JPS6156283B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to iron powder with high compressibility for use in high-strength powder metallurgy products and a method for producing the same.In particular, the present invention relates to atomized iron powder by mixing reduced iron powder fine powder with unfinished reduced atomized iron powder. The present invention relates to an iron powder that improves sinterability without impairing compressibility and has excellent sintered tensile strength, and a method for producing the same. Unlike reduced iron powder, atomized iron powder has no pores in the iron powder particles, and has relatively high purity, so it has excellent compressibility. On the other hand, since the particle shape of atomized iron powder is relatively smooth compared to reduced iron powder, its specific surface area is also small. As a result, atomized iron powder has better compressibility than reduced iron powder, but has poorer sinterability and lower strength after sintering. By the way, various attempts have been made to improve the sintering strength of atomized iron powder. For example, according to Japanese Patent Publication No. 54-32404, a method is proposed in which unfinished reduced atomized iron powder and reduced iron powder are mixed and then subjected to finish reduction and crushing to take advantage of the excellent properties of both iron powders. Iron powder produced by simply mixing powders with a mesh ratio of 80 mesh or less and 90 wt% or more only exhibits characteristics depending on the mixing ratio of atomized iron powder and reduced iron powder. Compressibility, which is an excellent property, has to be sacrificed, and the sintering strength of atomized iron powder is only slightly improved. Generally, as the amount of fine iron powder increases, the specific surface area increases, sinterability improves, and sintering strength improves, but when fine powder is added to atomized iron powder products,
Compressibility, moldability, green compact strength, etc. deteriorate, making it difficult to use for powder metallurgy. An object of the present invention is to provide an iron powder having high compressibility for use in high-strength powder metallurgy products and a method for producing the same, and by providing the iron powder and the method for producing the same as described in the claims. can be achieved. Next, the present invention will be explained in detail. The iron powder of the present invention is produced by adding a predetermined proportion of fine reduced iron powder of 250 mesh or less to unfinished reduced water atomized iron powder (hereinafter water atomized iron powder is simply referred to as atomized iron powder) before finishing reduction. The iron powder obtained by the above treatment has the characteristics that the compressibility is not impaired after finishing reduction, the sinterability is improved, and the sintered tensile strength is excellent, and the blending ratio of the fine reduced iron powder is relatively small. Therefore, it is an iron powder that has the characteristic that there is no decrease in compressibility or deterioration in formability. That is, the iron powder of the present invention is an iron powder obtained by adding and mixing a relatively small amount of reduced iron powder fine powder in the range of 5 to 30 wt% to atomized iron powder before finishing reduction, and then finishing reduction. The finished reduced atomized iron powder used in the present invention is a known unfinished reduced atomized iron powder whose composition is not particularly specified, and its particle size is 90 wt% or more of 100 mesh or less, and 325
Good results can be obtained when the amount of mesh is 30wt% or less, and especially when the content of 325 mesh or less is within the range of 10 to 25wt%. On the other hand, if the particle size is less than 100 mesh and it becomes less than 90wt%, that is, if the coarse particles increase, it cannot be used for powder metallurgy, and even if reduced iron powder fine powder is added to unfinished reduced atomized powder with such a particle size, the strength will not be improved. Have difficulty. On the other hand, if the amount of atomized iron powder 325 mesh or less exceeds 30wt%, the amount of fine powder will further increase due to the addition of fine reduced iron powder, so even if such a mixture is processed at the highest finishing reduction temperature specified by the manufacturing method of the present invention. There still remains a large amount of fine powder with a particle size of 325 mesh or less, and when molding is performed using a mold, this fine iron powder enters the gap between the punch and die, causing so-called galling and shortening the life of the mold. By the way, the fine powder to be mixed with the unfinished reduced atomized iron powder is preferably reduced iron powder in consideration of formability and sinterability. The composition of the reduced iron powder may be the same as that of pure iron powder in the field of powder metallurgy, and differences in composition caused by differences in the iron oxides used as raw materials do not pose a problem. That is, the reduced iron powder can be made from mill scale, ore, etc. as a starting material, and the composition of the reduced powder does not need to be particularly specified. It is sufficient that the particle size of the reduced iron powder to be mixed is 250 mesh or less, and the ratio of 325 mesh or less is 80 wt% or more. If the 325 mesh is less than 80 wt%, the effect of improving sintering strength by mixing fine powder, which is a feature of the present invention, is small due to insufficient amount of fine powder, which is not preferable. Next, the mixing ratio of fine reduced iron powder to be mixed with unfinished reduced atomized iron powder will be described. In the present invention, if the mixed amount of reduced iron powder exceeds 30 wt%, compressibility decreases and formability rapidly deteriorates.
It becomes difficult to use as iron powder for powder metallurgy. Further, even if the amount of the reduced fine powder added is increased beyond this level, not only is no significant improvement in tensile strength observed, but also a decrease in hardness occurs, which is not preferable. Furthermore, if the mixing amount is less than 5%, improvements in tensile strength, hardness, etc. are seen, but only slightly, and the effects of the present invention are insufficient. Therefore, the amount of fine powder mixed should be appropriately determined within the range of 5 to 30 wt% depending on the required tensile strength, moldability, etc. There is no need to specify a method for mixing the unfinished reduced atomized iron powder and the reduced fine powder, and a known V-type or cone-type mixer can be used, and the mixing time is preferably in the range of 15 to 60 minutes. Next, the atmosphere for final reduction of this mixture is a reducing gas, preferably H ₂ gas or ammonia decomposition gas, and the CO+CO ₂ content of the gas before use is preferably 2% or less. Further, since the dew point of the atmosphere used is determined by the carbon of the mixed powder, it can be appropriately selected within the range of 0 to 15°C depending on the amount of carbon. In addition, the dew point is 0℃
If the temperature is less than 15°C, the amount of carbon remaining in the iron powder after finishing reduction will be high, the compressibility of the iron powder will be deteriorated, and the dew point will be 15°C.
If the dew point exceeds 0 to 15°C, it is not only difficult to reduce the amount of oxygen, but also sintering of the atomized iron powder and reduced iron powder becomes insufficient. The reduction temperature should be within the temperature range of 850-1050℃, preferably 900-1000℃
It is more preferable to fall within the range of . If the temperature is lower than 850°C, the mixed iron powder will remain as it is without being sintered with the atomized iron powder during final reduction, resulting in deterioration of formability and is not preferred as iron powder for powder metallurgy. Meanwhile 1050℃
If it exceeds this, it will become difficult to crush the resulting iron powder cake, and the crushing yield will drop significantly. The final reduction time is 20 to 150 to ensure sufficient deoxidation and decarburization.
minutes, preferably 30 to 90 minutes. A finished reduced cake of high-density iron powder with excellent sinterability can be obtained by the above process, but crushing can be performed by a known method. For example, a hammer-type crusher can be used, and other crushers may also be used as long as they can reduce 100 mesh or less to about 80 wt% or more in the crushing process. Next, the present invention will be specifically explained by comparing examples with comparative examples.

