Water-atomized iron powder and method

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an iron powder useful in water-atomized powder metallurgy, and further relates to a method of manufacturing the iron powder.
2. Description of the Related Art
In general, water-atomized iron powder is made by atomizing molten steel with high pressure water. This is often followed by annealing, softening and reducing, removing oxide film from particle surfaces, and crushing. Performance of all of these steps is considered necessary. Thus, the possibility of cost reduction by eliminating processing steps is limited.
When sintered parts are made of iron powder, it is necessary to compact the iron powder with addition of lubricant and additive alloy component powders, followed by sintering the resulting green compact at a high temperature and further sizing for dimensional adjustment. Accordingly, the cost of the entire process is further increased.
Cost reduction is important. Every effort must be made to reduce manufacturing costs of, for example, automobile parts. For that purpose substantial efforts have been made.
However, omissions of any process steps, in particular, omission of annealing, softening and reducing steps has not been achieved because the water-atomized iron powder is solid due to its quenched structure and is difficult to compact. Further, although a considerable amount of oxygen is introduced into the iron powder as a sintering material, oxygen is generally considered harmful to sintered parts.
For example, although Japanese Patent Unexamined Publication No. Sho. 51-20760 discloses a method of manufacturing iron powder in which molten steel is produced in a converter and vacuum decarbonization apparatus, this method includes annealing and reducing powder atomized with water and drying.
Further, Japanese Patent Examined Publication No. Sho 56-45963 discloses a method of improving the characteristics of iron powder by mixing a finished powder that has been subjected to annealing and reducing with an atomized raw iron powder that was not subjected to annealing or reducing. Although it is desired to use atomizod raw iron powder not subjected to annealing or reducing, predetermined characteristics cannot be achieved by that powder alone.
Further, although Japanese Patent Unexamined Publication No. Sho 63-157804 discloses a process for manufacturing atomizod iron powder by suppressing oxidization and carburizing as much as possible by the addition of alcohol etc. to the atomizing water, the resulting iron powder contains 0.01% or more of C and is easily hardened an the cooling speed achieved by atomizod water, although it contains a small amount of oxygen. The resulting iron powder cannot be compacted in dies and requires further annealing and softening.
On the other hand, it is necessary to minimize dimensional changes caused in the manufacturing process.
In particular, since the achievement of dimensional accuracy without depending upon sizing leads to the omission of process steps and accordingly to cost reduction, efforts have been made along those lines.
For example, Japanese Patent Examined Publication No. Sho 56-12304 discloses and proposes a technology for improving dimensional accuracy by particle size distribution and Japanese Patent Unexamined Publication No. Hei 3-142342 discloses and proposes technology for predicting and controlling the dimensional change in sintering according to powder configuration.
Although iron powder for powder metallurgy contains added lubricant etc. in addition to Cu powder and graphite powder, since the iron powder is moved or transported to replace the container in which it is contained, the added Cu powder and graphite powder tend to segregate, so that the components of the powder are easily dispersed. Consequently, dimensional changes caused in sintering are likely to happen, and a subsequent sizing process is conventionally indispensable.
Taking the aforesaid defects of the prior art into consideration, an important object of the invention is to provide technology for producing at low cost iron powder that is suitable for sintering. Another object of the invention is to reduce manufacturing costs of iron powder while retaining compactibility (formability). Further, another object of the invention is to lower manufacturing costs of powder as well as to manufacture an iron powder for use in powder metallurgy having stable dimensional changes in sintering, and in particular having limited dimensional dispersion with respect to the dispersion of graphite.
SUMMARY OF THE INVENTION
The present invention relates to water-atomized iron powder for use in powder metallurgy which has a particle cross section hardness of about Hv 80 or higher to about 250 or lower when the iron powder is atomized with water and dried, further has a particle surface covered with oxides which are reducible in a sintering atmosphere, and further has an oxygen content of about 1.0 wt % or less.
In the iron powder of this invention, those particles having a particle size of from about 75 .mu.m or more to less than about 106 .mu.m, include a portion having a coefficient of particle cross-sectional configuration of about 2.5 or less and comprising in a numerical amount of about 10% or more, and the iron powder further contains particles having a particle size of about 45 .mu.m or less in an amount about 20 wt % or more.
In the foregoing, the coefficient of particle cross-sectional configuration of a particle is defined as a value obtained by dividing the square of the circumferential length of a particle cross section by 4.pi. times the cross-sectional area of the particle and is obtained by the steps mentioned below.
Step 1: Sieve iron powder and obtain particles having a diameter 75 .mu.m-106 .mu.m.
Step 2: Bury thus obtained particles into resin.
Step 3: Cut and polish thus obtained resin in an arbitrary section with iron particles and observe cross sectional configuration of iron particles using a micro-scope.
Step 4: Analyze 500-1000 particles concerning cross-sectional configuration of particles using an image analyzer and obtain a coefficient for each of said particles.
Further, water-atomized iron powder according to this invention contains elements that are more easily oxidizable than iron in an amount of 0.003 to 0.5 wt %, and has a particle surface covered with oxides which are unreducible in a sintering atmosphere.
This invention further relates to a method of manufacturing the iron powder covered with such oxides.
Other features of the present invention will be apparent from the accompanying detailed description and from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a chart which shows a relationship between hardness of atomized raw iron powder and the amount of C contained in the iron powder; and
FIG. 2 is another chart which shows a relationship between an amount of oxygen and the amount of Al, each in the iron powder.

DESCRIPTION OF THE PREFERRED EMBODIMENT
It has now been discovered that softening, annealing and reducing process steps can be eliminated under specified conditions.
Softening, annealing and reducing have been used to soften by annealing the hardened structure of the iron powder produced by atomizing with water. Raw iron powder in the water-atomized state has high hardness and is inferior in formability (compactibility) and cannot be used for powder metallurgy in that state.
The term "compactibility" refers to the green density obtained when iron powder is molded and pressed under the prevailing compacting pressure, and serves as an index for evaluating the characteristics of the green compact which is often used in powder metallurgy. When the compactibility index has a larger value, the green compact has better characteristics. Further, when iron powder is water-atomized, the iron powder particles tend to be covered with oxide films such as FeO, etc. These films interfere with formability of the iron powder and lower the strength of the sintered body. Thus, the oxide films have ordinarily been removed by softening, annealing and reducing.
The term "formability" as used herein relates to the strength of the green compact and may be represented by a "rattler value" which serves as an index for evaluating the characteristics of the green compact. A lower rattler value is preferable to a higher one.
According to this invention, water-atomized iron powder can remarkably be made with satisfactory compactibility, formability and sintering properties without the expense and burden of softening, annealing and reducing process steps.
It has been discovered that good compactibility can be achieved in atomized raw iron powder when the hardness of the particles is decreased to a Vickers hardness Hv value of about 80 to about 250.
As an example, one raw powder composed of C: 0.007 wt %, Mn: 0.005 wt %, Ni: 0.03 wt %, Cr: 0.017 wt %, Si: 0.008 wt %, P: 0.003 wt %, S: 0.002 wt % and the balance of substantial Fe had a low Vickers hardness Hv (100) of 107. When this powder was added and mixed with 1.0 wt % of zinc stearate and then compacted in metal dies at a compacting pressure of 5 t/cm.sup.2, an excellent green density of 6.81 g/cm.sup.3 was obtained and both the hardness of particle cross sections and the green density had excellent values similar to those of comparable prior art iron powders which had been subjected to softening, annealing and reducing.
