner et a1. 164/57 3,182,359 5/1965 Gero 164/55X 3,206,808 9/1965 Robinson 164/86 3,421,571 1/1969 Webber et al. 164/86 3,421,569 1/1969 Neumann 164/95X FOREIGN PATENTS 1,403,347 5/1965 France 164/57 505,427 5/1939 Great Britain 164/82 Primary Examiner.l. Howard F lint,.|r Assistant Examiner-R. Spencer Annear Altome vSandoe, Neill, Schottler and Wikstrom ABSTRACT: A method of producing steel castings by con- US. Cl .1 164/86, tinuous casting in which at least two separate jets of molten 1 steel of different chemical composition are poured simultane- Int. Cl B22d 11/10 ously into the mold under conditions such that the properties Field ofSeai-ch 164/82. 86, of the peripheral zone of the casting are different from those 7, 231 of the central corev I I I6 1 a I I I, {E I v I l t I I 1 1 "T I I 2 j I '5 IO 1 7 I r l v I A I I I I 'r-II 1 j s 2 \t m lbw-r5 147: 1/ 4 -;1 1 611p: 9 I 9 \g r I e 15 I4 1 i'] METHOD OF PRODUCING STEEL BARS BY CONTINUOUS CASTING The present invention relates to a method of producing steel castings by continuous casting, wherein liquid molten steel is poured in at least two jets simultaneously into an open-ended chill mould from which the casting formed with a solidified peripheral zone surrounding a liquid core is withdrawn and then guided as well as further cooled in a guide means following the mould.

The quality of the final products obtained from such continuous castings depends upon the quality of the surfaces and peripheral zones of the continuous castings. A clean surface and peripheral zone without cracks is essential'for further processing, generally in the form of a shaping process. Cracks or other surface defects prevent the continuous castings from being satisfactorily processed because the following shaping process does not remove them. Such defects are frequently caused by the presence of nonmetallic exogenic or endogenic occlusions which have not been successfully eliminated during the process of producing the steel. Nonmetallic occlusions are primarily deoxidation products, such as aluminum oxide. If these oxides appear in the peripheral zone, they give rise to structural weaknesses which in turn cause the said defects to appear on the surface and in the peripheral zone.

For achieving particular properties the addition of metals for alloying or improving the steel is often desired. For instance, it is conventional to introduce aluminum into the steel for the purpose of improving its resistance to aging, for deoxidising the steel, for refining its grain and so forth.

However, difficulties arise when it is desired in one casting to combine certain properties of the peripheral zone with different properties of the core. In order to meet such requirements the production of compound castings has been developed to permit properties which locally differ to be imparted to one and the same casting.

It has already been proposed'to produce compound continuous castings by a method in which the solidified casting emerging from one mould is conducted through a second mould in which it forms the core of a compound continuous casting. Another method consists in continuously casting a hollow bar which forms a mould for pouring the internal part of the casting into the same. It has also been proposed to produce compound castings by casting the ,core material between metal sheets or plates. However. in all these processes differences in the shrinkage rates and inadequate bonding between the two cast materials create considerable difficulties. Moreover. stresses generated during the casting must be relieved by a thermal treatment.

It is the object of the present invention to produce continuous steel castings in which the peripheral zones and the cores have different properties. by jointly casting steels possessing the different desired properties in such a way that an optimum bond will be formed and faults due to differential shrinkage avoided.

According to the invention this is achieved by different chemical compositions of the steel in the two jets and by the formation of the peripheral zone substantially from the steel of one jet which does not penetrate deeply into the liquid core but spreads in a substantially horizontal pattern of flow near the bath surface, the formation of said peripheral zone being assisted by a greater depth of penetration of the other jet into the liquid core in a direction of fiow principally confined to the longitudinal axis of the casting.

The proposed method and other features thereof will be more readily understood from the following more detailed description.

Steel is poured in two jets into a chill mould of any desired cross section, the chemical composition of the steels forming the two jets being different. Should it be desired to cast a slab it is preferred to make use of three jets, the chemical composition of the steel forming the two outside jets differing from that of the steel forming the centre jet. Since the depth of penetration of the two outer jets into the liquid core is only,

slight and this steel spreads primarily in the horizontal direction in the region of the bath surface, the steel from the two outer jets solidifies principally near the mould wall, so that a peripheral zone of the thickness required for further processing is formed substantially only from the steel of these two outerjets.

