JPS6136043B2 - - 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 subsequently annealing it in a non-oxidizing or reducing atmosphere with deoxidation, denitrification, and decarburization. γ, including cases where the carbon content is reduced to 0.4% by weight or less (the same applies to percentages below) through decarburization.
phase or mixed phase of γ phase and δ phase < less than or equal to (γ + δ)
The steel powder can be used as a steel powder in a phase state such as a main phase of γ or a mixed phase of a main phase of γ and a main phase of δ <hereinafter referred to as (γ + δ) main phase>, or a phase state in which these include some carbides. Compatible with 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 usually 10 to 50%. The sintered body using the atomized powder of this invention as a raw material powder is exposed to much harsher conditions than before due to the use of unleaded gasoline and LPG in internal combustion engines, which have seen significant increases in output in recent years.
Sufficient wear resistance is required as the valve slides under severe thermal shock every time the valve is operated at temperatures exceeding ~500℃, and damage and wear can occur on the contact surface with the valve. In addition, the present invention is intended to be suitable for use in other applications such as a cam ring or rotor of a power steering, a gear transmission part, or a high-temperature bearing material part, with a typical example being a valve seat member that is desired not to be supported. 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 component elements during sintering, and therefore, high-temperature and long-term sintering treatment is necessary. There are problems with deformation and quality variations caused by aging. 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:
A special atomized alloy powder containing 10-20% Co and 40-60% Co and exhibiting a spherical shape is used, but when the molten alloy is atomized with water, a large amount of CO gas is generated, causing pores inside the particles and on the surface. Open cavities are likely to be formed, and during sintering, due to the Kirkendall effect, voids are likely to be formed within the particles or at the boundaries due to diffusion. For this purpose, it is necessary to make the particle shape particularly spherical, and it also has the disadvantage that it cannot function satisfactorily as a hardening phase unless the diffusion of the component elements is suppressed by alloying or blending 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. Based on this basic concept, this invention uses iron powder such as pure iron powder, low-alloy steel powder, and stainless steel powder as a base material, and powders are prepared according to the mother alloy method (mother alloy method) in which the base material is blended with pure iron powder, low alloy steel powder, stainless steel powder, etc. It provides high alloy water atomized steel powder as a raw material powder suitable for manufacturing mechanical structural parts by metallurgical methods, C: 0.40% or less, Si: 1.50% or less, Mn;
0.40% or less, O; 1.00% or less, Cr; 10.0 to 40.0
%, Mo; 3.0 to 20.0% and W; 3.0 to 20.0% and /
or V; 3.0~20.0%, or further Ni; 3.0~
40.0% and/or Co; 3.0 to 40.0%, as water atomized raw steel powder, or C;
For high C water atomized steel powder exceeding 0.40%, the water quench hardening phase is removed in a non-oxidizing atmosphere or a reducing atmosphere at 900°C, preferably 1000°C or higher, until the C is below 0.40%, preferably below 0.20%. Charcoal annealing, simultaneous deoxidation, denitrification, coarsening of α or γ crystal grains, coarsening of carbides, and spheroidization precipitation, resulting in an apparent density of 2.00 to 3.20 g/cm ³ of the powder passing through an 80-mesh sieve, and molding. By providing irregular particle shape and compressibility with a compacted powder density of 6.00 g/cm ³ or more at a pressure of 7 t/cm ² , and increasing the effective area for diffusion of alloying elements by bringing them into close contact with the base steel powder particles, By promoting solid solution diffusion of α phase forming elements during solidification and without impairing it, γ
Through the synergistic effect of improving the diffusion of phase-forming elements, the base material is strengthened and its heat and wear resistance are further improved. In this case, the steel powder of the present invention blended into the base steel powder does not diffuse into solid solution to form a completely uniform composition, and the remaining diffused steel powder portion 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′ main phase,
An alloy consisting of (α + δ) main phase, γ or (γ + δ) main phase, and further formed into α main phase, γ main phase, or a mixture of the above phases by reduction annealing at an appropriate temperature and atmosphere. It is possible to produce steel powder, and by simultaneously reducing surface oxides, decarburizing annealing, and solution treatment, carbides, nitrides, intermetallic compounds, etc. are precipitated and solution treated.
Compressibility can be improved. In addition, the water atomization method has a wide range of conditions for producing irregular particles with an apparent density of 3.20 g/cm ³ or less due to the dynamic pressure friction and quenching effect of the jet water, and has excellent powder characteristics such as a wide particle size distribution. A suitable master alloy steel powder that is suitable for cold mold forming and has good diffusion of alloying elements during sintering due to the intertwining and adhesion of the particles due to the irregular particle shape. It can be said to be a manufacturing method. Now, C is one of the most important elements in each process of melting, component adjustment, injection, and water atomization. First, a hot metal pool is formed and the temperature of the hot metal is raised to 1600℃ or higher as soon as possible. Preferably
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 powder, as the C content of the poured molten metal increases, the number of particles with holes and cavities increases, and the shape of these 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%,
Eutectoid point in the Fe-C binary phase diagram, i.e. 0.80% by weight
It increases significantly when it exceeds . When using the steel powder 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. can be done. 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 done. 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 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 7t/ ^cm2 is It was found that the raw steel powder has a carbon content of 6.00 g/cm ³ or more, and the lower it is, the more the compressibility of raw steel powder is improved, and the deoxidation, decarburization,
Compressibility can be improved by denitrification annealing or solution treatment. 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, Si 1.50%