We have carefully examined the relationship between hardness and compactibility and have found that a green compact having advantageous green density can be obtained when the particle cross section of the iron powder had a Vickers hardness of about Hv 250. The lower the hardness of the particle cross section, the better its compactibility. It is not practical industrially to achieve a hardness less than about Hv 80 because the refining cost of the molten metal tends to be uselessly increased.
Therefore, the Vickers hardness of the particle cross section of the iron powder according to the present invention is maintained within the range of about Hv 80-250.
Such a particle cross section hardness can be obtained by reducing the amounts of harmful components such as C etc. as much as possible. As is shown in FIG. 1 of the drawings, when the amount of C is reduced the hardness of the iron powder is also reduced and approaches or betters the hardness of other finished iron powder that has been reduced and annealed.
When iron powder contains C in an amount of about 0.01 wt % or less, no significant hardening occurs even if the iron powder is atomized with water. When the content of C exceeds about 0.01 wt %, however, the powder hardness is increased. The C content is accordingly about 0.01 wt %, preferably about 0.005 wt % or less.
Mn, Ni and Cr greatly influence compactibility. As examples, various iron powders containing C in the range of about 0.01 wt % or less were atomized with water and dried, while the contents of Mn, Ni and Cr in the powders were changed through the range of about 0.40 wt % to none. When the content of Mn, Ni and Cr exceeded about 0.30 wt %, the hardness Hv (100) of the raw iron powder exceeded 250 and the iron powder was difficult to compact under pressure in metal dies. Further, sufficient green density could not be obtained. According to this invention the content of Mn, Ni and Cr should be about 0.30 wt % or less. The contents of these elements are preferably even about 0.1 wt % or less, but when they are excessively lowered, steelmaking cost is increased.
The total content of P and S should be about 0.05% or less. Although it is preferable to reduce the content of P and S as much as possible, when the total content is about 0.05% or less, no adverse hardness affect is caused.
The existence of oxygen (O) has been conventionally severely restricted; indeed O has been removed by reduction. We have discovered, however, that the presence of O is harmless to the sintering process if its content is within the parameters of this invention and if the percentage of O does not exceed a specific range. More particularly, unless the content of O exceeds about 1.0 wt %, the compactibility and formability of iron powder are satisfactory. In this case, O generally exists in combination with Fe, and when its content is within the above range, FeO is reduced to Fe in the reducing atmosphere that exists in the sintering process. Thus, the existence of O in the above range is surprisingly found to be permissible. While the O content can be any value below about 1.0 wt %, it is preferable from the viewpoint of formability to control the content of O as oxide reduced in the sintering process to about 0.5 wt % or less.
According to the present invention, Mo and/or Nb are further added in a preferable amount because these elements contribute to improvement of compactibility. Mo in a range of about 0.05 wt % to about 5.0 wt % improves compactibility and further promotes sintering and improves the strength of the sintered body. When the content of Mo exceeds about 5.0 wt %, compactibility is abruptly lowered.
Nb added in the range from about 0.005 wt % to about 0.2 wt % improves compactibility. When it is added in an amount exceeding about 0.2 wt %, however, compactibility is abruptly lowered.
Although the present invention successfully provides satisfactory iron powder for sintering, depending upon the hardness of the particles of the iron powder and a predetermined amount of oxygen contained therein, the iron powder in an atomized state has a hardness greater than that (Hv: 80-120) of generally used iron powder which has been subjected to annealing, softening and reducing. This is because of the creation of a partially hardened structure and the introduction of strain due to quenching. Therefore, it is preferable to consider and control the configuration of the iron powder particles in order to obtain good compactibility.
According to the present invention, particle configuration is represented in terms of a coefficient of particle configuration. The coefficient of particle configuration is represented by a value obtained by dividing the square of the circumference of the particle cross section by 4.pi. times the cross-sectional area of the particle. This value is 1 when the cross section of the particle is a perfect circle.
We have found that when particles having a coefficient of particle cross-sectional configuration of about 2.5 or less are present in an amount of about 10% or more by weight in those relatively coarse particles which have a particle size of from about 75 .mu.m or more to less than about 106 .mu.m, even if the cross section of the particles has a hardness exceeding about Hv 200, a green density of about 6.70 g/cm.sup.3 or more can be obtained at a compacting pressure of 5 t/cm.sup.2 when the powder is mixed with a 1 wt % of solid lubricant. This fact is highly important and advantageous.
It is important to consider those relatively coarse particles having a particle size of from about 75 .mu.m to about 106 .mu.m. The relatively coarse particles having a particle size of about 75 .mu.m or more greatly contribute to compactibility and have the heaviest weight when screened in normal powder metallurgy.
On the other hand, when a particle configuration is rounded, the resulting sintered body strength tends generally to be decreased. This problem can be solved by the existence in those relatively coarse particles of about 20% or more of relatively fine powder particles having a size of less than about 325 mesh, which particles are about 45 .mu.m or less in size.
A tensile strength of about 25 kgf/mm.sup.2 or more can be obtained in a sintered body having a sintered density of 6.8 g/cm.sup.3 which is obtained, for example, in such a manner that 2.0 wt % of Cu and 0.8 wt % of graphite and solid lubricant are mixed with Fe powder and compacted and then sintered at 1130.degree. C. for 20 minutes in a N.sub.2 atmosphere. However, when particles of -325 mesh (45 .mu.m or less) exceed 50 wt %, compactibility is undesirably reduced.
As described above, the green density and sintered body strength of the raw powder of the present invention can be controlled in accordance with the configurations of those particles which have particle sizes of from about 75 .mu.m or more to less than about 106 .mu.m, and by considering the amount of particles having sizes of about 45 .mu.m or less (-325 mesh). Such particle configurations and particle size distributions can be obtained when the atomizing water has a jet pressure in a range of from about 40 kgf/cm.sup.2 or higher to about 200 kgf/cm.sup.2 or lower, and when the water-to-molten-metal ratio is in the range of from about 5 to 15.
The raw powder after having been atomized with water is preferably dried at about 100.degree. to 200.degree. C. in a non-oxidizing atmosphere, as is usual. It is not necessary to soften, anneal or reduce the raw powder which is highly advantageous.
It is important to observe that when a sintered body is made of iron powder, its dimensional accuracy must be improved. We have found that the dimensional accuracy of sintered products can be greatly improved by the existence of specified amounts of oxides, not reduced in the sintering process, on the surfaces of the particles.
More specifically, we have discovered that the creation of FeO by oxidization in the atomizing process can be suppressed by the addition of other elements that more easily oxidizable than iron, such as Si, Al, V, Ti, Zr. These are hereinafter referred to for convenience as easy-to-oxidize elements. Iron powder having an unusual surface structure covered with oxides of the easy-to-oxidize elements can be obtained. We believe the easy-to-oxidize elements in the iron are selectively oxidized so that oxide films are formed on the surface of the iron powder and serve as protective films.
