DE1933389A1 - Process for the production of non-aging deep-drawing steel - Google Patents

Description

• Process for the production of non-aging deep-drawing steel

The invention relates to a method for producing non-aging deep-drawing steel and in particular a process for adding aluminum and nitrogen to liquid steel.

The content of dissolved Al and N ₀ in the steel produced by the process according to the invention should be in the most suitable range so that the best possible deep-drawability is achieved. To achieve this, an aluminum wire with a diameter of more than 5 mm is fed _{into the liquid steel at a} feed speed of flour · than 5 m / s and N o gas is blown into the liquid steel, which takes place through a refractory material that is well permeable and attached to the bottom of the ladle.

It is known to use either method in the manufacture of low carbon Al killed steel

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what chunky Al in the. Tapping stream from liquid Steel is thrown, or a process in which form— Cast Al attached to the ladle prior to tapping is commonly used. It is also common to increase the nitrogen content in the steel an Fe.-Mn-N alloy is added to liquid steel. In Fig. 2 is the distribution of dissolved Al and N_ in the steel shown as they are known in the case of the above-mentioned Procedure results in.

In general, the deep-drawability of a cold-worked steel is strongly influenced by the content of dissolved Al and N_ in the steel. The mutual relationships between dissolved Al and N _n in steel, which resulted from many experiments, are shown in FIG. It can be seen that the most suitable range of r the Lankford value for the Tiefziehfahigkeit to more than 2, oo raises between .einem content of dissolved Al of o, o to _t o2o o5o%, and nitrogen by o, oo45 to 0.0080 % . A comparison of Fig. 2 with Fig. 4 reveals that the range of dissolved Al and N ₀ in the known steel (Fig. 2) is far from the most suitable range (Fig. 4) for achieving excellent deep drawability. The reason for such results is that the distribution of dissolved Al and N _{Q is} remarkably large. I. E. _t that the deep drawability, the "dependent, and the highest frequency in Fig. 2 at a value of dissolved Al of o, O45 and N" of the concentration of dissolved Al and N was 0.0038, not that of FIG. 4 apparent Lankford value r of 1 _S 8 or close to this value. ,

It has also been found that such a method has the following disadvantages: There is a tendency to re-

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release of phosphorus (rephosphorization) by the slag and for a higher content caused by it on dissolved Al. At the same time, the inclusions of the aluminum oxide system will float up and separate the imperfect stirring effect after deoxidizing very bad, which leads to many mill chip defects and too - leads to increases in the constituents.

These disadvantages can be avoided by the method according to the invention can be eliminated by adding aluminum and nitrogen to the liquid steel. According to the invention the aluminum is continuously added to the molten steel in the ladle at high speed and gaseous nitrogen blown into the liquid steel through the bottom of the ladle.

The object of the present invention is to provide a method according to which the optimum content of dissolved Al and N ₁ as shown in Fig. 4 is obtained. The process should have the lowest distribution of the dissolved Al and N contents in the steel and the steel produced according to the invention should be a non-aging deep-drawing steel, which allows good yield and has an excellent surface quality.

An exemplary embodiment of the present invention is illustrated with reference to the accompanying drawings.

Fig. 1 shows in a view how according to the invention Aluminum and the nitrogen are added to the liquid steel in the ladle.

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Fig. 2 is a histogram showing the distribution of dissolved Al and N ₀ in steel when the aluminum and nitrogen are each added to the liquid steel by the known methods.

Fig. 3 is a histogram showing the distribution of dissolved Al and N ₀ in steel when the aluminum and nitrogen are added to the liquid steel according to the invention.

FIG. K shows in a diagram the change in the Lankford value r as a function of the dissolved Al and N content.

Ct · ■

The view shown in Fig. 1 shows schematically how the aluminum and nitrogen are added to the liquid steel in the ladle. The steel melt to which no aluminum has been added is drawn off into the pouring ladle 4. Aluminum wire wound around a drum 1 is then introduced into the liquid steel by a feed device 2 via a guide 3. In this case, aluminum wire larger than 5 mm in diameter is required to be added at a speed of 5 m / s. At the same time, gaseous nitrogen is blown into the liquid steel through refractory material with good permeability, for example through a porous stone 5, which is attached to the pouring ladle bottom, from a cylinder 6 standing outside. The blowing time is more than a minute. The liquid steel can be expected to be fully agitated as shown. As a result, the steel retains the appropriate levels of dissolved Al and N ₀ . If the diameter of the aluminum wire is less than 5 and the feed speed is less than 5 m / s, it is found that the added aluminum is the deep layers of the

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liquid steel can not reach. If the blowing time for the N ₂ gas is less than 1 minute, the stirring of the liquid steel is also insufficient and the N content in the steel hardly increases.

