DE2314743A1 - PROCESS FOR MANUFACTURING KNITTED PARTS FROM METAL POWDER - Google Patents

Description

Dipl.-Ing. H. Sauerland · Dr.-lng. R. König ■ Dipl.-Ing. K. Bergen

Patent Attorneys ■ 4000 Düssaidorf 3D · Cecilienallee 76 ■ Telephone 433732

March 23, 1973 28 503 K

International Nickel Limited, Thames House Millbank _London_S i. ¥ il /

"Process for the production of kneaded parts from metal powder

vern "

The invention relates to a method for producing kneaded, for example forged parts under Use of a compact made from an alloyed powder.

Usual powder metallurgically produced sintered parts generally have a certain porosity that their physical properties or mechanical properties such as the yield point and notched impact strength affect. The porosity can be determined by using certain techniques, for example reduce recompression and infiltration or hot pressing and high temperature sintering; this causes however, additional cost and difficulties in mass production.

Numerous attempts have therefore been made to eliminate the porosity by means of powder forging, that is suitable for automatic production. The invention is now based on the object of such

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To create procedures.

The above-mentioned object is achieved in a process in which a compact is forged from a pre-alloyed powder at a temperature in the two-phase region of the alloy, in which one metallic phase is cubic and the other metallic Phase body-centered or tetragonal body-centered and the volume fraction of the two phases is at least k% . However, the volume fraction of each phase is advantageously at least 1090, better still at least 20% or even 55 to 75% * The mean grain size of each phase preferably does not exceed ASTM 10, better still ASTM 12. A larger grain, for example with a size of ASTM 8, can impair the mechanical properties of the kneaded part, so that smaller grain sizes of for example ASTM 14 or below are particularly advantageous.

When forging an alloy with the aforementioned two-phase structure it was found that the two phases mutually affect one another in the direction of impeding grain growth influence during the recrystallization, so that a fine-grained product results. The flow resistance of the Alloy with the two-phase structure is generally less than that of a single-phase alloy, so that with relatively low deformation forces and temperatures can be worked. In this way, tool wear, warpage and breakage are reduced as well increases the service life. A lower resistance to deformation leads to better mold filling capacity, while lower deformation temperatures reduce the risk

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an oxidation "during deformation" resp. Forging decrease.

Volume fractions below h% per phase are not sufficient to avoid undesired grain growth and generally lead to a deterioration in flowability or an increase in deformation resistance during forging. Inclusions such as sulfides and silicates are not considered to be metallic phases in the sense of Invention, but are not harmful in small amounts.When cooling after forging, the metal structure can contain conversion products at least one of the two metallic phases.

The pre-alloyed metal powder is advantageously sprayed, i.e. from a melt of the desired composition made using air, steam, inert gas, water or in vacuum is processed directly into powder. The water spray method with or without inert gas is particularly suitable because it requires relatively little effort and yields well compressible irregular powder particles.

The use of the spray method in producing the powder has a number of advantages; this is the main way in which very fine particles can be produced. The particle size should not exceed 500 μm and is preferably not less than 275 μm . A particularly suitable powder consists of at most 25% particles below 40 μm, the remainder up to 225 or 275 μm. In addition, the particle surface should consist essentially, but ideally entirely, of an oxide film, which has a particularly favorable effect on preventing the grain growth of the individual particles and beyond the grain boundaries. However, too high an oxygen content can cause the

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technological properties of the precast part, the compaction and sintering before forging as well as the welding of the particles during forging. For this reason, the oxygen content of the powder preferably does not exceed 0.25% and is the thickness of the Oxide film at a maximum of 10 ^ m. Preferably the However, the oxygen content of the powder is 0.15% or less and the film thickness is not more than 0.15%

When carrying out the method according to the invention the powder can first be pressed and the pellet then heated to achieve the desired two-phase structure set and then forge the pellet at least to its final density. The starting powder a lubricant can be added; in addition, the compact can also be sintered in the usual way before forging will. Finally, depending on its composition, the forged part can be further treated, e.g. be processed by lifting or hardened.

