DE1958795A1 - Process for the production of dense metallic materials - Google Patents

Description

V-60.822-04 November 18, 1969

KRU / hhoe

THE BATTELLE DEVELOPMENT CORPORATION Columbus, Ohio

PROCESS FOR MANUFACTURING DENSE METALLIC MATERIALS

The invention relates to a process for preparing a dense metallic material, which is referred to in the patent _anm eldung.P 17 58 477.9 ^»m i following main patent application, is described.

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In the main patent application, a method for producing a material is claimed that essentially consists of metal with a density close to its theoretical maximum value and of a particulate Metal connection is established by the following four procedural measures:

(a) Prepare a compressible agglomerate by mixing a particulate metal compound

w bond with a plasticizer; whereby

the metal compound free reaction energy with hydrogen in the formation of elemental metal of less than about 15 kcal per gram atom at the reaction temperature and at least 35% by weight of the metal compound has a particle size of less than 10 / rev (10.10 mm),

(b) compressing the agglomerate obtained,

(c) treating the pressed product under a reducing atmosphere consisting essentially of hydrogen exists at temperatures below the evaporation and melting temperatures of the metal and the metal compound and above the evaporation temperature of all hydrogen-containing

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Components of the plasticizer lie, for a period of time necessary for the reduction of at least most of the aforesaid Particle is sufficient, and

(d) heating the pressed product until the metal particles obtained by the reduction are sintered.

It has now been found that other reducing agents for the reduction of the particulate Metal compounds to elemental metal can be used «It it was found that e.g. B. easily reducible metal compounds, such as the oxides of Fe, Co, Ni, Cu, Mo and ¥, the chlorides of Fe, Cr and Ta and the sulfides of Cu and Fe, in particular Iron oxide, can be reduced by a gas, in which the in the main patent application said hydrogen partially or completely by another reducing agent, especially carbon monoxide, is replaced. '

The invention accordingly relates to a method for the production of a material, which is essentially made of metal with one of their theoretical Maximum value close to density exists,

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from a particulate metal compound with the following four procedural measures:,

a) a compactable agglomerate of a particulate metal compound is mixed with a plasticizer or binders, the metal compounds having a standard free reaction energy with hydrogen in the formation of elemental metal of less than

Have +15 kilocalories per gram atom of hydrogen at ™ the reaction temperature and at least

35% by weight of the metal compound particles Grain size less than 10 / u;

b) the agglomerate is compacted;

c) the compact is placed under a reducing atmosphere exposed to a temperature below the Sublimation or melting temperatures of the details and the metal compound and above the

Evaporation or decomposition temperatures of all non-metallic compounds lies therewith for a period of time sufficient a major part of the particles is reduced and

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d) the compacted agglomerate is sintered until the particles obtained by the reduction elementary metal.

According to the invention, powder of metal compounds with any common particle shape (e.g. spherical, oblong, needle-shaped, rod-shaped, etc.) for compression, Reducing and sintering can be used. The sintered material obtained has an essentially pore-free structure, a smooth surface and generally has densities of over 90% of the theoretical possible material density. However, it has been found that metal oxide powder that obtained by spray drying a dissolved metal compound, excellent compacts (especially by extrusion), which are reduced and Provide sintered products with greater density and better surface and structure than this is possible with compacts of oxides from other sources.

The spray drying of metal compounds containing Solutions to obtain metal oxide powder is a well-known manufacturing process. This procedure will z. B. carried out to recover hydrochloric acid from the pickling solutions used in the iron and steel industry used to strike the hammer and other shapes

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to remove iron oxide from iron and steel products. The aqueous pickling solution used here solution containing up to about 11% by weight of free hydrochloric acid and Contains up to about 35% ferrous chloride, is sprayed through a nozzle into a heated room (at about 538 C), where the ferrochloride is converted into iron oxide and hydrochloric acid according to the following formula:

2 FeCl ₂ + 2 H ₂ O + 1/2 O ₂ * - * ^Fe ₂ ° 3 ⁺ ** ^HC1 *

One such method is described in the article "Liquor Regeneration Slashes Cost of Steel Pickling" by Joseph A. Buckley, Chemical Engineering, Jan. 2, 1967t Pages 56 - 58 ».

