JP6409953B2 - Method for producing alloy steel powder for sintered member raw material - Google Patents

Description

  The present invention relates to a method for producing alloy steel powder for sintered member raw material, and in particular, the alloying element when producing alloy steel powder containing an alloying element that is easily oxidized like Cr by the water atomization method. It is related with the method which can suppress the oxidation of and can manufacture an alloy steel powder stably.

  Powder metallurgy, in which iron powder or alloy steel powder is compressed into a desired shape using a mold and then sintered, is a technology that can manufacture machine parts having complex shapes at low cost, for example, automotive parts It is used in a wide range of applications, such as manufacturing. As iron powder or alloy steel powder (hereinafter sometimes simply referred to as “iron powder”) used as a raw material in powder metallurgy, solid-phase reduction of mill scale or iron ore using a carbon source such as coke as a reducing agent Sponge iron powder obtained by the above, water atomized iron powder pulverized by jetting a high-pressure water jet onto molten steel adjusted to a predetermined component, and the like are industrially produced.

  The iron powder produced by any method has a quality suitable for a raw material for powder metallurgy by performing a heat treatment (finish reduction treatment) in which annealing is performed in a reducing atmosphere such as hydrogen. In the heat treatment, carbon and oxygen contained in the iron powder are removed, strain contained in the iron powder particles is removed, and crystal grains grow.

  When a member requiring particularly high strength is produced by powder metallurgy, alloy steel powder to which an alloying element is added is used as a raw material powder. At that time, by using an element having a high effect of improving hardenability as the alloying element, it is possible to promote the action of the graphite mixed in the raw material powder diffusing into the raw material powder particles to form a strengthened structure. Among them, Cr has a high effect of improving hardenability despite its relatively low cost, and therefore, alloy steel powder containing Cr as a main alloying element and its application have been extensively studied.

  Alloy steel powder (Cr-containing alloy steel powder) containing Cr as an alloying element is preferably produced by a water atomization method. An example of a production flow of Cr-containing alloy steel powder using the water atomization method is shown in FIG. Although it is desirable to use high-purity materials such as electrolytic iron and base metal as the iron source as the main raw material, low-cost and relatively high-purity materials such as molten steel smelted in converters and high-purity scrap are also industrial. Can be used. The iron source is heated and melted, and a Cr source, other alloying elements, and auxiliary materials such as a slag component and a carburized material are added as necessary to obtain a raw material molten steel. Next, the raw molten steel is pulverized by a water atomizing method to form a water-atomized iron-based powder. In the water atomization method, molten steel is pulverized and solidified by spraying high-pressure water on the raw molten steel flowing out from the tundish nozzle. The obtained water atomized iron-based powder is further subjected to a heat treatment (finish heat treatment) for reduction, and a Cr-containing alloy steel powder suitable for producing a high-strength sintered member is obtained.

  However, since Cr is an element that is more easily oxidized than Fe, as described above, it is easily oxidized when the iron-based powder is produced by the water atomization method. When the amount of oxygen contained in the raw material powder increases, the compressibility during pressure forming decreases, so in order to produce high-quality Cr-containing alloy steel powder as raw material powder for sintered members, There is a need to reduce the amount of oxygen contained. Therefore, various methods have been proposed to reduce the amount of oxygen in the alloy steel powder.

  For example, Patent Document 1 discloses a method of reducing water atomized iron-based powder containing Cr as an alloying element by heat treatment in a vacuum, not in a reducing atmosphere. In the method, carbon contained in the water atomized iron-based powder functions as a reducing agent.

  Patent Document 2 discloses a water atomized iron-based powder containing Cr, Mo, and Mn as alloying elements, wherein the oxygen to carbon weight ratio O: C is 1 to 4, and the water atomized iron-based powder is dew point. Discloses a method of reducing in a controlled reduced pressure atmosphere.

In Patent Document 3, when a water atomized iron-based powder is heat-treated in an H ₂ gas atmosphere containing H ₂ O gas, the oxygen potential in the furnace is measured, and the amount of H ₂ O gas is determined based on the result. A method of adjusting is disclosed.

  In Patent Document 4, water atomized iron-based powder is heated in an inert gas atmosphere, the amount of CO gas generated at that time is monitored, and the CO gas is exhausted when the CO gas generation amount increases. A method is disclosed. By the method, the amounts of carbon and oxygen in the iron-based powder are reduced to C: 0.005% and O: 0.10%, respectively.

