JPS6136046B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing atomized iron powder for powder metallurgy with excellent formability and low apparent density, and in particular, to define the grain shape, that is, the apparent density, of raw iron powder by a liquid spray method, or to further improve the mutual interaction of the particles. By applying treatment to promote agglomeration and then reduction annealing, it increases the mutual sintering and agglomeration of particles, and in particular reduces the impact force that crushes and disintegrates the sintered cake (hereinafter referred to as "disintegration"). By limiting the above, the purpose is to propose an advantageous method for producing atomized iron powder for powder metallurgy that has excellent formability and low apparent density. In general, water-sprayed iron powder for powder metallurgy has a high apparent density of about 2.80 to 3.20 g/cm ³ and has excellent compressibility, so it is used as a raw material iron powder for high-density iron-based sintered materials. , the formability evaluated by Rattler value and compact transverse rupture strength is rather poor, and the mechanical strength of the sintered material is weak despite its high density, so it is difficult to apply it to medium- to low-density iron-based sintered materials. However, at present, it is limited to the above-mentioned uses. There is therefore a demand for atomized iron powder that has excellent formability while maintaining good compressibility, and development efforts are underway to improve the formability. For example, as described in Japanese Patent Application Laid-Open No. 114467/1983, the inverted conical injection angle of high pressure water is set to 80 to 120.
°, the atmosphere is suctioned under a negative pressure of 20 to 204 gf/cm ² to prevent back injection, and the amount of fine powder in the raw iron powder is increased by spraying, in a reducing atmosphere at a temperature of 1000 to 1200 °C. A method has been proposed in which, after annealing, the sintered cake is crushed so as to have a particle size distribution larger than that of raw iron powder. In addition, JP-A-1987-
According to Publication No. 115161, the particle size distribution is determined by measuring the cumulative amount of particles on the sieve and the receiving tray for each sieve of 100, 200, 230, and 325 mesh according to the American standard, and summing each cumulative weight ratio. , water spray raw iron powder whose value multiplied by 1/100 is in the range of 1.0 to 2.7,
Reduction annealing is performed at a temperature of 760 to 1149℃, and the sintered cake is milled with a mill gap of 0.245 to 2.45 mm and a rotation speed of 200 to 200.
A method of producing iron powder with an apparent density of 2.80 g/cm ³ or less by crushing with a disc mill at 5000 rpm has also been proposed. However, all of these methods simply increase the proportion of fine powder in the raw iron powder, cause the particles to sinter and agglomerate each other during reduction annealing, and then crush the sintered cake under a relatively light (low) load. This aims to increase apparent density and improve moldability. Generally, as the amount of fine powder in the water-sprayed iron powder increases, and as the reduction annealing temperature increases, sintering between particles is promoted, and the apparent density of the crushed iron powder decreases.
Therefore, although the moldability can be improved, the following technical problems are involved. In other words, if the reduction annealing temperature is too high (over 1100°C), the sintered cake will be difficult to crush, and if you attempt to increase productivity by crushing under high load, the apparent density will increase due to processing. Not only does it become impossible to improve formability, but compressibility also deteriorates, and even when the reduction annealing temperature is below 1100℃,
Unless raw iron powder is used with a correspondingly low apparent density corresponding to the apparent density of the final product iron powder, it will not only be impossible to improve formability, but also produce low apparent density iron powder with stable properties. is difficult. Note that the reduction annealing temperature is
If the temperature is too low, such as below 800℃, deoxidation, decarburization,
Annealing and recrystallization are insufficient and sufficient compressibility cannot be secured. Therefore, the purpose of this invention is to provide reduced iron powder (mill scale reduced iron powder, ore reduced iron powder, 2.00~ equivalent to iron powder)
The purpose of the present invention is to provide atomized iron powder at a low cost, which has an apparent density of 2.60 g/cm ³ , high fluidity, and better formability than reduced iron powder. This invention provides sprayed raw iron powder with a correspondingly low apparent density corresponding to the apparent density of the sprayed iron powder that is the final product,
Alternatively, in order to further reduce the apparent density and improve formability, atomized raw iron powder that has been treated to promote mutual agglomeration of particles can be used as a raw material, and sufficient reduction annealing and sintering agglomeration of mutual particles can be achieved. In reducing annealing temperature range and crushing sintered cake,
It has been found that the above object can be advantageously achieved by adjusting the conditions such that the iron powder maintains the irregular grain shape inherent in the liquid spray and the aggregated irregular grain shape formed by sintering and agglomeration. Now, as shown in Figure 1, the apparent density of water-sprayed raw iron powder; x [g/cm ³ ] and its single particle diameter; di [μ
m], x = almost constant for grain sizes exceeding 150 μm, di = ae ^{- bx} for grain sizes of 150 μm or less, where a, b: grain size constant, e is the base of the natural logarithm. And this relationship holds true for reduction annealed sintered cakes, especially 1×10 ⁵ Kgf・m/sec ²
The discoverers found that the same holds true for water-sprayed iron powder crushed by the impact force below. According to this knowledge, the apparent density of reduction-annealed iron powder is limited by the apparent density of atomized raw iron powder. In other words, for particle sizes exceeding 150 μm, it is difficult to make the apparent density of reduction-annealed iron powder lower than the apparent density of atomized raw iron powder, and the stronger the crushing, the higher the apparent density. Become. On the other hand, 150μm
For the following particle sizes, the apparent density of reduction-annealed iron powder is lower than that of atomized raw iron powder because the particles sinter and agglomerate each other to form irregular grain shapes.