Alloying in excess of this will harden the steel powder and inhibit its 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%. Up to 1.00%, there is no problem in practical use, but 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. Cr, Mo, and V are all 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 Or content increases, the γ phase formation region decreases and the Cr; 19 to 20
% disappears completely. Therefore, by increasing the Cr content and lowering the C content, the raw steel powder becomes α+δ phase by water atomization, and the compressibility of the raw steel powder improves. However, when the Cr content exceeds 40.0%, the melting point exceeds 1550℃, and when the temperature drop during molten steel processing for injection of molten steel is taken into account, it reaches 1700℃.
Therefore, when using a small-diameter molten metal nozzle, it must be superheated to over 1800°C, which causes problems in melting work and molten steel processing, such as damage to the furnace wall. 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 base matrix, and impart thermal wear resistance. Considering workability
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%. W and V are carbide-forming elements and are particularly effective in improving hardness as a hardening phase, and solid solution diffusion of these elements is expected to strengthen the base and improve heat and wear resistance. If W exceeds 30% in the alloy, the melting point will increase and the solubility will deteriorate. Also, in the binary system phase diagram with Fe, the practical alloying amount range is 3.0 to 3.0 for the same reason as Mo.
It is 20.0%. Since V has the same effect as W, it can be replaced with W, or they may coexist.
In the binary system phase diagram with Fe, the α phase stability region is
The content is 1.6% or more, but 3.0% or more is required in consideration of compounding workability as a master alloy steel powder (master alloy powder) and solid solution strengthening of the base material. The upper limit is set at 20.0% to avoid the formation of σ phase. 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 matrix base material as a solid solution without impairing their diffusion, improving matrix reinforcement, 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 as a residual component; 50.0%
or more is required. When mixed with base steel powder as master alloy powder (master alloy powder) and sintered, pores and voids are created within the master 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 reason 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 used in powder metallurgy has poor sintering properties, making the surface of the sintered material rough and causing quality variations, so powder that passes through an 80 mesh sieve is More preferably, a powder that passes through a 100 mesh sieve is used. The same applies to the steel powder of this invention, so JIS Z
2504 to measure the apparent density of the powder that passed through an 80-mesh sieve, and use it at the above particle size. In this invention, the apparent density is determined by the contents of C, Si, Mn, Cr, W, V, Ni, and Co among the alloy components, the injection molten steel temperature (superheat amount), water pressure, and spray form among the water atomization conditions. It changes depending on. For example, if the amount of superheat is increased, the Mn content is increased, and the injected molten steel is scattered and dropped from the atomization point (hereinafter referred to as the focal point) using low water pressure, the dynamic pressure friction of the jet water will increase by the time the droplets solidify. The cooling action becomes slower and the particles become spheroidized and have a higher apparent density. 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 lowered and the injected molten steel is focused from the 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 dynamic pressure friction and cooling effect of the jet water. However, the apparent density becomes lower. Of the alloy components, Si, Cr, W, V,
Ni and Co are elements that promote irregular shapes. 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
It will be lower than 2.00g/cm ³ . If the C content is 0.80% or less, preferably 0.40% or less, water atomization can produce solid irregular particles that are completely free of pores and cavities to a virtually acceptable degree. . 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/
Steel powder lower than cm ³ could not be obtained. Green density at molding pressure 7t/ ^cm2 : 6.00g/ ^cm3
Regarding the above: Green powder density is measured according to JSPM Standard 1-64 by mixing 1% (outer frame) of zinc stearate as a lubricant in powder in advance. The steel powder of this invention is a high-alloy steel powder suitable for use as a mother alloy powder in 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 should no longer be treated as a base material. Now, generally speaking, the density of heat-resistant and wear-resistant sintered material is 6.50g/
cm ³ or more is required, and the more irregular the raw material powder particles are, the more the particles become entangled with each other and the contact area increases, and during sintering, the solid solution diffusion of alloying elements 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 steel powder of this invention is most preferably pure iron powder as the base material, and therefore the steel powder of this invention is most suitable for pure iron powder.
When compounded at 50.0%, the value regulated as the green powder density value at the same compacting pressure of the steel powder of this invention that satisfies the green powder density of 6.50 g/cm ³ at a compacting pressure of 7 t/cm ² is 6.00 g/cm 3 . ^cm3 or more. In other words, the green density of the mixed powder is based on the proportionate mixing law of the density of the plain green 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. , in order to obtain a green powder density of 6.50 g/cm ³ or more with a 50.0% blend, the steel powder alone of this invention must have a density of 6.00.
g/cm ³ or more is essential. Here, the molding pressure is 7t/
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 since the operating methods differ depending on the raw material situation, and the current situation is that the method is based on know-how based on an economic perspective based on metallurgical reactions. However, the inventors established a rapid melting method that is particularly 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 iron and steel works. This will be explained below in comparison with the normal method. The following table shows the comparison of the steel powder manufacturing method of the present invention in which C is not alloyed with the conventional method in terms of operation contents, purpose, and characteristics by period.