JP-A-55-62101 JP 2010-159495 A Special Table 2000-514875 Special Table 2002-501123

  According to the methods disclosed in Patent Documents 1 to 4, it is possible to reduce the amount of oxygen contained in the alloy steel powder by reducing the water atomized iron-based powder containing Cr by heat treatment. However, since the oxidation of Cr mainly proceeds in the step of obtaining the iron-based powder before heat treatment, that is, the process of water atomizing the raw molten steel, in the conventional method, the Cr-containing iron-based powder is converted into the water atomizing method. Therefore, there is a problem that it cannot be stably manufactured.

  FIG. 3 is a diagram schematically showing a water atomizing apparatus 100 that is generally used for the production of iron-based powder. In the melting furnace 1, the raw molten steel 2 having a predetermined component composition is produced, and then the raw molten steel 2 is transferred to the tundish 3. The raw molten steel 2 passes through a molten steel nozzle 4 provided at the bottom of the tundish 3 and falls into the spray tank 6 as a molten steel flow 5. The molten steel flow 5 is pulverized by a high-pressure water jet 8 ejected from a water nozzle 7 to become a water atomized iron-based powder 9.

  At this time, the temperature of the raw molten steel 2 flowing down from the molten steel nozzle 4 is rapidly lowered by contacting with the surrounding atmosphere. As a result, the solubility of oxygen in the molten steel decreases, and oxygen above the saturation solubility reacts with Cr to produce Cr oxide. Part of the generated Cr oxide is deposited in the vicinity of the molten steel inlet 10, which is the tip of the molten steel nozzle 4, so as to close the molten steel inlet 10.

  As a result of the deposition of Cr oxide as described above, the molten steel injection amount decreases with time, and the production efficiency of the water atomized iron-based powder decreases. When the deposition of Cr oxide further proceeds, the molten steel inlet 10 is finally closed, so that it is necessary to stop the operation in order to remove the deposit, and the production efficiency is further reduced.

  Moreover, when the amount of molten steel injection | pouring reduces with time, the particle size, particle shape, etc. of the water atomized iron base powder obtained will change in connection with it. This leads to variations in the quality of the produced alloy steel powder, and as a result, it becomes difficult to produce an alloy steel powder suitable as a raw material for a sintered member.

  Thus, when Cr is added to improve the hardenability, problems such as a reduction in production efficiency due to the formation of Cr oxide in the molten steel and variations in the quality of the steel powder occur. Could not be produced efficiently and stably by the water atomization method. Since all of the conventional techniques disclosed in Patent Documents 1 to 4 relate to the treatment after obtaining the iron-based powder by the water atomization method, the above problems cannot be solved.

  The present invention has been made in view of the above circumstances, and suppresses oxidation of Cr that occurs when an iron-based powder containing Cr that is easily oxidized is produced by the water atomization method, and the Cr-containing alloy steel powder is made efficient. In particular, it is an object of the present invention to provide a method for stably producing. In addition, an object is to obtain dense powder particles with few pores inside the particles.

The gist configuration of the present invention is as follows.
1. A method for producing alloy steel powder for a sintered member raw material,
A water atomization process in which molten steel is water atomized to form a water atomized iron-based powder;
The water atomized iron-based powder has a heat treatment step of performing a heat treatment to obtain an alloy steel powder for a sintered member raw material,
The C content [C] (mass%) in the molten steel and the Cr content [Cr] (mass%) in the molten steel satisfy the relationship of the following formula (1),
The alloy steel powder for sintered member raw material is in mass%,
Cr: 0.3-3.5% and Mn: 0.08% or less,
The manufacturing method of the alloy steel powder for sintered member raw materials which has a component composition which consists of remainder Fe and an unavoidable impurity.
Record
0.10 ≦ [C] / [Cr] ^2/3 ≦ 0.35 (1)

2. The component composition of the alloy steel powder for sintered member raw material is mass%,
Mo: 0.1 to 2.0%
The manufacturing method of the alloy steel powder for sintered member raw materials of said 1 which further contains as an alloying element.

3. The molten steel contains 0.01 to 0.1% by mass in total of oxidizable elements whose standard free energy of formation of oxide is lower than that of the alloying element contained in the alloy steel powder for the sintered member raw material The manufacturing method of the alloy steel powder for sintered member raw materials of said 1 or 2 which does.

