JPS6148561B2 - - Google Patents

Description

[Detailed description of the invention]

This invention involves blending high-alloy water atomized steel powder, especially pure iron powder, in an appropriate amount into the base material, as a representative example, along with a dispersion medium, graphite powder, and various metal or alloy powders, etc., if necessary. This paper proposes an improvement in water atomized steel powder that contains a high proportion of alloying components so that it can be advantageously used in the production of powder metallurgy sintered bodies as a so-called mixed powder method. The high-alloy water atomized steel powder of the present invention can be produced by simply undergoing a water atomization process, or by annealing that involves deoxidation, denitrification, and decarburization in a non-oxidizing or reducing atmosphere. Including cases where the carbon content is reduced to 0.4% by weight or less (the same applies to percentages hereinafter) through decarburization,
γ phase or mixed phase of γ phase and δ phase < less than or equal to (γ+
δ) phase>, or a mixture of γ main phase or γ main phase and δ main phase <hereinafter referred to as (γ + δ) main phase>, or as a steel powder in a phase state such that these contain some carbides. Suitable for use. This invention has irregular particle shapes obtained by water atomization, and under the improved compressibility resulting from the diffusion of γ phase forming elements without impairing the diffusivity of α phase forming elements, The aim is to improve the mechanical properties, particularly the heat resistance and wear resistance, of powder metallurgy products using alloyed water atomized steel powder. The high-alloy water atomized steel powder according to the present invention is used in powder metallurgy by being blended with a base material, that is, pure iron powder, low-alloy steel powder, or stainless steel powder, and the blending amount is suitably 10 to 50%. The sintered body made from the atomized powder of this invention as a raw material powder has been exposed to much harsher conditions than before due to the use of unleaded gasoline and LPG in internal combustion engines, where output has increased significantly in recent years.
Sufficient abrasion resistance is required as the valve slides while receiving severe thermal shock every time the valve is operated at temperatures exceeding 400 to 500℃, and there is no risk of damage or wear on the contact surface with the valve. Typical examples include valve seat members that are desired to be exposed and not exposed, and are also intended for use in other applications such as power steering cam rings and rotors, gear transmission parts, or high-temperature bearing material parts. In general, in the production of sintered bodies for this type of high-strength mechanical parts, the premix method, the prealloy method, and more recently the blending of hard particles have been developed. The premix method (single powder mixing method)
Single metal powders such as Cu, Mn, Cr, Ni, Mo, and Co, mechanically crushed powders of ferroalloys used as deoxidizers and alloying agents in the steelmaking and refining process, and their atomized powders are used as graphite powders and lubricants. With,
They are mixed and used according to the properties and composition required for the final product, but excellent properties are difficult to obtain due to insufficient diffusion of the component elements into the sintered body, which requires sintering at high temperatures and for long periods of time. This causes problems such as deformation and variations in quality. In the pre-alloy method (pre-alloyed steel powder method), alloyed steel powder is prepared with a composition that excludes C from the viewpoint of compressibility, but in order to meet the required properties in terms of heat resistance and strength, it is necessary to prepare alloyed steel powder in a composite composition of two or more components. Since the amount of alloy is increased, there are still problems with formability and compressibility.
Manufacturing high-density, high-strength materials is difficult. In addition, in the case of a method in which a special alloy powder with a stellite composition is used as the dispersed hardening phase and partially diffused into the base material, C: 1.0 to 3.0%, Cr: 20 to 40%, W:
Where an atomized special alloy powder consisting of 10 to 20% and 40 to 60% Co and exhibiting a spherical shape is used,
When the molten alloy is atomized with water, a large amount of CO gas is generated, which tends to create pores inside the particles and cavities that communicate with the surface, and during sintering, due to the Kirkendall effect, pores inside the particles due to diffusion and voids are likely to occur. For this purpose, it is necessary to change the particle shape to a particularly spherical shape, and it is also necessary to change the particle shape to a spherical shape, and also to
It also has the disadvantage that it cannot function satisfactorily as a hardening phase unless the diffusion of the component elements is suppressed by Co. On the other hand, high carbon Cr alloy powder, especially Fe-Cr type, Fe-
The method using Ni-Cr-based σ-phase powder is ineffective unless it is made into a fine powder such as subsieve powder, and the use of σ-phase powder with a wide range of particle size compositions is
It is no different from the premix method mentioned at the beginning, and when blending high carbon Cr alloy powder, C: 6.0 to 9.5 is usually used.