The formation of this peripheral zone is assisted by imparting to the remaining, i.e. central jet a greater depth of penetration. This can preferably be done by introducing this jet through an extended pouring spout which dips into the bath to discharge the steel at a point below the bath surface in the direction of the longitudinal axis of the casting. The steel flowing from the two outer jets impedes the flow of the steel from the centre jet towards the bath surface and thus prevents the formation of a solidified shell from the unwanted material. Since the two outer jets impinge on the surface of the steel bath in the mould, the frequently observed formation of a freezing layer in the region of the bath surface is obviated by the immersion of the extended pouring spout.

The extended pouring spout which dips into the bath may have two additional lateral outlets from which the steel emerges below the bath surface parallel to the longer sides of the mould in such a way that it does not substantially interfere with the formation of the peripheral zone from the desired steel. Moreover, interference by flowing metal with the solidification of the surface in the centre region of the wider sides of the slab is thus likewise avoided.

The two outer jets may also be confined in and guided by extended pouring spouts which allow the steel to emerge in a suitable sideways direction for imparting a substantially horizontal direction of flow along the mould walls to the steel which is intended to form the peripheral zone.

Suitable apparatus for performing the method of this invention is illustrated by the accompanying drawing which is a vertical section through a mould and through a tundish which has three pouring spouts.

Referring to the drawing. stecl from the tundish 4 is teemed into a chill mould 5 through three pouring spouts, a central pouring spout II, and two outer pouring spouts I0 and I2 which are respectively at opposite sides of the central pouring spout II. The tundish is normally provided with three plugs 16. one for each pouring spout, for opening and closing the respective spouts.

The three pouring spouts extend below the surface of the bath of steel in the mould, the central spout ll extending deeper than outer spouts l0 and 12. The bottom end of the central spout II has a pouring opening 15 opening downward for conducting a middle jet 2 of steel down into the steel in the mould in the direction of the longitudinal (vertical) axis of the mould as indicated.

For producing a killed steel with a content of aluminum, aluminum is introduced into the middle jet 2 by feeding an aluminum wire 7 into it through an opening in the side wall of the central pouring spout.

The outer pouring spouts 10 and 12 each has an outlet 9 in the side facing the side wall of the mould and below the surface of the steel therein, so that the jets l and 3 of steel from the spouts l0 and 12 emerge laterally of the mould. The jets l and 3 are thus directed towards the side wall of the mould 5 at a depth indicated at 8, but the outer pouring nozzles 10 and 12 are spaced and arranged so that the jets l and 3 entering the bath of steel in the mould do not interfere with the solidification of the steel in the peripheral zone of the bath indicated at 14.

Different chemical compositions of the steels poured into the mould in three jets may be provided by subjecting a steel that has been obtained by any desired method of production to differential metallurgical treatments. Such treatments may comprise any method of deoxidation and alloying as well as combinations thereof.

The steel is tapped from a melting vessel into a pouring vessel, preferably a ladle, and then transferred to another pouring vessel, for instance into the tundish. From this tundish the steel is then teemed into the mould in three jets.

containing'alumin u'm may also be advantageous.

' the proposed method.

For instance, if it is desired to produce a killed steel withla content of metallic aluminum, then steel of the same chemical composition may be teemed from the tundish and aluminum simultaneously introduced into the mould at a point below the l a 1 bath surface. This aluminum is then conveniently introduced into the central of the three pouring jets, the term jet in this context being understood also to includethe jet of steel'after its discharge into the liquidcore. The aluminum is uniformly dispersed in the liquid core by' the effect of this jet. The aluminum may be introduced inthe liquid stateorby injecting it monoxide formed during solidification by the reaction of car-' in granular form below the bath surface into the region of flow of the centraljet. However, as a matter, of preference thealu-n minummaybe introduced into the jet in the form of a .wire

Since for the purpose of obtaining the required penetration in depth this jet is;preferably confined in anextended pouring spout thewire may be introduced through thewall of this spout. The pouring spout simultaneously protects the aluminum'from oxidation. This method has qualitative and economic advantages because it permitsaluminum to be introdu'ced into the steel in the desired quantitieswithout the formation of unwanted aluminum oxides by oxidation in contact with atmospheric. oxygen. The quantity of aluminum Another application of; the present inventiori'ariscsin the 'production of deep drawing sheet from continuous castings.

, bon and oxygen eseapes from the melt in theforrn of gas bub bies and causesthe steel to foam over the edge of the mould by the resultant violent oiling agitationQThis foaming effect, i.e. the intensity of the boiling action. depends inter alia very considerably upon the degree of deoxidation of the melt. A

procedure'whieh canbe carriedout within the scope of the required for obtaininga steel having particular properties,

such as resistance toagingyis substantially less thanthat required in conventional processes since nearlythe entire addition vof aluminum remains in}, thesteel in the metallic form.

present invention consists in producing a continuous casting in which the peripheral zone and the coreconsist of steels that have been deoxidised to different degrees. The term degree of.

