US3866662A

US3866662A - Method of casting quiet steel in molds

Info

Publication number: US3866662A
Application number: US306715A
Authority: US
Inventors: Robert Klages; Heinrich Kleeschulte
Original assignee: Hoesch AG
Current assignee: Fried Krupp AG Hoesch Krupp
Priority date: 1971-11-16
Filing date: 1972-11-15
Publication date: 1975-02-18
Anticipated expiration: 1992-02-18
Also published as: FR2160564B3; FR2160564A1; DE2156768B1; DE2156768C2; GB1407470A; DE2156768A1; JPS4859031A; IT973565B; BE791305A

Abstract

A method of casting quiet steel in a mold according to which prior to the casting casting powder with a bulk weight of from 250 to 750 gr/liter and in a quantity of from 1 to 3 kg/ton of steel is introduced into the mold at a distance of from 5 to 50 cm from the base of the mold, and in which when the liquid steel level reaches the desired height the slag layer is instantaneously and completely covered with water whereby the entire slag layer solidifies and lifts itself off the steel level so that the latter is contacted by the water.

Description

[451 Feb. 18, 1975 METHOD OF CASTING QUIET STEEL IN MOLDS Inventors: Robert Klages, Dortmund; Heinrich Kleeschulte, Dortmund-Barop, both of Germany Hoesch Aktiengesellschaft, Dortmund, Germany Filed: Nov. 15, 1972 Appl. No.: 306,715

Assignee:

Foreign Application Priority Data Nov. 16, 1971 Germany 2156768 US. Cl. 164/123, 164/128 Int. Cl B22d 27/04 Field of Search 164/128, 55, 123, 126,

References Cited UNITED STATES PATENTS 5/1946 Humes 164/126 2,402,833 6/1946 Mummu ct ill 1. 164/126 X FOREIGN PATENTS OR AlPPLlCATlONS 1,289,961 2/1969 Germany 164/123 570,097 12/1957 Italy 249/79 967,032 8/1964 Great Britain [64/56 Primary E.raminerFrancis S. Husar Assistant ExaminerJohn E. Roethel Attorney, Agent, or FirmWalter Becker 5 7] ABSTRACT A method of casting quiet steel in a mold according to which prior to the casting casting powder with a bulk weight of from 250 to 750 gr/liter and in a quantity of from 1 to 3 kg/ton of steel is introduced into the mold at a distance of from 5 to 50 cm from the base of the mold, and in which when the liquid steel level reaches the desired height the slag layer is instantaneously and completely covered with water whereby the entire slag layer solidifies and lifts itself off the steel level so that the latter is contacted by the water,

12 Claims, N0 Drawings 1 METHOD OF CASTING QUIET STEEL IN MOLDSv The present invention relates to a method of casting quiet or dead steel in molds to form ingots, blocks or slabs while utilizing casting powders.

Methods for bottom pouring of quiet steel are known. Of these known methods, two methods are employed in order according to an economic operation to produce qualitatively satisfactory steel ingots, blocks and slabs and to reduce possible inner and outer faults to a minimum. According to the first one of these known methods, which is also called chill casting, a forced solidification of the ingot, block or slab head is obtained by quenching with sufficient quantities of water. In this connection, the shrinking occurring in the interior of the ingot, block or slab is partly compensated for by a controlled post casting of steel. The modifications possible with this method are limited as to time to the phase from pouring to forced solidification. While an improvement in the quality of the ingots, blocks or slabs is obtained by certain steps, as for instance, by varnishing and covering the molds, by adding tar or naphthalene during the casting operation, the stirring of the steel level near the walls of the molds, or the insertion of floating frames, it is, however, not possible by means of these steps to assure a surface quality of the ingots, blocks or slabs which would meet modern requirements.

