WO2017051541A1 - 焼結部材原料用合金鋼粉の製造方法 - Google Patents
焼結部材原料用合金鋼粉の製造方法 Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
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- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
- B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
- B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/14—Treatment of metallic powder
- B22F1/142—Thermal or thermo-mechanical treatment
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
- B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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- the present invention relates to a method for producing an alloy steel powder for a sintered member raw material, and in particular, the alloying when producing an alloy steel powder containing an easily oxidizable alloying element such as Cr or Mn by a water atomizing method.
- the present invention relates to a method capable of stably producing alloy steel powder by suppressing element oxidation.
- 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 part parts having complex shapes at low cost. It is used for a wide range of applications such as parts manufacturing.
- 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 as 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.
- a heat treatment finish reduction treatment
- annealing is performed in a reducing atmosphere such as hydrogen.
- carbon and oxygen contained in the iron powder are removed, strain contained in the iron powder particles is removed, and crystal grains grow.
- alloy steel powder to which an alloying element is added is used as a raw material powder.
- 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.
- 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 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.
- high-purity materials such as electrolytic iron and base metal
- low-cost and relatively high-purity materials such as molten steel smelted in converters and high-purity scrap are also industrial.
- 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 raw material molten steel.
- the raw molten steel is pulverized by a water atomization method to form a water-atomized iron-based powder.
- 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.
- Patent Document 1 discloses a method in which a water atomized iron-based powder containing Cr as an alloying element is reduced by heat treatment in a vacuum rather than in a reducing atmosphere.
- carbon contained in the water atomized iron-based powder functions as a reducing agent.
- Patent Document 2 discloses that in a water atomized iron-based powder containing Cr, Mo, and Mn as alloying elements, the weight ratio O: C of oxygen to carbon 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.
- 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.
- Patent Document 4 discloses a method in which 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 amount of generated CO gas increases. 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 JP-T-2002-501123
- the water atomized iron-based powder containing Cr can be reduced by heat treatment to reduce the amount of oxygen contained in the alloy steel powder.
- 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.
- a raw molten steel 2 having a predetermined component composition is produced, and then the raw molten steel 2 is poured into 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 made into small particles by a high-pressure water jet 8 ejected from a water nozzle 7 to become a water atomized iron-based powder 9.
- the temperature of the raw molten steel 2 flowing down from the molten steel nozzle 4 is drastically lowered by coming into contact with the surrounding atmosphere.
- 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 form of plugging the molten steel inlet 10 in the vicinity of the molten steel inlet 10 which is the tip of the molten steel nozzle 4.
- the molten steel injection rate decreases with time, and the production efficiency of the water atomized iron-based powder decreases.
- 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.
- Patent Documents 1 to 4 all relate to the treatment after obtaining the iron-based powder by the water atomization method, and thus cannot solve the above problems.
- Mn and V have the property of being easily oxidized like Cr, it has been difficult to stably produce an iron-based powder containing these alloying elements by a water atomization method.
- the present invention has been made in view of the above circumstances, and suppresses oxidation of the alloying element that occurs when an iron-based powder containing an alloying element such as Cr or Mn is produced by a water atomization method, and is fired. It is an object of the present invention to provide a method for producing an alloy steel powder for a raw material for a binding member efficiently and stably. In addition, an object is to obtain dense powder particles with few pores inside the particles.
- the component composition of the molten steel and the component composition of the alloy steel powder for sintered member raw material are in mass%, S: The manufacturing method of the alloy steel powder for sintered member raw materials of said 1 or 2 further containing 0.3% or less.
- the iron-based powder containing Cr, Mn or the like as an alloying element is suppressed by oxidation of the alloying element produced when the water atomizing method is produced, and the alloy steel powder is efficiently and stably produced. Can be manufactured.
- 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 performing a heat treatment for reduction on the water atomized iron-based powder.
- a heat treatment step for obtaining alloy steel powder includes a water atomization step of obtaining a water atomized iron-based powder by water atomizing molten steel, and performing a heat treatment for reduction on the water atomized iron-based powder.
- FIG. 1 shows a manufacturing flow of alloy steel powder in one embodiment of the present invention.
- a raw material molten steel is manufactured by melting an iron source.
- an 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 be used, and a plurality of types of iron sources can be used in combination.