【table】

[Table] Unfinished reduced atomized iron powder and fine reduced iron powder having the composition shown in Table 1 were mixed for 20 minutes in a V-type mixer at the mixing ratio shown in Table 2. Table 3 shows the powder properties of the iron powder after these mixtures. The mixed iron powder was subjected to final reduction at 950°C for 45 minutes in ammonia decomposition gas with a dew point of 10°C. When finishing reduction is performed, the iron powder sinteres with each other and becomes cake-like. Table 4 shows the results of measuring the powder properties of the iron powder obtained by crushing it using a hammer-type crusher. Comparing the particle size distributions in Tables 3 and 4, the proportion of particles of 325 mesh or less decreases after finishing reduction. This is because the fine powder was sintered with each other or with the coarse powder and reduced during the final reduction.

【table】

【table】

[Table] Next, in order to investigate the characteristics of the green compact and sintered compact of the iron powder of the present invention, single Fe or Fe−2Cu−
Copper powder and graphite powder were added to give a composition of 0.8C, and 1wt% of zinc stearate was added as a lubricant.
After mixing for 15 minutes using a V-type mixer, green compacts of various shapes were formed, and the properties of the green compacts and sintered bodies were measured. The properties of the green compact, such as green density, Rattler value, and transverse rupture strength of the green compact, were measured and the following results were obtained. As shown in FIG. 1, the green powder density of Examples 1 and 2 is equivalent to that of Comparative Example 1 of atomized iron powder without the addition of fine powder. However, as shown in Comparative Examples 4 and 5, when the amount of fine powder mixed exceeds 30 wt%, the green density tends to decrease. Therefore, it was found that if the amount of fine powder mixed is 30% or less, the compressibility does not decrease due to the mixing of fine powder. The measurement results of Rattler values are shown in Figure 2. When atomized iron powder is mixed with atomized iron powder (Comparative Examples 2, 3, and 4), the Rattler value rapidly deteriorates as the amount of the mixture increases. However, the rattler value of the mixed reduced iron fine powder is 1.0% or less if the mixed amount is 30 wt% or less, and is almost the same as Comparative Example 1 in which the fine powder is not mixed. Therefore, it was found that deterioration of formability would not be a problem if the reduced iron powder was mixed at 30 wt% or less. Figure 3 shows the measurement results of the transverse rupture strength of the compact. When atomized iron powder is mixed (Comparative Examples 2, 3,
4) The transverse rupture strength of the green compact was determined by mixing fine powder in Comparative Example 1.
It is decreasing more. However, the transverse rupture strength of the green compact of the present invention is slightly superior to that of Comparative Example 1. Therefore, it can be said that there is no deterioration in the transverse rupture strength of the green compact due to the mixing of fine reduced iron powder. From the above measurement results of green powder density, Rattler value, and green compact transverse rupture strength, the compact properties of the iron powder of the present invention are superior to atomized iron powder without mixing fine powder in terms of compressibility, formability, and green compact strength. The properties are about the same, and it can be said that according to the production method of the present invention, there is no deterioration in the green compact properties due to the mixing of fine powder. Next, the green compact is placed in an ammonia decomposition gas atmosphere.
After dewaxing at 600°C for 30 minutes, it was sintered at 1120°C for 30 minutes. The sintered density, tensile strength, etc. of this sintered body were measured. These results are discussed below. As shown in Figure 4, in the present invention, the sintered density is not as bright as the atomized iron powder that is not mixed with fine powder, and it can be said that if 30% or less of fine powder is mixed, there is no decrease in sintered density. can. Next, the results of measuring the tensile strength of the sintered body are shown in FIG. Comparative example 2 in which atomized iron powder was mixed,
