DE1533476A1 - Continuous casting process for steel - Google Patents

Description

^ Continuous casting process for steel "

The invention relates to continuous casting processes for steel and particularly relates to such processes which the composition of the steel melt before casting it is set so that the Guuflbramies have good mechanical Have properties and are particularly suitable for re-rolling.

A large part of the requirements placed on shallow * · rolled steel, for example sheet metal and tinplate are made of the untreated, -drawn quality steel (DQ), which is produced in the usual rokilleh. Steel of this type usually has a low carbon content such as 0.03-0.065 * and a silicon content

Patent attorney · Dipl-ing.Martin Lkjif, Dtpl.-Wirltdi.-lno. Ax * lHontmann, Dipi.-Mtys.Stbatttan Hwrmann * 1. TMEItlffNITKASIT ti · TiWwSSH · Utfnmrn A4imu, U — Hi / Mfc. * »

. OAj ^ mtmtit-m »+ KW-Mr. M «S NrtrfnÄnc—, MMm Nr. MMIf ',

Ι * »'JATtMTAMWALTDI. ItIMMOLD ICMMIDT. . ·

not exceeding 0.02%. The stormy surge in the mold associated with the development of large quantities of gas, is characteristic of the casting of unkilled steel.

The steel compositions commonly used in the manufacture of unkilled steel are unsuitable for continuous casting because of the violent surge process. The development of larger amounts of gas in a continuous casting mold results in the formation of holes and cavities within the casting, since the gas has no way of escaping from the continuous casting mold, as in the case of an ordinary permanent mold. Accordingly, a steel is required for continuous casting, the composition of which causes little or no gas evolution in the casting mold. At the same time, however, requires that the mechanical in the continuous casting steel produced has properties which are as good at least vie those of unkilled, tiehfähigen steel Moreover Mus the amount of metal oxides, examples * \ s'pielsveise of the iron oxides, aluminum oxides and silicon oxides

* remain limited to a ..minimu », since these oxides have the tendency to ' have to accumulate on the surfaces of the cast strand and create castings of poor quality, which have a considerable

They require conditioning before they are rolled can. . .

The object of the invention is to 'compose' a steel . create "which is particularly suitable for the continuous casting of slabs that have been rolled flat

Products can be rolled, In the continuous casting of the

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Composite steel according to the invention should be in the form only a minimal amount of Qas will be released The cast slabs produced should have mechanical properties that are equal to or better than those of unquenched drawing steel »In addition, with the new type of continuous casting process, the amount of imported metal oxides are limited to a minimum «"

Further details and advantages of the subject matter of the invention emerge from the description and the examples listed therein,

The composition according to the invention of a melt of a steel-producing furnace is adjusted by adding magnesium and silicon and, if desired, aluminum so that that the molten steel has the following composition:

• C ·. 'O ₁ OI- 0.08%

Mn 0.20 - 0.60%

Si 0.03 - 0.08%

Al not over 0.015%

Fe and minor impurities rest

The molten steel of the above composition is used then poured into a continuous casting mold. They asked for results are achieved with a steel melt of the above composition.,

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where the sum of the Siücium content and 0.1 times the magnesium content is not less than the carbon • content.

The carbon content of the steel melt should not be below O ₁ OUi, otherwise the oxygen content of the steel will be too high for continuous casting if the carbon content falls below 0.01% 0.0i%. The carbon content of the molten steel should not exceed 0.08 t, because the sheet material produced by rolling from the castings, the carbon content of which is greater than 0.08 t, becomes too hard and is therefore unsuitable for deep-drawing processes if it is annealed according to the usual processes. . .

The magnesium and silicon contents of the molten steel can be selected, as these amounts of steel-cooperate in the prevention of) Feinlunkerporösität whose carbon content in the range of 0.01% - 0.08% is, In addition, the oxygen content of the steel can be more reliably estimated

and controlled when the magnesium content is in the range according to the invention than when the magnesium content is less.

The amount of acid soluble aluminum in the steel is. preferably not greater than 0 _f 0i5%, since larger contents the ·. Formation of excessive amounts of non-metallic particles

favor. In addition, too large amounts of aluminum oxides In the non-metallic inclusions are therefore particularly undesirable, especially metal oxide inclusions that Containing large amounts of alumina, tending along the side walls of the mold as the casting descends have to form massive agglomerates in the form of vitreous films. These massive agglomerates are made with the help of jets of cooling water located under the mold are very difficult remove and spoil a very large part of the surface of the cast, allowing extensive conditioning the slab is required.