- a Cr source, a Mn source, and other alloying elements can be added to the iron source so that an alloy steel powder having a desired component composition can be finally obtained.
- a carbonaceous material, other auxiliary materials (slag component etc.), and the "easy-oxidizable element" mentioned later can also be added as needed.
- 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.
- the obtained water atomized iron-based powder is subjected to heat treatment to produce alloy steel powder for sintered member raw material containing Cr and Mn.
- 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.
- the carbon and oxygen contained in the water atomized iron-based powder are removed by the heat treatment.
- 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.
- Component composition of molten steel As the molten steel, molten steel containing C, Cr, and Mn and having a component composition composed of the remaining Fe and inevitable impurities can be used. In another embodiment, the component composition of the molten steel further contains one or both of Mo: 0.1 to 2.0% and V: 0.1 to 0.5% as alloying elements. be able to. Moreover, in other embodiment, the component composition of the said molten steel can further contain S: 0.3% or less. In another embodiment, the component composition of the molten steel may further contain 0.01 to 0.10% by mass of oxidizable elements described later in total.
- the molten steel in one embodiment of the present invention may have the following component composition.
- [C] is defined by the ratio to [Cr] 2/3 , [Mn], and [V]. This is because the reaction in which each of the Cr oxide Cr 2 O 3 , the Mn oxide MnO, and the V oxide VO represented by the following formulas (2) to (4) is reduced by C is thermodynamically. This is because it is determined by [Cr] 2/3 , [Mn], and the ratio of [V] and [C].
- the alloy steel powder produced by the method of the present invention may contain Mo as an alloying element in addition to the above alloying elements.
- Mo is less oxidized than Cr, water atomization can be performed stably as long as the conditions of the present invention are satisfied.
- Patent Document 2 discloses a water atomized iron-based powder containing Cr: 2.5 to 3.5% and C: 0.1 to 0.9%. It is selected regardless of the element content.
- the C content in the molten steel is not particularly limited as long as it satisfies the relationship of the above formula (1), but is preferably C: 0.01 to 1.00%.
- the molten steel used for water atomization can also contain an easily oxidizable element.
- 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.
- the easily oxidizable element means an element having a lower standard free energy of formation of oxide than both Cr and Mn.
- the alloy steel powder contains Cr, Mn, Mo, and V
- the easily oxidizable element is an element having a lower standard free energy of formation of oxide than any of Cr, Mn, Mo, and V. means.
- the easily oxidizable element for example, Si, Al, Ti or the like can be used.
- the easily oxidizable element only one element can be used, or a plurality of elements can be used in combination. In view of the availability of inexpensive raw materials, it is preferable to use Si.
- the 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, even when the water is atomized, even if the molten steel is injected from the molten steel inlet and the temperature of the molten steel decreases, oxygen in the molten steel is less likely to be saturated and alloyed. Generation of elemental oxides 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. In addition, the amount of CO gas generated is also suppressed, and as a result, the phenomenon of pore formation in the water atomized iron-based powder is further suppressed.
- the total content of the easily oxidizable elements in the molten steel is preferably 0.01 to 0.10% 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 0.10% by mass, the amount mixed into the molten steel flow increases, and the oxide of the easily oxidizable elements adheres to the molten steel inlet and causes operational instability. This is not preferable.
- the alloy steel powder for sintered member raw material in one embodiment of the present invention contains Cr: 0.3-3.5% and Mn: more than 0.08%, 1.0% or less as an alloying element, and the balance Has a component composition that is Fe and inevitable impurities.
- the component composition of the alloy steel powder may further contain one or both of Mo: 0.1 to 2.0% and V: 0.1 to 0.5% as alloying elements.
- S: 0.3% or less can be further contained.
- 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 at the time of sintering increases, and the generated oxide becomes a starting point of fatigue failure, and reduces the fatigue strength of the sintered member. . 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%.
- the Cr content of the molten steel used in the water atomization process should be 0.3 to 3.5%. preferable.
- Mn more than 0.08%, 1.0% or less
- Mn is an element having a function of improving the strength of the sintered member by improving hardenability, solid solution strengthening, and the like.
- the Mn content is more than 0.08%.
- the Mn content is preferably 0.10% or more.