4). 4. The method for producing alloy steel powder for sintered member raw material according to 3 above, wherein the easily oxidizable element is 1 or 2 or more selected from the group consisting of Si, V, Ti, and Al.

  According to the present invention, the oxidation of Cr that occurs when an iron-based powder containing Cr as an alloying element is produced by the water atomization method is suppressed, and a Cr-containing alloy steel powder is produced efficiently and stably. be able to.

It is a figure showing the manufacture flow of Cr content alloy steel powder in one embodiment of the present invention. It is a figure showing an example of the manufacturing flow of the conventional Cr containing alloy steel powder using the water atomization method. It is the figure which showed the general water atomization apparatus typically.

  Next, a method for carrying out the present invention will be specifically described. In addition, in the following description, the “%” indication regarding the component means “% by mass” unless otherwise specified. The “iron-based powder” refers to a metal powder having an Fe content of 50% or more.

  The method for producing alloy steel powder for a sintered member raw material of the present invention includes a water atomization step of obtaining a water atomized iron-based powder by water-atomizing molten steel, and subjecting the water atomized iron-based powder to a heat treatment for reduction. A heat treatment step for obtaining alloy steel powder.

  In FIG. 1, the manufacturing flow of Cr containing alloy steel powder in one Embodiment of this invention is shown. First, a raw material molten steel is manufactured by melting an iron source. As said iron source, arbitrary things, such as converter molten steel and a high purity scrap, can be used. A high-purity iron source such as electrolytic iron can also be used, and a plurality of types of iron sources can be used in combination. In the production of raw molten steel, a Cr source and other alloying elements can be added to the iron source so that an alloy steel powder having a desired component composition is finally obtained. Moreover, a carbonaceous material, other auxiliary materials (slag component etc.), and the "easy-oxidizable element" mentioned later can also be added as needed.

  Any Cr source can be used. Examples of the Cr source that can be used include ferrochrome and metallic chromium. The alloying element can be added in any form such as the alloying element alone (metal), an alloy containing the alloying element, a compound containing the alloying element, and the like. For example, metal manganese or ferromanganese can be used as the Mn source. Any carbon-containing material can be used as the carbon material. Examples of the carbon-containing material include an iron material having a high carbon concentration, such as cast iron, in addition to a carbon material such as coke and graphite powder.

  The raw molten steel obtained as described above is poured into a water atomizer and pulverized to obtain a water atomized iron-based powder. The production of the water atomized iron-based powder by the water atomization method is not particularly limited, and any water atomizer such as the one shown in FIG. 3 can be used.

  Thereafter, the obtained water atomized iron-based powder is subjected to heat treatment for reduction, whereby alloy steel powder for sintered member raw material containing Cr is produced. For the heat treatment, any method can be used as long as it can reduce the water atomized iron-based powder, such as the methods described in Patent Documents 1 to 4.

  By the heat treatment, the water atomized iron-based powder is reduced to remove carbon and oxygen. In addition, the iron-based powder is annealed by the heat treatment, the strain contained in the iron powder particles is removed, and crystal grains grow. The amounts of C and O contained in the alloy steel powder after the heat treatment are preferably C: 0.1% by mass or less and O: 0.2% by mass or less. What is necessary is just to adjust the conditions of heat processing according to the quantity of C and O contained in the water atomized iron-base powder.

[C and Cr content of molten steel]
In the present invention, the C content [C] (mass%) in the molten steel subjected to water atomization and the Cr content [Cr] (mass%) in the molten steel satisfy the relationship of the following formula (1). It is important to.
0.10 ≦ [C] / [Cr] ^2/3 ≦ 0.35 (1)
By adjusting the C content according to the Cr content so as to satisfy the above formula (1), an iron-based powder containing Cr as an alloying element is efficiently and stably produced by the water atomization method. can do. The reason will be described below.

When C is present in the molten steel, the C reacts with O to generate CO gas. Therefore, if the C content is adjusted so that the C content with respect to the Cr content is a certain ratio or more, specifically, 0.10 ≦ [C] / [Cr] ^2/3 , C becomes O and The reaction in which CO gas is generated by reaction occurs preferentially over the reaction in which Cr reacts with O to produce Cr oxide. As a result, Cr oxide is prevented from being generated during water atomization and adhering to the molten steel injection nozzle port, and the molten steel can be injected stably. A more preferable range is 0.15 ≦ [C] / [Cr] ^2/3 .

