EP0108175B1 - Verfahren zur Herstellung von Stahllegierungspulver - Google Patents

Verfahren zur Herstellung von Stahllegierungspulver Download PDF

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Publication number
EP0108175B1
EP0108175B1 EP82305820A EP82305820A EP0108175B1 EP 0108175 B1 EP0108175 B1 EP 0108175B1 EP 82305820 A EP82305820 A EP 82305820A EP 82305820 A EP82305820 A EP 82305820A EP 0108175 B1 EP0108175 B1 EP 0108175B1
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Prior art keywords
powder
steel powder
atmosphere
alloy steel
decarburizing
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EP82305820A
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English (en)
French (fr)
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EP0108175A1 (de
Inventor
Toshihiko Kubo
Minoru Ichidate
Eijiro Tamura
Isamu Karasuno
Masahide Umino
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Nippon Steel Corp
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Sumitomo Metal Industries Ltd
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Priority to DE8282305820T priority Critical patent/DE3277966D1/de
Priority to EP82305820A priority patent/EP0108175B1/de
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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
    • 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
    • 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
    • B22F1/145—Chemical treatment, e.g. passivation or decarburisation
    • 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
    • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy

Definitions

  • This invention relates to a process for producing alloy steel powder, particularly to a process for producing low-oxygen, low-carbon alloy steel powder, in which the oxidation of easily oxidizable elements, such as chromium, manganese, etc. has been suppressed effectively.
  • This process employs water as an atomizing agent. Therefore, the contamination of the resulting powder with oxides is inevitable during atomization. The formation of oxides is so great that the addition of easily oxidizable elements to an alloy system should be restricted. Thus, in designing the alloy, the addition of easily oxidizable elements is limited.
  • the oxygen level of as-atomized powder is made as low as 0.5% by weight, it is necessary to treat the as-atomized powder at a temperature higher than 1150°C for five hours or longer so as to obtain powder having a practical level of oxygen.
  • the resulting powder having the intended level of oxygen is sintered and requires a heavy duty disintegration step.
  • the shape and size of the resulting powder particles will differ very much from those of the as-atomized powder, and their compressibility, compactibility and sintering applicability will be impaired.
  • This method results in less contamination with oxides.
  • gas cooling the cooling rate of the atomized powder is small, and the resulting particles tend to become round. Round particles are difficult to compact. It is, therefore, necessary to compact such powder by means of canning compaction techniques through cold (or hot) isostatic pressing etc.
  • the compaction of this type is very complicated and is costly, so this method is not often used.
  • gas atomization method is practiced for special purposes, it is rarely used for the production of steel powder to be sintered or sintered-forged, which is the major application in the field of powder metallurgical technology.
  • the alloy steel powder contains easily oxidizable elements such as Cr, Mn, V, Nb, B, Si, etc., it is easier to carry out decarburization than to carry out reduction on once oxidized steel powder.
  • no process has been proposed for carrying out decarburization in an efficient and continuous manner.
  • H 2 As a decarburizing gas H 2 , H 2 0, CO-C0 2 , etc. are known in the art. Of them H 2 gas is not practical, because the decarburizing rate with H 2 gas is very low.
  • a decarburizing gas which contains an oxidizing gas such as H 2 0, CO 2 , etc. can remarkably accelerate the decarburization, the oxidation of an element, such as Cr, Mn, V, Nb, B, Si, etc. is inevitable under the decarburizing temperature and atmospheric conditions under which the decarburization proceeds, because such conditions put these elements in an oxidizing region defined by thermo-dynamic equilibrium conditions. Therefore, special care is necessary to control the decarburizing conditions.
  • Patent document GB-A-20 94 834 describes an oil atomized low alloy steel powder having improved compressibility, compactability and hardenability with a specified chemical composition after a decarburization process.