Grain shape constant; b has a positive value, and industrial realization of a negative value is difficult. Therefore, in order to produce atomized iron powder with an apparent density of 2.60 g/cm ³ or less by reduction annealing, the apparent density (g/cm ³ ), x≦, is required for particle sizes exceeding 150 μm.
2.60, for particle sizes of 150 μm or less di = ae ^{- bx} where di; average diameter of two sieves of Tyler standard sieve (di
= d ₁ + d ₂ /2) (μm), a, b; particle size constant b≧
The raw material must be atomized raw iron powder that satisfies the relationship 1.5. In particle sizes of 150 μm or less, particles are sintered and agglomerated to form irregular grain shapes, and in order to further promote lower apparent density, it is possible to mix particles by particle size and liquid,
It has been discovered that magnetization is effective for the following reasons. By first sieving the sprayed raw iron powder according to particle size, it is possible to efficiently aggregate and coarsen the fine particles by sintering and agglomerating each other, and considering the workability of sieving, it is practical to use 200 mesh as the boundary. , if necessary, blending may be performed after reduction annealing. As the liquid filling the interparticle spaces of the atomized raw iron powder packed bed evaporates, the liquid level moves and the particles move due to its surface tension, which has the effect of agglomerating fine powder especially around coarse powder. As the liquid to be mixed with, water, oil, organic compounds such as alcohol, and mixtures thereof are used. A range of 2 to 20% by weight is effective and practical. Liquid-sprayed raw iron powder is rapidly cooled by high-pressure liquid and has a distorted lattice, so it is easily magnetized and has residual magnetism, which is especially noticeable in water-sprayed raw iron powder, which causes the particles to attract each other and coagulate. . Next, the reduction annealing temperature in a reducing and decarburizing atmosphere and the crushing impact force of the sintered cake are important factors that determine the apparent density of crushed iron powder. When the reduction annealing temperature is lower than 800°C, reduction, annealing, and mutual sintering and aggregation of particles are insufficient, resulting in a decrease in apparent density and failure to ensure compressibility. If the reduction annealing temperature is higher than 1100°C, it becomes difficult to crush, and if it is crushed under a high load, it becomes smooth polyhedral grains with high apparent density, and at the same time undergoes work hardening and deteriorates compressibility. Therefore, the reduction annealing temperature is suitably in the range of 800 to 1100°C, but the holding and soaking time does not need to be particularly limited as long as it is appropriately selected to be sufficient for the above heat treatment. As a crusher for sintered cakes, machines that cut the particles, make the particle surfaces into flat polyhedrons or plates, or crush them into balls should be avoided, such as repulsive or impact hammer mills, disk integrators, etc. Adopt machines such as (Dage Mill). As a result of investigating the relationship between the impact force and the apparent density of crushed iron powder, it was found that as the impact force increased, the apparent density increased over the entire particle size range, 10 ⁵ Kgf・
If it exceeds m/sec ² , the apparent density will be higher than the raw material sprayed raw iron powder. Therefore, the impact force is 10 ⁵ Kg
The upper limit is f・m/sec ² . For example, it is necessary to consider the diameter of the rostle gap or screen hole installed in a hammer mill so as not to lose the inherent irregularity of the liquid sprayed raw iron powder and the aggregated irregularity due to sintered agglomeration, but the apparent density There is no need to limit it because the contribution rate of factors to this is small. The chemical composition of the sprayed iron powder according to this invention is equal to or higher than that of reduced iron powder (mill scale reduced iron powder, ore reduced iron powder), that is, 1-Zn・St (zinc stearate) - 99 wt% Fe mixed powder. 5t/