On the other hand, the higher the C content, the higher the effect of suppressing the formation of Cr oxide. Therefore, it is preferable to increase the C content from the viewpoint of preventing the adhesion of Cr oxide. However, if the C content becomes excessively high, the amount of CO gas generated increases, and the generated CO gas remains in the atomized iron-based powder, forming voids. Therefore, in order to suppress the formation of the vacancies, the C content is adjusted so that [C] / [Cr] ^2/3 ≦ 0.35. A more preferable range is [C] / [Cr] ^2/3 ≦ 0.25.

In the above equation (1), a suitable range of [C] is defined by a ratio to [Cr] ^2/3 . This is because [C] and [Cr] ^{2 represent} whether the reaction represented by the following formula (2) in which Cr ₂ O _3, which is an oxide of Cr, is reduced by C is established thermodynamically. ^This is because it is determined by the ratio of ^{/ 3} .
C + (1/3) Cr ₂ O ₃ → (2/3) Cr + CO (2)

  The C content of the raw material molten steel can be controlled by adjusting the input amount of the carbonaceous material in the step of melting the iron source. Similarly, the Cr content in the raw molten steel can be controlled by adjusting the amount of Cr source added when the molten steel is produced. Therefore, it is preferable to control the addition amount of the carbonaceous material and the Cr source at the time of manufacturing the molten steel so as to satisfy the relationship of the above formula (1).

  The alloy steel powder produced by the method of the present invention contains Mn and optionally Mo as alloying elements in addition to Cr. However, Mo is less likely to be oxidized than Cr, and Mn is more easily oxidized than Cr, but its amount is 0.08% by mass or less, which is sufficiently small compared to the amount of Cr, so long as the conditions of the present invention are satisfied. Further, oxidation of alloying elements other than Cr is suppressed.

  In the conventional techniques as disclosed in Patent Documents 1 to 4, attention has been paid to the conditions when the iron-based powder obtained by the water atomization method is reduced by heat treatment. Thus, it has not been performed to control the relationship between the C content and the Cr content in the molten steel during water atomization. In addition, it has not been known that such control can improve the operational stability and suppress the formation of pores in the iron-based powder. For example, Patent Document 2 discloses a water atomized iron-based powder containing Cr: 2.5 to 3.5% and C: 0.1 to 0.9%. Selected regardless of content.

[Easily oxidizable elements]
In the present invention, the molten steel used for water atomization can further contain an easily oxidizable element. Here, the “easily oxidizable element” means an element whose standard free energy of formation of oxide is lower than an alloying element contained in an alloy steel powder described later. For example, when the alloy steel powder contains Cr and Mn, the easily oxidizable element means an element having a lower standard free energy of formation of oxide than both Cr and Mn. Moreover, when alloy steel powder contains Cr, Mn, and Mo, the said easily oxidizable element means the element whose standard formation free energy of an oxide is lower than any of Cr, Mn, and Mo. However, among Cr, Mn, and Mo, since Mn is most likely to form an oxide (the standard free energy of formation of the oxide is the lowest), the oxidizable element is a standard of oxide rather than Mn. It can also be regarded as an element with low free energy of formation (easily oxidized).

  As the easily oxidizable element, for example, Si, V, Al, Ti, or the like can be used. As the easily oxidizable element, only one element can be used, or a plurality of elements can be used in combination.

  The easily oxidizable element reacts with oxygen dissolved in the molten steel to become an oxide, thereby reducing the amount of molten oxygen in the molten steel. Therefore, by adding an easily oxidizable element to the molten steel, when water atomization is performed, even if the molten steel is injected from the molten steel inlet and the temperature of the molten steel decreases, the oxygen in the molten steel is less likely to be saturated, and the alloy Formation of oxides of chemical elements is suppressed. By this action, adhesion of the alloying element oxide to the molten steel nozzle is further suppressed, and the operation is further stabilized. Moreover, the generation amount of CO gas is also suppressed, and as a result, the formation of pores in the water atomized iron-based powder is suppressed.

