DE1583378A1 - Process for the production of steel suitable for further processing on electrical sheets (so-called dynamo steel) - Google Patents

Description

PATENT Attorneys 1 R Q "3" 3 7 Q DIPL. ING. e. STOBPBL · DIPL ·. ING. W. GOLIWITZBB I O O O J / O LANDAU / PALATINATE 'AMSCHUTZBNHOF

July 10, 1967

Koninklijke Nederlandsche Hoogovens en Staalfabrieken N.V.,

Ijmuiden (Netherlands)

"Process for the production of for further processing Steel suitable for electrical sheets (so-called Dynamostafry

The invention relates to a process for the production of so-called dynamo steel, i. H. one for further processing steel material suitable for electrical sheets and / or transformer sheets.

In the manufacture of dynamo steel it is necessary to have a Steel material to create the low watt loss and good magnetic Has properties. It is well known in the professional world that this is promoted by as low a carbon content as possible, the presence of silicone and possibly Aluminum, a coarse ferrite grain (crystallites), the smallest possible Amount of excretions and, if any, to make them as coarse as possible and the least possible remaining stresses and strains in the steel.

So far it is in the manufacture of cold-rolled dynamo steel It is customary to make use of the knowledge that by cold rolling and annealing a completely new grain structure is achieved by the choice of the size of the cold cross-section reduction, the temperature

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and the period of annealing thereafter, the size of the new grains of the structure can be predetermined.

In the state of the art as it is today, it was common to ♦ by means of cold rolling and subsequent recrystallization annealing The aim was to achieve a coarse grain in the end product by using a small one Reduction percentage in cold rolling, in imparting a small number of centers or germs for the Growth of new grains. It is also known that secondary waxes of the grains resulting from a high annealing temperature, with primary grains being generated after recrystallization are made to grow at the expense of other grains.

Especially with a low silicon content (e.g. lower than 1.5%) or in the absence of silicon, the coarse grains,

which is desirable for the electrical and magnetic properties were considered to have the disadvantage of a low yield strength and Tensile strenght. This leaves difficulties in punching and the like Operations arise because the punched plates along

the edges are not flat enough and have a considerable inclination towards the Have formation of ridges.

It is possible to avoid this disadvantage by doing the cold rolled material stamps before annealing. Has in this state it has a high yield strength. Only then is it annealed, which means that the recrystallization then gives rise to coarse grains. So had one practically worked in the United States of America, but with high capital investments for annealing furnaces by the users of the metal were required, which only appear economically viable for large consumers.

To avoid punching difficulties, the suggestion is also there made of additions of a ferrite amplifier. This could be done, for example, by introducing a higher content of silicon,

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Aluminum or phosphorus. However, that makes the steel more expensive than necessary in view of the watt losses. Furthermore, the magnetic induction at high field strength lower what for Electric motors is a disadvantage.

The invention is based on the knowledge that it is possible the above mentioned disadvantages in a simple and surprising way and ways to avoid taking this knowledge in the first moment seems to contradict the requirements that have been made so far have always been considered necessary for high quality dynamo steels, including electrical and magnetic ones Characteristics. In this regard, a method, as indicated by soldering, according to the invention is characterized in that steel with Q, 15% carbon or less, 0-2% silicon, 0-0.7% aluminum, 0.15-0.16% manganese and a maximum of 0.06% phosphorus too hot a band is rolled out, after which this band in decarburizing Way (i.e. with removal of the carbon) in a Carbon content of 0.01% or less is annealed, simultaneously or exclusively in such a manner It is annealed again so that coarser grains are obtained, until finally very coarse grains are obtained (ASTM 3 or coarser, e.g. ASTM 0), with the hot-rolling scale before or after this annealing treatment is removed and that finally, after the annealing processes, the strip is cold-rolled and, after cold-rolling, a recrystallization annealing is subjected to the cold rolling area reduction and the time interval and temperature of the recrystallization annealing are selected to be much finer Grains finer than ASTM 5 can be achieved.