Bine preferred. Composition of molten steel for the continuous casting, according to the invention, is listed below:

C 0.03-0.06X

Mn 0.35 - 0.45%

Si 0.03 - 0.08 *

Al not more than 0.0i5%

Fe and insignificant impurities rest

The sum of the silicon content and 0.1 times the magnesium content in the preferred compositions of the steel melt according to the invention is not less than the carbon content.

The sas def molten steel, OCE and n compositions within the above-mentioned preferred range are, 100882/0784

castings produced exhibit unusual mechanical Properties when they have been machined using the known methods,

Carbon contents of at least 0.03% are desirable, because the amount of oxygen in the steel, which is less than 0.03% Contains carbon, are often so large that they cause harmful gas development in the form as well

"the oxidation of steel and deoxidizing elements, for example magnesium, aluminum and silicon, causing excessive amounts of non-metallic inclusions to be formed carbon contents in the range of 0.03% - 0.06% are also advantageous because they are used for annealing flat-rolled products, for example those after rolling of the existing strip material, very good results can be achieved.

The molten steel for the present process can be obtained from any steel making furnace such as a basic oxygen process furnace (BOP) or an electric furnace, the former being preferred. Is used in the present process for the production of steel, a basic oxygen process furnace, the composition of the melt furnace is usually as follows:

C. fewer as 0 , 03 - 0 .06% Si 0 , 02 * Mh , 0 , 01 - 0 .25 * 0 fewer as 600 - 900 PPM S. fewer as 0 , 02 * P. 0 , 015 *

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The standard furnace for the basic oxygen process also called oxygen blowing process furnace, and those with it related procedure sser production of low

Carbonized steel grains can be used without modification. "However, it is often advantageous to modify ordinary oxygen-blast furnace practice by adding enough manganese to the furnace so that there is at least" 0.1% residual manganese in the furnace snow "". the Manganrestgähalt in the Ofenschmelee "ufl least O ₁ IOJt be if the sulfur content of the fed into the furnace Si sen s in the normal range of about O, O253t - is 0.050%, thereby the sulfur content in the furnace melt to an acceptable level, the is not greater than 0.02 #, to keep »residual manganese contents of over 0.1% are achieved by adding a manganese ore to the furnace charge or by adding hot» metal (iron from the blast furnace) that contains enough manganese

contains to increase the residual manganese content to at least 0.156 obtained. The use of manganese ore is preferred because the high manganese hot metal usually contains so much phosphorus that the amount of phosphorus present in the cast steel exceeds the acceptable catenae. By using manganese ore, the desired residual manganese content can be achieved in the furnace melt without an excessive increase in the phosphorus content occurring at the same time. Manganese ores of both high and lower quality can be used. The amount of the ore is at least about 0 _f i Gew.Ji Mh, starting from the total weight of the furnace charge · la Generally, larger amounts may be required because a large part of the

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Manganese is released into the furnace slag and is thus lost.

The temperature in the furnace is usually in a range of 1 566 - 1 649 ⁰ C maintained. Temperatures higher than 1649 ° C should be avoided because they lead to rapid wear and tear of the furnace lining, as a result of which there are too large amounts of heat-resistant oxidic slag in the furnace melt,

* It is impossible to produce a furnace melt with the desired composition which is suitable for feeding into a continuous casting mold according to the method of the invention. The equilibrium conditions existing between the carbon and silicon at ordinary furnace temperatures require that either the carbon content be above the acceptable maximum of 0.08% or the silicon content below the minimum of 0.03%. It is necessary to produce a furnace melt which has the desired carbon content - but which cannot be satisfactorily reduced in the steel melt after it has been tapped from the furnace and to add the required amount of silicon to bring the silicon content to the desired level. Manganese must also be added in order to increase the manganese content for the process according to the invention. A large part of the manganese content of the steel melt poured into the mold is added after the tapping of the melting furnace, because it is in view of the excessive manganese losses due to the discharge

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the furnace slag would be disadvantageous for the entire amount of manganese required to produce the desired manganese content is to enter into the basic oxygen process furnace.