Sufficiently precise determinations of the particle size in finely ground powders are difficult to carry out, especially when the distribution of particle sizes of such powders also includes a fraction whose 'Particle size less than 10 / U in diameter (or

even less). Such provisions are extreme difficult if the individual particles are not of the same shape. For example, if the particles are crushed from or ground oxides of the spray-dried hydrochloric acid pickling liquor are probably many Particles shaped relatively elongated so that

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it is difficult to determine the smallest particle sizes. Elongated particles are not passed through Go sieve, with its mesh sorts relatively similarly shaped particles with equivalent mass will. Therefore, the measurement results differ from the Particle size and size distribution for a given powder determined by known procedures and working methods to make such determinations vary considerably.

It has now been found that one can determine ^{the size of finely ground particles relatively accurately by using the "Coulter counter 11} analysis. In this analysis the particles are suspended in an electrically conductive liquid which flows through a small opening. By means of two in the When the electrodes are placed opposite one another, a current is sent through the liquid in the opening. As the particles flow through the opening, the respective change in electrical resistance is

des measured between the electrodes to determine the particle size. The measurement is therefore based on the Particle mass and is not determined by the shape of the particle influenced.

For the description of the invention and its claims, apart from fc * i U ^ n cases specifically listed below,

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all particle size determinations by "Coulter counter "measurements, including those Regulations in which metal particles and particles of metal compounds come together - regardless of regulations the particle size by other means.

A difficulty arises in the precise determination of the particle size and the particle size distribution extremely fine powders (less than 10 / U in diameter) and Although the fact that the fine particles have a tendency to form agglomerates or larger particles from many smaller caking particles. ¥ enn such agglomerates containing powders through the conventional means such as "coulter counter" analysis then measure the agglomerates as much larger particles which lead to an erroneous determination of the particle size distribution.

We have found that the iron oxide particles obtained by spray drying k the hydrochloric acid pickling liquor have a particular tendency to agglomerate. Examination with a scanning electron microscope (scanning electron microscope) shows that the actual particle size of the oxide is much smaller than indicated by the "Coulter counter" measurements »What at a magnification of 2000 times as a single particle with a diameter of appears about 25 / U, arises at a

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10,000 times. Magnification emerges as an agglomerate of small particles averaging 3000 to 50 % (0.5 to 1.6 / U).

This discovery has drawn our attention to the fact that, while the invention is feasible, when the metal compounds (such as iron oxide) have a particle size of at least 35% less than 10 / U in diameter, and when the preferred mean particle size is no greater than 6 λχ with a fraction of at least 25% by weight with a particle size not exceeding 2.5 / U, optimal results will be obtained when the apparent average particle size of the powder is less than 1 micron in diameter.

This average particle size of less than 1 / U in diameter can be determined by "Coulter counter" measurements can be determined or ascertained when there is no agglomeration. However, if the particles tend to To agglomerate, as in the case of spray-dried metal oxides, then an accurate determination of the particle size is necessary not possible by such means as the "coulter counter" measurements. However, we have found that such determinations by determining the surface area can be carried out. Duron, the investigation the total surface area of a given powder

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one can easily get the average particle size determine if one assumes completely smooth, spherical particles'. Such determination can be made by application the formula

D = K

d χ SA

be carried out in which

D = average diameter in λχ

ideal balls,
K = the constant 6, d = density in g / ccm

SA = surface of the particles in m / g

If you z. B. determined the surface of iron oxide (Fe ₃ O) to be 5m / g and the density to 5 »24 g / ccm, then is

D =

5.2k χ 5, · ■■ '■ · or D = 0.23 / u.

There are a number of known methods of determination the surface area in powders, which, however, in their results differ a lot. It was pinned down that of Dr, Paul Emmet and his collaborators BET-Mathode developed in the last 30ar years

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for measurements of the available surface area of catalysts for the determination of the surface area in powders Metal connections works very reliably.

According to the BET method, the surface area of each Particles coated with a monomolecular layer of an adsorbable gas. This is achieved by that a known amount of a gas such as nitrogen (bp. -195 C), carried out at the boiling point of the gas through a weighed sample of the powder. Under these Conditions, the gas molecules form a densely packed monomolecular layer on the surface of the sample. Di · Determination of the by the sample in the case of monomolecular Adsorption of spent gas compared to standard samples easily gives a relatively accurate determination the surface in the powder.

The particle size determinations of less than 1 / U made for the invention are in agreement evaluated with the BET measurements.