【table】

[Table] In addition, when alloying C, the steel powder production 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 steel, etc., the Cr reduction method is known as a non-oxidizing melting method in which the steel enters reduction refining from burn-through, or as one of the operating methods in a converter, but these methods In this method, raw materials are charged and melted, and Cr alloying agents such as Fe-Cr are added to the molten steel, but oxidation of Cr is unavoidable. However, only the alloying agent containing the recarburizer and Cr is charged into the hearth, heated and melted, and the temperature of the hot metal is quickly maintained at 1600℃ or higher, preferably 1700℃ or higher, and the alloying agents with the highest melting point are sequentially melted. By melting and reductively refining Si and Cr at high temperatures from beginning to end, it is possible to dissolve Si and Cr without oxidizing them. Therefore, in this invention, it is necessary to carefully select the recarburizing agent, alloying agent slag forming agent, and iron source.
This is because impurities are not particularly removed by oxidative refining such as P removal. In particular, the amount of carbon additive should be kept to a minimum to prevent oxidation of Si in the low temperature range from the initial stage of melting, and to avoid contamination with P, S and other impurities.
% or more, Si: 1.50% or less, and P, S and other impurities each preferably 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 carbon additive to melt the Cr-containing alloying agent, 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 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,
Fe-W, Fe-Mo, Fe-V or even metals
After melting Co and Fe-Ni (or metal Ni) in this order, the molten steel temperature was confirmed to be 1700°C, metal Si was added to adjust the Si, and finally, low-carbon rimmed steel pieces were added and melted. At this time, if the process from the start of melting to tapping is carried out in a fixed period of time, [C] or [Si]% - total amount of charged carbon or total amount of charged Si (%) - amount of C or Si combustion loss (%) will be constant. can be controlled. When C is not alloyed (C; 0.10% or less) or both C and Si are not alloyed (C; 0.10% or less,
(Si; 0.10% or less); After charging low carbon ferrochrome No. 1 (FCrL1) into the hearth and melting, apply full power to quickly maintain the molten steel temperature at 1700℃ or higher, and then adjust the temperature to meet the target composition. Ta
Fe-W, Fe-Mo, Fe-V, metal Co, Fe-Ni
After melting (metallic Ni) in this order, check that the molten steel temperature is 1700℃ and add metal Si to adjust the Si (however, Si;
(If it is less than 0.10%, do not add it).Finally, low carbon rimmed steel pieces were added and melted. Molten steel temperature is 1700℃
Since Cr oxide, Fe oxide, and Si oxide are not formed on the hot water surface, the alloying agent dissolves quickly.
Alloying yields of all alloying agents were 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 kept in a deoxidized state and became overoxidized, producing a large amount of steel slag of Cr oxide and Si oxide. 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 heated to 800 to 1000℃ in advance.
The molten metal is poured into a tundish which has been sufficiently heated as described above, and is injected from a nozzle made of a refractory material such as zirconia or alumina buried in the bottom of the tundish so that a columnar falling flow of 6 to 30 mmφ is obtained.
Steel powder is obtained by colliding high-pressure water of 180 kg/cm ² G with this columnar falling flow. The molten steel injection and water atomization atmosphere at this time are selected appropriately, but in order to obtain steel powder with a low O amount, an inert atmosphere is selected.
The O ₂ concentration is preferably 0.5% by volume or less.
In addition, the dehydration and drying atmosphere should be 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 a dehydration method, and the drying conditions are below 200℃. at a temperature of
Oxidation weight gain during drying can be ignored as long as drying is carried out under a vacuum higher than 100 torr or in an inert atmosphere with an O ₂ concentration of 3% by volume or less.