It will be found that the silicon content of the steels used for the invention is considerably higher than the silicon content of the steels used for the manufacture of raw drawn steel. The silicon content according to the invention is in the range from 0.03-0.0856, while the silicon content of the non-killed drawing steels from which flat-rolled products are to be made must usually not be more than 0.02%. Surprisingly, the higher silicon content according to the invention is not harmful, but is actually beneficial for the mechanical properties of the rolled steel. In addition, the higher silicon content is necessary to avoid the swelling effect, which leads to cavities and gas bubbles in the continuously cast part.

The manganese can be poured into the ladle in the form of manganese silicon, higher or medium carbon manganese iron or electrolytic manganese can be used. Through the Addition of the manganese silicon also feeds in all of the silicon which must be added in order to achieve the silicon content The composition of the molten steel to the desired level of 0.03-0.085 pounds is common about 2.72 - 4.54 kg per ton of manganese silicon and about 0.907 - 1.81 kg per ton of medium carbon ferromanganese to add the required manganese to the molten steel

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and to supply silicon. Instead of adding manganese with a medium carbon content, manganese can also be added high carbon content or electrolytic manganese can be added. Often the required amounts of manganese are with a high carbon content somewhat lower than the normally required quantities of ferromanganese with a medium carbon content, and in most cases only 0.454-0.9o7 kg per ton,

The silicon manganese and the ferromanganese become common while the tapping pan is being filled, it is added to the furnace melt that is being produced in the steelmaking furnace. The best results can be achieved if the silicon manganese and ferromanganese are used during the filling of the middle third of the ladle. In addition to the manganese and silicon are common small amounts of Altwiniua introduced into the racking pan, in order to improve the properties of the non-metallic inclusions and thus the conditioning of the continuously cast brass produced in the present process Limit minimum size. In. found me in this regard, that one feeds about 0.227 to about 0.681 kg of aluminum per ton of hot metal, in the QieB pan, to one Simplification of the problems posed by the inclusions present in the solid slabs leads, after the: The composition of the steel has been adjusted so that it is either in the broad or preferred range described above.

The steel is then poured into the upper end of the water-cooled continuous casting mold that is open at the top. The hardening of the steel is initiated in the mold. A cast strand is then drawn from the bottom of the mold, which has a hardened outer skin that surrounds a liquid metal core. The consolidation of the entire cross-sectional area is done by means of the water jets located below the form, this usually vie like in the continuous casting of the case.

The solidified slab can be further treated, for example by hot rolling to obtain flat rolled products such as steel strip. These flat-rolled products can be annealed and coiled and finished according to ordinary metalworking techniques will.

The subject matter of the invention is now referred to

to specific embodiments on the basis of examples

shown. · ^

EXAMPLE

The following procedure was used for all of this Example described melt paths used:

A steel melt was tapped into a tapping pan by a basic oxygen processing furnace (BOP). the

Melt steel was made low by a modified standardized oxygen blowing (BOP) process

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9.07 were leg of a manganese ore containing manganese about $ 50 per ton, used - carbon steel produced, wherein 75% Gev _t hot metal (iron from a blast furnace), and 25% by weight of oven scrap plus 4.54.. The operating mode was as usual when the manganese ore was not added. The carbon and manganese content of the steel as tapped from the furnace was determined. The furnace melt contained insufficient amounts of magnesium and silicon

P and was therefore unsuitable for producing a steel of the composition required for a continuous "casting process". Therefore, manganese and silicon were added to the steel melt in the tapping pan. The supply of manganese came in the form of silicon manganese and either medium carbon ferromanganese, ferromanganese high carbon or electrolytic manganese, as indicated for each melt run. The silicon manganese also provided the required silicon, as well as the addition

_k of aluminum in the ladle was made in the amounts indicated. Adding manganese, silicon and aluminum to the ladle deoxidized the steel sufficiently, ¹ so that gas bubbles and other phenomena of "open" or unkilled steel in the mold were avoided, Injder Table I below lists the carbon and manganese content of the furnace melt, as well as the amounts of silicon manganese, ferromanganese and aluminum added to the tapping pan,

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TABLE I. Pans added, kg / ton