This insufficient surface quality of steel ingots, blocks or slabs produced in conformity with the so-called chill casting was one of the reasons for introducing the method known as hot top casting with casting powder according to which the steel is cast underneath a layer of casting powder, and the solidification of the ingot top is delayed in the so-called hot tops. With this method, the purpose of the casting powder consists in avoiding by its insulating effect heat losses by radiation and the capping or top freezing inherent thereto, and furthermore consists in forming oneor more viscous slag phases depending on the composition at the phase border steel-casting powder layer, which slag phase is adapted in conformity with the layer thickness and the wetting effect to take up the deoxidation products and other impurifications ascending from the steel. The melting behavior and the viscosity of the casting powder is, in part, so adjusted that the slag will at the respective height of the steel level fully wet the mold walls and will, during the rising of the steel, flow into the gap between the steel meniscus and mold. As a result thereof, a complete surrounding of the block by a slag layer will be obtained, which slag layer will then prevent a direct contact between the mold wall and the steel and will make surface damaging influences at said contacting surface impossible for all practical purposes. The added quantity of casting powder is so selected that with the intended melting speed still with the entrance into the hot top a sufficient thickness of the layer remains. The top tops keep the ingots, block or slabs in liquid condition for a longer period than is the case with the first mentioned method, the chill casting method; accordingly, the shrinking of the steel in the lower block range caused by'the starting solidification can be in part compensated for by the liquid component from the head range. Pouring below a casting powder due to the necessary large hood volume automatically cause a considerable proportion of head waste. In addition thereto, the delayed solidification of the ingot, block or slab head makes necessary considerably extended periods of keeping the blocks or slabs in the molds. This factor leads to undesired liquation or segregation and at certain temperature ranges, for instance, with aluminum containing steels alloyed with from 1 to 1.5 percent manganese causes the wellknown tears.

It is an object of the present invention to provide a method of the above mentioned general type by means of which the drawbacks of heretofore known methods will be avoided and by means of which the output of rolled steel will be increased in a simple manner while a high surface quality of the ingots, blocks and slabs will be assured. The above outlined objects have been realized by the method according to the present invention which is characterized by the combination of the following steps:

a. Prior to the start of the casting, at a distance of from 5 to 50 centimeters, preferably 20 to 40 centimeters from the foot of the mold, the casting powder is introduced into the mold with a bulk weight or pouring weight from 250 to 750 grams per liter, preferably 300 to 500 grams per liter and in a quantity of from 1 to 3 kilograms per ton of steel;

b. When the desired steel block or slab height has been reached which is indicated, for instance, by the liquid steel level reaching a certain marking in the mold, the molten slag layer involving the completely used-up casting powder is instantaneously and completely covered with water on the steel level so that the entire slag layer solidifies, lifts itself off from the steel level and the steel level is contacted by the water. According to a further development of the invention, advantageously, prior and/or during and/or after the pouring in of the water onto the slag layer, further steel is poured again in a continuous or batch wise manner for making up the shrinking of the block or slab head.

According to an expedient and advantageous way, the method according to the invention is practiced in such a manner that a quantity of approximately from 1 to 2.4 kilograms of casting powder per ton of raw steel is introduced into the mold and a quantity of from 1 to 1.5 liters of water more than was used formerly during the water casting is sprayed onto the molded slag layer per kilogram of the slag formed on the block surface.

According to a preferred method of the invention, for purposes of obtaining a block or slab with a proper surface and in order to avoid sources of errors during the casting operation, for instance, to avoid the formation of pouring cones of the casting powder on the steel level, a carbon-free casting powder with a humidity content of approximately 1 percent is added which casting powder has the following composition:

From 50 to of blast furnace slag,

From 30 to 40% of pearlite, and

From 0 to 10% of fluxing agent, said casting powder having a chemical analysis of substantially: related 20 to 30% CaO 42 to 50% SiO,

8 to 14% M 0 3 to 8% MgO o to 6% Na O or B 0 0 to 3% K 0 This carbon-free casting powder is introduced into the mold with a complete fusion occurring at a temperature of less than 360C. As fluxing agent with this composition there may be employed preferably soda or colemanite (calciumborate).