"Coulter counter" and BET measurement results of some Samples of the "HCl · 'iron oxide are shown in Table A below. The BET results show slight differences in terms of surface area and apparent particle size, when the ojcyd is calcined or calcined and in a vibration ball mill (V.B.M.) at 217,728 kg / h

1 09 887/06 83

was treated. The BET results show a consistent one Increase in surface area and decrease in apparent particle size, like the V.B.M. treatment is decreased. Show the "Coulter counter" results on the other hand, a large increase in particle size when the oxide was calcined, and a large exception, when grinding at 217 »728 kg / h. The results show no definite decrease in particle size with reduced V.B.M. treatment.

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sample

Table A.

BET surface area

m / g

Average Particle size

apparent after "Coulter

Part size counter ", 30 sec

/ U # dispersion

Medium Max.

<2.5

/ ^U

lost 11

Treated in a ball mill for 3 hours

calcined **

calcined and treated in a ball mill for 3 hours

calcined U.V.B.M. *** ground

217.728 kg / h

calcin, and in V.B.M.

ground

113.4 kg / h

calcine. u. in V.B.M. 2 χ ground 113.4 kg / h

calcine. u. in V.B.M.

ground

53.525 kg / h

4.8

0.24

0.8 12 75

7.8 0.16 0.8 10 81 4.4 0.26 27 100 0 5.6 0.20 5 4o 32 3.6 0.32 6.5 38 23 4.6 0.25 2.5 50 50 5.5 0.21 4.6 37 28 7.6 0.15 7.9 50 28

* These figures are based on completely smooth and spherical particles with a weight of 5.24 g / ccm. Irregularly shaped
Particles with a rough surface would be average
to be taller.

** The "HCl" -Eisenoxyd 8 hours heated to approximately 455 ⁰ C, remove excess acid to.

*** A continuously working ball mill in which the vibration is combined with the grinding process.

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- ί4 -

From the results in Table A it can be seen that by "Coulter counter" the size of the particle agglomerates in the oxide obtained by spray drying the hydrochloric acid pickling solution, during the BET test which measures the surface area, the total agglomeration plus the surface area of at least some of the Indicates individual particle sizes within the agglomerates.

The results in the manufacturing examples below show that oxide obtained by spray drying of pickling liquor, which has been ground in a ball mill for 3 hours, can be used for the production of 0.25 μm wires of high density with excellent surface quality . Since the surface measurements, as obtained by BET tests, show an average apparent particle size of this material below 1 / a , it has been clear that such determination of the particle size is important for the quality of the wire * products to be manufactured.

The same applies to the method according to the invention Metal compounds suitable as in the process of the main application that are reducible with hydrogen are and with hydrogen free standard reaction energy have less than +15 kilocalories per gram atom of hydrogen at the reaction temperature.

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It is to be understood, however, that as a reducing -Gas not hydrogen must be used, but carbon monoxide as well, just as well.

The wording used in the main patent application “a metal compound with a standard free reaction energy with hydrogen to form elemental metal of less than +15 kilocalories per gram atom Hydrogen at reaction temperature " relate to Δ F (standard free energy of reaction), the is defined as follows:

worm

H = standard heat of reaction at temperature T S = standard entropy of reaction at temperature T T =? the desired temperature (i.e. the reduction temperature),

The word "standard" in relation to Δ h °, Δ S ° and £ y F ° denotes the standard state for condensed phases (feat or liquid) of the pure materials (i.e. metal compounds) at atmospheric pressure and the temperature of interest (T) and the standard state for gas phases at fugacity * 1 (ideal gas state) and the temperature of interest (T.).

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Using the formula, the temperature T is in degrees Kelvin specified. '

In the parent patent application a measure is described ¹ to achieve high density metal alloy articles, wherein metal particles of at least one metal other than the metal of the particulate metal compounds are mixed with the latter to form a metal alloy in the reduction and sintering of the metal compounds form. It has now been found that the addition of metal particles to the finely divided or particulate metal compounds reduces the shrinkage of the sintered product. In each sintering process, the pressed metal body shrinks in its outer periphery thanks to the disappearance of the voids between the particles when the particles sinter together to form a dense solid mass. It was determined, . that pressed bodies made of metal compounds, such as metal oxides, which according to the invention are first reduced and then sintered

especially shrink because the reduced particles are smaller than those of the metal compound particles and therefore have larger voids between the particles. Such shrinkage can be caused by the addition of elemental metal to the particulate metal compounds are greatly reduced before being compressed, z. B. It may be desirable to add up to 65% by weight of iron powder add to the shrinkage of the pressed body

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Reduce.