【table】

【table】

[Table] The embodiment of this invention shown in Table 1 is disclosed in Patent No. 892659.
This steel powder is water atomized by spraying high-pressure water using a water nozzle described in the specification (Japanese Patent Publication No. 52-19540). 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 numbers 7, 8, 9 and 10 are Mo
High apparent density high alloy steel powder that does not contain C;
These are high-alloy steel powders with a low apparent density of 2.41%, and both are comparative examples for the steel powders of the present invention. Comparative Examples 7, 8, 9, and 10 cannot satisfy the desired strength of the sintered material due to poor combustibility, and Comparative Example 11 has a carbon content far exceeding 0.80%, so the majority of the material is hollow. It became a shape particle. The photograph in FIG. 1 shows a cross-sectional photograph of the steel powder of the present invention in Example 5, and the cross-sectional photograph of the particle in Comparative Example 11 and the photograph of the particle shape taken by a scanning electron microscope are compared in FIG. 2 a and b. The steel powder of this invention is mainly used by cold molding a mixed powder (premix powder or master alloy powder) mixed with other steel powders using powder metallurgy methods, and therefore has the best compressibility and formability. This is one of the important characteristics. Table 2 shows water atomized raw steel powder (Example 2) consisting of an α-based phase with a C content of 0.2% or less,
A water-atomized raw steel powder (Example 3) consisting of an α'-based phase with a C content of 0.7% was subjected to decarburization annealing to reduce the C content to 0.4% or less, and the compressibility was improved (Example 3). 3A, 3B, 3C) Further, water atomized raw steel powder consisting of a γ phase or a γ-based phase with a C content of 0.40% or less and a green powder density of 6.00 g/cm ³ or more at a compacting pressure of 7 t/cm ² (Example 5, 6) and annealed powder 5A of Example 5,
Chemical analysis (O, C, N), green density, and Rattler value of 5B are shown. The Rattler value is JSPM standard 4-
This is the value measured at 69.

【table】

[Table] By annealing in this way, the water-quenched state of water atomization is restored, the α-phase or γ-phase crystal grains are coarsened, carbides are coarsened and spheroidized with decarburization, the surface oxide film is reduced, Denitrification further improves compressibility and formability. In the second, symbols 3A, 3B, and 3C are in pure hydrogen with a melting point of -40℃,
900℃×3hr and 1000℃ with temperature increase of 10deg/min respectively
×3hr and 1000℃×6hr Also, symbol 5-A is dew point-
Temperature increase in pure hydrogen at 40℃; 10℃/min, 1150℃×90
Figure 3 shows the results of the annealed powder that was annealed under the conditions of 10 minutes and then cooled in the furnace. Symbol 5-B is the result of the annealed powder under the conditions of 1000°C x 2 hours in a mixed gas of 75% by volume of _H2 and 25% by volume of _N2 with a dew point of 0°C, with the same temperature rise and fall. If annealing is performed in an atmosphere containing nitrogen, the steel powder will be nitrided and hardened, resulting in a slight decrease in compressibility. Therefore, it is preferable to perform annealing or solution treatment in an atmosphere that does not contain a nitriding source. Figure 4 shows commercially available water atomized iron powder (-80#).
The solid line shows the green powder density and Rattler value at a compacting pressure of 7 t/cm ² when the steel powder of this invention listed in Example 5 is blended. Commercially available stainless steel powder;
The density of green powder mixed with SUS316L (-100#) is shown by the chain line for comparison. As seen in FIG. 4, 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 3 shows examples 2 and 5 and their annealed powders 5-A, 5-B,
Comparative Examples 9 and 10 (-80#) and commercially available stainless steel powder; SUS316L (-100#) were manufactured by a mixed powder method (premix method) in which SUS316L (-100#) was blended as a master alloy steel powder (master alloy powder). Indicates the characteristics of the sintered body. The target composition of this sintered body is in weight%.
0.75C−3Cr−2Ni−4Mo−1W, and to match this, graphite powder (ACP500), ferromolybdenum powder (ground powder, -100#), ferrotungsten powder (ground powder, -100 #) was blended with 1% zinc stearate (outer frame) as a lubricant and 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 Z2505. Sintering conditions: temperature increase: 10℃/min, dewaxing: 600℃, 30 minutes,
Soaking temperature, time: 1150°C, 30 minutes, temperature drop: furnace cooling, atmosphere: H ₂ 75% by volume + N ₂ 25% by volume.