The advantages of the method according to the in- 4 0.18% of carbon 0.42% ofsilicon 1.35% of manganese 0.027% of phosphorous vention are seen particularly in the fact that with a con- 5 0.020% of sulfur siderably reduced proportion in head scrap with a con- 0.040% of aluminum siderably reduced liquation in the block or slab head, and a correspondingly increased output in rolling steel, From the rolling mill there was ordered six slabs of II at the same time and in a simple manner there is obtons each from 12 ton molds and a residual block of at tained a highly satisfactory surface quality of the blocks least 3 tons. The required molds were divided up into and slabs whereby the dispatch of proper rolling matethree mold groups of two molds each. rial is clearly increased. Prior to the start of the casting, at a distance of 30 Furthermore, it is possible at the same time better to centimeters from bottom, four bags each with 5 kilodivide up the content of that casting ladle considerably grams of casting powder, corresponding to a quantity producing any desired raw block or slab length thereby of 1.67 kilograms of casting powder per ton of raw steel obtaining a reduction in the no longer rollable residual were suspended in the molds. blocks. in view of the raw block height being variable The casting powder consisting of approximately 60% to a g at extent. according to the p esent invention, of blast furnace slag, 35 percent of pearlite, and 5 perthere is obtained the possibility of reducing the number cent of soda with a melting flux occurring between ofmold types. Since, according to the invention, it is no l220 to 1240 C had the following compositions A and longer necessary to isolate the block head, hoods and B respectively:

Fe ges. FeO MnO P205 CaO SiO Al O A) 0.94 l.2l 0.69 0.044 28.0 45.3 l0.0 B) 0.82 0.76 0.65 0.042 26.5 46.0 10.0

Mg() TiO C CO2 H2O S ges. Na O K20 A) 4.5 0.70 2. l3 0.85 0.92 3.92 l.54 B) 4.7 0.63 2.49 l.l3 0.82 4.18 1.59

cover powder become superfluous. Consequently, also The bulk or pouring 2 for the composition A amounted the residual quantities of substances for aiding the castto 497 grams per liter and for the composition B ing operation which increase the wear of the pit furamounted to 485 grams per liter. nace and recuperators are greatly reduced. Further- 35 The quantity f the Casting powder which had to be more, the considerably shorteneq pP or Standmg introduced into the mold and which is to be employed time of the molds until the sQhdlfiflauon of h blocks for obtaining a sufficiently melted residual slag layer and slabs result on one hand in an increased life of the consisting f acid glass phase on the Steel level when molds and Q relief of h Castmg P and'on othef reaching the required block or slab height, is deterhand result 1n a reductlon of the heat-up t1me 1n the pit 40 mined primarily by the geometric Conditions f the furnaces in view of the possible hotter insertion of the molds while principally large block weights have a raw Steel blocks mm h P furnaces' cific lower consumption than small ones, and square- T method of F g qulet steel now be shaped ones have a lower consumption than rectangu- Plamed m the followmg lar ones, and round shapes have a lower consumption 45 than square shapes. EXAMPLE The following table for frequently employed mold From an open hearth furnace there were tapped at 21 types indicate the dependency of the quantity of casttemperature of 1620 C and quieted in a casting ladle ing powder from the geometry of the molds.

Mold Type Width Thickness Height Casting Casting in tons Head Foot Head Foot in mm. Powder of Powder in mm. in mm. Quantity per ton per block Raw Steel in kg. in kg.

6 5115 650 5x5 650 2.400 10 L67 7175) 7x0 840 5x0 640 2.400 12.5 1.77 10 1045 1100 660 720 2,150 17.5 1.75 11 1175 1230 625 685 2,150 20 1.82 12 1325 I380 640 700 2,150 22.5 1.x7 13 1425 1480 650 710 2.150 1.93 15 1042 908 2,350 25 1.67

9210 17 1600 I640 700 760 .250 1.77 20 1590- 1640 745 825 2.500 1.75 25 I630 I680 810 890 immer 1.60

sion

tons of raw steel of a carbon-manganese fine grain steel for heavy plates with a melting analysis of:

Therefore, advantageously with block and slab molds having a volume of from 5 to 25 tons of raw steel, the

P kg 17.7 kglm tK m (l/lO) M m 7 kg In this equation:

P Indicates the quantity of casting powder sufficiency K Indicates the heated surface of the steel block M Indicates the mantle surface of the steel block With the great number of different mold shapes, it is advantageous to check in a simple pre-test the quantity of casting powder per mold ascertained from the above formula.