Any pretreatment with regard to a fine-grain structure of the finished part is required in the method according to the invention not mandatory. This is in contrast to the conventional methods of making kneaded ones Alloys and parts with a fine-grain structure are essential Advantage; namely, these require cold deformation at room temperature and then an annealing in the multi-phase region above the recrystallization temperature or deformation on cooling on or through the multiphase region. The forging according to the invention closes basically an isothermal treatment during which a continuous recrystallization takes place.

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For the method according to the invention, among other things, powders made of steels with one at the forging temperature are suitable Austenitic-ferritic structure, both low-alloy steels and ferritic-austenitic stainless steels, nickel-chromium powders and nickel-chromium-iron alloys including stainless steels with a structure of a face-centered cubic

ή phase and a body-centered cubic i ^ phase as well as powder made of copper alloys with a finely distributed cubic or tetragonal body-centered · "'phase in the face-centered -τν phase.

Powders made from low-alloy steels include those with 0.4% carbon, 0.8 to 2.5% silicon, up to 2% Manganese, 0.5 to 4% nickel, 0.2 to 2% molybdenum, 0 to 0.2% niobium, 0 to 2% copper, up to 0.25% oxygen each 0 to 3% cobalt, chromium, tungsten and vanadium individually or next to each other and 0 to 0.5% aluminum and titanium, The remainder, including impurities from the smelting process, iron.

Contaminants include residues of deoxidizing and refining agents such as boron. The steel powders mentioned above are new and therefore also fall under the invention; they can be at temperatures of 760-816 ⁰ C, for example at 788 ⁰ C to their theoretical density brought, during the usual low-A-phase steels must be compacted at temperatures of 900 to 98O ⁰ C.

In the steel powders according to the invention, the nickel content of 0.5 to 4% contributes to increasing the strength and Hardenability at; it also extends the temperature

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■ Area of the stable ferritic-austenitic structure. On the other hand, the nickel acts on the ferrite-forming silicon contrary, although higher nickel contents lead to an increase in costs and the deformation resistance "during. forging due to the. increase in the austenite content in the structure. The manganese content preferably exceeds 0.4% not because the manganese has the toughness of the kneaded Partly impaired and the risk of oxidation increased. The molybdenum content does not need to be 1.2% exceed. With nickel contents of 1% and 3%, higher molybdenum contents are likely to impair the tensile strength; accordingly, molybdenum levels of 0.2 to 0.696 are special suitable. The niobium increases the flow resistance, which is why the niobium content should not exceed 0.1%. on the other hand the niobium contributes to increasing the tensile strength, so that the niobium content is preferably 0.02 to 0.08%. Although the silicon is a ferrite former, the silicon content advantageously does not exceed 2% because that Silicon affects the toughness of the finished product. The carbon increases the strength of the finished product, so that the alloy proves to be at least Contains 0.02 or 0.04% carbon. However, carbon contents above 0.4% can result in a completely austenite appearance Lead structure at the forging temperature. Contains the Alloy chromium, aluminum, vanadium, titanium, tungsten and cobalt, so must the effect of these alloy components on the ferrite and austenite content in the structure are taken into account. .

In view of a low deformation resistance in the temperature range of 760 to ⁰ 816 C and a room temperature yield strength from 550 to 825 MN / m at an elongation of over 7.5%, the steel powder is 0.05 to 0.15% carbon, 0 , 8 to 1.5% silicon, 0.5 to 1.2%

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Nickel, 0.2 Ms $ 0.4 molybdenum, 1 to 2? Ό copper and up to 0.1% niobium, the remainder iron including impurities caused by the smelting, especially. If the kneaded part is still to be carburized, the alloy should be copper-free or contain less than 0.5% copper. Higher yield strengths of 895 MN / m, for example, can be achieved if the powder contains 2 to 2.5% silicon, 2 to 3% nickel and 0.8 to 1.2% molybdenum.