Although the reason why dimensional accuracy can be improved by the existence of the oxides of the easy-to-oxidize elements on the surface of iron powder is not yet clarified, we believe that the diffusion of carbon from graphite added in the sintering process into the particles of the iron powder is suppressed. Thus, the amount of C invading and diffusing into the iron powder is kept substantially at a specific level regardless of changes of the amount of added graphite or changes of its particle size. As a result, the amount of so-called expansion due to Cu is also stabilized.
With this arrangement, the dispersion of dimensional changes of a Fe-Cu-C system which is sensitive to the dispersion of graphite can be suppressed to a low level.
The amount of oxygen in the form of FeO on the powder is simultaneously reduced by the addition of the easy-to-oxidize elements, whereby the formability of the iron powder is further improved.
FIG. 2 of the drawings shows a typical relationship between the amount of Al dissolved in the molten steel and the content of O in a water-atomized raw iron powder.
The easy-to-oxidize elements in accordance with this invention include Si, Al, V, Ti and Zr. They may be present or added independently or as a mixture. Preferable ranges of addition are as follows: Si: about 0.01-about 0.1 wt %, Al: about 0.003-about 0.05 wt %,
V: about 0.008-about 0.5 wt %, Ti: about 0.003-about 0.1 wt %,
Zr: about 0.008-about 0.1 wt %.
The content of the easy-to-oxidize elements is better to be from about 0.003 wt % or more to about 0.5 wt %. When this amount is less than about 0.003 wt %, there is substantially no reduction of oxygen content, whereas an amount exceeding about 0.5 wt % tends to increase the content of oxygen, and resulting sintered body strength is abruptly decreased.
It is important to observe that to achieve improvement of dimensional accuracy of the product, the easy-to-oxidize elements must have an oxidizing ratio of about 20 wt % or more. When the oxidizing ratio is less than about 20 wt % there is less reduction of the variable range of dimensional changes in sintering with respect to the dispersion of added graphite. Even in this case, however, the oxygen content in the iron powder is limited to about 1% and preferably to about 0.5% or less, for the purpose of maintaining formability.
In order for the easy-to-oxidize element (Si, Al, V, Ti, Zr) to be added to molten steel to thereby create suitable oxide films on the surface of iron powder, the iron powder is atomized with water in a non-oxidizing gas atmosphere containing oxygen (O.sub.2) with a concentration of about 5.0 vol % or less and dried in hydrogen, nitrogen or vacuum.
EXAMPLES
Example 1
Molten metal containing C: 0.002 wt %, Mn: 0.002 wt %, Ni: 0.006 wt %, Cr: 0.013 wt %, Si: 0.005 wt %, P: 0.002 wt %, S: 0.002 wt % was prepared in such a manner that molten steel was refined in a converter and decarbonized by the use of a vacuum decarbonizing apparatus. This molten metal was atomized with water at a water pressure of 75 kgf/cm.sup.2 and a water-to-molten-steel ratio of 10. The resulting powder was dried at 125.degree. C. in an atmosphere of N.sub.2 and then screened to 1000 .mu.m or less without being annealed and reduced.
The hardness of the powder was determined by measuring the cross section of the powder in terms of Vickers hardness with a load of 100 g. The coefficient of cross-sectional configuration of the particles was measured by means of an image processing apparatus. Green density was measured in such a manner that 1.0 wt % of zinc stearate was added to and mixed with raw powder and a tablet having a diameter of 11.3 mm.phi. was compacted at a pressure of 5 t/cm.sup.2. Sintered body strength was determined by measuring tensile strength of Fe-2.0 Cu-0.8 composition with a sintered density of 6.80 Mg/m.sup.3 which was obtained in such a manner that a mixed powder of raw iron powder, Cu powder, graphite powder and solid lubricant was compacted and then sintered at 1130.degree. C. in an endothermic gas (propane converted gas) atmosphere for 20 minutes.
Comparative Example 1 was obtained by subjecting commercially available water-atomized iron powder for sintering which had been reduced and annealed to the same process as the aforesaid. Table 1-1 shows chemical composition of the iron powders and Table 1-2 shows powder hardness, sintered body strength and the like.
Example 1 can obtain the powder hardness, green density and sintered body characteristics which are substantially the same as those of the conventional iron powder of Comparative Example 1 even without annealing or reducing.
TABLE 1-1______________________________________ Chemical composition of raw powder (wt %) C Mn Ni Cr Si P S O______________________________________Example 1 0.002 0.002 0.006 0.013 0.005 0.002 0.002 0.53Comparative 0.001 0.11 0.013 0.008 0.01 0.014 0.008 0.09example 1______________________________________
TABLE 1-2__________________________________________________________________________ Pressure of Number % of Particles wt % of Green density Sintered body strength Powder atomizing having coefficient of Particle through compacted at Sintered body hardness water configuration of 2.5 or less 325 mesh 5t/cm2 density 6.8 Mg/m3 (Hv(100)) (kgf/cm2) (Particles size 75.about.106 .mu.m) (-45 .mu.m) (Mg/m3) (MPa)__________________________________________________________________________Example 1 102 75 35 27 6.93 370Comparative 100 -- -- 21 6.94 370example 1__________________________________________________________________________
Examples 2-11, Comparative Examples 2-9
After having been refined in a converter or an electric furnace, molten metal containing C: 0.002-0.04 wt %, Mn: 0.4 wt % or less, Ni: 0.4 wt % or less, Cr: 0.4 wt % or less, Si: 0.005-0.03 wt %, P: 0.002-0.025 wt %, S: 0.002-0.03 wt % was prepared by use of a vacuum degassing apparatus. The molten metal was atomizod with water under a water pressure of 30-250 kgf/cm.sup.2 and with a water to molten steel ratio of 10. The thus obtained powder was dried at 125.degree. C. in an N.sub.2 atmosphere, except in Comparative Example 7. Comparative Example 7 was dried at 125.degree. C. in the atmosphere. These raw powders were screened to 1000 .mu.m or less without being annealed or reduced.
Particle hardness, coefficient of particle cross-sectional configurations of the raw powders, green density and sintered body strength were measured using the same methods as Example 1.
Table 2-1 shows chemical composition of raw iron powders of Examples 2-11 and Comparative Examples 2-9. Table 2-2 shows powder hardness, atomized water pressure, ratio of particles having a coefficient of configuration of 2.5 or less in the particles having a particle size of 75-106 .mu.m, ratio of particles having a size of -325# (45 .mu.m or less), green density not subjected to a finishing reduction, and sintered body strength.
Although any of Examples 2-11 exhibits a practically applicable green density and sintered body strength, Comparative Examples 2-7 have the composition of raw powders which exceeds a proper range. Thus, the hardness of particles is Hv (100) 250 or higher and a green density of 6.70 Mg/m.sup.3 or more cannot be obtained at a compacting pressure of 5 t/cm.sup.2. Since Comparative Example 8 has an atomizing pressure exceeding a proper range, the ratio of the particles having a coefficient of configuration of 2.5 or less is 10% or less in the particles having a particle size of 75-106 .mu.m. Thus, a green density of 6.70 Mg/m.sup.3 or more cannot be obtained at a compacting pressure of 5 t/cm.sup.2. Since Comparative Example 9 has an atomizing pressure exceeding a proper range, particles of -325# are 20% or less and thus a sintered body strength of 300 MPa cannot not be obtained at a sintered body density of 6.80 Mg/m.sup.3.