% of high hardness particles are dispersed in the base material to obtain wear resistance, but the atomization method has a problem in that it creates pores and cavities. Generally, the sintering of metal powder progresses as it is sintered at higher temperatures and for longer periods of time. However, even when iron powder is sintered at a high temperature, the sintering does not proceed much and a dense sintered body cannot be obtained.
This is because the diffusion of Fe is slower, and therefore it is an element that stabilizes the α phase during sintering, for example, an element that forms a γ loop with Fe, which is shown in a binary phase diagram.
By adding Si, Cr, Mo, W, V, Al, etc., it is possible to obtain a strong sintered body with solid solution strengthening of the added elements. Most of the methods for obtaining high-strength sintered bodies by powder metallurgy methods, such as the premix method (single powder mixing method) and the prealloy method (prealloyed steel powder method), are based on this fact. In this invention, based on this basic idea, powder metallurgy is carried out in accordance with the mother alloy method, in which steel powders such as pure iron powder, low alloy steel powder, and stainless steel powder are blended as a base material. The present invention provides high-alloy water atomized steel powder as a raw material powder suitable for manufacturing mechanical structural parts by a conventional method, with C: 0.40% or less, Si: 1.50% or less,
Mn: 0.40% or less, O: 1.00% or less, Cr: 10.0~
40.0%, Mo: 3.0~20.0% and further Ni: 3.0~40.0
%, Co: 3.0 to 40.0%, and water atomized raw steel powder as it is, or high C water atomized steel powder exceeding 0.40%, is hardened by water quenching. The phase is decarburized and annealed in a non-oxidizing atmosphere or a reducing atmosphere at 900°C, preferably 1000°C or higher, to C: 0.40% or less, and at the same time deoxidized,
Denitrification, coarsening of γ crystal grains, coarsening of carbides, and spheroidal precipitation caused the apparent density of the powder passing through an 80-mesh sieve to increase.
2.00 to 3.20 g/cm ³ , with a compacted powder density of 6.00 g/cm ³ or more at a compacting pressure of 7 t/cm ² , with an irregular particle shape and compressibility, and the effective area for diffusion of alloying elements by bringing them into close contact with the base steel powder particles. By increasing this, the base material can be further strengthened through the synergistic effect of improving the diffusion of the γ phase forming elements without impairing the solid solution diffusion of the α phase forming elements during sintering. The aim is to improve heat resistance and abrasion resistance over time. In this case, the steel powder of the present invention blended into the base steel powder does not diffuse into a solid solution to form a completely uniform composition, and the remaining undiffused steel powder portion also functions as a dispersed hardening phase together with the generated carbides. In producing the steel powder of this invention, the water atomization method is not only excellent in mass production and economy on an industrial scale, but also
Due to water quenching, depending on the alloy composition, α′-dominant phase, (α
+δ) Alloy steel powder consisting of a main phase, γ or (γ+δ) main phase, and further comprising an α main phase, a γ main phase, or a mixture of the above phases by reduction annealing at an appropriate temperature and atmosphere. The compressibility is improved by precipitating carbides, nitrides, intermetallic compounds, etc. and solution treatment through decarburization annealing and solution treatment at the same time as surface oxide reduction. be able to. In addition, the water atomization method uses the dynamic pressure friction and rapid cooling effect of the jet water to reduce the apparent density.