- the Mn content is 1.0% or less.
- the Mn content is preferably 0.8% or less. Similar to Cr, according to the method of the present invention, there is almost no decrease in the amount of Mn in molten steel due to the precipitation of Mn oxide.
- the Mn content of the molten steel used in the water atomization process is more than 0.08% and 1.0% or less. It is preferable to do.
- Mo 0.1-2.0%
- Mo is an element having a function of improving the strength of the sintered member by improving hardenability, solid solution strengthening, precipitation strengthening, and the like.
- the Mo content is preferably 0.1% or more.
- the Mo content exceeds 2%, the toughness decreases, so the Mo content is preferably 2.0% or less. Therefore, when Mo is added, the Mo content is set to 0.1 to 2.0%.
- the minimum with preferable Mo content is 0.1%, More preferably, it is 0.2%.
- the upper limit with preferable Mo content is 1.5%, More preferably, it is 1.0%.
- V 0.1-0.5%
- V is also an element having a function of improving the strength of the sintered member by improving hardenability, solid solution strengthening, precipitation strengthening and the like.
- the V content is preferably 0.1% or more.
- the V content exceeds 0.5%, the toughness decreases, so the V content is preferably 0.5% or less. Therefore, when V is added, the V content is 0.1 to 0.5%.
- the minimum of V content is 0.2%.
- the upper limit of V content is 0.4%.
- the S content of the alloy steel powder is preferably set to 0.3% or less.
- the lower limit of the S content after sintering is not particularly limited and can be 0%, but industrially it may be more than 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.
- the inevitable impurities include C, O, and P.
- the alloy steel powder of the present invention can contain 0.3% or less of S, but even when S is not added, the alloy steel powder contains S as an inevitable impurity. Can do. Furthermore, 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.
- the amount of P contained as an impurity in the alloy steel powder is preferably 0.01% or less.
- the minimum of P content is not specifically limited, although it can be 0%, industrially it may exceed 0%.
- 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.
- the molten steel sample was extract
- the stability of the molten steel injection rate in the water atomization process was evaluated as follows.
- the stability of molten steel injection is defined as the initial molten metal injection rate M i , the average molten steel injection rate for 2 minutes from the 5 minutes after the start of molten steel injection, and the final molten metal injection rate M f for 2 minutes from 5 minutes before the completion of the injection.
- an injection rate stability rate R M defined by the following equation was obtained.
- R M (M f / M i ) ⁇ 100 (%)
- grain contained in water atomized iron base powder 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 ⁇ m and 75 ⁇ m. Subsequently, after embedding the obtained particle
- N T The total number of particles contained in the photographed optical microscope image
- N V the number of particles including pores having a diameter of 20 ⁇ m or more
- R V (1 ⁇ N V / N T ) ⁇ 100 (%)
- R M and R V are shown in Table 1.
- high R M it was excellent in injection stability of the molten steel.
- 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.
- [C] / ⁇ [Cr] 2/3 +2 ([Mn] + [V]) ⁇ is lower than the range of the present invention.
- the molten steel inlet was closed at the time when about 500 kg of raw molten steel was injected, but in the inventive example that satisfied the conditions of the present invention, the total amount of raw molten steel could be atomized.
- the R V was high and the resulting water atomized iron-based powder was excellent in the denseness.
- 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.
- 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.
- the oxidation of the alloying elements in the molten steel is suppressed. Therefore, the contents of alloying elements in the alloyed steel powder produced by heat treatment are shown in Table 1. The content of alloying elements in the molten steel was substantially the same. 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.