TABLE 2-1______________________________________ Chemical composition of raw powder (wt %) C Mn Ni Cr Si P S O______________________________________Example 2 0.002 0.001 0.005 0.001 0.005 0.001 0.002 0.61Example 3 0.006 0.005 0.011 0.01 0.010 0.005 0.002 0.45Example 4 0.010 0.01 0.011 0.02 0.018 0.006 0.009 0.47Example 5 0.010 0.012 0.013 0.025 0.020 0.006 0.008 0.45Example 6 0.006 0.29 0.005 0.001 0.005 0.002 0.002 0.65Example 7 0.006 0.05 0.29 0.002 0.007 0.001 0.003 0.52Example 8 0.007 0.006 0.004 0.3 0.006 0.004 0.002 0.62Example 9 0.005 0.004 0.004 0.003 0.005 0.015 0.019 0.51Example 10 0.004 0.004 0.005 0.004 0.005 0.002 0.002 0.55Example 11 0.004 0.003 0.005 0.003 0.005 0.003 0.003 0.55Example 12 0.005 0.004 0.003 0.002 0.006 0.004 0.004 0.55Comparative 0.032 0.01 0.013 0.2 0.029 0.007 0.011 0.41Example 2Comparative 0.005 0.38 0.003 0.004 0.005 0.002 0.002 0.7Example 3Comparative 0.004 0.004 0.41 0.003 0.005 0.002 0.003 0.53Example 4Comparative 0.004 0.003 0.003 0.42 0.005 0.002 0.002 0.68Example 5Comparative 0.003 0.003 0.004 0.004 0.008 0.025 0.030 0.51Example 6Comparative 0.003 0.002 0.002 0.003 0.003 0.002 0.004 1.2Example 7Comparative 0.003 0.003 0.004 0.004 0.008 0.005 0.005 0.65Example 8Comparative 0.003 0.003 0.004 0.004 0.008 0.005 0.005 0.6Example 9______________________________________
TABLE 2-2__________________________________________________________________________ Pressure of Number % of Particles wt % of Green density Sintered body strength Powder atomizing having coefficient of Particle through compacted at Sintered body hardness water configuration of 2.5 or less 325 mesh 5t/cm2 density 6.8 Mg/m3 (Hv(100)) (kgf/cm2) (Particles size 75.about.106 .mu.m) (-45 .mu.m) (Mg/m3) (MPa)__________________________________________________________________________Example 2 81 75 35 25 6.94 400Example 3 155 75 32 30 6.8 390Example 4 196 75 32 31 6.72 380Example 5 245 75 33 32 6.7 360Example 6 240 75 30 30 6.71 370Example 7 248 75 30 30 6.7 390Example 8 247 75 28 33 6.75 380Example 9 230 75 29 33 6.72 360Example 10 100 40 43 25 7 350Example 11 101 150 29 36 6.76 390Example 12 110 200 15 41 6.72 400Comparative 315 75 30 30 6.5 400Example 2Comparative 290 75 32 31 6.61 380Example 3Comparative 305 75 31 30 6.57 390Example 4Comparative 283 75 29 29 6.58 370Example 5Comparative 295 30 43 10 6.52 300Example 6Comparative 260 75 29 21 6.59 300Example 7Comparative 150 250 5 45 6.6 390Example 8Comparative 155 30 43 10 6.53 290Example 9__________________________________________________________________________
Examples 12-24, Comparative Examples 10-19
After having been refined in a converter or an electric furnace, molten metal containing C: 0.002-0.03 wt %, Mn: 0.4 wt % or less, Ni: 0.4 wt % or less, Cr: 0.4 wt % or less, Si: 0.005-0.03 wt %, P: 0.002-0.025 wt %, S: 0.002-0.03 wt %, Mo: 6.0 wt % or less, Nb: 0.3 wt % or less was prepared by use of a vacuum degassing apparatus. This molten metal was atomized with water under a water pressure of 30-250 kgf/cm.sup.2 and a water-to-molten-steel ratio of 10. The thus obtained powder was dried at 125.degree. C. in a N.sub.2 atmosphere, except in Comparative Example 19. Comparative Example 19 was dried at 125.degree. C. in the atmosphere. These raw powders were screened to 1000 .mu.m or less without being annealed or reduced.
Particle hardness, coefficient of particle cross-sectional configuration of the raw powders, green density and sintered body strength were measured by the same methods as Example 1. Table 3-1 shows chemical composition of the raw iron powders of Examples 12-24 and Comparative Examples 10-19, and Table 3-2 shows powder hardness, atomized water pressure, ratio of the particles having a coefficient of configuration of 2.5 or less in the particles having a particle size of 75-106 .mu.m, ratio of particles having a size of -325# (45 .mu.m or less), green density, and sintered body strength of these examples and comparative examples.
Although Examples 12-24 exhibit a practically applicable green density and sintered body strength, Comparative Examples 10-16 have compositions of raw powders which exceed a proper range. Thus, the hardness of the particles is 250 or more and the green density of 6.70 Mg/m.sup.3 or more cannot be obtained at a compacting pressure of 5 t/cm.sup.2. Since Comparative Example 17 has an atomizing pressure exceeding a proper range, the ratio of the particles having a coefficient of configuration of 2.5 or less is 10% or less in the particles having a particle size of 75-106 .mu.m. Thus, a green density of 6.70 Mg/m.sup.3 or more cannot be obtained at a compacting pressure of 5 t/cm.sup.2. Since Comparative Example 18 has an atomizing pressure exceeding a proper range, the particles of -325 mesh are 20% or less and thus a sintered body strength of 300 MPa cannot not be obtained at a sintered body density of 6.80 Mg/m.sup.3. Comparative Example 19 has an amount of oxygen in the raw powder which exceeds a proper range because it is dried under improper drying conditions. Thus, a green density of 6.70 Mg/m.sup.3, or more or a sintered body strength of 300 MPa, cannot be obtained.