In the main patent application it is stated that when carrying out the claimed process for the production of iron and steel articles, particular success is achieved through the use of iron oxide powder (hereinafter referred to as "HCl oxide"), which is a by-product of the hydrochloric acid pickling process , was achieved. This HCl oxide is ^ -Fe 0, known as hematite. Another source of iron oxide, which is particularly useful, is "mill scale" (hammer blow, mill scale, etc.), consisting of oxidation products resulting from the action of heat and corrosion, which during the manufacture of iron and steel articles from these by other means than by pickling acid are removed, and consist of a mixture of FeO, Fe "O _U nd Fe_0" ferric oxide in the form of Fe "0th however, it is more difficult to reduce than FeO or Fe "0", so that "mill scale" is also more difficult to reduce than HCl oxide; but "mill scale" has the advantage that it is pure and

r is inexpensive. It has also been found that iron

v ore successful in the method according to the invention

can be used. This finding is essential since the available supply of HCl oxide or on "Mill scale" is limited and a different usability of these substances. The usability of iron ore or another mineral secures a downright un-

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limited supply of inexpensive raw material for. Purposes of the invention.

For best results, the iron ore used should be as free of impurities as possible. The amount of contaminants that can be allowed affects the quality of the last product received. Apparently ores can with only 30 to kO wt -% ferric oxide not be used for the production of fine wire or thin tubes. however, such ores may be prepared by suitable methods in concentrates with at least 90 wt .- $> iron oxide and are also to be converted to 98 ° i. Such concentrates can be used in the process of the invention. Likewise, hematite deposits, which _{consist essentially of Fe 2} O, are to be preferred to magnetite ores, which consist mainly of Fe 2 O.

We have found several known high-grade (more than 95% by weight of iron oxide) Hematite iron oxide stock exist which are excellent sources of iron oxide. One such camp is called "Indian Blue Dust" is known and another is' a similar Brazilian camp. These ores can for the production of iron and steel products are used according to 'the method according to the invention, without that they must be preliminarily cleaned or concentrated,

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except that they are married to the desired one To get particle size.

A surprising and novel peculiarity of the method according to the invention relates to the "active" state of the; Metal after the reduction of the metal compound particles before sintering, metal powders tend to take on a thin oxide coating or film, and almost all metal powders of very small particle size are provided with such a film, which prevents the rapid oxidation or even the air flammability of such materials. Such a film makes the particles "passive" so that they can be exposed to the normal atmosphere. Such a film that retards sintering is difficult to reduce. If the metal compound particles are compressed and reduced according to the invention and sintered immediately after the reduction without exposure to an oxidizing gas, high density products can be obtained at much lower temperatures during extremely good times of the reduction period thanks to the "active" nature of the reduced particles will. This discovery adds to the value of the invention because the firing cost required for the process, and so the cost of the process, is much lower than that of the earlier known processes.

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For example, in a continuously carried out process, extruded iron oxide (powder obtained by spray-drying the hydrochloric acid pickling liquor, which was ground for 3 hours in a ball mill and then mixed with starch mixed in water as a binder) for wire production through an oven with two temperature zones - one for reduction each and to sintering - passed, first through the reduction zone at a temperature of about 498 ° C to 6k9 ° C and then directly into the sintering zone, the temperature of which is normally kept above 1159 ° C (preferably at about 1177 ° G or 1203 ° C). The hydrogen gas is introduced into the high temperature zone of the furnace in countercurrent to the direction of movement of the wire and exits the furnace through the low temperature zone. Thus, the strand of the wire to be produced does not come into contact with oxidizing agents but with reducing gas which is gradually becoming cleaner from the reduction zone of lower temperature to the sintering zone of higher temperature. The dwell time in each furnace zone (reduction and sintering zone) depends on the speed at which the wire rope is fed through the furnace.

It has been found that low sintering temperatures, such as 815 C, with a short exposure time, for example

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5 minutes, yield an iron wire which has surprisingly high tensile strength properties. Sinterungstemperatüren of 983 ⁰ C, 1O38 ° C and 1092 ° C give densities (greater than 90% of theoretical density), high-strength, ductile Bisendraht having a pore-free, commercially acceptable surface. These properties are recorded in the results in Example VI and in Table 5.