It is minimum necessary to ensure a green density of 6.70 g/cm ³ or more at a molding pressure of cm ² , and from this point of view, in weight %, O: 0.25 or less, C: 0.05 or less, N: 0.01 or less, Si; 0.10 or less, Mn: 0.40 or less, P: 0.05 or less, S: 0.10 or less, Sn: 0.50 or less, and the balance essentially consists of iron, of course unavoidable impurities are allowed. Regarding particle size, if there are too many coarse particles in iron-based sintered materials, there will be a large number of irregular coarse pores, leading to embrittlement of mechanical strength. Limited to iron powder containing 80% by weight or more of the following particle sizes: Next, the present invention will be explained in detail based on examples. The molten metal atomization and pulverization device described in Japanese Patent Publication No. 1952-19540 related to Patent No. 892659 has a convergence angle α of a plurality of jet impingement flows and a film-like flow in which the plurality of jet impulsion flows are deflected by a guide. The angle difference from the focusing angle β of 0°≦(α−β)≦6° and (α−
β) > 6°, water pressure in the range of 40 to 180 kgf/cm ² G, molten metal nozzle diameter in the range of 8 to 14 mmφ, and water spray conditions of 230/min, as shown in Figure 1. Apparent density: x [g/cm ³ ] and single particle diameter: di=d ₁ +d ₂ /
Three types of water-sprayed raw iron powder having a relationship of 2 [μm] were manufactured. Next, it is sieved with a Tyler standard sieve to -80#, and soaked in ammonia decomposition gas for 10 to 120 minutes at a temperature of 700 to 1150°C to perform reduction annealing, at a temperature that does not cause reoxidation in the air, i.e., 180°C or less. After cooling in a furnace, the sintered cake was taken out into the atmosphere and crushed using a hammer mill, and sieved using an 80# sieve. In addition, for water-sprayed raw iron powder that has the relationship between apparent density and single particle size shown by the symbol : in Figure 1,
Mixed with 10% water, magnetized using a magnetic separator with a maximum magnetic force of 1300 gauss, and subjected to treatment for two different particle sizes by sieving into 80-200 mesh and -200 mesh, and reduction annealing under the same conditions as above. The particles were then crushed and the sintering agglomeration effect between the particles was investigated. For crushing the sintered cake, the rotation speed: 2800rpm, the distance from the main shaft axis to the hammer tip: 150mm,
Number of hammers: 20, unit weight of hammer: 500grf
First, the material was crushed using a hammer mill with mechanical specifications of 1, equipped with a hole diameter screen of 3 mmφ, and then sieved using an 80 mesh sieve. Next, this +80 mesh iron powder was crushed by attaching a screen with a hole diameter of 1 mm, and was sieved using an 80 mesh sieve. In the same manner, screens with hole diameters of 0.5 mmφ and 0.3 mmφ were sequentially attached and the crushing and sieving process was repeated, and a total of four times of -80 mesh iron powder was blended. The sintered cakes, which were reduced and annealed into two particle sizes of 80 to 200 mesh and -200 mesh, were crushed and sieved four times under the same conditions and procedures as above, and then blended once. The particle size ratio of 80-200 mesh and -200 mesh was reblended, ie, 80-200 mesh was 3/10 and -200 mesh was 7/10. The powder characteristics of the water-sprayed raw iron powder, the powder characteristics of the reduction annealed iron powder, and the green compact characteristics described above are shown in Table 1 together with the particle agglomeration treatment and reduction annealing conditions.

【table】

【table】

[Table] As shown in Table 1, the symbols in Figure 1;
-80 Reduction annealing of water-sprayed raw iron powder with the relationship di=6×10 ³ e ^{-1 .49x} for grain sizes of 150 μm or less
Metsuyu's iron powder (test number 1) has an apparent density of 2.80 g/cm ³ as shown in Table (2), and the symbols in Figure 1 are:
As shown in _a , x=
2.60, di=1.5× for particle size below 150μm
10 ⁷ e ^-4 . ⁴⁷ It can be seen that the formability of the material is inferior to that of the comparative material (mill scale reduced iron powder). On the other hand, the symbols in FIG.