  • the composition of the "as atomized” steel powder is unspecified as is whether the decarburized powder is cooled in an inert or a reducing atmosphere and whether the powder is prepared in a continuous or discontinuous manner.
  • Document GB-A-1 236 271 teaches a continuous decarburizing treatment for an "as atomized” steel powder with 0.8% carbon and an unspecified amount of oxygen. The process includes pre-heating and cooling steps that are carried out in air or by water cooling.
  • the present invention provides a process for producing low-oxygen, low-carbon alloy steel powder, the process including the steps of:
  • molten steel which contains at least one easily oxidizable element selected from the group consisting of chromium, manganese, vanadium, niobium, boron and silicon;
  • adjusting the amount of carbon of said as-atomized alloy steel powder by passing said as-atomized alloy steel powder continuously through a decarburizing zone comprised of a pre-heated section, a decarburizing section and a cooling section, said pre-heating and cooling sections being kept in an inert or reduced atmosphere; and maintaining said powder in the decarburizing section in an atmosphere containing at least H 2 and H 2 0 gases under either of the below-defined conditions (A) or (B); and cooling the thus obtained powder to room temperature.
  • P H2 means a partial pressure of hydrogen gas and the "P H20” means that of steam.
  • the preparation of molten steel may be carried out in any conventional manner, and is not limited to a specific one. Since the molten steel of this invention process contains at least one easily oxidizable element selected from Cr, Mn, V, Nb, B and Si, the preparation of molten steel is preferably carried out in such way that the oxidiation of these elements is suppressed as thoroughly as possible.
  • an atomizing agent which preferably contains a medium selected from mineral oils, animal oils, vegetable oils and mixtures thereof may be employed.
  • a non-oxidizing medium comprised of an oil selected from the above-mentioned oils may be employed as an atomizing agent.
  • An oxidizing agent such as water may be incorporated in the atomizing agent so long as the resulting medium is non-oxidizing in nature as a whole.
  • oils employed in this invention include machine oil, quench oil, turbine oil, whale oil, rapeseed oil, soybean oil, etc.
  • the oxygen content of the atomized steel powder obtained in accordance with this invention is restricted to 0.2% by weight or less. It may be 0.1 % by weight or less, preferably 0.05% by weight or less. This is because substantially all the oxygen of the atomized powder remains in the final decarburized powder, though deoxidization to some extent can be effected during the following decarburization step. The lower the oxygen content the better. It is to be noted that it is possible to reduce the amount of oxygen significantly by effecting the de-oxidization of molten steel prior to atomization, and by preventing oxidation thereafter, particularly by preventing oxidation of the molten steel as well as atomized powder during atomization. The carbon content of the thus obtained atomized steel powder is 0.1% by weight or more. Such a large amount of carbon comes from carburization of the atomizing agent.
  • the inventors of this invention found that when the ratio of partial pressure of hydrogen to partial pressure of steam in an atmosphere containing hydrogen and steam is suitably adjusted, efficient decarburization takes place without resulting in substantial oxidation of the before-mentioned easily oxidizable elements or Fe, and the inventors carried out a series of experiments to determine critical conditions thereof to arrive at this invention.
  • Fig. 1 is a graph summarizing the experimental data of a series of decarburizing tests with respect to decarburizing temperature.
  • Cr-Mn low alloy steel powder Cr: 1.0% by weight; Mn: 1.5% by weight; C: 0.6% by weight; oxygen: 0.09% by weight
  • the atmosphere comprised H 2 , H 2 0 and N 2 , the ratio of P HZ /P H2o was 33.3 and P H2 was 70% of the total pressure of the atmosphere.
  • the boat was heated under the atmosphere to effect decarburization. Changes in the amounts of carbon in powdered steel (C) and oxygen in powdered steel (O) were determined with respect to treating period of time at the indicated temperature.
  • sample steel powder the steel composition and particle size distribution of which are shown in Table 1 was packed into a stainless steel boat to a depth of 20 mm, then heated and maintained at the indicated temperatures under pre-determined atmosphere to effect decarburization.
  • the decarburized powder was then cooled to room temperature in a dry hydrogen atmosphere.
  • Zone (I) shows the area where the oxidation occurs
  • Zone (II) shows the area of this invention