  The total content of the easily oxidizable elements in the molten steel is preferably 0.01 to 0.1% by mass. If the total content of easily oxidizable elements is less than 0.01% by mass, the above-described effects cannot be obtained sufficiently. In addition, since the oxide of an easily oxidizable element is absorbed by the slag on the surface of the raw molten steel, the oxidizable element that is inevitably contained as an impurity is not mixed into the molten steel stream to be atomized. However, when the total content of easily oxidizable elements exceeds 0.1% by mass, the amount mixed into the molten steel flow increases, and the oxides of the easily oxidizable elements adhere to the molten steel inlet and cause operational instability. This is not preferable.

[Component composition of alloy steel powder]
The alloy steel powder for sintered member raw material in one embodiment of the present invention contains Cr: 0.3 to 3.5% and Mn: 0.08% or less as alloying elements, with the balance being Fe and inevitable impurities. It has a certain composition. Moreover, Mo: 0.1-2.0% can also be further contained as an alloying element as needed. Hereinafter, the reasons for limiting the component composition will be described.

Cr: 0.3-3.5%
Cr is an element having a function of improving hardenability and improving tensile strength and fatigue strength of the sintered member. Further, Cr has the effect of increasing the hardness after heat-treating the sintered member and improving the wear resistance. In order to obtain these effects, the Cr content is set to 0.3% or more. On the other hand, if the Cr content exceeds 3.5%, the amount of Cr oxide generated during sintering increases, and the generated oxide becomes the starting point of fatigue failure, and the fatigue strength of the sintered member is increased. Reduce. Therefore, the Cr content is 3.5% or less. The Cr content is preferably 0.5 to 3.5%, more preferably 1.0 to 3.5%. In addition, according to the method of this invention, since the oxidation of Cr in molten steel is suppressed, the decrease in the amount of Cr in molten steel due to precipitation of Cr oxide hardly occurs. Therefore, in order to make the Cr content in the alloy steel powder for sintered member raw material of the present invention within the above range, the Cr content of the molten steel used in the water atomization process should be 0.3 to 3.5%. preferable.

Mn: 0.08% or less Mn is an element having a function of improving the strength of the sintered body by improving hardenability, solid solution strengthening, and the like. In order to acquire the said effect, in this invention, the alloy steel powder which contains Mn as an alloying element is manufactured. However, if the Mn content exceeds 0.08%, the amount of Mn oxide generated during sintering increases, and the generated oxide serves as a starting point for fatigue failure and reduces the fatigue strength of the sintered member. Let Therefore, the Mn content is 0.08% or less. On the other hand, the lower limit of the Mn content is not particularly limited and can be more than 0%. From the viewpoint of obtaining a sufficient effect of adding Mn, the Mn content is preferably 0.01% or more, and more preferably 0.04% or more.

Mo: 0.1 to 2.0%
Mo is an element having a function of improving the strength of the sintered body by improving hardenability, solid solution strengthening, precipitation strengthening, and the like. In order to obtain the effect sufficiently, the Mo content is preferably 0.1% or more. On the other hand, if the Mo content exceeds 2.0%, the toughness decreases, so the Mo content is preferably 2.0% or less. Therefore, when adding Mo, the Mo content is set to 0.1 to 2.0%.

  The alloy steel powder for sintered members of the present invention comprises the above components, the remainder Fe and inevitable impurities. The alloy steel powder for sintered members of the present invention can also contain other trace elements as long as the effects and effects of the present invention are not impaired.

  Examples of the inevitable impurities include C, O, S, and P. Moreover, when the said easily oxidizable element is added to molten steel, the residue of this easily oxidizable element is also contained in alloy steel powder as an inevitable impurity.

  Note that S has a property of segregating at the crystal grain boundaries and lowering the grain boundary strength. However, when Mn is present, MnS, which is a non-metallic inclusion, is formed. In this invention, since Mn content is suppressed to 0.08% or less, S which reacts with Mn and forms MnS decreases, and S which segregates at a crystal grain boundary increases. Therefore, when excessive S is contained in the alloy steel powder, the decrease in grain boundary strength due to segregation of S becomes remarkable. In order to prevent this, the amount of S contained as an impurity in the alloy steel powder is preferably 0.01% or less. In addition, the minimum of S content is not specifically limited, Although it can be set to 0%, industrially it may exceed 0%.

  Similarly, P also has the property of segregating at the grain boundaries and reducing the grain boundary strength. Therefore, the amount of P contained as an impurity in the alloy steel powder is preferably 0.01% or less. In addition, the minimum of P content is not specifically limited, Although it can be 0%, industrially it may exceed 0%.