x≦2.60, 150μm for particle sizes exceeding 150μm
-80 mesh iron powder (Test No. 3 ^, 4, 6, 7, 8, 9 and 10)
As shown in Table (2), the apparent density is as low as 2.60 g/cm ³ or less, and the compressibility and moldability of the 2Cu-0.8C-1Zn・St-96.2 wt% Fe mixed powder are lower than that of the comparative material. (Mill scale reduced iron powder; test numbers 11 and 12),
It turns out that they are the same or better than them. It can be seen that the iron powders (test numbers 6, 7 and 8) obtained by subjecting the sprayed raw iron powder with the symbol; to particle agglomeration treatment and reduction annealing (test numbers 6, 7 and 8) have further decreased apparent density and improved formability. On the other hand, when the reduction annealing temperature is too low such as 700℃ (test number 2), deoxidation, annealing, and mutual sintering of the particles are insufficient, so the -80 mesh iron powder subjected to reduction annealing is The hanging density could not be lowered completely, and both compressibility and formability did not reach the level of the comparative materials (mill scale reduced iron powder; test numbers 11 and 12). In addition, when the reduction annealing temperature is too high (1150℃) (test number 5), sintering of the particles progresses and it is difficult to break up the sintered cake, resulting in smooth, multifaceted particles, and the appearance of reduction annealed iron powder. The hanging density is higher than that of the sprayed raw iron powder, and due to work hardening during crushing, both compressibility and formability are deteriorated compared to the comparative materials (mill scale reduced iron powder; test numbers 11 and 12). Figure 2 shows the impact force when the sintered cake obtained by soaking the water-sprayed raw iron powder with the symbol in Figure 1 in an ammonia decomposition gas for 950℃ x 45 minutes and crushing it with a hammer mill and -80 This is the result of investigating the relationship between the apparent density of mesh iron powder. As is clear from this,
The impact force affects the apparent density of the crushed iron powder, and if an impact force exceeding 10 ⁵ Kgf·m/sec ² is adopted, the apparent density will be higher than the apparent density of the atomized raw iron powder. Although the above embodiments have been explained using water-sprayed raw iron powder as an example, the present invention can be applied to any raw iron powder that is produced using a liquid as a spray medium and requires reduction or annealing. As described above, this invention has established a manufacturing technology for atomized iron powder for powder metallurgy that has excellent formability and has a low apparent density of about 2.00 to 2.60 g/cm ³ . Apparent density sprayed iron powder can be advantageously used as a raw material for medium to low density iron-based sintered materials, and can not only be used as a substitute for reduced iron powder (mill scale reduced iron powder, ore reduced iron powder), but also Since it also has high compressibility, it can also be used for high-density iron-based sintered materials.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the apparent density and single particle size of water-sprayed raw iron powder and reduction-annealed and crushed product iron powder, and Figure 2 is a graph showing the relationship between water-sprayed raw iron with the symbol in Figure 1. It is a graph showing the relationship between the impact force of one hammer and the apparent density of -80 mesh product iron powder when a sintered cake obtained by reduction annealing of the powder is crushed with a hammer mill.

Claims (1)

[Claims] 1. The relationship between the apparent density x (g/cm ³ ) and the particle size expressed as the arithmetic mean di (μm) of the two sieve openings d ₁ and d ₂ of the Tyler standard sieve is as follows: Raw iron powder that satisfies both the conditions of formulas (1) and (2) is heated directly at 800 to 1100°C in a reducing and decarburizing atmosphere, either directly or after particle aggregation treatment is applied to the raw iron powder. The resulting sintered cake was subjected to reduction annealing at a temperature in the range of 1×10 ⁵ Kgf・m/
Pulverize and disintegrate by applying an impact force of s ² or less to a particle size of 150
Contains 80% by weight or more of particles smaller than μm and has an apparent density
A method for producing atomized iron powder for powder metallurgy with excellent formability and low apparent density, which comprises obtaining iron powder of 2.00 to 2.60 g/cm ³ . For particles with a particle size of over 150 μm, x≦2.60 …(1) For particles with a particle size of 150 μm or less, di=a・e ^-bx …(2) Where a, b; particle shape constant b≧1.5 2 Reduction The method according to claim 1, wherein the atomized raw iron powder to be subjected to annealing is classified powder that has been sieved in advance according to particle size. 3. The method according to claim 2, wherein the sintered cake is pulverized and granulated, and then blended. 4. The method according to claim 1, 2 or 3, wherein the particle aggregation treatment is addition or mixing of a liquid. 5. The method according to claim 1, 2 or 3, wherein the particle aggregation treatment is magnetization. 6 The atomized iron powder that has undergone reduction annealing contains oxygen in weight%.
0.25 or less, carbon 0.05 or less, nitrogen 0.01 or less, silicon
0.10 or less, manganese 0.40 or less, phosphorus 0.05 or less, and sulfur 0.10 or less, or even tin 0.50 or less.
The method described in 3, 4 or 5.