After the customary waiting time of the filled casting ladle with a discharge opening of 50 millimeters in diameter the pouring of the first group was started. After the pouring, the bags with casting powder burned, and the casting powder was distributed over the entire steel surface. In the lower third of the molds, over the riser openings there formed so-called bald heads, which means the powder cover tore open, and bare steel became visible. These bald heads did not reach the mold wall and closed again in the second third of the mold.

If in an exceptional case the bare steel level should not be covered again by the already present casting powder and should reach the mold wall, it is advantageously not necessary to cast slower, but instead merely additional small quantities of casting powder are deposited upon the bare steel in the vicinity of the mold wall until the bare steel is covered up again.

During the rising of the steel level in the mold it is expediently cast with a rising speed of from 20 to 30 centimeters per minute-- the casting powder was consumed, liquified and placed itself between the steel meniscus and the mold wall. After a casting time of 7 minutes and 10 seconds, the high mark was reached for a l2 ton raw steel block. Thereupon the casting jet was throttled and a quantity of water was applied which was sufficient to immediately quench the steel surface of the head on which there was lying a molded slag cover of approximately a thickness of 10 millimeters. For this purpose, a three-arm sprinkler or nozzle with bore holes spaced from each other by approximately two centimeters was employed from which were discharged approximately 40 liters of water per minute. This addition of water was increased by at once adding from buckets additional 10 liters of water per mold after the first quenching by the sprinkler or nozzle. The impurities and de-oxidation products which rose on the slag layer of casting powder melted onto the steel level and also rising from the steel solidified instantaneously and disintegrated in view of the occurring internal and inherent tensions into small fragments while the steel level was contacted by water.

Simultaneously, with the addition of water, steel was slowly cast further while the post casting time amounted to four minutes and 30 seconds. In view of the direct contact steel-water, a sufficiently thick cover I of solifified steel formed, which cover withstood the pressure exerted by the differential height between funnel and steel level and did not break open.

Following the same operation, the next following groups were cast. Their casting times amounted to:

Second group casting time 7 minutes and 40 seconds Post casting time 7 minutes Third group casting time 8 minutes and 30 seconds Post casting time 6 minutes and 20 seconds 5 After a standing time of from to minutes which was reduced over the hood casting by about 50 percent, the slabs were stripped, loaded and moved to the pit furnace dumping place. Here they were introduced into the pit furnace and heated up to rolling temperature. The slabs should be pre-blocked to pre-slabs for introduction in a coarse plate line. The shop rule is cut straight, out off over rolling.

After the rolling to the desired! dimensions, behind the shears for the melt an output of 89.2 percent is obtained with regard to raw steel which means an increased output by 6 percent over the hood casting. This advantage is also noticeable with the output of the large plate train or line.

It is, of course, to be understood that the present invention is, by no means, limited to the specific example set forth above, but also comprises any modifications within the scope of the appended claims.

What we claim is:

1. A method of casting quiet steel in a mold into blocks and slabs, which includes in combination the steps of: suspending in the mold at a distance of from 5 to 50 cm from the base of the mold casting powder with a bulk weight of from 250 to 750 grams per liter and in a quantity of from 1 to 3 kg per ton of steel, introducing the steel to be cast into the mold at the bottom, and when the liquid steel reaches the desired steel level in the mold instantaneously and completely covering with water the liquid sslag layer covering the steel level involving completely molten casting powder to thereby cause the entire slag layer to solidify and rise off the steel level so that the latter is contacted only by the water.

2. A method in combination according to claim 1, in which the casting powder is introduced into the mold at a distance of from 20 to 40 cm from the base of the mold.

3. A method in combination according to claim 1, which includes the step of at the latest after covering the slag layer with water pouring additional steel into the mold to make up for shrinkage of the steel in the mold.