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Abstract
Description
1.焼結部材原料用合金鋼粉の製造方法であって、
C、Cr、およびMnを含有し、残部Feおよび不可避不純物からなる成分組成を有する溶鋼を水アトマイズして水アトマイズ鉄基粉末とする水アトマイズ工程と、
前記水アトマイズ鉄基粉末に熱処理を行って焼結部材原料用合金鋼粉とする熱処理工程とを有し、
前記溶鋼中におけるC含有量[C](質量%)と、前記溶鋼中におけるCr、Mn、およびVの含有量[Cr]、[Mn]、および[V](質量%)とが、下記(1)式の関係を満たし、
前記焼結部材原料用合金鋼粉が、質量%で、
Cr:0.3~3.5%および
Mn:0.08%超、1.0%以下、
を合金化元素として含有し、残部Feおよび不可避不純物からなる成分組成を有する、焼結部材原料用合金鋼粉の製造方法。
記
0.07≦[C]/{[Cr]2/3+2([Mn]+[V])}≦0.23 …(1)
(ただし、前記溶鋼がVを含有しない場合、[V]は0とする)
Mo:0.1~2.0%、および
V :0.1~0.5%の一方または両方を、合金化元素としてさらに含有する、上記1に記載の焼結部材原料用合金鋼粉の製造方法。
S :0.3%以下
をさらに含有する、上記1または2に記載の焼結部材原料用合金鋼粉の製造方法。
本発明の一実施形態においては、前記溶鋼として、C、Cr、およびMnを含有し、残部Feおよび不可避不純物からなる成分組成を有する溶鋼を用いることができる。また、他の実施形態において、前記溶鋼の成分組成は、Mo:0.1~2.0%、およびV :0.1~0.5%の一方または両方を、合金化元素としてさらに含有することができる。また、他の実施形態において、前記溶鋼の成分組成は、S:0.3%以下をさらに含有することができる。また、他の実施形態において、前記溶鋼の成分組成は、後述する易酸化性元素を、合計で0.01~0.10質量%さらに含有することもできる。
C、
Cr、
Mn、
任意に、Mo:0.1~2.0%およびV:0.1~0.5%の一方または両方、
任意に、S:0.3%以下、および、
任意に、易酸化性元素を合計で0.01~0.10質量%を含有し、
残部Feおよび不可避不純物からなる成分組成。
本発明では水アトマイズに供する溶鋼中におけるC含有量[C](質量%)と、前記溶鋼中におけるCr、Mn、およびVの含有量[Cr]、[Mn]、および[V](質量%)とが、下記(1)式の関係を満たすようにすることが重要である。
0.07≦[C]/{[Cr]2/3+2([Mn]+[V])}≦0.23 …(1)
なお、前記溶鋼がVを含有しない場合、上記(1)式の[V]は0とする。上記(1)式を満たすように、合金化元素の含有量に応じてC含有量を調整することによって、Cr等の酸化されやすい元素を合金化元素として含有する鉄基粉末を、水アトマイズ法により効率的に、安定して製造することができる。その理由を以下に説明する。
Cr2O3+3C → (2/3)Cr+3CO …(2)
MnO+C → Mn+CO …(3)
VO+C → V+CO …(4)
本発明においては、水アトマイズに用いる溶鋼が、易酸化性元素を含有することもできる。ここで、「易酸化性元素」とは、後述する合金鋼粉中に含まれる合金化元素よりも酸化物の標準生成自由エネルギーが低い元素を意味する。例えば、合金鋼粉がCrおよびMnを含有する場合、前記易酸化性元素とは、CrおよびMnの両者よりも酸化物の標準生成自由エネルギーが低い元素を意味する。また、合金鋼粉がCr、Mn、Mo、およびVを含有する場合、前記易酸化性元素とは、Cr、Mn、Mo、およびVのいずれよりも酸化物の標準生成自由エネルギーが低い元素を意味する。
本発明の一実施形態における焼結部材原料用合金鋼粉は、Cr:0.3~3.5%およびMn:0.08%超、1.0%以下を合金化元素として含有し、残部がFeおよび不可避不純物である成分組成を有する。また、該合金鋼粉の成分組成は、Mo:0.1~2.0%およびV:0.1~0.5%の一方または両方を合金化元素としてさらに含有することもできる。また、S:0.3%以下をさらに含有することもできる。以下、前記成分組成の限定理由について説明する。
