DE2056405A1 - Process for the continuous casting of steel - Google Patents

Description

McCONCO DETROIT (MICHIGAN)

Process for the continuous casting of steel

The invention relates to a method for continuous casting of steel, especially low carbon steel.

It is known, flat-rolled strip or sheet, cold or hot rolled, as the starting material for a number of deep drawing processes of manufactured products. For this purpose, unquenched steel was produced in the SM furnace, electric furnace or in an oxygen converter and cast in a conventional way. Steel like that had a carbon content of about 0.03 to 0.25% and equivalent Manganese content. The surface quality and drawing properties of the sheet rolled from it were good. To train a resistance to aging of unkilled, conventionally cast steel, it is known to add the element boron in such a way Amount that the nitrogen is bound in the steel. These steels produced in this way, however, are not suitable for casting in the continuous casting process, which requires rapid solidification. The resulting boiling reaction and the amount of gas released are too violent or too large for the continuous casting process. On the one hand there is an overflow of steel from the mold and on the other hand the released one results Amount of gas due to insufficient escape time, gas bubbles and voids in the cast product.

It is therefore the object of the invention, egg nes steel to adjust the composition so that it is suitable for casting on a continuous casting, the melt is solidified under NUJ ¹ low gas discharge in the mold and the produced cast product in the mechanical properties at least equivalent to the unkilled, is conventionally cast steel in upright molds. The composition of the steel should also be such that slabs cast from the steel are suitable for the production of flat-rolled products.

This object is achieved in that the steel melt with the addition of manganese, aluminum and boron has the following composition is set:

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I. O, - 20% C. 0.01 - O, 60% Mn 0.15 - 0 , 12% Al 0.015 - 0.015% B. 0.0001

Fe (and minor impurities) remainder

and this molten steel is poured into a continuous casting mold.

Not with ^{regard to} S ^{on the} carbon content, it is stated that this / should be below 0.01%, since otherwise the production of steel in the basic steelmaking process would result in such high oxygen contents that the refractory lining of the steel-producing furnace would be attacked. This value of 0.01% is also favorable with regard to continuous casting. The upper limit given for the carbon content should be 0.2%, since at higher carbon contents the deformability drops sharply due to the strength-increasing effect of the carbon and the steel is no longer suitable for deformation and deep drawing.

The steel melt to be adjusted to the specific composition can be produced in any steelmaking process, e.g. SM furnace, electric furnace or oxygen blower converter. For example In the latter, low-carbon steel is produced with the following composition:

C 0.03 - 0.06%

Si less than 0.02%

Mn 0.05 - 0.25%

S less than 0.04%

P less than 0.05%

0 600 - 900 p.p.m.

Those necessary to achieve the composition according to the invention Manganese, aluminum, boron and possibly carbon can be added to the pan during or after tapping.

The manganese can be added to the pan as ferromanganese with suitable Carbon content or as electrolytic manganese can be added. When using ferromanganese with low or medium carbon content An addition of around 2 to 6 kg per ton of steel is sufficient. Because of the avoidance of hot brittleness, the manganese is

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send rolling process important. Test trials on a continuous caster with a straight mold have shown that the manganese content can be reduced to 0.15% without surface cracks with an arch system However, the manganese content should not be below 0.20% in order to avoid cracks on the surface during straightening.

The aluminum can be in any form, e.g. as bars or as Alloy added in an amount of 1.75 to 3 kg Al per ton of steel will. According to the invention, 0.015 to 0.12% must be shown in the composition of aluminum. It was found that * under 0.015% of the steel was not sufficiently settled and gas voids were formed due to entrapment of escaping gas. Over 0.12% Aluminum proved to be disadvantageous because the steel quality deteriorates due to the impairment of the mechanical properties. Also is an addition above this upper limit is relatively expensive.

It has been found that relatively low levels of boron in combination with aluminum, the hardness of the steel is reduced and the casting of fully killed low-carbon steels is allowed, at least have the quality of conventionally cast unkilled steels. This is a surprising effect since boron is related with the usual deoxidizing agents was known as a hardness enhancer.