  • Zone (III) shows the area where de-carburization is insufficient.
  • P H2 /P H2O ratio, temperature (t°C) and treating time [8 min) can be derived on the basis of the data given in Figs. 2-7 as follows (wherein the treating time, 8, is a function of P H2 /P H2O ):
  • the minimum treating time required to reduce the carbon content to 0.1% by weight or less at a temperature of 600-950°C can be given by:
  • the maximum treating time required to suppress the oxidation of the powder to 0.2% by weight or less can be given by:
  • Atmosphere (P H2 /P H2O ) P H2 /P H2O ⁇ 0.5
  • the temperature should be limited to within a certain range.
  • Fig. 8 shows the relationship between the temperature and the adhesiveness of each particle. As is apparent from the graph, when the temperature goes up beyond 1250°C, the adhesive force between particles rapidly increases, resulting in welded particles, in which case a strong disintegrating force is required in a step following decarburization.
  • the treating time of decarburization may be restricted to less than several hours, desirably less than approximately one hourfrom a practical viewpoint.
  • the thus decarburized steel powder is then cooled to room temperature in an inert or reducing atmosphere.
  • the type of atmosphere is not limited to a specific one so long as the reoxidation can be prevented, but it is preferable to employ a dry hydrogen atmosphere.
  • the alloy steel of this invention includes high alloy steel as well as low alloy steel, as disclosed in the working examples hereinafer described.
  • Fig. 9 shows a diagrammatical view of a decarburizing apparatus for carrying out this invention process, in which the steel powder 1 produced in the oil-atomizing step is first placed in a hopper 2 and then is continuously charged onto the steel belt 3 actuated by means of rollers 4.
  • the steel belt 3 is successively passed through a decarburizing apparatus 5 which comprises a pre-heating chamber 6, a decarburizing chamber 7 and a cooling chamber 8. While the powder passes through the apparatus, the steel powder 1 is pre-heated, decarburized and then cooled, successively. After passing through the apparatus, the decarburized steel powder 9 is discharged out of the discharge end of the apparatus onto the chute.
  • a non-oxidizing gas (H 2 gas, for example) is supplied to the pre-heating chamber 6 and the cooling chamber 8 to keep the atmosphere non-oxidizing.
  • the dotted lines in the drawing show the supply system of the non-oxidizing gas.
  • Gases (H 2 0 and H 2 ) are supplied to the decarburizing chamber 7 to adjust the atmosphere. If necessary N 2 gas may also be supplied to the chamber through lines 11. These gases, each supplied through its respective supply system (not shown), will be combined in a gas-mixing tank (not shown) to adjust the gas composition prior to being supplied to the chamber.
  • the gas discharge out of the chamber through line 12 is collected in a dust separator 13 where solids entrained with the gas is separated. Carbon oxides formed during decarburization is removed out of a gas-separator 14 through line 15. The recovered gas is then supplied to the decarburizing chamber through line 11. Further explanation on this gas supply system will be eliminated since the above explanation will be enough to the person skilled in the art.
  • the as-atomized alloy steel powder of this invention may be continuously carried out on a conveyor through a decarburizing zone comprised of the decarburizing apparatus 5 where the as-atomized powder is continuously decarburized to a level of 0.1% by weight or less of carbon.
  • the decarburizing zone may comprise a pre-heating section, a decarburizing section and a cooling section. The pre-heating and cooling sections are kept in an inert or reduced atmosphere.
  • Cr-Mn low alloy steel powder which was produced through atomization using mineral oil as an atomizing agent, was subjected to decarburuzation using the decarburization apparatus shown in Fig. 9.
  • the chemical composition and particle size distribution of the as atomized steel powder are shown in Table 2.
  • This example treats a low alloy steel powder which contains not only Cr and Mn, but also other easily oxidizable elements such as V, Nb, B and Si, etc.
  • the steel powder having a chemical composition and particle size distribution shown in Table 5 was treated with the decarburizing apparatus shown in Fig. 9.
  • the atomized steel powder employed in this example was produced by using mineral oil containing 5% by weight of water as an atomizing agent, and was characterized in that the carbon content of the steel is less than that of the powder used in Examples 1 and 2.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Manufacture Of Metal Powder And Suspensions Thereof (AREA)

