JPS61190003A - Heat treatment of ferrous powder - Google Patents

Abstract

PURPOSE:To make uniform the effect of a heat treatment and to produce a product having high quality by mixing respectively the powders of which the oxidation reduction equaivalents of the components are respectively oxygen-rich and carbon-rich in the stage of packing ferrous raw material powder into a vessel for heat treatment. CONSTITUTION:The ferrous raw material powder is packed into the vessel and is heat-treated in a reduced pressure atmosphere by which the raw material powder is deoxidized and decarburized and the low-oxygen and low-carbon product is produced. The powder in which the content of oxygen is in excess of the carbon equiv. and the powder in which the content of carbon is in excess of the oxygen equiv. while the other components are approximately the same in content are mixed or packed in an alternately laminated state into the vessel and are subjected to the heating treatment. The C/O molar ratio is so adjusted as to attain an about 0.7-2.0 range.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a method of reducing iron-based raw material powder such as pure iron-based powder or iron alloy-based powder produced by water atomization etc. by heating it under reduced pressure. -Relates to heat treatment methods such as annealing.

(Prior art) As a method for producing low-oxygen, low-carbon products (alloy steel powder) by heat-treating pure iron-based powder or iron-based raw material powder containing oxides or carbides of iron alloy elements such as Cr and Mn, depressurization is used. Furnace (
A heat treatment method using a vacuum furnace) is used.

In this case, in the reduction and decarburization reactions, the oxygen content (hereinafter referred to as "0") contained in the raw material powder reacts with the carbon content (hereinafter referred to as "C"), resulting in deoxidation and decarburization. Therefore, it is essential to balance the 0 content and C content in the raw material powder.

Moreover, in order to carry out these reactions in a short time and increase productivity, it is desirable to perform the heat treatment at as high a temperature as possible, ie, 900° C. or higher.

Conventionally, as a method for balancing O and C in raw material iron powder, as seen in JP-A No. 52-100308, when a powder with high O content is produced during the manufacturing process of raw material powder, this method is used. A method was adopted in which an appropriate amount of a reducing agent, that is, a carbon source such as graphite powder, was mixed in an equivalent amount necessary to reduce the carbon.

(Problems to be Solved by the Invention) However, when using the above-mentioned conventional technology, in the case of alloyed copper powder containing Cr'PMn etc., due to the large difference in apparent density between steel powder and graphite powder, uniform It is difficult to mix properly, and once mixed, it separates again during the process of filling the container. On the other hand, if C is high, decarburization is carried out by changing the furnace atmosphere to a high dew point gas, but if it contains easily oxidizable metals such as Cr and Mn, the disadvantage is that the easily oxidizable metals oxidize preferentially. ing.

(Means for Solving the Problems) In order to solve the problems faced by the above-mentioned prior art, the present invention aims to reduce the oxidation and reduction of components when heat-treating iron-based raw material powder in a reduced pressure atmosphere for deoxidation and decarburization. A heat treatment method for iron-based powder is employed, which is characterized in that two types of powder, one equivalent to oxygen-rich and one rich in carbon, are mixed or filled in a container in an alternately laminated state and heated.

That is, when manufacturing iron-based powder of pure iron-based powder or iron alloy-based powder containing oxides of iron alloy elements, the raw material powder obtained in the manufacturing process has a carbon content in excess of the equivalent amount of oxygen, Two or more types of raw material powders with almost the same composition as above, in which the oxygen content is in excess of the carbon equivalent, are made into low-carbon, low-oxygen iron powder by using the carbon and oxygen contained in each powder itself. This method is characterized by filling the materials in a desired state, that is, mixing or stacking the materials into a heat treatment container, and then heat-treating the mixture.

(Function) The raw material powder for the pure iron-based or iron alloy-based powder used in the present invention includes mechanically pulverized powder of chips generated by crushing or cutting sponge iron, mill scale powder, or atomized powder such as water atomized powder. etc.

For example, typical iron powder is obtained by spraying molten iron melted to a predetermined target composition and temperature in an electric furnace or the like using a water atomization method. At this time, the steel is melted and refined to have the target composition, but there are many cases where the C content is too low or the steel is tapped with a high C content, and the composition does not meet the target composition. When this is subjected to water atomization treatment, the oxygen content in the raw material powder also differs, and the C1° contained during heat treatment alone does not provide a preferable content for decarburizing and deoxidizing to low carbon and low oxygen. That is, the raw material powder has a carbon content in excess of the oxygen equivalent, and a raw material powder has an oxygen content in excess of the carbon equivalent.