Crは、焼入性を向上させて、焼結部材の引張強度および疲労強度を向上させる機能を有する元素である。さらに、Crは、焼結部材を熱処理した後の硬さを高め、耐摩耗性を向上させる効果がある。これらの効果を得るため、Cr含有量を0.3%以上とする。一方、Cr含有量が3.5%を超えると、焼結時に生成するCr酸化物の量が多くなり、生成した酸化物は疲労破壊の起点となって、焼結部材の疲労強度を低下させる。そのため、Cr含有量を3.5%以下とする。なお、Cr含有量は、0.5~3.5%とすることが好ましく、1.0~3.5%とすることがより好ましい。なお、本発明の方法によれば、溶鋼中のCrの酸化が抑制されるため、Cr酸化物の析出による溶鋼中Cr量の減少は殆ど発生しない。したがって、本発明の焼結部材原料用合金鋼粉におけるCr含有量を上記範囲とするためには、水アトマイズ工程で用いられる溶鋼のCr含有量を0.3~3.5%とすることが好ましい。
Mnは、焼入性向上、固溶強化などによって、焼結部材の強度を向上させる機能を有する元素である。前記効果を得るために、Mn含有量を0.08%超とする。Mn含有量は0.10%以上とすることが好ましい。一方、Mn含有量が1.0%を超えると靱性が低下する。そのため、Mn含有量を1.0%以下とする。Mn含有量は、0.8%以下とすることが好ましい。なお、Crと同様に、本発明の方法によれば、Mn酸化物の析出による溶鋼中Mn量の減少は殆ど発生しない。したがって、本発明の焼結部材原料用合金鋼粉におけるMn含有量を上記範囲とするためには、水アトマイズ工程で用いられる溶鋼のMn含有量を0.08%超、1.0%以下とすることが好ましい。
Moは、焼入性向上、固溶強化、析出強化などによって、焼結部材の強度を向上させる機能を有する元素である。前記効果を十分に得るためには、Mo含有量を0.1%以上とすることが好ましい。一方、Mo含有量が2%を超えると靭性が低下するため、Mo含有量を2.0%以下とすることが好ましい。したがって、Moを添加する場合は、Mo含有量を0.1~2.0%とする。なお、Mo含有量の好ましい下限は0.1%であり、さらに好ましくは0.2%である。一方、Mo含有量の好ましい上限は1.5%であり、より好ましくは1.0%である。
Vもまた、焼入性向上、固溶強化、析出強化などによって、焼結部材の強度を向上させる機能を有する元素である。前記効果を十分に得るためには、V含有量を0.1%以上とすることが好ましい。一方、V含有量が0.5%を超えると靭性が低下するため、V含有量を0.5%以下とすることが好ましい。したがって、Vを添加する場合は、V含有量を0.1~0.5%とする。なお、V含有量の下限は0.2%であることが好ましい。またV含有量の上限は0.4%であることが好ましい。
Sは、Mnと結合してMnSを形成し、焼結後の切削加工性を改善する作用を持つ。しかしながら、過剰にSを添加すると固溶Sが増加し、Sの偏析に起因する粒界強度の低下が顕著となる。これを防ぐために、合金鋼粉のS含有量を0.3%以下とすることが好ましい。なお、焼結後S含有量の下限は特に限定されず、0%とすることができるが、工業的には0%超であってよい。
水アトマイズ工程における溶鋼注入速度の安定性を、以下のようにして評価した。溶鋼の注入開始後5分の時点から2分間の平均溶鋼注入速度を初期注入速度Mi、注入完了5分前から2分間の平均溶鋼注入速度を終期注入速度Mfとし、溶鋼注入の安定性の指標として、次式で定義される注入速度安定率RMを求めた。
RM =(Mf/Mi)×100(%)
また、水アトマイズ鉄基粉末に含まれる個々の粒子内部の空孔生成状態を以下のようにして評価した。まず、上述の方法で製造された水アトマイズ鉄基粉末を、目開き106μmと75μmの篩の間に分級した。次いで、得られた粒子を樹脂に埋め込んだ後、粒子断面を鏡面研磨し、得られた断面を、光学顕微鏡を用いて観察した。観察倍率を100倍とし、800μm×600μmの視野で10箇所写真撮影を行った。撮影された光学顕微鏡像に含まれる粒子の総数をNT、そのうち直径20μm以上の空孔を含む粒子数をNVとし、粒子の稠密性の指標として、次式で定義される粒子稠密率RVを求めた。
RV =(1- NV/NT)×100(%)
2 原料溶鋼
3 タンディッシュ
4 溶鋼ノズル
5 溶鋼流
6 噴霧槽
7 水ノズル
8 高圧水ジェット
9 水アトマイズ鉄基粉末
10 溶鋼注入口
100 水アトマイズ装置
Claims (5)
- 焼結部材原料用合金鋼粉の製造方法であって、
C、Cr、およびMnを含有し、残部Feおよび不可避不純物からなる成分組成を有する溶鋼を水アトマイズして水アトマイズ鉄基粉末とする水アトマイズ工程と、
前記水アトマイズ鉄基粉末に熱処理を行って焼結部材原料用合金鋼粉とする熱処理工程とを有し、
前記溶鋼中におけるC含有量[C](質量%)と、前記溶鋼中におけるCr、Mn、およびVの含有量[Cr]、[Mn]、および[V](質量%)とが、下記(1)式の関係を満たし、