Surprisingly, it has been shown that on the one hand electrical and magnetic properties, as described above, can be achieved and maintained despite the very fine grain in the final product, and that on the other hand by this fine grain

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and the resulting improved mechanical properties the punching properties are very good.

It should be mentioned at this point that both the subject matter of the invention and the use of various known methods the known possibility can be made use of, through an appropriate choice of the cold-rolling cross-cut reduction, the annealing temperature and the time interval during the annealing processes to achieve a grain of precisely predetermined size. However, if these measures are used within the scope of the invention is done, this is done by contrasting these mutable be chosen to what is customary in the known processes, so that the cold rolling cross-section reduction is so great that this results in a large number of "germs or centers for new grains, while the final recrystallization anneal at such a low one Temperature and / or is carried out for such a short period of time, that secondary grain growth is avoided at least to a significant extent, so that fine grains (finer than ASTM 5) can be achieved in the final product.

The size of the cold rolling cross-section reduction and the time intervals between the individual treatment stages and the temperatures in the various annealing processes can be within the limits of the invention vary considerably depending on various factors such as the exact composition of the Steel before and after decarburization and the exact desired Size of the grains as well as the desired thickness of the material at the beginning and at the end of the procedure and finally (the chosen gaseous atmosphere during the decarburization process.

It is not possible to give precise values for all these variable quantities. For the ones given below However, details are given in examples. In addition, the person skilled in the art is readily able in every case that occurs

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to determine how best to choose these variables / on the basis of the information given in the documents of this application Hints. Of course, it is also true in this case that annealing at low temperature has a longer annealing duration requires and vice versa. The grain size can be changed at any stage determine the procedure in a simple manner and thus provide an indication for the choice and correctness of the temperatures to be used, the duration of the annealing processes, etc., so that there is also a possibility is to correct these variables during the procedure.

The invention will then be illustrated by means of several examples explained:.

example 1

It was made from a steel belt with the following chemical Composition assumed: -

0.08% carbon
0.31% manganese
0.028% phosphorus
0.010% sulfur
0.85% silicon
0.01% aluminum

Remaining iron and remaining impurities rolled out hot to a thickness of 2.0 mm.

This tape is rolled up into an open coil and placed in an annealing furnace for open coils: In the annealing furnace, a gas becomes Decarburizing put into circulation, allowing free access to the entire surface of steel 'hat. As the decarburizing gas, any gas suitable for the purpose, such as a Mixture of nitrogen, hydrogen and water vapor or hydrogen and water vapor. In practice, this example

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used a gas containing 18% hydrogen and 82% nitrogen, moistened with water to a dew point of 18 C, The decarburization was continued until the carbon content of the steel was reduced to 0.005%. After that, the humidification of the gas interrupted and the annealing process / with drying gas continued for a period of four hours at 850 C in order to seal the steel through and through anneal until grains larger than or equal to one size are produced, which is known as ASTM -micr ο -size number 0.

Then the hot-rolled scale was pickled with sulfuric acid (Sulfur trioxide) removed. This removal can also be achieved by a mechanical operation, if desired such as sandblasting, grinding and brushing.

The strip was then cold-rolled to a thickness of 0.5 mm. It was then rolled up into a closed, tightly wound spool and annealed for six hours at a temperature of 650 ° C. The final product had a fine grain, namely ASTM-8).

Example H

It was made of a steel with

0.07% carbon
0.17% manganese
0.018% phosphorus
0.010% sulfur
1.12% silicon
0.29% aluminum

gone out, with the remainder being iron and the usual impurities. This material was also decarburized to a carbon content of 0.005% at 850.degree. The dry glow through to achieve coarser Grit was also carried out at 850 C until the grit was so was roughly as in Example I. In this case, six hours were for

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. this soaking in a dry atmosphere necessary what means that it took two hours longer than in Example I. There was a difference, which was clear from the composition of the steel was determined, in particular by the silicon and aluminum content,

The temperature, however, has a stronger influence on the Duration of the annealing process, as can be seen from the following Example results.

Example III

A steel according to Example I was after decarburization at 700 ° C Annealed through and through. The annealing time that was necessary to achieve the same grain size was 25 hours in this case.