In the following Table I the compositions of three powders according to the invention are compiled, the alloy residue of which in each case consists of iron including impurities caused by the melting process. These powders were produced by spraying a melt at 1565 ^° C. with argon in my argon atmosphere.

O C.
(%) Si
(X Tabel 22nd Ni
00 I. Mon
(% ) Cu
(% ) Nb 0
w , 06 O , 069 1" 38 1 0, 24 1 , 4 0.015 0 , 04 stole O , 11 2, 44 2.6 0, 93 1 , 0 0.071 0 , 05 1 , 11 2, 2.5 0, 89 - * - 0 2 3

0/0975

The properties of the kneaded parts made from the above-mentioned powders become apparent from the following Table II. The steels 1 and 2 were prepared by a four-hour curing at 538 ⁰ C with air cooling examined while the steel 3 after a 40 minute anneal at 927 ⁰ C, oil quenching and three hours of tempering at 150 ^° C. and cooling in air was investigated.

Table II

Steel stretch limit

tensile strenght

(MN / m ² ) (MN / m ² )

See stretching. Hardness (%) {%) (Rc)

1 863 863 11.5 30.5. 27.2 2 901 1027 5.5 15th 33.5 3 • 967 1301 14.5 33 -

The deformation resistance of the two steels 1 and 2 was also with three different expansion speeds

■) O

ten at 788 C with the following result:

stole

tension
(MN / m ² )

31.5
63
103

Strain rate

(cm / cm / min)

0.006 0.062 0.606

Steel 2

Tension . Elongation - .. dizzy.

(cm / cm / min)

(MM / m ² )

39 , 5 O-, 006 73 0, 064 126 0, 528

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When cooling down from the forging temperature, the structure of the steel consists of ferrite and conversion products of the Austenite, i.e. from martensite and bainite, as well as a certain amount of residual austenite, whereby the structural proportions depend on the composition and the cooling conditions.

Nickel-chromium and nickel-chromium-iron alloys with 25 to 50%, for example 32 to 40% chromium, 0 to 25%, for example 14 to 22% iron, 0 to 1%, for example, are also suitable for the process according to the invention 0.2 to 0.8% titanium, up to 0.1% carbon, 0 to 1%, for example 0.2 to 0.8% silicon and 20 to 60% nickel. Such alloys can also contain other elements such as niobium, vanadium and aluminum in amounts that are customary in conventional nickel-chromium and nickel-chromium-iron superalloys. Such an alloy contains, for example, 37% chromium, 18% iron, 0.5% titanium, 0.05% carbon and 0.5% silicon, the remainder including impurities caused by the melting process, nickel. A powder of this alloy with up to 0.15% oxygen can be forged ^{at 980 to 1200 °} C., preferably at 1038 to 1093 ^{° C.} If the powder is produced by the spraying process, each powder particle consists of a quenched, face-centered cubic > r phase with nickel and chromium and optionally iron in solid solution. When reheated to at least 980 ⁰ C. K. phase separates the?, That is, the chromium-rich body-centered cubic, nickel and optionally iron-containing solution in fine distribution in the <from phase.

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A stainless steel powder suitable for the process according to the invention contains 15 to 35% chromium, Ms 12%, for example 2 Ms 10% nickel. Ms 1% or 1.5% titanium, up to 1% vanadium, up to 0.5%, preferably 0.025 to 0.15% oxygen, up to 0.25% carbon, up to 1% silicon, up to 1% manganese, up to 3% or 4% molybdenum, up to 2% cobalt, up to 2.5% or 3% copper. Such steels may be hot worked at 927 to 1093 ⁰ C, wengleich a temperature is preferable from 954 to 1010 ⁰ C. In this case, the structure consists of a ferritic matrix with finely dispersed austenite. A particularly suitable stainless steel contains 25 to 31% chromium and 5.5 to 7% nickel.