1 Tapping C. Mn Middle manganese Alu Melting line 2 Slab composition 0.037 0.15 Carbon-
Perro silicon 8.88 minium No. 3 No 0.024 0.14 manganese 8.69 1, 42 4th 2 0.040 0.18 2.22 + -6.39 1, 39 5 5 0.038 0.16 6.80 8.79 1 0.040 0.25 2.66 6.64 0.93 5 0.040 0.25 2.83 6.64 0.91 1 0.040 0.25 2.77 6.64 0.91 2 0.040 0.25 2.77 6.64 0.91 6th 3 0.040 0.25 2.77 6.64 0.91 4th 0.036 . 0.17 2.77 7.05 0.91 5 0.036 0.17 2.77 7.05 1.41 1 0.036 0.17 2.35 7.05 1, 41 2 0.036 0.17 2.35 7.05 1, 41 3 2.35 1, 41 4th 2.35

5 0.036 0.17 2.35 7.05 1.41

6 0.036 0.17 2.35 7.05 1.41

+ Electrolyte manganese

The molten steel was poured from the ladle into the top of an open ended, water-cooled, tubular continuous casting mold, while da ^ mtere

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End of the mold was closed by a starting block. Partial solidification of the steel then began in the mold. As soon as the mold was essentially filled with molten steel, the starting block and the cast body adhered to it, which had a solid outer skin and a liquid core, were lowered under the mold as the pouring of the molten metal from the ladle continued. The cast strand was superficially cooled by water jets as it sank under the mold until it had completely solidified. The strand was then cut into slabs of a certain length. These slabs were now allowed to cool to room temperature.Samples of these slabs were taken for the purpose of analyzing carbon, manganese, silicon, aluminum and oxygen. The results of these analyzes are shown in Table II below. On the surface of the continuous-caster mold located in) the molten metal at each melt was low gear Amount of foam observed, consisting essentially of iron oxide and oxides of the deoxidizing species, i.e. manganese, silicon and aluminum. The amount of this foam varied somewhat from melt to snow. The biggest Part of this foam wandered along the river with the Cast sidewalls downwards and was in the. Water jet cooling zone removed. The metal slabs were fastened by bits Removal of superficial impurities and

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Conditioned surface imperfections, most of these Defects resulted from mechanical damage that arose in handling the finished slab. The pretty ·. · small percentage of surface area to be subjected to conditioning is listed in Table II below.

TABLE II

Steel composition,? I (Slab analysis)

Enamel
corridor,
No. Slabs
No. C. Mn Si Total 0
^A1 2
pm condition
renation 1 2 0.0 38 0.47 0.032 0.004 166 15th 2 5 0.048 0.33 0.040 0.006 197 8th ·. 3 1 0.060 0.45 0.038 0.00 5 297 5 4th 5 0.0 50 0.36 0.024 0.011 212 5 Ul 1
2
3
4th
5 0.055
0.055
0.055
0.055
0.055 0.48
0.48
0.48
0.48
0.48 0.040
0.040
0.040
0.040
0.040 0.00 8
0.008
0.008
0.008
0.008 T 71 2
1
1
2 6th 1
2
3
4th
5
6th 000000
000000
UlUI UlUl UlUI
OOOQOO 0.40
0.40
0.40
0.40
0.40
0.40 0.040
0.040
0.040
0.040
0.040
0.40 0.005
0.005
0.005
0.005
0.00 5
0.005 217 1
2
3
8th
4th
2

The cold slabs were reheated and hot rolled in a hot strip mill. This rolling mill had several rough rolling stands and several finishing stands followed by a winder. The temperature measurement of the steel 809882/0784

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took place immediately behind the last rough rolling stand and immediately behind the finishing or fine rolling stand as well as directly in front of the winding device. These temperatures are shown in Table III below as raw rolling, Fine rolling and winding temperatures listed.

The hot strip coil was descaled and then cold rolled in a multi-stand cold rolling mill. The W percentage decrease in thickness, which results from the difference between the original and the final thickness, divided by the original thickness and multiplied by 100, was 61.4% in all cases,

The cold-rolled steel strip was in an inert atmosphere for a certain time and in the Table III listed below annealed.