前記焼結部材原料用合金鋼粉が、質量%で、
Cr:0.3~3.5%および
Mn:0.08%超、1.0%以下、
を合金化元素として含有し、残部Feおよび不可避不純物からなる成分組成を有する、焼結部材原料用合金鋼粉の製造方法。
記
0.07≦[C]/{[Cr]2/3+2([Mn]+[V])}≦0.23 …(1)
(ただし、前記溶鋼がVを含有しない場合、[V]は0とする) - 前記溶鋼の成分組成および前記焼結部材原料用合金鋼粉の成分組成が、質量%で、
Mo:0.1~2.0%、および
V :0.1~0.5%の一方または両方を、合金化元素としてさらに含有する、請求項1に記載の焼結部材原料用合金鋼粉の製造方法。 - 前記溶鋼の成分組成および前記焼結部材原料用合金鋼粉の成分組成が、質量%で、
S :0.3%以下
をさらに含有する、請求項1または2に記載の焼結部材原料用合金鋼粉の製造方法。 - 前記溶鋼の成分組成が、前記焼結部材原料用合金鋼粉中に含まれる前記合金化元素よりも酸化物の標準生成自由エネルギーが低い易酸化性元素を、合計で0.01~0.10質量%さらに含有する、請求項1~3のいずれか一項に記載の焼結部材原料用合金鋼粉の製造方法。
- 前記易酸化性元素が、Si、Ti、およびAlから選択される1または2以上である、請求項4に記載の焼結部材原料用合金鋼粉の製造方法。
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US20180290213A1 (en) * | 2017-04-10 | 2018-10-11 | Hyundai Motor Company | Method of manufacturing iron powder and iron powder manufactured thereby |
CN109249019A (zh) * | 2018-10-24 | 2019-01-22 | 湖南大学 | 一种高铬铸铁的变温烧结工艺 |
WO2022044931A1 (ja) * | 2020-08-28 | 2022-03-03 | 住友金属鉱山株式会社 | アトマイズ装置、金属粉体の製造方法、並びに有価金属の製造方法 |
JP2022039952A (ja) * | 2020-08-28 | 2022-03-10 | 住友金属鉱山株式会社 | アトマイズ装置、金属粉体の製造方法、並びに有価金属の製造方法 |
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US20180290213A1 (en) * | 2017-04-10 | 2018-10-11 | Hyundai Motor Company | Method of manufacturing iron powder and iron powder manufactured thereby |
KR20180114423A (ko) * | 2017-04-10 | 2018-10-18 | 현대자동차주식회사 | 철계분말의 제조방법 및 이에 의해 제조되는 철계분말 |
CN108687356A (zh) * | 2017-04-10 | 2018-10-23 | 现代自动车株式会社 | 制备铁粉的方法及由其制备的铁粉 |
US10926332B2 (en) * | 2017-04-10 | 2021-02-23 | Hyundai Motor Company | Method of manufacturing iron powder and iron powder manufactured thereby |
KR102288887B1 (ko) * | 2017-04-10 | 2021-08-12 | 현대자동차주식회사 | 철계분말의 제조방법 및 이에 의해 제조되는 철계분말 |
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WO2022044931A1 (ja) * | 2020-08-28 | 2022-03-03 | 住友金属鉱山株式会社 | アトマイズ装置、金属粉体の製造方法、並びに有価金属の製造方法 |
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JP7168034B2 (ja) | 2020-08-28 | 2022-11-09 | 住友金属鉱山株式会社 | アトマイズ装置、金属粉体の製造方法、並びに有価金属の製造方法 |
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