  Next, the present invention will be described more specifically based on examples. The following examples show preferred examples of the present invention, and the present invention is not limited to the examples. Embodiments of the present invention can be modified as appropriate within the scope of the gist of the present invention, and any of them can be included in the technical scope of the present invention.

  Water atomized iron-based powders were produced from molten steel having various component compositions using the water atomizing apparatus having the configuration shown in FIG. First, 2000 kg of molten steel having the component composition shown in Table 1 was prepared using an induction heating furnace. The molten steel was charged into a tundish, dropped from a molten steel injection nozzle at the bottom of the tundish into a spray tank, and the molten steel flow was pulverized with a water jet having a water pressure of 15 MPa to obtain an atomized iron-based powder. During atomization, the total weight of the induction furnace was continuously measured with a load cell. In addition, the amount of charging from the induction heating furnace to the tundish was adjusted so that the liquid surface height of the molten steel in the tundish was constant during atomization. Therefore, the injection rate of the atomized molten steel flow can be estimated from the rate of decrease per unit time of the total weight of the induction heating furnace. In addition, the molten steel sample was extract | collected from the induction heating furnace just before the molten steel injection | pouring start, and the component was analyzed by cant back | bag (Quantovac, spark discharge emission spectrometry). The component composition of the molten steel shown in Table 1 is obtained by the above analysis. Of the component composition of the molten steel, the balance other than the elements shown in Table 1 as the component composition of the molten steel is Fe and other inevitable impurities. S and P are contained as inevitable impurities in the molten steel. In addition, “Tr.” In the table means that it is below the detection limit. The water atomized iron-based powder thus produced was heat-treated at 1200 ° C. for 2 hours in a dry hydrogen atmosphere to produce alloy steel powder for a sintered member raw material.

[Infusion rate stability rate]
The stability of the molten steel injection rate in the water atomization process was evaluated as follows. Stability of molten steel injection, with the average molten steel injection rate M _i for 2 minutes from the beginning of 5 minutes after the start of molten steel injection as the initial injection rate M _i and the average molten steel injection rate for 2 minutes 5 minutes before the completion of the injection as the final injection rate M _f As an index, an injection rate stability rate R _M defined by the following equation was obtained.
R _M = M _f / M _i × 100 (%)

The closer _RM is to 100%, the more stable water atomization can be achieved without changing the injection rate from the initial stage to the final stage. On the other hand, as the R _M is small, indicating that the molten steel injection rate with the lapse of operating time has become unstable operation decreases. Therefore, _RM is preferably as close to 100%. Incidentally, R _M is preferably 70% or more.

[Particle density]
Moreover, the void | hole production | generation state inside each particle | grain contained in the alloy steel powder for sintered member raw materials was evaluated as follows. First, the water atomized iron-based powder produced by the above-described method was classified between sieves having openings of 106 μm and 75 μm. Subsequently, after embedding the obtained particle | grains in resin, the particle | grain cross section was mirror-polished and the obtained cross section was observed using the optical microscope. At that time, the observation magnification was 100 times, and 10 places were photographed in a field of view of 800 μm × 600 μm. The total number of particles contained in the photographed optical microscope image is N _T , of which the number of particles including pores having a diameter of 20 μm or more is N _V, and the particle density ratio R defined by the following equation is used as an index of particle density. _V was obtained.
R _V = (1−N _V / N _T ) × 100 (%)

It is shown that the closer the R _V is to 100%, the smaller the particles containing large vacancies and the denser the particles. On the other hand, the smaller the R _V , the greater the number of particles that contain larger pores. Therefore, R _V is preferably closer to 100%. R _V is preferably 80% or more.

The calculated values of R _M and R _V are shown in Table 1. In satisfies invention of the present invention, high R _M, it was excellent in injection stability of the molten steel. On the other hand, in the comparative example which has a low C content and does not satisfy the condition of the formula (1) of the present invention, the injection stability of the molten steel was inferior. Further, No. [C] / [Cr] ^2/3 is lower than the range of the present invention. In 16 comparative examples, the molten steel inlet was closed at the time when about 500 kg of raw molten steel was injected, but in the inventive example satisfying the conditions of the present invention, the total amount of raw molten steel could be atomized. From the above results, it can be seen that according to the method of the present invention, the production of Cr oxide during water atomization is suppressed, and Cr-containing alloy steel powder can be produced efficiently and stably.