, :deoxidation isiritended 'to embrace anystatc in the range between unkilled and fully killed steel. Within the specified meaning a difference therefore exists for instance between an unkilled, a partly or a fully killed steel.- i

The difference in the degree of 'deoxidation can be established in apouring vessel by the introduction of deoxi- Moreover, no aluminum or only a small amount of aluminum,

i and of its oxide reach the peripheral zone. f

An alternative method of producing slabs of killed steel in this procedure the steel is tapped from the furnace into a ladle and poured into a tundish. This tundish is divided into compartments from which the steel is poured into the mould in three jets, the two outer. jets having-the same composition but differing from that of the central jet.

dants or by some othertreatment, such as a vacuum treatment of thc stccl. From themelting vessel thcisteelmay be tapped into two ladles or intoone divided ladle, the steel in one ladle orinonc compartmentof a single ladlejbeing submitted to a different treatment to that in the other ladle or ladle compartment. Steels of different chemical compositions are then teemed into a divided tundish and thence allowed to run into the mould. Alternatively, steels of different degrees of deoxidation may be tapped from two furnaces into two ladies and The steel can be transferred in one ladle with two teeming spouts or in two ladies. Moreover, the tundish may be so con structed that the steel can overflow from one compartment I into the other, in which case'only one ladlewith one teeming spout is required. A portion of or all the aluminum needed for achieving the desired properties may be introduced into the steel in one compartment of the tundish, preferably in the vicinityof the pouring spout, in such manncrgthat the centre jet of the three jets from the tundish contains metallic alu-f minum which is then evenly distributed in the liquidicore of the slab.- However, convenicntly'only. a portion of the aluminum that is to'be added is introduced into the tundish. the remainder being introduced into the casting jet that iseonfined inthe extended pouring spout. This procedure has the j advantage. that the reaction products formed with oxygen can at leastpartly separate in the tundish. If for any reason the introduction of aluminuminto the centre jet is interrupted, the;

it is naturally possibleito perform any kind of preliminary then poured into the mould from the divided tundish. if the employment oftwo latll'cs or of a divided ladle should be impossible. thenthc steel may be treated in the divided tundish.

A preferred dcoxidant is aluminum, but any desired preliminary deoxidation may be performed for instance with manhganese. sili'con. vanadium or'with deoxidising alloysindivi'dually or in combination- Another feasible procedure comprises tapping an unkilled steel'into a ladle. adding vanadium andadjusting to the final degree of deoxidation required either in one compartment of deoxidation in the furnace or in the ladle in conjunction with ilt is well known-that killed steelsoften have surface faults,

" known as pinholing' which do notclose and fuse together during the further processing, and which therefore lead to unacceptable fnal products. it has been established that an the peripheral zone of the casting.

In the production of alloyed steels the alloying elements may be added in the furnace or, if the additions are small, they may be introduced into the ladle, as is conventional. By using two pouring vessels containing differently alloyed steels ir the 7 method according to the invention, castings can be produced which consist of differently alloyed steels in their cores and surface zones.

thedividcd tundish or in theextended pouring spout of the central jet. steels of different degrees of deoxidation being pourcdinto thc mould.

I Formany applications the material should be resistant to aging; Since aluminum inactivates the. nitrogen in the steel vwhich causes aging by binding the same as a nitride, steels that have been fully killed with aluminum are. also largely resistant to aging provided the addition of aluminum is adequate to bind the nitrogen besides the oxygen."

A very useful method of performing the present invention consists in combining the properties of unkilled steel with the properties of a killed steel'in one and the same cast product.

For the production of slabs for making deep drawing sheet that is resistant to aging an unkilled steel ispreferably used for forming the peripheral zone and a killed. steel for forming the corel'The advantages afforded bytheinvention consist in that the unkilled steel solidifies in a peripheral zone which has a clean surface favourable for further-processing and thatthe undesirable foaming which occurs when an. unkilled steel is cast does not occur because the aluminum-enriched cores of fully killed steel at least substantially prevents the generation of CO bubbles in the transitional region to the peripheral zone that has been formed. e

. Moreover, it is also desirable to avoid the undesirable both, thereby to produce a steel in the core that has been fully killed with aluminum and that is also resistant to aging. The quantity of aluminum that should be added may amount to but not exceed about 800 g/ton of steel. This is far less than the quantity normally needed. However, for achieving resistance to aging other elements capable of binding nitrogen may likewise be used. such as vanadium alone or incombination with the aluminum.