TABLE 3-1__________________________________________________________________________ Chemical composition of raw powder (wt %) C Mn Ni Cr Si P S Mo Nb O__________________________________________________________________________Example 12 0.003 0.03 0.005 0.01 0.006 0.008 0.006 0.5 0.005 0.51Example 13 0.004 0.04 0.01 0001 0.006 0.01 0.005 1.0 0.007 0.45Example 14 0.005 0.03 0.01 0.011 0.007 0.008 0.006 2.0 0.006 0.52Example 15 0.003 0.05 0.008 0.012 0.008 0.008 0.006 4.0 0.006 0.44Example 16 0.002 0.05 0.007 0.004 0.01 0.009 0.008 0.5 0.01 0.5Example 17 0.002 0.04 0.011 0.006 0.006 0.008 0.006 0.5 0.05 0.42Example 18 0.002 0.04 0.008 0.008 0.006 0.008 0.006 0.5 0.05 0.42Example 19 0.002 0.04 0.011 0.006 0.006 0.008 0.006 0.2 0.15 0.42Example 20 0.006 0.01 0.01 0.005 0.02 0.01 0.015 0.3 0.02 0.35Example 21 0.01 0.02 0.005 0.005 0.008 0.007 0.002 0.2 0.02 0.5Example 22 0.003 0.25 0.006 0.005 0.008 0.008 0.006 0.1 0.03 0.5Example 23 0.002 0.03 0.25 0.005 0.008 0.007 0.006 0.2 0.008 0.47Example 24 0.002 0.03 0.012 0.25 0.008 0.007 0.006 0.5 0.009 0.53Comparative Example 10 0.03 0.04 0.011 0.006 0.006 0.008 0.006 0.2 0.15 0.42Comparative Example 11 0.002 0.4 0.008 0.01 0.01 0.01 0.009 0.2 0.007 0.5Comparative Example 12 0.005 0.1 0.4 0.01 0.01 0.008 0.009 0.5 0.007 0.56Comparative Example 13 0.004 0.06 0.01 0.4 0.01 0.008 0.009 0.5 0.007 0.55Comparative Example 14 0.003 0.11 0.01 0.009 0.01 0.025 0.03 0.5 0.008 0.61Comparative Example 15 0.003 0.1 0.01 0.011 0.008 0.007 0.008 6.0 0.01 0.57Comparative Example 16 0.003 0.1 0.01 0.01 0.007 0.011 0.007 0.4 0.3 0.59Comparative Example 17 0.005 0.02 0.005 0.005 0.008 0.007 0.002 0.2 0.02 0.5Comparative Example 18 0.005 0.02 0.005 0.005 0.008 0.007 0.002 0.2 0.02 0.5Comparative Example 19 0.002 0.11 0.011 0.009 0.01 0.011 0.008 0.1 0.008 1.5__________________________________________________________________________
TABLE 3-2__________________________________________________________________________ Pressure of Number % of Particles wt % of Green density Sintered body strength Powder atomizing having coefficient of Particle through at Sintered body hardness water configuration of 2.5 or less 325 mesh 5t/cm2 density 6.8 Mg/m3 (Hv(100)) (kgf/cm2) (Particles size 75.about.106 .mu.m) (-45 .mu.m) (Mg/m3) (MPa)__________________________________________________________________________Example 12 121 120 35 27 6.87 550Example 13 125 120 33 30 6.9 610Example 14 127 120 35 32 6.91 750Example 15 130 120 37 32 6.92 820Example 16 128 120 30 31 6.89 555Example 17 125 120 30 30 6.88 550Example 18 170 150 28 33 6.85 590Example 19 175 150 29 35 6.88 510Example 20 180 150 28 32 6.8 530Example 21 220 100 30 36 6.75 515Example 22 177 100 25 35 6.78 480Example 23 180 200 10 45 6.77 500Example 24 164 40 72 20 6.8 540Comparative ex. 10 310 120 30 30 6.5 505Comparative ex. 11 280 120 32 31 6.55 500Comparative ex. 12 270 120 31 31 6.53 540Comparative ex. 13 285 120 29 32 6.61 545Comparative ex. 14 288 120 28 30 6.6 550Comparative ex. 15 268 120 30 28 6.52 830Comparative ex. 16 280 120 29 25 6.51 530Comparative ex. 17 125 250 5 55 6.65 510Comparative ex. 18 130 30 80 10 6.89 250Comparative ex. 19 135 120 29 21 6.92 280__________________________________________________________________________
Examples 25-29, Comparative Examples 20-22
After having been refined in a converter or an electric furnace, molten metal containing C: 0.01 wt % or less, Mn: 0.1 wt % or less, Ni: 0.1 wt % or less, Cr: 0.1 wt % or less, Si: 0.02 wt % or less, P: 0.02 wt % or less, S: 0.02 wt % or less, Al: 0.1 wt % or less was prepared by use of a vacuum degassing apparatus. This molten metal was atomized with water under water pressure of 120 kgf/cm.sup.2 and a water-to-molten-steel ratio of 10. The thus obtained raw powders were dried at 125.degree. C. in an N.sub.2 atmosphere. The raw powders were screened to 250 .mu.m or less without being annealed or reduced. Table 4 shows particle hardness, chemical composition of iron powders, green density, rattler value, tensile strength, and impact value. Examples 25-29 have an oxygen content of 0.4% or less because it contains a proper amount of Al. As a result, these examples exhibit a green density of 6.7 g/m.sup.3 or more, sintered body strength of 40 kgf/mm.sup.2 or more and rattler value of 1.5% or less, but Comparative Examples 20, 22 exhibit a rattler value of 1.5% or more and a lowered formability because they contain Al in an amount exceeding a proper range although having a green density of 6.7 g/m.sup.3 or more. Further, Comparative Example 21 has a green density of 6.5 g/m.sup.3 or less because it has a hardness exceeding Hv 250.
TABLE 4__________________________________________________________________________ Chemical composition of iron powder (wt %) Green Rattler Fe and other indispensable Hardness density value Tensile strength Impact value Al (%) C (%) O (%) impurities Hv (100 g) (g/cm3) (%) (kg/mm2) (kg-m/cm2)__________________________________________________________________________Example 25 0.006 0.003 0.38 the remainder 120 6.70 0.85 42 0.9Example 26 0.010 0.004 0.36 the remainder 124 6.75 0.9 43 0.95Example 27 0.021 0.003 0.35 the remainder 130 6.74 1.0 44 0.88Example 28 0.031 0.002 0.33 the remainder 133 6.80 1.2 43 0.87Example 29 0.046 0.002 0.30 the remainder 135 6.81 1.4 41 0.85Comparative 0.001 0.003 0.55 the remainder 135 6.71 1.9 40 0.83Example 20Comparative 0.020 0.025 0.34 the remainder 270 6.45 3.8 32 0.65Example 21Comparative 0.070 0.002 0.30 the remainder 140 6.80 1.5 31 0.63Example 22__________________________________________________________________________
Examples 30-36, Comparative Examples 23-26
After having been refined in a converter or an electric furnace, molten metal containing C: 0.01 wt % or less, Mn: 0.1 wt % or less, Ni: 0.1 wt % or less, Cr: 0.1 wt % or less, Si: 0.02 wt % or less, P: 0.02 wt % or less, S: 0.02 wt % or less, Si+Ti+Zr: 0.2 wt % or less was prepared by use of a vacuum degassing apparatus. This molten metal was atomized at a water pressure of 130 kgf/cm.sup.2. The thus obtained raw powders were dried at 125.degree. C. in an Ns atmosphere. The raw powders were screened to 250 .mu.m or less without being annealed or reduced.
Table 5 shows particle hardness, chemical composition of iron powders, green density, rattler value, tensile strength and impact value.