Irregular particles of 3.20 g/cm ³ or less are suitable for cold mold forming due to their powder properties such as a wide range of production conditions and a wide particle size distribution, and are made possible by the irregular particle shape. This can be said to be a suitable method for producing master alloy steel powder, which has good diffusivity of alloying elements during sintering due to the intertwining and adhesion of particles. Now, C is one of the most important elements in each process of melting, component adjustment, injection, and water atomization.It first forms a hot metal pool and quickly raises the hot metal temperature to 1600℃ or higher, preferably. teeth
By heating and maintaining the temperature above 1700℃, other alloying elements are dissolved in a reduced state due to preferential oxidation of C, suppressing oxidation of Si and Cr, and suppressing particle surface oxidation during water atomization. This is because it is useful. In water atomized steel powder, as the injection molten metal C content increases, the number of particles with pores and cavities increases, and the shape of such hollow particles tends to become spherical, and the surface becomes smooth, resulting in poor sinterability. Moreover, since it is hollow, high-strength materials cannot be obtained. These hollow particles differ somewhat depending on the alloy composition, but C
It is now recognized when the amount exceeds 0.40%,
It increases significantly when it exceeds the eutectoid point in the Fe-C binary phase diagram, that is, 0.80%. When using the steel of the present invention as a master alloy steel powder (master alloy powder) or a dispersion hardening phase, the amount of alloy C may be changed as appropriate depending on the properties required for the final product, especially the hardness, and the amount of alloying elements forming carbides. obtain. In this case, if the steel powder hardness is too hard, there will be problems such as damage to the mating material, so when using water atomized raw steel powder as is, the microvitkers hardness of the particle cross section should be set to 1000 or less. Therefore, the upper limit of C content is set to 0.40.
Must be %. In addition, when used as a master alloy steel powder (master alloy powder) or a dispersion hardening phase, it is important that it has excellent compressibility and formability. It hardens and forms α' phase or fine carbides when water atomized, impairing compressibility. C: By water atomizing molten steel with a concentration of 0.40% or less, preferably 0.20% or less, it is possible to produce raw steel powder in a phase state containing almost no α' phase, and the green powder density at a compacting pressure of 7 t/cm ² is 6.00 g/cm ³ or more, and the lower the C, the more the compressibility of raw steel powder is improved, and it is also possible to improve the compressibility of raw steel powder by deoxidizing, decarburizing, denitrifying annealing, or solution treatment. This can improve compressibility. For this reason, it is not necessary to set a lower limit value. In molten steel containing Cr, [C] or [Si] or both are increased to maintain the molten steel temperature in the preferential oxidation region of [C] or [Si]. When compressibility and moldability are important, the C amount is preferably 0.10%.
By injecting molten steel in the preferential oxidation region of [Si] and atomizing with water, the amount of steel powder O becomes 0.20% or less due to the protective coating formed on the surface of the particles. However, alloying with Si in excess of 1.50% hardens the steel powder and inhibits compressibility. Therefore, the upper limit is 1.50%. Although it is desirable for the oxide film on the surface of the steel powder particles to be thinner in terms of compressibility, sinterability, or dimensional stability, the O content of the master alloy steel powder (master alloy powder) or steel powder used as the dispersion hardening phase is 1%. However, if it exceeds 1.00%, the thickness of the oxide film becomes thick and inhibits the diffusion of alloying elements during sintering. Next, Mn is an element that tends to make particles spheroidal, impairing formability, and when the amount of Mn increases in molten steel containing Cr, the preferential oxidation region of [Mn] expands, and Mn
If it exceeds 0.40%, the oxidation of the particle surface during water atomization will become significant, and the generated MnO will be difficult to reduce during sintering and will inhibit sintering. Therefore, Mn needs to be 0.40% or less. Both Cr and Mo are α phase-forming elements, and form an α phase during sintering to promote sintering. Further, some of these alloying elements react with pre-alloyed C or blended graphite powder to form carbide. Cr and Mo are one of the basic components from the viewpoint of solid solution strengthening, sintering promotion, heat resistance, oxidation resistance, and carbide formation, and are important for melting workability as well as compressibility, sinterability, and other properties required for the final product. From this, the alloy composition and the blending amount when used in the mixed powder method are determined. In the binary system phase diagram with Fe, Cr forms an α phase during sintering in an amount of about 13% or more. The γ phase generation region is Cr
There is a C concentration range depending on the content, but as the Cr content increases, the γ phase generation region decreases, and Cr: 19 to 20
% disappears completely. Therefore, by increasing the Cr content and lowering the C content, the water atomized raw steel powder becomes α+δ phase, and the compressibility of the raw steel powder improves. However, when it exceeds 40.0%, the melting point
The temperature exceeds 1,550℃, and if the temperature drop during molten steel processing work for injecting molten steel is expected, a temperature of 1,700℃ or higher is required, and when using a small diameter molten metal nozzle.