In the present invention, similar raw material powders having almost the same other components and different C1O contents are adjusted and mixed or alternately stacked and packed in a heat treatment container so that the C1 and O0 are removed to low C1 and low O. In this method, iron powder for powder metallurgy with low C and low O is obtained by charging the powder into a heat treatment furnace under reduced pressure or vacuum. low C
In order to achieve a low C10 ratio of 1.0, the C10 molar ratio may be mixed or alternately stacked and packed, but this may vary thermodynamically depending on the heat treatment conditions (degree of vacuum, temperature, time). , C10 molar ratio is adjusted within a range of 0.7 to 2.0.

Alternatively, raw material powders with high C1 and high 0 may be mixed in advance using a mixer or the like so as to have a predetermined C10 molar ratio, and the mixture may be filled into the heat treatment container.

(Example) FIG. 1 shows an example of equipment for implementing the present invention, and numeral 1 shown in the figure is a dish-shaped heat treatment container, into which iron powder 2 is uniformly mixed and filled.

Figure 2 shows multiple types of iron powder 2°・-2 as shown in Figure 3.
This is an example of equipment for stacking and filling f, and the supply chute 3
, 4.5. That is, the supply chute 3.4
．． Three types of raw material powders with different ingredients etc. are stored in 5.
The conveying device 6 simultaneously controls the cutting amount so that a mixed layered state with a predetermined thickness and amount is obtained from each chute.
is controlled to move the container 1 to form a predetermined filling layer.

In actual filling, the supply chute 3 has an O content of C
On the other hand, the supply chute 4 stores powder in which the content of C is in excess of the equivalent of O, and the supply chute 5 stores powder in which the content of C is in excess of the equivalent of O. Powder that gives image c2 low 0 is stored.

Therefore, as shown in FIG. 3, for example, in the first filling, a predetermined amount of high C powder is cut out from the supply chute 3, and on top of that, a high C powder is cut out from the supply chute 4 (in the second filling). layer). By repeating the filling process as described above, even if the balance between C and O is disrupted, it is possible to maintain a predetermined low C content by appropriately controlling the ratio of the powder filling thickness in the container.
1. Heat treatment to obtain steel powder with low O quality was achieved.

In addition, a simple powder such as graphite powder is stored in the supply chute 5 instead of the above-mentioned raw material powder, and the graphite is sandwiched between the raw material powder with high 0 content from the supply chute 4 etc.
The results did not change even after filling with a packed layer). In this case, it was more effective to apply tapping from the bottom surface of the filling container to promote uniform mixing of the graphite powder and the raw material powder.

Graphite was added and mixed to the unbalanced raw material on the 0 excess side as shown in Table 1, and the total carbon content was set to 0.545 wt%.
First, it is filled using the conventional filling method using the equipment shown in Figure 1.
The heat treatment was carried out at 0°C for 3hs at a vacuum level of I Torr, and the raw materials shown in Table 1 and the raw materials with an imbalance toward the excessive C side as shown in Table 2 were treated using the equipment shown in Figure 2. Filling is carried out alternately in equal amounts using the filling method according to the invention, and 115
Table 3 shows the product properties of the Cr 1.0wt%-Mn0.7i% copper powder for powder metallurgy obtained by heat treatment at 0°C for 3 hours at a vacuum degree of I Torr.

As can be seen from Table 3, as a result of filling the raw materials listed in Table 1 with the conventional method in the equipment shown in Figure 1 and heat-treating them, there was a large amount of residual T and 0 in the chemical components of the product. As a result, the density of the green powder was low. This seems to be due to separation of graphite and raw material powder during filling. In an embodiment of the present invention (method shown in Fig. 2) in which the raw material powders listed in Table 1 and Table 2 are stacked and packed alternately, preferably in equal amounts,
It has become clear that both the oxygen and carbon contents in the product have been reduced to values sufficient for use in powder metallurgy, and as a result, the green density has also been greatly improved.

(Effects of the Invention) As explained above, according to the present invention, even when heat treating a mixture of multiple types of powders with different properties such as different densities, uniform filling is achieved, so a uniform heat treatment effect can be achieved. You can get high quality products.

[Brief explanation of drawings]

Figure 1 is a diagram illustrating one embodiment of the method of the present invention, Figure 2 is a diagram illustrating another embodiment of the inventive embodiment, and Figure 3 is a diagram illustrating an embodiment of the method of the present invention. FIG. 1-Container 2--Iron powder 3.4.5--Supply chute 6--Transporting device

Claims (1)

[Claims] 1. When heat-treating iron-based raw material powder in a reduced pressure atmosphere for deoxidation and decarburization, two types of powder with redox equivalents, one rich in oxygen and one rich in carbon, are mixed in a container. Alternatively, a heat treatment method for iron-based powder characterized by filling the powder in an alternately laminated state and heating it.