The one suitable for making wire or tubes Extruded strand shrinks during reduction and sintering. The amount of shrinkage varies depending on the Composition of the mixture of metal compound and Binder. This shrinkage can be determined by direct measurement or with a high degree of accuracy be calculated. In general, the shrinkage will be 30 to 50 #, so that for the production of 0.508 mm wire or pipe wall thicknesses a pressed strand of about 0.7 ^ 2 mm thickness or wall thickness is used must become.

As stated in the main patent application, was found that when using oxide particles for the production of iron, steel or other iron alloys the distribution of the particle sizes is essential for obtaining sufficiently dense products. Although in the manufacture of articles, such as wire

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and pipes, surprisingly high values were obtained when at least 35% by weight of the Oacydpialver have a particle size of less than 10 μm, it has been found that products with better densities and mechanical properties are obtained, about the mean particle size of the powder 6 / U is. Particularly high density and good mechanical properties are achieved when at least 25% by weight particles with a size of W 2.5 / U or less are added to the powder with an average particle size of 6 / U, and optimal properties are achieved obtained when the apparent average particle size of the powder is less than 1 / U.

Although the inventors do not want to be constrained by theory, their belief is that that such a distribution of particle sizes results in a more compact mass. With other I ren words, if the mean oxide particle size

6 / U and less and at least 25 wt .- ^ of the particles are less than 2.5 / U in size, then the compressed particles are closer together and. the resulting reduced and the sintered articles have a greater density {substantially 100% of the theoretical value), and therefore -Hünschenwertere ■> ^v on mechanical properties.

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It has also been found that the method according to the invention is particularly suitable for the production of objects stainless steel when using a. Mixture of Iron, chromium and nickel compound particles are suitable is. In particular, the inventive Process stainless steel in the composition of AISI types 304 and 430 from a mixture of finely ground Fe "0", Cr_0 and NiO.

The method of the invention enables the user to use the reduced, compressed agglomerate at lower levels To effectively sinter temperatures and shorter periods of time than for equally compressed Metal powder would normally be required. The one used for the production of fine wire and thin-walled Pipes suitable extrusions, which consist essentially of iron oxide, can be continuously connected through one behind the other hot zones are led to reduce the oxide and the reduced metal too Butt, using sintering temperatures, which are up to 344 C below those normally used Temperatures lie.

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■ - - ■ ■■■■■■■■. \

The following exemplary embodiments are intended to provide the method the invention explained, but by no means the claims, be restricted. ^

Example I.

This example concerns the production of a tight Iron or steel wire (0.254 mm diameter) under Use of various mixtures with iron oxide as a finely divided or particulate metal compound.

P The iron oxide used is iron oxide ore with about 99% by weight pure iron oxide (Indian Blue Dust) and HCl oxide powder. Both were ground differently and mixed to obtain different particle size distributions determined by a "Coulter counter ". These particle size distributions are listed in Table 1 below, from which it can be seen that all Examples (except No., T5 ') within the scope of the invention

. fall.

The various oxide examples were mixed with a plasticizing / binding agent, which is described in Example XII A of the main patent application, then introduced into the die chamber and pressed with a hydraulic press to form a thread or strand with a diameter of 0.16 mm. The compression pressure was about 10.5 fcg / in ² . All threads or strands were on one for 90 minutes

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Reduced temperature of 593 C under a hydrogen atmosphere and then for 30 minutes at 1159 <? sintered. .

Some of the wire products, even though they were tight, were relatively brittle, so that the usefulness ■ of these products is limited to applications where brittleness is not an issue. The other products were both continuous as well as ductile and showed: accordingly an optimum of size distribution.

The optimum size distribution is best shown by the curves in the accompanying graphic drawing, which correspond to the values in Table 1. In the drawing are the different Size distributions of individual amounts of powder in agreement with the proportions (in% by weight) of particles having a size that is smaller as a given particle size (in λ). For example Curve 5 consists of values of particle sizes of a single amount of powder in which at least 50 wt. Powder has an average particle size of about 6 / U exhibit.