Examples 30-36 have an oxygen content of 0.5% or less because they contain a proper amount of any of Si, Ti or Zr. As a result, these Examples exhibit a sintered body strength of 40 kgf/mm.sup.2 or more and rattler value of 1.5% or less, but Comparative Examples 23 exhibits a rattler value of 1.5% or more and a lowered formability because it contains Si, Ti, Zr in an amount less than the proper range. Comparative Example 24 has a green density of 6.5 g/m.sup.3 or less because it has a particle hardness exceeding Hv 250. Further, Comparative Examples 25 and 26, which contain Si, Ti, Zr in an amount exceeding a proper range, have a lowered sintered body strength.
TABLE 5-1__________________________________________________________________________ Atomizing conditions Atomizing Pressure 130 kgf/cm2 Water to molten Atmosphere Analyzed value of atomized raw powder Composition value of molten steel (wt %) steel (O2 (wt %) Si (%) Ti (%) Zr (%) C (%) O (%) ratio .delta. concentration) Si (%) Ti (%) Zr (%) C O__________________________________________________________________________ (%)Example 30 0.020 0.002 0.002 0.008 0.010 8 N2(1.0) 0.020 0.002 0.002 0.002 0.38Example 31 0.013 0.002 0.002 0.009 0.007 7.5 N2(1.0) 0.012 0.002 0.002 0.003 0.45Example 32 0.032 0.002 0.003 0.010 0.005 7 N2(0.5) 0.030 0.002 0.003 0.004 0.33Example 33 0.004 0.020 0.022 0.008 0.009 7 N2(1.0) 0.004 0.020 0.020 0.002 0.35Example 34 0.004 0.016 0.015 0.007 0.006 7.5 N2(0.5) 0.004 0.015 0.015 0.002 0.40Example 35 0.001 0.002 0.018 0.005 0.007 7 Ar(0.3) 0.001 0.002 0.017 0.003 0.45Example 36 0.021 0.021 0.015 0.006 0.005 6.5 N2(2.0) 0.020 0.020 0.015 0.003 0.40Comparative ex. 23 0.003 <0.001 <0.001 0.005 0.020 7 N2(2.0) 0.002 <0.001 <0.001 0.003 0.60Comparative ex. 24 0.015 0.010 0.002 0.035 0.007 7 N2(1.0) 0.015 0.010 0.002 0.020 0.40Comparative ex. 25 0.121 0.010 0.005 0.007 0.007 8 N2(1.0) 0.120 0.010 0.005 0.003 0.35Comparative ex. 26 0.055 0.150 0.033 0.007 0.005 7.5 N2(1.0) 0.050 0.030 0.030 0.002 0.38__________________________________________________________________________
TABLE 5-2__________________________________________________________________________ Characteristic of green compact Characteristic of sinterd body Hardness Green density Rattler value Tensile strength Impact value HV (100 g) (g/cm3) (%) (kg/mm2) (kg-m/cm2)__________________________________________________________________________Example 30 130 6.72 0.8 44 0.95Example 31 125 6.75 0.9 42 0.92Example 32 130 6.76 1.0 45 0.88Example 33 130 6.82 1.1 43 0.87Example 34 128 6.80 1.3 41 0.85Example 35 135 6.71 1.2 40 0.8Example 36 138 6.60 0.9 42 0.85Comparative Example 23 135 6.70 2.0 39 0.75Comparative Example 24 270 6.45 3.8 31 0.6Comparative Example 25 150 6.60 1.4 29 0.5Comparative Example 26 145 6.63 1.4 30 0.55__________________________________________________________________________
Examples 37, Comparative Example 27
Molten metal containing C: 0.004 wt %, Mn: 0.03 wt %, Ni: 0.005 wt %, Cr: 0.01 wt %, Si: 0.006 wt %, P: 0.008 wt %, S: 0.006 wt %, Al: 0.004 wt % was prepared in such a manner that molten steel was refined in a converter and decarbonized by use of a vacuum decarbonizing apparatus. This molten metal was atomized with jet water having a water pressure of 70 kgf/cm.sup.2 in an N.sub.2 atmosphere having an oxygen concentration of 0.5%. The thus obtained powder was dried at 180.degree. C. in a H.sub.2 atmosphere and then screened to 250 .mu.m or less without being annealed and reduced.
Green density was measured in such a manner that 1.0 wt % of zinc stearate was added to and mixed with raw powder and a tablet having a diameter of 11.3 mm.phi. was compacted at a pressure of 5 t/cm.sup.2. Sintered body strength was measured in such a manner that powder prepared by mixing raw iron powder, Cu powder, graphite powder and zinc stearate as lubricant was compacted to a JSPM standard tensile strength test piece and the tensile strength of a sintered body (sintered density: 6.8 Mg/m.sup.3, a composition of Fe-2.0 Cu-0.8 C) obtained by sintering the test piece at 1130.degree. in an endothermic gas (propane converted gas) atmosphere for 20 minutes was measured. A dimensional change in sintering was examined with respect to amounts of graphite of two levels or Fe-2.0% Cu-0.8% Gr and Fe-2.0% Cu-1.0% Gr and a difference of the respective changes of sintered dimension was used as a "variable range of dimensional changes". At that time, the test piece was formed to a ring shape with an outside diameter of 60.phi., inside diameter of 25.phi., height of 10 mm, and green density of 6.85 g/cm.sup.3 and sintered at 1130.degree. C. in an endothermic gas (propane converted gas) atmosphere for 20 minutes.
Comparative Example 27 was obtained by subjecting commercially available water-atomized iron powder for powder metallurgy which had been reduced and annealed to the same process as the aforesaid one. Table 6-1 shows a chemical composition of iron powders and a ratio of oxidization of easy-to-oxidize elements, and Table 6-2 shows a hardness of particle cross section, green density, sintered body strength and variable range of dimensional changes. Example 37 not only has substantially the same green density as that of Comparative Example 27 but also exhibits a variable range of dimensional changes superior to that of the iron powder of Comparative Example 27 regardless of that Example 37 is not annealed and reduced.
TABLE 6-1__________________________________________________________________________ Ratio of oxidization of Chemical composition of raw powder (wt %) easy-to-oxidize C Mn Ni Cr Si P S Al O elements (%)__________________________________________________________________________Example 37 0.004 0.03 0.005 0.01 0.006 0.008 0.006 0.004 0.45 35Comparative Example 27 0.001 0.11 0.011 0.009 0.01 0.012 0.009 -- 0.1 --__________________________________________________________________________
TABLE 6-2__________________________________________________________________________ Green density Sintered body strength Variable range compacted at Sintered body density of dimentional 5t/cm2 6.8 Mg/m3 changes Hardness (Mg/m3) (MPa) (%) (%)__________________________________________________________________________Example 37 6.86 440 0.06 110Comparative Example 27 6.91 430 0.2 100__________________________________________________________________________
Examples 38-52, Comparative Examples 28-31
After having been refined in a converter or an electric furnace, molten metal containing C: 0.01 wt % or less, Mn: 0.1 wt % or less, Ni: 0.1 wt % or less, Cr: 0.1 wt % or less, P: 0.02 wt % or less, S: 0.02 wt % or less, a total amount of Si, Al, Ti and V: 0.6 wt % or less was prepared by use of a vacuum degassing apparatus. This molten metal was atomized with water having a pressure of 100 kgf/cm.sup.2 in an N.sub.2 atmosphere with an oxygen concentration of 10% or less. The thus obtained raw powders were dried at 100.degree.-300.degree. C. in H.sub.2, N.sub.2 or vacuum for 60 minutes and then screened to 250 .mu.m or less without being-annealed and reduced.