4. A method in combination according to claim 3, in which the additional steel is added in a continuous manner.

5. A method in combination according to claim 3, in which the additional steel is added in batches.

6. A method in combination according to claim 1, which includes the step of introducing into the mold a quantity of approximately from 1 to 2.4 kg of casting powder per ton of raw steel, and spraying onto the melted slag layer per kg of the slag formed on the surface of the steel a quantity of from 1 to 1.5 liter of water more than is customary with the water casting.

7. A method in combination according to claim I, which includes the step of adding into a mold a quantity of casting powder corresponding to the equation P kg 17.7 kg/m (K m (I/ll0)M m 7 kg in which P is the quantity of casting powder in kilograms, K is area of the top of the surface of the block head in square meters and Mp is the total area of the surface of the sides of the block in square meters.

8. A method in combination to claim 1, which ining the casting in an unchanged manner. cludes carbon-free casting powder with a moisture con- 11. A method of casting quiet steel in a mold which tent of approximately 1% and composed of i l d 50 to 60 of blast fu'maCe slag, l. introducing molten steel to be cast into the bottom 30 to 40 of P and of the mold to fill the mold;

O to of a fluxlng agent 2. adding carbon-free casting powder on the upper wlth Chemlcal analysls of Substamlally from surface of the molten steel when it reaches a level 20 to 30 C210 42 to 50 z intermediate the top and bottom of the mold;

3. when the steel reaches the desired top level in the g :2 Z 3 8 10 mold, instantaneously and completely discharging 0 to 6 5 or B 0 water on to the liquid slag layer covering the steel, 0 to 3 6 2 3 thereby causing the slag layer to solidify and sepa- A method in combination according to claim 8, in rate from the steel, so that the latter is contacted which fluxing agent added to the casting powder a subby the water stance is employed selected from the group consisting A f q of casting Claimed in Claim in f Soda and Colemanite (calcium boratey which said casting powder 18 added after the molten 10. A method in combi ti according to l i 1, steel rises above the bottom of the mold, so that the which includes the step of during the casting p o s slag layer forms between the walls of the mold and the adding a small quantity of casting powder for covering 20 steel. bare steel in the vicinity of the mold wall while continu-

Claims

1. introducing molten steel to be cast into the bottom of the mold to fill the mold;

1. INTRODUCING MOLTEN STEEL TO BE CAST INTO THE BOTTOM OF THE MOLD TO FILL THE MOLD.

2. ADDING CARBON-FREE CASTING POWDER ON THE UPPER SURFACE OF THE MOLTEN STEEL WHEN IT REACHES A LEVEL INTERMEDIATE THE TOP AND BOTTOM OF THE MOLD;

3. when the steel reaches the desired top level in the mold, instantaneously and completely discharging water on to the liquid slag layer covering the steel, thereby causing the slag layer to solidify and separate from the steel, so that the latter is contacted by the water.

7. A method in combination according to claim 1, which includes the step of adding into a mold a quantity of casting powder corresponding to the equation P kg 17.7 kg/m2(KFm2 + (1/10)MFm2) - 7 kg in which P is the quantity of casting powder in kilograms, KF is area of the top of the surface of the block head in square meters and MF is the total area of the surface of the sides of the block in square meters.

8. A method in combination to claim 1, which includes carbon-free casting powder with a moisture content of approximately 1% and composed of 50 to 60 % of blast furnace slag, 30 to 40 % of pearlite and 0 to 10 % of a fluxing agent with a chemical analysis of substantially from 20 to 30 % CaO 42 to 50 % SiO2 8 to 14 % Al2O3 3 to 8 % MgO 0 to 6 % Na2O or B2O3 0 to 3 % K2O.

9. A method in combination according to claim 8, in which fluxing agent added to the casting powder a substance is employed selected from the group consisting of soda and colemanite (calcium borate).

10. A method in combination according to claim 1, which includes the step of during the casting process adding a small quantity of casting powder for covering bare steel in the vicinity of the mold wall while continuing the casting in an unchanged manner.

11. A METHOD OF CASTING QUIET STEEL IN A MOLD WHICH INCLUDES:

12. A method of casting as claimed in claim 11, in which said casting powder is added after the molten steel rises above the bottom of the mold, so that the slag layer forms between the walls of the mold and the steel.