It must be superheated to over 1800℃, which causes problems in melting operations and molten steel processing, such as damage to the furnace walls. Furthermore, when raw steel powder with a Cr content of more than 40.0% is annealed, the amount transformed into the σ phase increases, which impairs compressibility. Therefore, the upper limit for Cr is 40.0%. A high Cr content is desirable in order to blend the steel powder according to this invention as a master alloy steel powder, strengthen the matrix by solid solution diffusion into the matrix base material, and impart heat and wear resistance. Considering gender
The lower limit is 10.0%. By allowing Mo to coexist with Cr, α during sintering can be
It promotes phase formation and can strengthen the diffusion layer and improve heat and wear resistance due to the synergistic effect of solid solution diffusion. Although Mo is an element that promotes the σ phase transformation, by setting the annealing temperature of the water atomized raw steel powder to preferably 1000° C. or higher, the formation of the σ phase can be suppressed and the compressibility can be improved. In the binary phase diagram of Mo with Fe, the α phase stability range is 3 to 35%, but the practical alloying amount considering the sintering temperature in an industrial furnace is 3.0 to 35%.
It is 20.0%. Both Ni and Co are γ phase stable elements, so they can be used as γ phase in water atomized raw steel powder, or suppress the formation of σ phase during annealing, and promote the spheroidization of carbides, improving compressibility and formability. During sintering, the α-phase forming elements diffuse into the base material as a solid solution without impairing their diffusion, improving base strength, heat resistance, oxidation resistance, and corrosion resistance. In order to form a γ phase and improve compressibility, the content of Ni or Co or both elements must be 3.0% or more. These two elements together lower the melting point, promote dissolution, and improve the flow of the metal. However, if the alloy exceeds 40.0%, the γ phase will be stabilized and sinterability will be impaired. Also, from the economic point of view, it is preferable that the alloying amount of these elements is low. The steel powder of this invention has Fe: 50.0% as a residual composition.