Boron can be added to the pan as ferroboron or in the form of other boron alloys can be added. When using ferroboron with 18% boron, 0.12 to 1.0 kg of ferroboron per ton of steel is usually sufficient.

If necessary, the melt in the ladle can be carburized by adding coke, anthracite, graphite or petroleum derivatives take place.

All additions can be made in sequence or together, but preferably at intervals during tapping, by one to ensure even distribution.

An advantageous steel composition for continuous casting according to the invention is as follows:

C 0.03 - 0.15%

Mn 0.20 - 0.50%

Al '0.020-0.030%

B 0.0003 - 0.006%

Fe (and insignificant impurities) remainder.

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The carbon content of O, O3% is therefore advantageous to the To keep the oxygen content in the steel so low that only a moderate pasentwicklung takes place in the mold. The limited oxygen content also prevents over-oxidation of the steel and excessive formation of non-metallic inclusions from the deoxidation elements Manganese and aluminum.

After the desired steel composition has been set, the steel is poured into the mold via an intermediate container rfer strand is continuously pulled out. If desired, the strand can be further deformed using the casting heat or in an intermediate stage, brought to a uniform deformation temperature in a heating furnace. Of course you can the strand is first divided, cooled to room temperature and then warmed up again. After deformation, e.g. hot rolling, For example, the flat rolled bath can be annealed, pickled, cold rolled, or treated in any other known manner.

The subject matter of the invention is explained further using an example.

example

The following procedure was used with all of the melts described in this example.

The steel melt was from an oxygen converter, in which it was used according to normal practice for the production of low-carbon Steel was melted, tapped into a pan. Depending on the melt analysis it became manganese, aluminum, boron and in some cases carbon added to the pan. The following table shows the additions for 14 melts in kg per ton of steel.

Table 1

Pans added, kg / ton stole 2.37 Ferroboron (18%) melt No. Coke ferromanganese aluminum 2.5 0.5 1786 2.5 2.37 0.5 2154 2.5 2.37 0.5 2321 2.5 2.25 0.5 2493 2.5 5 0.5 1112 0.25 4.25 - 4 -
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Melt no. Coke fferromangan aluminum ferroboron (18%)

2316 1.15 2.25 2.25 0.5 2324 2.5 2.37 0.5 3071 2.25 2.25 0.5 3505 2.5 2.5 0.5 4209 2.5 2.5 0.5 10038 6.0 2.0 0.5 11602 2.5 2.25 0.25 11604 2.5 2.5 1.0 11606 2.25 2.25 1.0

The steel melt was then from the ladle via an intermediate container in a water-cooled continuous casting mold with brainmen format, the lower end of which was closed by a starter line, poured off. A flux was applied to the bath mirror surface in order to Inclusions of aluminum-containing, non-metallic impurities to avoid if possible. The strand partially formed in the mold was drawn out and cooled in a secondary cooling zone. After this. Separation to the specified length and cooling of the slab to room temperature, samples were taken and the content of carbon, manganese, Aluminum and boron examined. Table II gives the results:

Table II

Steel composition, manganese Weight percent boron Melt no. carbon 0.29 aluminum 0.0008 1786 0.05 0.22 0.068 0.0015 2154 0.04 0.36 0.030 0.0050 2321 0.06 0.25 0.065 0.0020 2493 0.03 0.48 0.015 0.0025 1112 0.11 0.34 0.021 0.0020 2316 0.05 0.38 0.114 0.0034 2324 0.05 0.38 0.075 0.0036 3071 0.06 0.31 0.109 0.0019 3505 0.04 0.31 0.048 0.0035 4209 0.07 0.50 0.118 0020 10038 ^: 0.17 0.29 0.075 0.0020 11602 0.04 0 9 55 0.040 - 5 -
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Melt no. Carbon manganese aluminum boron 11604 0.05 0.34 0.120 0.0142 11606 0.05 0.38 0.057 0.0110