In samples 3 and 4, an increase in tensile strength was observed due to an increase in the amount of fine powder, but the increase was slight. However, the tensile strength of the product of the present invention containing reduced fine powder is improved by about 5 kg/mm ² compared to the comparative example. This is considered to be because the sinterability was improved by mixing the fine reduced iron powder.
Figure 6 shows the measurement results of the elongation of a sintered body containing only Fe, and the elongation increases as the amount of fine powder increases. Therefore, it can be said that according to the present invention, both tensile strength and elongation can be improved by improving sinterability by mixing fine powder. Figure 7 shows the measurement results of the hardness of the sintered body. The hardness has a maximum value when the fine powder mixture amount is 30 wt%, and the maximum value is H compared to Comparative Example 1 in the present invention in which reduced iron powder is mixed.
_R B is about 15 larger. The characteristics of the sintered body of the iron powder of the present invention, which is a mixture of atomized iron powder and fine reduced iron powder, are significantly higher than those of Comparative Example 1 in which the fine powder is not mixed, and Comparative Examples 2, 3, and 4 in which fine atomized iron powder is mixed. All properties have been improved through significant improvements. In particular, the tensile strength can be improved by 5 kg/mm ² and the hardness can be improved by about 15 in H _R B, which is a great effect. As described above, the iron powder of the present invention has a relatively small amount of reduced iron powder added to the atomized iron powder before final reduction, so that the iron powder has good sinterability without deterioration of green compact properties.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the amount of reduced iron powder mixed into atomized iron powder and the green density.
The figure shows the relationship between the mixed amount of reduced iron powder fine powder mixed in atomized iron powder and the green powder density. Figure 2 shows the relationship between the mixed reduced iron powder fine powder mixed amount in atomized iron powder and the Rattler value. Figure 3 is a diagram showing the relationship between the amount of reduced iron powder mixed into atomized iron powder and the transverse rupture strength of the green compact, and Figure 4 is a diagram showing the relationship between reduced iron powder and fine powder mixed into atomized iron powder. Figure 5 is a diagram showing the relationship between the mixing amount and sintered density. Figure 5 is a diagram showing the relationship between the amount of reduced iron powder mixed in the atomized iron powder and the tensile strength. Figure 6 is the relationship between the amount of reduced iron powder mixed in the atomized iron powder and the tensile strength. Figure 7 shows the relationship between the mixed amount of reduced iron powder and elongation.
The figure is a diagram showing the relationship between the amount of reduced iron powder mixed in the atomized iron powder and the hardness.

Claims (1)

[Scope of Claims] 1. A mixture consisting of unfinished reduced water atomized iron powder and reduced iron powder subjected to finishing reduction is crushed by a conventional method after finishing reduction to have a particle size ratio of 100 mesh or less.
In iron powder for powder metallurgy products consisting of 80 wt% or more, the mixture has a particle size ratio of 100 mesh or less.
Unfinished reduced water atomized iron powder consisting of 90wt% or more and a particle size ratio of 325 mesh or less is 30wt% or less, and the remainder is finished reduction consisting of 80wt% or more of a particle size ratio of 325 mesh or less. An iron powder with high compressibility for use in high-strength powder metallurgy products, characterized by comprising iron powder. 2 Unfinished reduced water atomized iron powder 70~ consisting of a particle size ratio of 100 mesh or less of 90wt% or more and a particle size ratio of 325 mesh or less of 30wt% or less
The particle size ratio is 95wt% and the remainder is 325 mesh or less.
A mixture consisting of reduced iron powder that has been subjected to finish reduction of 80wt% or more is heated to 850% in a reducing atmosphere with a dew point of 0 to 15℃.
After finishing reduction by a conventional method within a temperature range of ~1050℃, the resulting finished reduction cake was crushed by a conventional method.
A method for producing iron powder having high compressibility for use in high-strength powder metallurgy products, in which the proportion of powder of 100 mesh or less is 80 wt% or more.