or more is required. When mixed with base steel powder as master alloy powder and sintered, pores and voids are created within the mother alloy steel powder grains and inside and outside of the alloying element diffusion layer due to the Kirkendall effect, resulting in material deterioration. This often results in Therefore, this is suppressed by setting Fe to 50.0% or more. Next, the reasons for limiting the physical property values of the water atomized steel powder according to the present invention will be explained. Apparent density: 2.00 to 3.20 g/cm ³ Usually, coarse powder in powder metallurgy has poor sintering properties, and the surface of the sintered material becomes rough, causing quality variations, so powder that passes through an 80 mesh sieve is More preferably, powder that passes through a 100 mesh sieve is used, and the same applies to the steel powder of this invention, so JIS Z 2504
The apparent density of the powder passing through an 80-mesh sieve was measured by
Use the above particle size. In this invention, the apparent density is determined by the contents of C, Si, Mn, Cr, Ni, and Co among the alloy components and the water atomization conditions, especially the injection molten steel temperature (superheat amount), water pressure, and spray form. It's going to change. For example, increase the amount of super heat,
When the Mn content is increased and the injected molten steel is scattered and fallen from the atomization point (hereinafter referred to as the focal point) using low water pressure, the power friction and cooling effect of the jet water become slow by the time the droplets solidify, and the particles It becomes spherical and its apparent density increases. Furthermore, as the C content increases, when a large amount of CO gas is generated, the particles become hollow, and their surfaces become smooth due to expansion. When the apparent density exceeds 3.20 g/cm ³ and the apparent density becomes spheroidized, the segregation of blended powder and graphite powder becomes significant when cutting out the blended powder. Furthermore, the strength of the green compact becomes weak, making it impossible to convey the green compact, and the sinterability deteriorates, causing problems such as variations in the quality of the sintered material. Therefore, in this invention, the upper limit of the apparent density of steel powder is set to 3.20 g/cm ³ . On the other hand, if the amount of superheat is reduced and the injected molten steel is focused from a focal point using high water pressure and falls in the form of a water column, the droplets will solidify into irregular particles due to the sufficient dynamic pressure friction and cooling effect of the jet water. , the apparent density becomes lower. Among the alloy components, Si, Cr, Ni, and Co are elements that promote irregular shape formation. One of the reasons for this is thought to be that if an oxide with a solidification point much higher than that of molten steel is formed on the surface of the particles, the grains become irregular. Contains these irregular shape promoting alloying elements and has a C content of 0.80%
As the temperature increases beyond
Lower than 2.00g/ ^cm3 . If molten steel has a C content of 0.80% or less, preferably 0.40% or less, it is possible to produce solid irregular particles with virtually no problems or completely without pores or cavities by water atomization. . In addition, in the alloy composition of the steel powder according to the present invention, the apparent density of the water atomized raw steel powder is 2.00 g/cm ³ within the range of water atomization conditions shown in the examples.
No lower steel powder was obtained. Green density at a compacting pressure of 7t/ ^cm2 : 6.00g/cm3 or ^higher Green density is determined by adding 1% zinc stearate as a lubricant in the powder in advance according to JSPM Standard 1-64.
(Outer frame) Depends on the method of mixing and measuring. The steel powder of this invention is a high-alloy steel powder suitable for use as a mother alloy powder mixed into a base material of steel powder such as pure iron powder, low-alloy steel powder, or stainless steel powder. As mentioned above, the blending ratio is in the range of 10.0% or more and 50.0% or less. If this blending ratio is less than 10.0%, the effect of improving material quality will not be noticeable, and if it exceeds 50.0%, it will no longer be treated as a base material. In general, the density of heat-resistant and wear-resistant sintered materials must be 6.50 g/ ^cm3 or more. Dissolution diffusion is promoted and the material becomes tougher. Also, the higher the density, the tougher it becomes. Therefore, both the steel powder serving as the base material and the master alloy steel powder are required to have irregular shapes and high compressibility. The most suitable base material for the steel powder of the present invention is pure iron powder. Therefore, when a maximum of 50.0% of the steel powder of the present invention is blended with pure iron powder, the green powder density at a compacting pressure of 7 t/cm ² 6.50g/ ^cm3
The value regulated as the green density value of the single steel powder of this invention at the same compacting pressure that satisfies the following is 6.00.