The histogram shown in Fig. 3, which results from the data of 53 batches, relates to the present invention. The x value of dissolved Al and N is 0.0297 % and 61.2 ppm, respectively. The Lankford value r, which depends on these x values, is more than 2.0, as shown in FIG. The inventive method is thus far superior to the known processes in which the x value of the dissolved Al and N ₂ o _t o439% and 38.2 ppm, and the corresponding r-value of about l, 7o in Fig. Is 4. In addition, FIG. 3j shows that the dispersion of dissolved Al and N is very small according to the present invention;

The following examples are carried out in comparison with the known methods. The chemical composition and the process conditions are as follows:

TABLE I.

Chemical composition (by weight) C Mn P S N dissolved. Al

A. ο, ο5 ο, 3ο ο, oll ο, οίο ο, οο37 ο, ο28 B. ο, ο6 ο, 32 ο, ο12 ο, ο15 ο, οο3 ^ ο, ο57 C. ο, ο5 ο, 3ο ο, ο12 ο, οΐ6 ο, οο39 O ₁ O ₄ I. D. ο, ο5 ο, 29 ο, οΐ8 ο, οΐ8 ο, οο56 ο, ο3 ^ E. ο, ο5 ο, 27 OjOl'i ο, ο 1 β OjOo63 ο, ο26

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Process conditions:

Steel A, B and C: known processes

Steel D and E: method according to the invention

Amount of Al added: approx. 1 kg / t

Feed speed: 6 m / s

Injected nitrogen volume: about 4 m / loo t

Blowing time: 6 minutes

Hot rolling stage:

Final treatment temperature: 830 ° C Coiled temperature: 52o ° C final thickness. : 2.8 mm

Cold forming stage:

Final thickness: ο, 8 now

Annealing treatment condition: 15 h at 7oo ° C in the chamber furnace

Post-treatment rollers: 0.7 %

The mechanical properties of the above Steels are listed in Table II.

Table II mechanical properties Slnf *

r> ^). Zug- Deh- Erichsen- Kegel- J ^ H * cifttM'g, strengthening cupping cupf- r Y Af ^ * keit worth

. , 2
kg / mm kg / well % mm 1 8th mm 1.34 ASTM No. A. 18.7 31.3 47.8 'lo, 37.6 1.44 9, o B. 18.4 31, o 46.5 H ₁ 3 37.8 1.74 8.6 C. 16.7 29.4 48.6 H, 7th 36.8 1.87 7.5 D. 15.4 28.9 5o, 2 H, 8th 36.5 2, ol 7.1 E. 15.1 28.5 5o, 8 11.1 36.1 6.9

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From Table II it can be seen that the steels produced according to the invention are far superior to the known steels. Based on the most suitable range of 0.02 to 0.04 % of dissolved Al or ^ o to 7 «ppm N_, the proportion of dissolved Al and N_ achieved is about 95 %. The process according to the invention and that according to this process manufactured steel have the following advantages:

1. The floating and separation of inclusions of the aluminum oxide system are accelerated.

2. The reaction for the re-release of phosphorus is considerably reduced.

3 · No segregation or separation of Components are determined.

H. There is only a slight oxidation loss of added Al through the atmosphere and the slag,

The inventive method is effective not only in the production of Al-killed steel with low carbon content, but also in the regulation of deoxidation of ordinary killed steel _s semi-killed steel and the like. In this case, gaseous argon is more desirable than nitrogen.

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Claims (2)

PATENT CLAIMS as 3 asses =: zs ss =: sse = s 1. A process for the production of non-aging deep-drawing steel, characterized in that liquid steel, refined in a furnace, is drawn off into a ladle in a state where no aluminum has yet been added, that aluminum wire with a diameter of more than 5 is now in liquid steel in the; The ladle is continuously fed at a feed speed of more than 5 m / s and the content of dissolved Al in the steel is set in the range from 0.02 to 0.05 % and at the same time gaseous nitrogen or nitrogen-rich inert gas is introduced into the liquid steel through refractory material good permeability is blown, which is attached to the ladle bottom, and that the N_ content in the steel is set in the range of 0.04 to 0.0080 % . . 2. The method according to claim 1, characterized in that the content of Al dissolved in the steel is from 0.02 to 0.04 % and the nitrogen content in the steel is from 0.0050 to 0.0070 % . 209809/0670 Blank page