Claims (6)

1. Verfahren zum Erzugen eines sauerstoffarmen und kohlenstoffarmen Stahllegierungspulvers mit folgenden Schritten:
Es wird eine Stahlschmelze erzeugt, die mindestens ein leicht oxidierbares Element enthält, das aus der Gruppe ausgewählt ist, die aus dem Chrom, Mangan, Vanadium, Niob, Bor und Silicium besteht;
mit Hilfe eines Zerstäubungsmittels, das ein nichtoxidierendes Medium enthält, wird die Stahlschmelze zerstäubt, wobei ein im Zerstäubungszustand befindliches Stahllegierungspulver erhalten wird, das höchstens 0,2 Bew.% Sauerstoff und mindestens 0,1 Gew.% Kohlenstoff enthält;
zum Einstellen des Kohlenstoffgehalts des im Zerstäubungszustand befindlichen Stahllegierungspulvers wird das im Zerstäubungszustand befindliche Stahlleoierungspulver kontinuierlich durch eine Abkohlungszone geführt, die einen Vorwärmteil, einen Abkohlteil und einen Kühlteil besitzt, wobei in dem Vorwärm- und dem Kühlteil eine inerte oder reduzierend wirkende Atmosphäre aufrechterhalten wird, das Pulver in dem Abkohlteil in einer Atmosphäre gehalten wird, die mindestens H2 und H2O-Gas unter einer der nachstehend unter (A) und (B) angegebenen Bedingungen enthält, und das so erhaltene Pulver auf Zimmertemperatur abgekühlt wird; Bedingung (A):
Temperatur (t"C): 600°C ≦ t ≦ 950°C
Atmosphäre
Figure imgb0028
Behandlungszeit (8 min):
Figure imgb0029
Figure imgb0030
Bedingung (B):
Temperatur (t°C): 950°C < t ≦ 1250°C
Atmosphäre (PH2/PH2o) : PH2/PH2O ≧ 0.5
Behandlungszeit (8 min):
Figure imgb0031
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das nichtoxidierende Medium aus den Mineralölen, tierischen Ölen, pflanzlichen ölen und deren Gemischen ausgewählt ist.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die genannte Atmosphäre H2- und H20-Gas enthält.
4. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die genannte Atmosphäre H2-H20 und N2-Gas enthält.
5. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß der Sauerstoffgehalt des im Zerstäubungszustand befindlichen Stahllegierungspulvers höchstens 0,1 Gew.% beträgt.
6. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß der Sauerstoffgehalt des im Zerstäubungszustand befindlichen Stahllegierungspulvers höchstens 0,05 Gew.% beträgt.
EP82305820A 1982-11-02 1982-11-02 Verfahren zur Herstellung von Stahllegierungspulver Expired EP0108175B1 (de)

Priority Applications (2)

Application Number Priority Date Filing Date Title
DE8282305820T DE3277966D1 (en) 1982-11-02 1982-11-02 Process for producing alloy steel powder
EP82305820A EP0108175B1 (de) 1982-11-02 1982-11-02 Verfahren zur Herstellung von Stahllegierungspulver

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EP82305820A EP0108175B1 (de) 1982-11-02 1982-11-02 Verfahren zur Herstellung von Stahllegierungspulver

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104148657A (zh) * 2014-09-03 2014-11-19 四川理工学院 一种利用晶间腐蚀制备高压缩性水雾化合金钢粉的方法

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Publication number Priority date Publication date Assignee Title
SE509049C2 (sv) * 1996-04-18 1998-11-30 Rutger Larsson Konsult Ab Förfarande och anläggning för framställning av atomiserat metallpulver, metallpulver samt användning av metallpulvret
US6747734B1 (en) 2000-07-08 2004-06-08 Semitool, Inc. Apparatus and method for processing a microelectronic workpiece using metrology
WO2017051541A1 (ja) * 2015-09-24 2017-03-30 Ｊｆｅスチール株式会社 焼結部材原料用合金鋼粉の製造方法

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1236271A (en) * 1967-09-28 1971-06-23 Smith Corp A O Method of forming steel powder

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57164901A (en) * 1981-02-24 1982-10-09 Sumitomo Metal Ind Ltd Low alloy steel powder of superior compressibility, moldability and hardenability

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1236271A (en) * 1967-09-28 1971-06-23 Smith Corp A O Method of forming steel powder

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104148657A (zh) * 2014-09-03 2014-11-19 四川理工学院 一种利用晶间腐蚀制备高压缩性水雾化合金钢粉的方法

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EP0108175A1 (de) 1984-05-16

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