g/cm ³ or more. In other words, the green density of the mixed powder is determined by the proportional mixing law of the density of the plain powder, and generally the green density of commercially available pure iron powder at a compacting pressure of 7 t/cm ² is 7.00 g/cm ³ or more. from,
In order to obtain a green powder density of 6.50 g/cm ³ or more with a 50.0% blend, it is essential that the steel powder alone of this invention has a density of 6.00 g/cm ³ or more. Here, the molding pressure of 7 t/cm ² is usually the maximum molding pressure that can be adopted from the viewpoint of mold life. Next, a method for producing water atomized steel powder according to the present invention will be described. The manufacturing feature of the steel powder of this invention lies in its melting method. In other words, among those skilled in the art, there is no unified method because operating methods differ depending on the raw material situation, and the current situation is that there is a strong focus on know-how based on economic viewpoints based on metallurgical reactions. The inventors have established a rapid melting method that is especially economical and improves the accuracy of C and Si, which are difficult to achieve target values, against the background of the raw material availability situation in integrated steelworks. This will be explained below in comparison with the normal method. The method for producing steel powder according to the present invention in which C is not alloyed is shown in the table below, comparing the operation details, purpose, and characteristics with the conventional method.

【table】

【table】

[Table] In addition, when alloying C, the steel powder manufacturing method of the present invention is similar to the conventional method in that the [C] deoxidation of molten steel by the carburizer works effectively until the end;
The invention method has a much better accuracy rate for C and Si. Conventionally,
In the refining of alloy steels, the Cr reduction method is known as a non-oxidizing melting method in which the steel enters reduction refining from burn-through, or as a method for operating in a converter. In this method, Cr is charged and melted, and Cr alloying agents such as Fe-Cr are added to the molten steel, but oxidation of Cr is unavoidable. However, by charging only the recarburizing agent or only the recarburizing agent and an alloying agent containing Cr into the hearth and heating and melting it, the temperature of the hot metal can be quickly raised to 1600°C or higher, preferably 1700°C.
It is possible to melt Si and Cr with almost no oxidation by maintaining the above temperature, melting the alloying agent in order from the one with the highest melting point, and carrying out reduction melting at a high temperature from beginning to end. Therefore, in this invention method, it is necessary to carefully select the carburizing agent, alloying agent, slag-forming agent, and iron source, since impurities are not particularly removed by oxidative refining such as de-S and de-P. It is. In particular, the amount of carburizing agent added should be kept to a minimum to prevent oxidation of Si in the low temperature range from the initial stage of melting as much as possible, and to avoid contamination with P, S and other impurities, C: 4.00% by weight. %that's all,
It is desirable that Si: 1.50% or less, P, S and other impurities each be 0.100% or less. In summary, not only when C is not alloyed, but also when C is alloyed, first Cr
Cr-containing alloying agent or iron pig iron (hot metal) is used as a recarburizing agent to melt the Cr-containing alloying agent to form the molten steel or hot metal pool, and rapidly heat it to 1600℃.
As mentioned above, by maintaining the temperature preferably at 1700°C or higher and using Si or C to bring [O] below the equilibrium value with [Cr], the subsequent steps can be carried out in a reduced state.
It is possible to shorten the melting time of other alloying agents and iron sources, improve the accuracy of target alloy composition, and control the combustion loss of Si or C using only time as a factor. Next, embodiments of this invention will be described. Regarding the preparation of the raw material molten steel necessary before water atomizing the steel powder of this invention, a melting method in an atmospheric atmosphere using a high frequency induction melting furnace will be described. When alloying C: Steelmaking pig iron (C: 4.40%, Si: 0.54%, Mn: 0.83
%, P: 0.096%, S: 0.034%) was charged to the hearth,
After heating and melting, the hot metal temperature was maintained at 1700°C or higher as quickly as possible by applying full power. Next, ferrochrome is charged and completely melted, depending on the target composition,
After melting Fe-Mo, metal Co, and Fe-Ni (or metal Ni) in this order, check that the molten steel temperature is 1700℃, add metal S to adjust Si, and finally add low carbon rimmed steel pieces. Melted. At this time, if the process from the start of melting to tapping takes a certain period of time, [C] or [Si] weight% = total amount of charged carbon or total amount of charged Si (weight%) -
C or Si combustion loss amount (wt%) can be constantly controlled. When C is not alloyed (C: 0.10% or less) or C
and Si (C: 0.10% or less, Si:
0.10% or less): After charging low carbon ferrochrome No. 1 (FCrL1) to the hearth and melting, apply full power to quickly maintain the molten steel temperature at 1700℃ or higher, and reduce Fe according to the target composition.