Green density, sintered body strength and variable range of dimensional changes of sintered body were measured by the same methods as those of Example 37. Table 7 shows the a chemical composition of iron powders, ratio of oxygen in easy-to-oxidize elements, hardness of particle cross-section, sintered body strength and variable range of dimensional changes of Examples 38-52 and Comparative Examples 28-31.
Any of Examples 38-52 exhibit a practically applicable green density and sintered body strength. Further, they exhibit an excellent dimensional accuracy with a variable range of dimensional changes of 0.1% or less.
With Example 51, where a small amount of easy-to-oxidize elements is contained, and Example 52, where a ratio of oxidization of easy-to-oxidize elements is 20 wt % or less, although dimensional accuracy was lowered, practically useful green density and sintered body strength were obtained.
Because a total amount of Si, Al, Ti and V in Comparative Examples 28 to 31 exceeds the upper limit of a proper range, only a low sintered body strength was obtained.
TABLE 7__________________________________________________________________________ Chemical composition of iron powder Ratio of oxidization of easy-to- Powder Green Tensile Vari- Atomizing Drying oxidize hardness density strength able atmosphere condition elements (HV (g/ (kg/ range O2 concentration (%) Si (%) Al (%) Ti (%) V (%) O (%) (%) (100)) cm3) mm2) (%)__________________________________________________________________________Example 38 0.5 150.degree. C. H2 0.01 <0.001 <0.001 <0.001 0.30 35 115 6.91 40 0.10Example 39 0.5 150.degree. C. H2 0.05 <0.001 <0.001 <0.001 0.32 29 115 6.93 40 0.09Example 40 0.5 150.degree. C. H2 0.10 <0.001 <0.001 <0.001 0.32 31 120 6.91 41 0.09Example 41 0.5 200.degree. C. H2 0.002 0.004 <0.001 <0.001 0.26 39 130 6.28 40 0.09Example 42 0.5 250.degree. C. H2 0.008 0.004 <0.001 <0.001 0.30 35 128 6.89 45 0.10Example 43 0.1 150.degree. C. N2 0.002 0.010 <0.001 <0.001 0.30 40 135 6.85 44 0.08Example 44 1 150.degree. C. 0.002 0.05 <0.001 <0.001 0.31 24 139 6.82 40 0.06 vacuumExample 45 2 150.degree. C. H2 0.002 <0.001 0.005 <0.001 0.35 26 135 6.9 42 0.05Example 46 1 150.degree. C. H2 0.002 <0.001 0.10 <0.001 0.33 32 130 6.91 41 0.07Example 47 0.2 150.degree. C. N2 0.002 <0.001 <0.001 0.01 0.35 34 135 6.89 42 0.08Example 48 0.3 150.degree. C. N2 0.002 <0.001 <0.001 0.40 0.32 28 135 6.9 41 0.07Example 49 0.5 180.degree. C. H2 0.010 <0.001 <0.001 0.10 0.32 35 130 6.89 40 0.09Example 50 0.5 180.degree. C. H2 0.002 0.003 0.003 0.05 0.32 31 120 6.91 41 0.10Example 51 0.5 180.degree. C. H2 0.002 <0.001 <0.001 <0.001 0.80 50 150 6.78 40 0.21Example 52 6 180.degree. C. H2 0.005 0.005 <0.001 0.01 0.85 15 220 6.75 41 0.20Comparative 0.3 150.degree. C. N2 0.20 0.001 0.001 0.001 0.56 22 210 6.77 32 0.12Example 28Comparative 0.03 150.degree. C. N2 0.005 0.10 0.001 0.001 0.58 20 180 6.74 33 0.11Example 29Comparative 0.3 150.degree. C. N2 0.005 0.003 0.20 0.01 0.52 22 190 6.76 31 0.10Example 30Comparative 0.3 150.degree. C. N2 0.005 0.003 0.40 0.60 0.55 22 190 6.72 31 0.12Example 31__________________________________________________________________________
Examples 53-68, Comparative Examples 32-38
After having been refined in a converter or an electric furnace, molten metal containing C: 0.02 wt % or less, a content of each of Mn, Ni, Cr: 0.3 wt % or less, P: 0.002-0.02 wt %, S: 0.002-0.02 wt %, Mo: 6.0 wt % or less, Nb: 0.3 wt % or less, a total content of Si, V, Al, Ti and Zr: 1.5 wt % or less was prepared by use of a vacuum degassing apparatus. This molten metal was atomized with water having a pressure of 80-160 kgf/cm.sup.2 in an atmosphere with an oxygen (O.sub.2) concentration of 10 vol % or less and then dried at 100.degree.-300.degree. C. in hydrogen, nitrogen or vacuum. The raw powders were screened to 250 .mu.m or less without being annealed or reduced.
Green density, sintered body strength and variable range of dimensional changes of sintered body were measured by the same methods as those of Example 37.
Table 8-1 shows chemical compositions of iron powders of Examples 53-68 and Comparative Examples 32-38, and Table 8-2 shows atomizing conditions, drying conditions, ratios of oxidation of the easy-to-oxidize elements, powder hardness, ratios of the particles having a coefficient of configuration of 2.5 or less in the particles having a particle size of 75-106 .mu.m or less, ratio of the particles having a particle size of -325 mesh (45 .mu.m or less), and green density without finishing reduction, sintered body density and variable range of dimensional changes of these examples and comparative examples.
All of Examples 53-68 exhibit practically applicable green density and sintered body strength. Further, Examples 53-66 exhibit excellent dimensional accuracy with a variable range of dimensional changes of 0.1% or less.
With Example 67, where a ratio of oxidization of easy-to-oxidize elements is 20 wt % or less, and Example 68, where a small amount of easy-to-oxidize elements is contained, although dimensional accuracy was lowered, practically useful green density and sintered body strength were obtained.
Because a total amount of Si, Al, Ti and V in Comparative Examples 28 to 31 exceeds the upper limit of a proper range, only a low sintered body strength was obtained.
On the other hand, Comparative Examples 32-38 have a low green density or low sintered body strength because proper ranges of the present invention were exceeded.
The iron powder for powder metallurgy according to the present invention does not need an annealing step or a reducing process after the iron powder has been atomizod with water, as has been needed for conventional water-atomized iron powder, so that the iron powder can be compacted in dies as a raw powder. Further, when the iron powder according to the present invention is sintered with the addition of Cu, graphite, the dimensional changes thereof caused in the sintering are less varied with respect to the dispersion of added graphite as compared with conventional iron powder for powder metallurgy. As a result, a sintered body having excellent dimensional accuracy can be made, even allowing a sizing process to be omitted. Consequently, manufacturing of sintered parts can be simplified and shortened when the iron powder according to the present invention is used. Further, manufacturing cost of sintered parts can be decreased without damaging the characteristics of the product.