The slabs were further brought to rolling temperature, flamed and hot rolled in the strip mill, the temperatures being checked several times. Table III shows the temperatures immediately behind the raw seam stand and fine roll stand as well as in front of the reel:

Table III

Hot rolling ^{temperatures, 0} C melt no. Bund No. Raw rolls, fine rolls, reels

1786 685 1049 882 593 2154 3345 1038 876 610 2321 4791 1038 865 616 2493 5635 1054 879 676 1112 4308 1038 887 654 2316 4832 1065 882 632 2324 4837 1054 893 660 2321 4839 1071 905 676 3071 309 1054 882 649 3505 2820 1093 898 643 4209 7496 1051 893 695 10038 3164 1093 905 610 11602 238 1116 882 827 11604 242 1076 898 716 11606 247 1076 849 621

The yield strength, tensile strength and elongation in the longitudinal direction were determined according to ASTM standards. Table IV gives these values:

Table IV

Melt Carbon Bund Yield Strength Tensile Strength Elongation in% No. % No. in kg / cm ² in kg / cm2 to 5 cm

Longitudinal direction Longitudinal direction Longitudinal direction

1112 0.11 4308 23.7 38.0 37 2316 0.05: 4832 23.0 35.2 41 2324 0.05 4837 23.5 35.3 40 2321 0.06 4839 23.4 35.2 40 - 6 - 109826/0955

Melt Carbon Bund Yield Strength Tensile Strength Elongation in% No. % No. in kg / cm ² in kg / cm ² to 5 cm

Longitudinal direction Longitudinal direction

3071 0.06 309 25.2 36.4 36 3505 0.04 2S20 21.3 33.1 36 4209 0.07 7496 23.9 34.8 42 10038 0.17 3164 27.2 41.8 32 11602 0.04 238 24.7 33.1 40 11604 0.05 242 22.0 33.5 40 11606 0.05 247 24.9 34.8 38

If subsequent cold rolling was necessary, the hot bath was used etched and deformed in a cold rolling mill, the percentage decrease in thickness being between 40 and 70% in all cases. After annealing of the bath in an inert protective gas atmosphere at approx. 700 ° C. for 12 to 20 hours were the lower yield point, tensile strength and elongation determined lengthways according to ASTM standards. Table V shows the results:

Table V

Melt no. Carbon bundle yield point tensile strength elongation in%

in% No. in kg / cm ² in kg / cm ² to 5 cm

Longitudinal direction Longitudinal direction Longitudinal direction

1786 0.05 6S5 22.3 33.5 38 2154 0.04 3345 21.3 31.3 42 2321 0.06 4791 20.7 31.7 39 2493 0.03 5635 18.0 28.6 43

The steels produced in this way are of high quality and toughness at least equivalent to the conventionally produced non-killed steels and can therefore be used instead of these steels or replace these.

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Claims (5)

ΡΛΤΕ N TANSPRUEC II E 1. A method for the continuous casting of steel, characterized in that that the steel melt is adjusted to the following composition with the addition of manganese, aluminum and boron: C 0.01-0.20% Mn 0.15-0.60 % Al 0.015 - 0.12% B 0.0001 - 0.015% Fe (and insignificant residual impurities) and this steel melt is poured into a continuous casting mold. 2. The method according to claim 1, characterized in that the adjustment of the aluminum and boron content by adding these elements in the pan. 3. The method according to claim 1, characterized in that aluminum, boron and part of the manganese are added to the pan will. 4. The method according to claim 3, characterized in that 1.75 to 3.0 kg of aluminum, 2.0 to 6.0 kg of ferromanganese and 0.12 kg up to 1.0 kg of ferroboron (liiw boron) per ton of steel was added to the pan v / earth. 5. The method according to claim 1, characterized in that the steel melt is adjusted to the following composition: C 0.03 - 0.15 % Mn 0.20-0.50 ^r ; O Al 0.020-0.080 'o B 0.0003-0.0OG Tc Fe (and insignificant remainder impurities). McCONCO, DETROIT ⁸ "EAD ORIGINAL 109826/0 ^f l 55