After melting −Mo, metal Co, and Fe−Ni (metal Ni) in this order, check that the molten steel temperature is 1700℃, and then add metal Si.
The Si content was adjusted (however, if Si was 0.10% or less, it was not added), and finally, low carbon rimmed steel pieces were added and melted. The molten steel temperature is as high as 1700℃, and Cr oxides and Fe
Since oxides and Si oxides were not formed on the hot water surface, the alloying agents were quickly dissolved, and the alloy yield of all alloying agents was over 95%. For the above melting method, first, low carbon rimmed steel, which is the iron source, is charged into the hearth and melted, and then 0.25% of Fe-Si is added as a deoxidizer to the molten steel heated to 1600℃. Then, when Fe-Cr was added, the molten steel could not be maintained in a deoxidized state and became overoxidized, producing a large amount of steel slag of Cr oxide and Si oxide, and the Fe-Cr added Cr was covered and could not be dissolved. In addition, Fe-Si was added as a deoxidizing agent at a Si content of 0.25%, and then steelmaking pig iron was added as a recarburizing agent, but most of the C was burned, resulting in bumping and molten steel. It was difficult to blow up and proceed with the melting work. Next, the target alloy composition was obtained by the melting method described above for the present invention, and the molten steel maintained at 1700° C. or higher was pulverized by a conventional water atomization method to obtain the steel powder of the present invention shown in Table 1. In the normal water atomization method, molten steel that has been melted and refined to a target alloy composition is placed in a tundish that has been sufficiently heated to 800 to 1000℃ or higher, and a molten metal nozzle made of a refractory material such as zirconia or alumina is buried in the bottom of the tundish. from 6
Inject to obtain a columnar falling flow of ~30mmφ,
High-pressure water of 30 to 180 kg/cm ² G is made to collide with this columnar falling flow from around it to obtain steel powder.
The molten steel injection and water atomization atmosphere at this time are selected as appropriate, but in order to obtain steel powder with a low O content, an inert atmosphere is used, and the O ₂ concentration is preferably 0.5% by volume or less. In addition, the dehydration and drying atmospheres are selected appropriately, and oxidation during dehydration can be ignored unless a vacuum filtration method is adopted in which air is forcibly supplied to the dehydrated steel powder layer as the dehydration method.
Oxidation weight gain during drying can be ignored as long as the drying is carried out at a temperature below 0.degree. C. under a vacuum higher than 100 torr or in an inert atmosphere with an O ₂ concentration of 3% by volume or more.

【table】

【table】

【table】

[Table] The embodiments of this invention shown in Table 1 are described in Japanese Patent No.
This steel powder is water-atomized by spraying high-pressure water using a water nozzle described in the specification of No. 892659 (Japanese Patent Publication No. 1989-19540). The alloy composition of the injected molten steel was almost the same as that of the water-atomized steel powder, except for the O content. Among these, Sample No. 6 is a high-apparent-density high-alloy steel powder that does not contain Mo, and Sample No. 7 is a low-apparent-density high-alloy steel powder with C: 2.41%, both of which are comparative examples for the steel powder of the present invention. Comparative Example 6 had poor sinterability and could not satisfy the desired strength of the sintered material, and Comparative Example 7 had a C content of more than 0.80%, so the majority were hollow particles. The steel powder of this invention is mainly used by cold molding a mixed powder (premix powder or master alloy powder) blended with other steel powders using powder metallurgy methods, and therefore compressibility and formability are of the utmost importance. This is one of its unique characteristics. Table 2 shows that the density of the green powder at a compacting pressure of 7 t/cm ² is 6.00 g/cm 2 and consists of a γ-based phase with a C content of 0.28%.