The quality of the casting and final product depends not exclusively upon the purity of the surface and of the peripheral subsurface zone, but also upon the thickness of this latter zone. For a given set of casting parameters this thickness can be controlled by adjusting the relative proportion of the steel poured in the two outer jets to the steel poured in the centre jet as well as by appropriately adjusting the depth of immersion of the extended pouring spout in the bath, i.e. the depth below the bath surface at which the jet forming the core actually emerges.

When casting is to begin the mould is preferably first filled with the steel that is to form the peripheral zone, the steel that is to form the core not being poured until the process of withdrawal begins.

In the majority of applications of the proposed method the use of a'plug or the like for controlling the volumes of steel that are to be poured is advisable.

During the process of continuous casting it is impossible to prevent fluctuations in the withdrawal rate due to technical causes. These must be compensated by suitably controlling the rate of pouring the steel into the mould. In order to ensure that the quality of the casting is uniform it is advisable to regulate the quantity of aluminum that is introduced by reference to the rate of withdrawal of the casting.

The above mentioned examples do not exhaust the possibilities that are inherent in the invention. For instance, it may also be desired to impart particular properties to the peripheral zone by alloying specific elements with the steel for forming this zone.

We claim:

1. A method of producing a compound casting having a peripheral zone and a core, composed of steel having respectively different properties, by continuous casting wherein liquid steel is poured in one end of an open-ended chill mould that solidifies a peripheral zone of steel surrounding a liquid core to form a casting which is withdrawn from the other end of the mould and thereafter further cooled, said method comprising simultaneously pouring into the mould by separate jets of liquid steel of respectively different chemical composition for supplying steel of different chemical composition respectively to the peripheral portion of the mould and to the core portion, thereby to form a steel casting having a peripheral zone and a core of respectively different chemical composition, a jet of steel for forming the core being directed to penetrate more deeply into the liquid in the mould in the direction of the longitudinal axis of the casting than a jet of steel for the peripheral zone, said jet for the peripheral zone being directed to spread in a substantially horizontal pattern of flow near the free surface of liquid steel in the mould.

2. The method of claim 1 in which the pouring of metal into the mould for the peripheral zone is begun before starting withdrawal of a casting from the mould, and the pouring of metal for the core is begun after withdrawal of said casting is started.

3. The method of claim l in which the relative amounts of metal poured into the mould by the respective jets for the core and peripheral zone are varied for adjusting the relative thickness of the peripheral zone.

4. The method of claim 1 in which ajet of metal for the core is conducted and discharged into metal in the mould below the surface of said metal.

5. The method of claim 4 in which the relative amounts of metal poured into the mould by the respective jets for the core and peripheral zone and the depth below the surface of metal in the mould at which metal for the core is discharged, are

varied for adjusting the relative thickness of the peripheral zone.

6v The method of claim 1 in which at least one of said jets impinges on the surface of metal in the mould.

7. The method of claim 1 in which said jets are each conducted and discharged into metal in the mould, below the surface of said metal, a jet of metal for the peripheral zone being directed to flow along a wall of the mould in the region of the surface of said metal.

8. The method of claim I wherein said mould has a lateral elongated cross section for easing a slab in which metal is poured into the mould in three jets, there being two jets of metal for the peripheral zone and one of metal for the core, said jet of metal for the core being discharged into metal in the mould below the surface of said metal, and said jets of metal for the peripheral zone being directed to penetrate below the surface of metal in the mould less than the jet of metal for the core.

9. The method of claim 1 wherein said mould has a laterally extended cross section ofcasting a slab, in which ajet of metal for the core is discharged into metal in the mould, below the surface of said metal. in the direction of the elongated dimension ofthe mould.

10. The method ofclaim 9 in which metal is poured into the mould in three jets. there being two jets of metal for the peripheral zone and one of metal for the core. the two jets of metal for the peripheral zone each being conducted and discharged into metal in the mould, below the surface thereof, and each being directed for the metal for the peripheral who to flow along walls of the mould.

11. The method of claim 1 in which said separate jets are jets of metal having different properties respectively.

12. The method of claim I in which each of the jets are jets of the same metal and a different metal to commingle with the metal of one of the jets is introduced therein.

13. The method of claim 12 in which said different metal is introduced in powder form.

14. The method of claim 1 in which a wire of a metal is introduced into the jet of metal for the core.

15. The method ofclaim l in which each of the jets ofmetal are jets of liquid steel, and in which aluminum is introduced into the jet of metal for the core below the surface of metal in the mould.

16. The method of claim 15 in which the aluminum is in granular form.

17. The method of claim 15 in which the aluminum is in the form ofa wire.

Images