Example IV

For comparison purposes, a hot-rolled strip was used Example I first pickled, then cold to a thickness of 0.5 mm rolled and then a decarburization annealing to a carbon content of 0.005%. The material was then thoroughly annealed at 700 ° C. for six hours. The end product had fine grain and the steel showed no coarse grain at any stage of the treatment.

Example V ■,. ■

For comparison purposes, a steel according to Example I was used treated a known process, namely: by hot rolling to 2 mm, pickling, cold rolling to 0.56 mm, decarburization annealing as open coil on 0.005% carbon and six hours through and through annealing at 700 C, 12% critical deformation due to rolling (and thus down to 0.5 mm thickness) and six hours of glowing as a tight, closed coil at 650 C. After that, the end product had a coarse grain.

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Of the end products obtained according to Example I, IV and V obtained grain size, yield strength, tensile strength and watt losses at 50 Hz and 10,000 Gauss (V10) were determined. The results are shown in the following table.

Example I Example IV Example V

ASTM micro size Q number 8th 8.5 1 4th Yield strength kg / mm 23.9 27 _; 5 18 7th Tensile strength kg / mm 35.8 39.5 32, 7th V 10 watts / kg 2.7 3.8 2,

From this table it is clear that a steel according to Example IV has a good yield point and tensile strength. However, he is due the high watt losses should be rejected. 3.6 watts / kg will usually be assumed as the limit for material that is said to be suitable as dynamo steel. The known steel of Example V has low watt loss but presents difficulties in stamping and similar operations (Burrs) due to the low yield strength. The steel obtained according to the invention (Example I) is related to both factors cheap.

Hot rolling scale removal should be performed prior to cold rolling take place, but could also take place before or after the decarburization has taken place. After decarburizing, the scale is not actually more of an oxide layer, but it transforms into an iron matrix in which the oxides of the alloying elements are dispersed.

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Claims (4)

PATE NTANWil / DB IPL. ING. AM SCHÜTZENHOff DIPIi. ING. C. STOEFSL · DIPL. ING. W. GOLLWHZBR - 3 * .10. July 1967 Claims: 1.) Process for the production of so-called dynamo steel, characterized in that steel with 0.15% carbon or less, 0-2% silicon, 0-0.7% aluminum, 0.15-0.16% manganese and at most 0.06% phosphorus is rolled out hot to a band, that then this band .zum decarburization (with removal of carbon) to is annealed to a carbon residue of 0.01% or less that at the same time or afterwards the band of a further annealing is subjected, the coarser to very coarse grain size (ASTM 3 or coarser, e.g. ASTM 0) results in that before or after this Annealing treatment of the hot rolling scale is removed and that afterwards and after these annealing treatments, the strip is cold-rolled and, after cold-rolling, subjected to a recrystallization annealing process : becomes, at the cold rolling cross section reduction, time duration and Temperature can be chosen so that much finer grain size, finer than ASTM 5, is produced. 2.) The method according to claim 1, characterized in that the decarburization annealing, while the steel is rolled up into an open coil, at 600 C or higher in the protection of a non-oxidizing one Gas atmosphere with 5% or more hydrogen and the remainder nitrogen, moistened with water, to a dew point of betweenO C and + 35. C takes place in such a way that once the carbon content drops to approximately 0, 005% is reduced, the gas is passed on in the dry state over the steel and the annealing process for several ^ hours 009833/0293 continues at 800 C or higher until very coarse grains (crystallites) is achieved, wherein the steel after removing the surface layer is cold-rolled with a reduction in area of 40% or more and the steel after cold rolling as a dense, closed coil for a short period of recrystallization annealing at a Temeratur of between 600 C and 700 C is subjected, in such a way that no secondary grain growth occurs, the grains rather stay smaller than ASTM 5. 3.) Process according to claims 1 or 2, characterized in that the decarburization annealing as well as the spwohl Annealing to obtain very coarse grains take place at about 850 ° C. 4.) The method according to any one of the preceding claims, characterized in that the tape up to a thickness of about 2 mm is hot rolled and cold rolling to a final thickness of about 0.5 mm or less. 009833/0293