The green powder density and Rattler value of water atomized raw steel powder (Example 5) of cm ³ or more are shown. Furthermore, the Rattler value is
This is a value measured according to JSPM standard 4-69. Figure 1 shows commercially available water atomized iron powder (-80#).
The effect on green powder density at a compacting pressure of 7 t/cm ² when the steel powder of this invention listed in Example 5 is blended is compared with the green powder density when commercially available stainless steel powder: SUS316L (-100#) is blended. Compare and show. As seen in FIG. 1, it can be seen that the proportional mixing law holds true for the density of the green powder relative to the blending ratio of the mixed powder.

[Table] Table 3 shows commercially available water atomized iron powder (-80#), Examples 5 and 6 (-80#), and commercially available stainless steel powder:
The characteristics of a sintered body manufactured by a mixed powder method (premix method) in which SUS316L (-100#) is blended as a master alloy steel powder (master alloy powder) are shown. The target composition of this sintered body is 0.75C−3Cr−2Ni in weight%.
−4Mo−1W, graphite powder (ACP500), ferromolybdenum powder (pulverized powder, −
100#), ferrotungsten powder (crushed powder, -
100#) and 1% (outer frame) zinc stearate as a lubricant were mixed in a V-type mixer.
The sintered body was subjected to a tensile test and the sintered density was measured based on JSPM Standard 2-64 and JIS Z 2505. Sintering conditions: temperature increase: 10℃/min, dewaxing: 600℃, 30 minutes, soaking temperature, time: 1150℃, 30 minutes, temperature decrease: furnace cooling, atmosphere: H ₂ 75% by volume + N ₂ 25% by volume It is.

[Table] From the results, it can be seen that when a high apparent density high alloy powder containing no Mo (Comparative Example 6) is used, the strength of the sintered body is inferior due to poor sinterability. Furthermore, the steel powder of the present invention exhibits the same sintered body strength as commercially available stainless steel powder: SUS316L, despite having a lower sintered density. By heating and holding only the molten steel and hot metal pool containing Cr to a high temperature in the preferential oxidation region of either or both of [C] and [Si] elements as described above, Cr high to prevent oxidation of
Damage caused by the generation of large amounts of Cr oxides during the melting process of Cr alloy steel, such as high melting point Cr
Advantageously, it can be quickly melted without reducing the fluidity of oxide steel slag or unmelting the alloying agent due to steel slag coating, improving productivity and improving precision in determining the amount of each alloy such as C and Si. The steel powder of the present invention can be easily produced by water atomizing the high-alloy molten steel produced in this way. The steel powder of this invention forms an α phase during sintering.
It has excellent sinterability because it contains Cr and Mo, and by strengthening the base with Mo and creating a γ phase with Ni and Co, it improves compressibility and formability, and improves the heat resistance, oxidation, and corrosion resistance of the base. It is also useful, and is particularly suitable as a mother alloy steel powder (mother alloy powder) for producing heat-resistant and wear-resistant materials. The steel powder of the present invention can be used not only for heat-resistant and wear-resistant mechanical parts, but also for high-strength mechanical parts, sintered filters, etc., and can be expected to find expanded use as raw material powder for cutting tool steel materials and special stainless steel.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the blending ratio and green powder density when water atomized iron powder and steel powder of the present invention are blended.

Claims (1)

[Claims] 1 Carbon up to 0.40% by weight, silicon up to 1.50%, manganese up to 0.40%, oxygen up to 1.00% and chromium from 10.0% to 40.0%, from 3.0%
It has a composition containing up to 20.0% molybdenum, and nickel and/or cobalt in the range of 3.0% to 40.0%, together with substantially iron, which accounts for more than 50% of the balance, and has a particle size that passes through an 80 mesh sieve. High-alloy water atomized steel powder having an apparent density of 2.00 to 3.20 g/cm ³ and a green density of 6.00 g/cm ³ or more under a compacting pressure of 7 tons/cm ² as a load per unit area.