Moreover, in the invention examples satisfying the conditions of the present invention, the R _V was high and the resulting water atomized iron-based powder was excellent in the denseness. On the other hand, in the comparative example which has high C content of molten steel and does not satisfy | fill the conditions of (1) Formula of this invention, the density of the water atomized iron-base powder was inferior. From this result, it can be seen that according to the method of the present invention, it is possible to suppress the formation of vacancies due to the CO gas generated by the reaction of C in the molten steel with oxygen remaining in the powder.

Further, in the invention examples of adding Si is oxidizable elements, Al, at least one of Ti to the molten steel was improved R _M and R _V as compared to the example without addition of easily oxidizable elements.

In Table 1, [C] / [Cr] ^2/3 in molten steel In the present invention example within the scope of the present invention, oxidation of alloy elements in molten steel is suppressed, so alloy steel manufactured by heat treatment The content of alloying elements in the powder was substantially the same as the content of alloying elements in the molten steel shown in Table 1. In addition, as a result of oxidation of C and removal as CO gas, C did not remain in the alloy steel powder of the present invention example, except for those present as inevitable impurities. Therefore, the alloy steel powder in the examples of the present invention satisfied the component composition conditions in the present invention. On the other hand, in the comparative example in which [C] / [Cr] ^2/3 in the molten steel is lower than the range of the present invention, the Cr amount contained in the alloy steel powder is 0.1 mass% or more lower than the Cr amount in the molten steel. It was. In the comparative example in which the amount of [C] / [Cr] ^{2/3 in} the molten steel is higher than the range of the present invention, although the particle density ratio is low, the oxidation of the alloy elements in the molten steel is suppressed. The alloying element content was almost the same as the molten steel composition.

DESCRIPTION OF SYMBOLS 1 Melting furnace 2 Raw material molten steel 3 Tundish 4 Molten steel nozzle 5 Molten steel flow 6 Spraying tank 7 Water nozzle 8 High-pressure water jet 9 Water atomized iron-based powder 10 Molten steel inlet 100 Water atomizer

Claims (4)

A method for producing alloy steel powder for a sintered member raw material,
A water atomization process in which molten steel is water atomized to form a water atomized iron-based powder;
A heat treatment step of heat-treating the water atomized iron-based powder to obtain an alloy steel powder for a sintered member raw material,
The C content [C] (mass%) in the molten steel and the Cr content [Cr] (mass%) in the molten steel satisfy the relationship of the following formula (1),
The alloy steel powder for sintered member raw material is in mass%,
Cr: 0.3-3.5% and Mn: 0.08% or less,
The manufacturing method of the alloy steel powder for sintered member raw materials which has a component composition which consists of remainder Fe and an unavoidable impurity.
Record
0.15 ≦ [C] / [Cr] ^2/3 ≦ 0.25 (1) A method for producing alloy steel powder for a sintered member raw material,
A water atomization process in which molten steel is water atomized to form a water atomized iron-based powder;
A heat treatment step of heat-treating the water atomized iron-based powder to obtain an alloy steel powder for a sintered member raw material,
The C content [C] (mass%) in the molten steel and the Cr content [Cr] (mass%) in the molten steel satisfy the relationship of the following formula (1) ,
Before Kishoyui member feedstock alloy steel powder, in mass%,
Cr: 0.3-3.5% and Mn: 0.08% or less,
The contained as an alloying element, have a component composition and the balance Fe and unavoidable impurities,
The molten steel contains 0.01 to 0.1% by mass in total of oxidizable elements whose standard free energy of formation of oxide is lower than that of the alloying element contained in the alloy steel powder for the sintered member raw material The manufacturing method of the alloy steel powder for sintered member raw materials.
Record
0.10 ≦ [C] / [Cr] ^2/3 ≦ 0.35 (1)   The manufacturing method of the alloy steel powder for sintered member raw materials of Claim 2 whose said oxidizable element is 1 or 2 or more selected from the group which consists of Si, V, Ti, and Al. The component composition of the alloy steel powder for sintered member raw material is mass%,
Mo: 0.1 to 2.0%
Further contained as an alloying element,
The manufacturing method of the alloy steel powder for sintered member raw materials as described in any one of Claims 1-3 whose C content in the component composition of the said alloy steel powder for sintered member raw materials is 0.1 mass% or less. .

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