CS248998B1 - A method for producing steel powder with higher metal chip sintering - Google Patents

Abstract

The purpose of the solution is to prepare powder steel of higher sintering capacity from waste metal chips, which are formed during machining of carbon steels, which is used for the production of components and materials by powder metallurgy processes. In contrast to known processes, the method is characterized by the fact that the chips are first decarburized and then subjected to grinding in a vortex impact mill, in which a deformation-strengthened powder is formed, which is then annealed. The powder after this processing has a higher sintering capacity due to a finer-grained structure and a greater degree of crystal lattice defects. The concentrations of carbon and oxygen in the powder are less than 0.1 percent by mass.

Description

The invention relates to the manufacture of high-sintering powder steel from metal chips resulting from the machining of carbon alloy steels, which is preferably used for the production of materials and high-performance components by powder metallurgy processes.

Several methods are known for the production of powder steels suitable for the manufacture of powder and materials by powder metallurgy processes from various steel wastes. It is mainly processing of metal chips, which arise during machining of steels by cutting, such as turning, milling, drilling, planing and the like. Such chips have different shapes and dimensions and are often long and twisted. The processing conditions for the powder must be adapted to this. The basic condition for the use of such wastes for the production of powder steel is that the wastes are of one type of steel, so that the powder produced has stable and reproducible advantageous physical and chemical properties. The powder thus produced must meet the requirements in terms of granulometric composition, compressibility and chemical purity, often characterized by an oxygen concentration, which should normally have less than 0.2% by weight. The oxygen concentration is increased in comparison with the compact oeel both in machining and in powder processing processes. Several methods have been known so far for the production of powder steels from metal chips. According to one of these, low carbon steel chips are pulverized such that after pre-treatment to a suitable size they are ground in a special mill in which they are pre-cooled with liquid nitrogen. As a result, the chips become brittle and in this state they can be ground into powder. The disadvantage of this method is that it requires a special mill and a large amount of liquid nitrogen. According to another method, the chips to become brittle, are first carburized and then either directly from the carburizing temperature or, after cooling and careful heating, become cloudy and then ground to a powder by known methods. According to the irradiated method of alloy steel chips with a carbon concentration of 1% by weight. are heated to a temperature of about 950 ° C in a protective atmosphere from which they are quenched into water. After this treatment, the chips are ground to a powder by known methods. In all cases, the grinding of the chips is carried out in known mills, such as e.g. ball, bar, pin, plate, cone, impact or vibration mills. The selection of the mills is determined by the requirement to produce, in the shortest possible time, a powder of advantageous grenulometry with the largest proportion of particles of a size predominantly less than 0.315 mm. The grinding in all cases is followed by annealing of the powder in reducing atmospheres, most often in split ammonia. The purpose of this annealing is to reduce the carbon concentration sufficiently to make the powder compressible and, decisively, to reduce the oxygen concentration in the powder, which has been increased compared to its concentration in steel by the previous processes of processing the chips into powder to below 0.2% %, since only powder steel with such an oxygen concentration can be successfully used for the production of components by powder metallurgy processes.

A disadvantage of both of the latter is that they require special technological operations to increase the fragility of the chips, either by carburizing or by heating to a quenching temperature, which are energy-intensive operations. In the first case, carbon is supplied to the chips by carburization, which must then be removed. Furthermore, in both cases, artificial atmospheres are needed which make production more expensive. A further common drawback of these processes is that in the above-mentioned milling thermal processes, which are carried out most often at temperatures of 900 to 1000 ° C, additional chips oxidation occurs, especially at the metallographic grain boundaries. Since such poles are predominantly alloyed with manganese and chromium, which are elements of high affinity for oxygen, their oxides are readily reducible, and only at temperatures above 1,200 degrees Celsius. Therefore, after the final reduction annealing of the powder, which is carried out at temperatures of 900 to 1050 ° C in order to avoid a significant sintering, the steel powder still has an oxygen concentration of about 0.5% by weight. This makes it impossible to use such powder steel to produce sophisticated machine parts by powder metallurgy processes. A further disadvantage of the above-mentioned methods is that the particles of the powder thus produced, by being formed from flat chips, have a relatively small specific surface and that their final operation is high-temperature annealing, they are characterized by less sintering activity which results in lower mechanical properties of the sintered components. compared to powders prepared by other methods, e.g. spray.