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TABLE III Varmyal zd at en Fine Wrap Glow dates Hour average Raw rolling Soaking through Soaking Melting Slab
KS-M rolling Time, 695 gang ^ No. Rr. 871 638 693 1101.5 879.5 627 18th 695 1 2 1093 879.5 632 22nd 695 2 UI 1088 879.5 643 24 699 3 1 1088 832 627 19th 695 4th Ul 1071 832 627 21 695 5 1 1077 832 627 21 695 2 1082 827 627 21 695 3 1074 832 627 21 695 4th 1077 871 621 21 685 Ul 1027 871 624 22nd 695 6th 1 1046 877 632 17th 695 2 1066 877 627 22nd 695 3 1066 854 621 22nd 699 4th 1038 877 632 22nd 5 1049 29 β

In the longitudinal direction, the lower yield point, tensile strength and elongation were determined in accordance with the ASTM standard method. The results are given in Table IV below.

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TABLE IV

Enamel Lower
Slabs yield strength Tesi Tensile stress
ksi Percentage
Elongation in % aisle no, Kr. Longitudinal direction Longitudinal direction on 5 cm 25765 Longitudinal direction 1 2 25400 45635 42 CM Ul 26300 45745 42 3 . 1 25730 46670 43 4th 5 27400
24705
26165
25875
24960 45725 43 Ul 1
2
3
4th
5 26560
29025
25075
28115
25960
27105 48290
44990
46715
46355
45115 41
39
42
43
42 6th 1
2
3
4th
5
6th 470 5ο
46525
44420
46180
46810
46065 43
40
41
43
44
42

The steels listed above are the unkilled ones Tensile steels (EQ) with regard to their deformation properties for the production of drawn molded parts without breaking appear, equal or superior "

Claims (1)

PATENT LAWYERS PATENTANWÄLTE LICHT, HANSMANN, HEKRMANN I MÖNCHEN 2 THERESIENSTCASSE 33 UNITES} STATES STEEL CORP. Pitt sbur gh, Perm sylvani a William Penn Place 525 DipUng. MARTIN LICHT Dr. REINHOLD SCHMIDT Dipl.-Wirtsch.-Ing. AXEL HANSMANN Diploma Phys. SEBASTIAN HERRMANN Mönehen, September 13, 1966 / UP Patent application? "Continuous casting process for steel" Claims 1, process for the continuous casting of steel by adjusting the composition of the steel melt, so that molten steel results with the following composition: C. <· 0 , 01. - 0.08 * Mn 0 .20 - 0.60% Si no over O , 03 - 0.08% Al and insignificant 0.015% Fe Impurities rest and introducing the molten steel into a continuous casting mold. 909882/0784 Patent attorneys Dipl.-Ing. Martin Licht, Dipl.-Wirttch.-lng. Axel Hantmann, Phyt. Sebastian Herrmann MÖNCHEN 2, THEiESlENSTRASSI 33 · T * from »2102 · Tileeramm-Aii ™ ···! Upofli / MfcKfwn Banlcwrbin & ineen: Dwhche Bank AO, Fill ·! · Min * · «, D« p. 7Μβ «Μ Bayer. Vweinsbanfc Mönch «), branch. O.kor-voo-Millw-ting, account no. 8824 «· Podschadc account in MOndten No. 1Ö397 Opfwnaver ISro> PATENT ADVOCATE OR. REINHOLD SCHMIDT 2, method 'according to claim ι, characterized in that that the sum of the silicon content and 0.1 times the manganese content of the molten steel is 'not smaller' than the carbon content » 3, method according to claim T _1, characterized in that the molten steel has the following composition: C. no over 0.03 - 0.06% Mn 00.35 - 0.45% Si 0.03 - 0.08 * Al 0.01 5% Fe and insignificant Impurities rest ■ ir - - '■ ι 4, method according to claim 1, characterized in, that the residual manganese content of the furnace melt is not smaller than 0.1%. , -H 5, method according to claim 1, characterized in that * that the furnace melt from a basic oxygen process | Steelmaking furnace (oxygen blast furnace) is tapped ^,! , * * ■■ '■'. ■ - "ι 6, The method of claim 5, characterized in that said manganese ore is fed in an amount of at least 0.1 wt. Per cent "of the total weight of the furnace charge in the furnace 909882/0784 ORlßlNAL SNSPECTEO 7. The method according to claim 1, characterized in that that the molten steel does not exceed -0.02 / £ Contains sulfur, 8, the method according to claim 1, characterized by the Process steps of the formation of a solidified steel ■ _ slab in the continuous casting mold and rolling the slab into a flat-rolled product, 909882/0784