[Table] This result shows that when high-apparent-density high-alloy steel powder that does not contain Mo is used, the strength of the sintered body is inferior due to poor sinterability. Furthermore, the steel powder of the present invention has a lower sintered density than commercially available stainless steel powder; SUS316L, but has better sintered body strength. Furthermore, the strength of the sintered body can be adjusted by appropriately selecting the particle size of either or both of the steel powder and base material iron and steel powder of the present invention. Table 4
Example 5 was added to the master alloy steel powder (master alloy powder).
(-80#) is used as the base material, water atomized iron powder (commercially available). Note that both the target composition of the sintered body and the sintering conditions are the same as those in Table 3.

[Table] As described above, only the molten steel and hot metal pool containing Cr are rapidly heated and maintained at a high temperature in the region of preferential oxidation of either or both of the elements [C] and [Si]. , high Cr to prevent oxidation of Cr
In the melting process for alloy steel, large amounts of Cr oxide are generated, resulting in damage, such as a decrease in the fluidity of high-melting point Cr oxide steel slag, and undissolved alloying agents due to steel slag coating. Advantageously, rapid dissolution is possible.
The powder of the present invention can be easily produced by water atomizing the high-alloy steel produced in this manner, which improves productivity and accuracy in determining the amount of each alloy including C and Si. The steel powder according to this invention forms an α phase during sintering.
Since it contains both Cr and Mo, it has excellent sinterability, and Mo strengthens the base of the material.Also, although it contains W and V, they are elements that form α phase during sintering, so they impair sinterability. In particular, by forming carbides without oxidation, it improves heat and wear resistance.Furthermore, by creating a γ phase with Ni and Co, compressibility and formability are improved, and the heat, oxidation, and corrosion resistance of the base is improved. It is also useful for improvement, 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 and sintered filters, and furthermore, its use can be expected to expand as raw material powder for cutting tool steel materials and special stainless steel.

[Brief explanation of the drawing]

Figure 1 is a particle cross-sectional micrograph showing the steel powder of this invention in Example 5 (3% nital etched; Figure 2a shows that most of the particles are hollow because C is 2.41% by weight). Particle cross-section micrograph of Comparative Example 11 (nitric acid and vinegar mixture etching), Figure 2b
2 is a scanning electron micrograph showing the appearance of the particles in FIG. It is a graph showing an example of the blending ratio, green powder density, and Rattler value when water atomized iron powder and steel powder of the present invention are blended.

Claims (1)

[Scope of Claims] 1 Up to 0.40% carbon, up to 1.50% silicon, up to 0.40% manganese, up to 1.00% oxygen and from 10.0% to 40.0% chromium, up to 3.0% by weight
It has a composition containing up to 20.0% molybdenum, and further contains tungsten and/or vanadium in the range of 3.0% to 20.0%, together with substantially iron accounting for the remaining 50% or more, at a particle size that passes through an 80 mesh sieve. Apparent density is 2.00 to 3.20g/
cm ³ and a compacted powder density of 6.00 g/cm ³ or more under a compacting pressure of 7 tons/cm ² at a load per unit area. 2 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%
Contains up to 20.0% molybdenum, further contains tungsten and/or vanadium in the range of 3.0% to 20.0%, nickel and/or cobalt in the range of 3.0% to 40.0%, and substantially iron with the balance 50% or more. The apparent density at the particle size that passes through an 80-mesh sieve is
2.00 to 3.2 g/cm ³ , and the green density under a compacting pressure of 7 tons/cm ² as a load per unit area is 6.00 g/cm 3 .
High-alloy water atomized steel powder that is not ^less than cm3.