Suitable copper alloys can contain 8 to 14% aluminum and optionally up to 6%, for example 3 to 5% iron. Other examples of copper alloys are those which contain substantial amounts of zinc, for example 35 to 50% zinc, or 8 to 12% magnesium. A particularly suitable nickel-zinc-copper alloy contains 4 to 71%, preferably 8 to 40% nickel and 29 to 40% zinc, the remainder being copper and the usual accompanying elements a space-centered cubic or body-centered tetragonal ß- phase in finely dispersed distribution; it can be forged at this temperature. The binary copper-zinc alloy with 38 to 50% zinc, the remainder copper, also has a face-centered cubic rA_ structure with a space-centered high-temperature phase. The forging temperature of this alloy is 454 to 65Q ⁰ C.

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The method according to the invention is "suitable in use." Low-alloy steel powder, for example for the manufacture of automobile parts, pinions, gears, connecting rods and epicyclic gear moldings. Furthermore, the method according to the invention can be used for manufacturing of pump gears, pipe and valve fittings, guide vanes, V-belt pulleys, surgical instruments, and instrument keys are used.

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Claims (11)

International Nickel Limited, Thames House Millbank London S «W.1 / England Patent claims: 1. A method for producing kneaded parts using a compact made from an alloyed powder, characterized in that the compact is deformed at a temperature at which its structure consists of at least k% of a surface-centered cubic and a body-centered cubic or tetragonal body-centered phase consists. 2. The method according to claim 1, characterized in that that the volume fraction of the phases is at least 10% and the grain size of the phases at most ASTM 10 is. 3. The method according to claim 2, characterized in that that the volume fraction of a phase is 55 to 75%. 4. The method according to one or more of claims 1 to 3, characterized in that the mean grain size of the phases is at most ASTM 12. 5. The method according to one or more of claims 1 to 4, characterized in that the structure is ferrite and austenite at the deformation temperature contains. - 3098AO / 0975 6. The method according to claim 5, characterized in that a compact made of a steel powder with Ms 0.4% carbon, 0.8 to 2.5% silicon, up to 2% manganese, 0.5 to 4% nickel, 0.2 up to 2% molybdenum, 0 to 0.296 niobium, 0 to 2% copper, up to 0.25% oxygen, each 0 to 3% cobalt, chromium, tungsten and vanadium individually or side by side and 0 to 0.5% aluminum and titanium, remainder including iron impurities caused by the smelting process. 7. The method according to claim 5, characterized in geken that a pellet made of a nickel-chromium-powder alloy with 25 to 50% chromium, 0 to 25% iron, 0 to 1% titanium, up to 0.1% carbon, 0 to 1% Silicon and 20 to 60% nickel is deformed. 8. The method according to claim 5, characterized in that that a pellet made of a stainless steel powder with 15 to 35% chromium, up to 12% nickel, up to 1.5% Titanium, up to 1% vanadium, up to 0.5% oxygen, up to 0.25% carbon, up to 1% silicon, up to 1% manganese, 4% molybdenum, Up to 2% cobalt and up to 3% copper, the remainder including impurities caused by the melting process, iron is pressed. 9. The method according to one or more of claims 1 to 4, characterized in that a pellet from the powder of a copper alloy, the structure of which at the deformation temperature consists of, ^ - and "> Phase exists. 10. steel alloy powder for the method according to claim 1, consisting of up to carbon, 0.8 to 2.5% silicon, ' up to 2.0% manganese, 0.5 to 4% nickel, 0.2 to 2% molybdenum, 309840/0 9 75 O Ms 0.2% niobium, 0 to 2% copper, up to 0.25% oxygen, each 0 to 3% cobalt, chromium, tungsten and vanadium individually or next to each other as well as 0 to 0.5% aluminum and titanium, remainder including iron impurities caused by the smelting process. 11. steel alloy powder according to claim 10, but 0.05 up to 0.15% carbon, 0.8 to 1.5% silicon, 0.5 to 1.2% nickel, 0.2 to 0.4% molybdenum, up to 2% copper and Contains up to 0.1% niobium, the remainder including impurities caused by melting iron. 30 9 840/0975