DE1076158B - Soft magnetic sintered iron body with high dimensional accuracy - Google Patents

Description

GERMAN

The invention relates to a soft magnetic sintered iron body of high dimensional accuracy, which consists of a Iron powder is produced with a grain frequency between 250 and 700 μ and a coercive force below 1 Örsted has. Sintered bodies with a grain frequency of about 500 μ are particularly advantageous. Such Sintered bodies produced by the method described in more detail below have a coercive force of about 0.8 Örsted and at a field strength of 20 amperes / cm an induction of about to 16,000 Gauss.

The new sintered iron body according to the invention has the significant technical advantage that it consists of one approve, e.g. B. iron powder produced by pressure atomization can be produced and at the relatively cheap powder metallurgical processes an inexpensive soft magnetic component represents.

The required of a soft magnetic body low coercivity less than 1.5 oersted is ^ao as observed by the new sintered body, as the demands on the permeability; a field strength of 20 or 200 amperes / cm should result in an induction of 15,000 or 19,000 Gauss. Finally, for many purposes of application, it is important that the sintered body according to the invention is distinguished by high dimensional accuracy.

The listed properties of the new sintered body form the prerequisites for a versatile Use as a soft magnetic body, in particular in electrical engineering. The advantages are particularly evident when of the Magnetic body large numbers are required. In this case, the advantages of powder metallurgy take effect Manufacture particularly cheap, it being of particular importance that the spread of the magnetic values is very small.

It is known that the coercive force of pure iron increases with grain size, i.e. H. the size of the individual crystals. However, this cannot influence the influence of the grain size of the starting powder on the coercive force of sintered iron bodies, which in the course of sintering undergo recrystallization.

The invention is based on the result of experimental work which surprisingly showed that the coercive force of sintered iron bodies depends on the grain frequency of the starting powder. Grain frequency is understood to mean that grain size or that grain size range which in terms of numbers significantly predominates in a powder. So it is given in a longitudinal dimension. The width of the grain frequency of the starting soft magnetic sintered iron body used for producing the sintered iron body according to the invention
high dimensional accuracy

Applicant:

Siemens-Schuckertwerke

Corporation,

Berlin and Erlangen,

Erlangen, Werner-von-Siemens-Str. 50

Dr. techn. habil. Horst Schreiner, Nuremberg,

and Dipl.-Ing. Ulrica Baumann, Berlin,

have been named as inventors

powder should not be too big and at least within 250 to 700 μ, but if possible in an even narrower one Range around 500 μ. In other words, if you look at the particle sizes in a diagram of a powder depending on its frequency, then the resulting Gaussian or Rosin-Rammler distribution curve not too large Have mean value range; it should be in the range given above between 250 and 700 μ. at the aforementioned experimental investigations have been found that in sintered bodies made of an im generally used pressure-atomizing iron powder with a maximum of the grain size distribution 100 to 200 μ are produced, the coercive force 1.3 to 1.5 Örsted exceeds, but that with increasing Grain size can significantly reduce the values of the coercive force. A grain size limitation is given by the worsening of the edge properties of the sintered bodies which increases with it. To According to the teaching of the invention, the most favorable grain frequency is between 250 and 700 μ.

In the diagram of the drawing, the coercive force (H _c in amperes / cm) of a sintered iron body according to the invention is shown as a function of the grain frequency of the starting powder. The arrows indicate the limitation of the sieve fraction and thus the smallest and largest grain size occurring in the powder, the grain frequency and the mean value width lying between these limits.

The sintered body is manufactured using the following process:

909 757/327

The starting iron powder is subjected to a heat treatment between 700 and 800> ° C. in a reducing atmosphere, preferably in hydrogen, before it is melted. The first sintering takes place for about 5 hours between 1000 and 1300 ° C. in a reducing atmosphere, preferably in hydrogen. The pressing of the sintered body under a pressure of about 8 t / cm ² is followed by a second sintering for about 1 hour between 1200 and 1400 ° C., likewise in a reducing atmosphere, preferably in hydrogen. The density of a sintered body produced by this method with a starting iron powder with a grain frequency of about 500 to 600 μ was 7.6 g / cm ³ , the coercive force 0.75 Örsted; field excitation of 20 to 200 amperes / cm resulted in induction of 16800 and 19,900 Gauss, respectively.

Claims (2)

Patent claims: 1. Soft magnetic sintered iron body with a coercive force below 1 Örsted, characterized in that that it consists of an iron powder with a grain frequency between 250 and 700 μ, preferably of 500 μ, is made. 2. A method for producing a sintered body of high dimensional accuracy according to claim 1, characterized in that the starting powder is subjected to a heat treatment between 700 and 800 ° C in a reducing atmosphere, preferably in hydrogen, before pressing and that the first sintering for 5 hours between 1000 and 1300 ° C in a reducing atmosphere, preferably in hydrogen, the sintered body is further pressed at about 8 t / cm ² and the second sintering takes place for 1 hour between 1200 and 1400 ° C in a reducing atmosphere, preferably in hydrogen. Considered publications:
F. Pawlek, Magnetische Werkstoffe, 1952, p. 111; R. Kieffer and W. Hotop, Sintereisen und Sinterstahl, 1948, pp. 161, 162, 224, 225. 1 sheet of drawings ι 909 757/327 2.