The above-mentioned disadvantages of the known processes for producing powder steels from carbon alloy steel waste chips are avoided by the process according to the invention, which consists in that the steel chips are shredded into pieces preferably shorter than 10 millimeters, which are degreased and then calcined at 700 to 700 ° C. 1150 ° C, for 0.5 to 6 hours in a hydrogen-containing reducing atmosphere, followed by milling in a fluidized-bed mill, which is then calcined at a temperature of 000 to 900 ° C for 0.5 to 3 hours in a reducing atmosphere, containing hydrogen and finally the annealed partially sintered powder is ground and screened to the desired fractions.

The main advantage of the process according to the invention is that the powdered steel produced is characterized by a higher sintering performance than powders produced from waste chips by the said processes. Sintering is here characterized by increasing the density of the samples during sintering. The higher specificity of the powder produced according to the invention is due to the fact that the chips are first dehumidified so that they can be ground in a whirling impact mill, as only the tough metals can be milled in this mill. , in contrast to known processes, which in turn require high chip fragility in order to be ground in the aforementioned mills. The milling of poppy chips in a whirling impact mill results in a powder due to the high deformation hardening occurring there. This consolidation-removing powder to be compressible is then annealed to achieve a structure having a greater number of failures and a finer-grained structure than powders that have not been deformed in other ways. This powder can advantageously be used for the production of sintered components of higher mechanical properties, and in particular of dynamically stressed components, since the initial powder has a carbon and oxygen concentration of less than 0.1% by weight. . and said finer structure.

If desired, additional alloying may be admixed with the powder steel of the present invention, since the powder has a higher sintering effect, which exhibits a higher structural activity, during sintering, will accelerate the alloying of the matrix with the added elements than with powders prepared by other methods.

Example

Turning chips of steel, concentrates

Claims (1)

? The effect of the powder of the present invention is due to the fact that the chips of the present invention are de-blasted to allow the mash to be milled in a vortex impact mill, since only the milky metals can be milled in this mill, as opposed to known processes, in which, on the contrary, high chip fragility is required to allow them to be milled. in the previously mentioned mills. The grinding of the soft chips in the vortex impact mill due to the high deformation hardening there occurs generates a powder. The powder to be compressed is then calcined to achieve a structure which breaks down the number of defects and finer-grain structure than powders that have not been deformed in other ways. This results in a higher susceptibility of such a powder due to the acceleration of the diffusion processes. Such a powder can be advantageously used to produce sintered components of higher mechanical properties and, in particular, components dynamically stressed because the powder in the initial state it has a carbon and oxygen concentration of less than 0.1 wt.%. and said fine-grained structure. If desired, further alloying agents may be admixed to the powdered steel of the invention, wherein the powder has a higher susceptibility to a higher structural activity, during which the matrix is more quickly alloyed with the elements added than the sintered material during sintering. in powders prepared by the methods. Example Turning chips made of steel, concentrates - A method for producing steel powder of a higher metal chip performance resulting from the processing of carbon alloy steels, characterized in that the steel chips are shredded, preferably shorter than 10 mm, which is degreased and they are then calcined at 700 to 115.0 ° C for 0.5 to 6 hours in a reducing atmosphere containing hydrogen, a manganese content of 0.3%, a chromium of 1.5% and a carbon content of 1.0% by weight. pieces smaller than 10 mm were broken in the crusher, which were degreased in trichlorethylene. Then, the pieces of steel chips were annealed at 850 ° C for 4 hours in cleaved ammonia. Shreds after this annealing have a low carbon concentration of 0.09%. In this state, the grinding chips were an impact swirl mill of 0.315 mm particle size. The powder was then calcined at 700 ° C for 2 hours in the digested ammonia. The baked cake was pulverized and the powder was sieved. From the powder with the addition of 0.8% zinc stearate as a lubricant, bars were pressed with a pressure of 590 MPa, which had a density of 6.6 grams. cm-3. Sintering at 1 200 degrees Celsius for 1 hour in cleavage gave samples a density of 6.75 g. In comparison, when the powder-sprayed same chemical composition was prepared by the same method, the density increased by only 0.03 g. Similar powder steel specimens prepared from metal-milled turning chips in a whirling mill in decarburized stock, after compression, reached a density of 6.3 g. cm < 3 > 3a after sintering under the same conditions of 6.35 g. tin-3. The indicated data confirm that the powdered steel 1 made from the turning chips according to the invention has a higher sintering capacity than the powdered compacts. OF THE INVENTION, followed by fluidized-bed grinding to a powder which is then annealed at a temperature of 600 to 900 ° C for 0.5 to 3 hours in a reducing atmosphere containing water, followed by milling partially sintered powder and sifting to the desired fraction.