TABLE 8-1__________________________________________________________________________ Chemical composition of raw powder (wt %) C Mn Ni Cr P S Mo Nb Si V Al Ti Zr O__________________________________________________________________________Example 53 0.003 0.01 0.005 0.01 0.003 0.006 0.01 0.005 0.005 <0.001 0.004 <0.001 <0.001 0.3Example 54 0.004 0.04 0.01 0.01 0.01 0.005 0.5 0.007 0.005 <0.001 0.006 <0.001 <0.001 0.35Example 55 0.005 0.03 0.01 0.011 0.008 0.006 1.0 0.006 0.004 <0.001 0.02 <0.001 <0.001 0.45Example 56 0.001 0.2 0.008 0.012 0.008 0.006 2.0 0.006 0.006 <0.001 0.05 <0.001 <0.001 0.44Example 57 0.002 0.1 0.007 0.004 0.009 0.008 4.0 0.01 0.008 <0.001 0.001 <0.001 <0.001 0.5Example 58 0.002 0.04 0.3 0.006 0.004 0.006 0.5 0.05 0.05 0.01 0.006 <0.001 <0.001 0.42Example 59 <0.001 0.04 0.008 0.008 0.008 0.003 0.5 0.05 0.1 <0.001 0.002 <0.001 <0.001 0.42Example 60 0.002 0.04 0.011 0.006 0.02 0.006 0.2 0.15 0.006 0.05 0.006 <0.001 <0.001 0.42Example 61 0.006 0.01 0.01 0.005 0.01 0.015 0.3 0.2 0.008 0.15 <0.001 <0.001 <0.001 0.33Example 62 0.009 0.02 0.005 0.006 0.007 0.002 0.2 0.02 0.008 0.45 <0.001 <0.001 <0.001 0.33Example 63 0.003 0.3 0.006 0.005 0.008 0.006 0.1 0.03 0.005 0.01 0.003 0.01 <0.001 0.3Example 64 0.002 0.03 0.3 0.005 0.007 0.006 0.2 0.008 0.005 0.01 0.008 0.1 <0.001 0.28Example 65 0.002 0.03 0.012 0.3 0.007 0.006 0.5 0.009 0.009 0.01 0.004 <0.001 0.01 0.44Example 66 0.001 0.1 0.01 0.01 0.006 0.007 1.0 0.01 0.007 0.007 0.003 <0.001 0.1 0.45Example 67 0.002 0.05 0.01 0.01 0.007 0.007 0.2 0.05 0.007 0.007 0.005 0.01 0.01 0.53Example 68 0.003 0.04 0.011 0.006 0.008 0.006 0.5 0.01 0.002 <0.001 <0.001 <0.001 <0.001 0.84Comparative ex. 32 0.022 0.09 0.008 0.01 0.01 0.009 0.2 0.007 0.002 0.007 0.01 <0.001 <0.001 0.42Comparative ex. 33 0.003 0.1 0.01 0.011 0.007 0.008 1.0 0.01 0.2 0.009 0.002 <0.001 <0.001 1.1Comparative ex. 34 0.003 0.1 0.01 0.01 0.011 0.007 0.4 0.3 0.01 0.6 0.007 <0.001 <0.001 0.59Comparative ex. 35 0.004 0.1 0.01 0.01 0.01 0.007 2.0 0.01 0.01 0.009 0.07 <0.001 <0.001 0.58Comparative ex. 36 0.005 0.02 0.005 0.005 0.007 0.002 0.2 0.02 0.02 0.015 0.008 0.2 0.005 0.5Comparative ex. 37 0.005 0.02 0.005 0.005 0.007 0.002 0.2 0.02 0.02 0.015 0.008 0.002 0.2 0.5Comparative ex. 38 0.002 0.11 0.011 0.009 0.011 0.008 0.1 0.008 0.008 0.01 0.01 <0.001 <0.001 1.5__________________________________________________________________________
TABLE 8-2__________________________________________________________________________ Atomizing conditions Ratio of wt % of Atomizing Drying oxidization of Number % of Particles Particles atmosphere Atomizing conditions easy-to-oxidize Powder having coefficient through 3 O2 concentration pressure Gas elements hardness configuration of 2.5 or 25 mesh (%) (kgf/cm2) Temperature (%) (Hv (100)) (Particle size 75.about.106 .mu.m) (-45__________________________________________________________________________ .mu.m)Example 53 0.5 100 H2-180.degree. C. 35 115 35 30Example 54 0.5 100 H2-180.degree. C. 34 120 40 28Example 55 0.5 100 H2-180.degree. C. 25 125 35 33Example 56 0.5 100 H2-180.degree. C. 28 130 35 32Example 57 0.5 100 H2-130.degree. C. 30 137 38 33Example 58 1 120 H2-180.degree. C. 45 138 30 35Example 59 1 120 N2-150.degree. C. 49 140 32 35Example 60 1 120 N2-150.degree. C. 35 135 28 36Example 61 1 120 N2-150.degree. C. 50 150 30 34Example 62 2 80 Vac.-150.degree. C. 33 175 45 22Example 63 2 80 H2-280.degree. C. 38 135 42 23Example 64 0.2 160 H2-280.degree. C. 25 130 25 40Example 65 0.2 160 H2-280.degree. C. 35 120 26 43Example 66 0.2 130 N2-150.degree. C. 36 110 28 40Example 67 5 130 N2-150.degree. C. 15 125 28 38Example 68 0.5 120 H2-180.degree. C. -- 130 25 35Comparative 0.5 80 H2-180.degree. C. 38 280 45 22ex. 32Comparative 0.5 80 N2-180.degree. C. 42 260 42 22ex. 33Comparative 0.5 100 N2-180.degree. C. 38 270 35 20ex. 34Comparative 0.5 100 N2-180.degree. C. 40 280 36 21ex. 35Comparative 0.5 100 N2-180.degree. C. 36 270 38 23ex. 36Comparative 0.5 100 N2-180.degree. C. 35 260 35 30ex. 37Comparative 8 100 N2-180.degree. C. 18 190 35 28ex. 38__________________________________________________________________________
TABLE 8-3______________________________________Green density Sintered body strength Variable rangecompacted at Sintered body density of dimentional5t/cm2 6.8 Mg/m3 changes(Mg/m3) (MPa) (%)______________________________________53 6.85 420 0.0654 6.87 560 0.0555 6.89 615 0.0756 6.91 735 0.0757 6.83 820 0.0758 6.82 550 0.0659 6.8 545 0.0760 6.9 595 0.0561 6.82 605 0.0562 6.79 500 0.0963 6.86 510 0.0564 6.87 515 0.0765 6.88 555 0.0866 6.89 605 0.0767 6.88 520 0.1568 6.8 520 0.1432 6.67 410 0.133 6.68 380 0.0934 6.65 375 0.135 6.66 350 0.136 6.68 395 0.137 6.68 355 0.138 6.69 390 0.2______________________________________

Number	Date	Country
5-115523	May 1993	JPX
5-196170	Aug 1993	JPX
5-256807	Oct 1993	JPX

Number	Name	Date
4209320	Kajinaga et al.	Jun 1980
5067979	Kiyota et al.	Nov 1991
5328500	Beltz et al.	Jul 1994
5462577	Ogura et al.	Oct 1995

Water-atomized iron powder and method

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