Where the particle size distribution includes fractions less than 0.8 / U, the curves are or Value series interrupted because it is not appropriate

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even finer text size determinations by the "Coulter counter" method of making .. This is however so to understand that the curves, which are not entirely Show 1ÖO $ ige distribution * necessarily up to Baseline of the graphic division continued Need to become. Hence 'it is evident that the curves T - 5 »12» 13 and 16 when fully registered be, the line A as well as the line B of the gfäphi- ■ So the representation would cross. ■ ^

All powders with a size distribution according to their plotted curves * which cross the lines A and B gave a dense metal wire with optimal properties (continuous and of relatively high ductility). All; these optimal values characterize powder sorters which have an average particle size of not
greater than 6yu, all containing at least 2.5% by weight of particles with 2.5 / U or less. the
Line C extending for the average particle size \ of 2.5 / U or less of 6 up to 25 wt -. $> It should be noted that no curve of the optimum powder crosses the line. ■

It is from the data in Table 1 and the graph Representation easily seen that when carrying out the method according to the invention, optimal pro *

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Λ -27-

products which are competitive and the like produced by conventionally known means can be obtained
Outperform products when the distribution of particle sizes is such that they give a curve on the graph which crosses lines A and B.

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Table 1

oxide

rehearse

Code number

Raw material

Maximum particle size

Mean particle size

<2.5

Results

2
3
4th
5
6th

10-12

13th
14th
15th
16

5tand.HCl oxide

Endian Blue Dus sintered oxide sintered oxide Sintered Oxide Indian Blue Dus Cndian Blue Dus

50% sintered oxide ( 70% " HGl-Oxyd

g. oxide

30% "HCl-Ocyd

50 # sintered * Oxyd > 0% "HCl oxide

30?% Es int. Oxide 10% "HCl oxide

309% esint.0xyd 0% "HCl-Oxide

9.5

15.0 14.0 9.5 35 17 25 2) 44

44 44 44 105

0.8

1.3 2.1 2.9 5.4 8.0 7.2 1.6

2.3 9.0 40
1.6

85.0

56.0 55.0 43.0 25 2.0

"if 59,0

51.0 42 17 59.0

more impeccable
Wire (1) Il ti Il Il wire M. Il ti Il Il wire more brittle Il Il more impeccable
Wire (1) Il more brittle

flawless wire (1)

(1) Good wire was sufficiently ductile and allowed kinking. * (2) HCl-Ocyd sintered and ground to control the particle size.

Example II

"HCl oxide" powder in a ball mill as described in the example I marry the main patent application so that at least

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35 Gew.-96 has a particle size of less than 10 / U, is mixed with a binding / plasticizer made from corn starch and extruded into threads with a diameter of 0.4064 mm. These filaments are then reduced at 593 ⁰ C with Kohlenmoncxydgas. The resulting wire appeared to be of good quality and could be bent into a tight loop. The diameter of this wire was the same as a hydrogen reduced wire (approximately 0.254 mm).

Example III

Stainless. Steels with compositions of AISI types 304 and 430 in the form of 0.254 mm wire were produced from finely ground Fe ₂ O-, Cr'O- and NiO by the method according to the invention. The iron oxide powder was prepared from HCl oxide according to Example I of the main application (35% by weight below 10 / u). The NiO was 99.1% pure and the Cr ₂ O ₃ was CP.Chromoxyd (JT Baker Chemical Company).

The dry oxide powders were in a steel lined ball mill with an inner diameter of 203.2 mm mixed. 10.150 g of oxide powder were used for one batch with 1500 g of steel balls (19.05-25.4 mm in Diameter). The oxide mixtures were at for 6 hours

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a mill speed of 80 rpm.

After the grinding process, the oxide powders were mixed with the hot corn starch binder mixed and extruded to 0.406 mm thick oxide threads. The ratio of oxide to binder was

22.7 grams: 3.5 grams The oxide threads were pulled by means of a

2 75 ton hydraulic press at pressures of 2.016 to 5.04 kg / mm and then at 149 ° C for 30 minutes for removal dried from excess water before reducing and sintering.

The reduction of the oxides and sintering of the filaments to the wire was made carried out under dry hydrogen as follows:

1. reduced at 593 ° C for 10 minutes;

2. gradually heated to 1203 ° C and held at this temperature for 60 minutes;

3. Quickly cooled to room temperature.

The hydrogen to be used is supplied by means of an Engelhard ' see hydrogen cleaners down to a dew point of -54 ° C dried. This dew point was measured at the inlet and outlet ends of the furnace with an Alnor dew point meter.

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checks. When the furnace exits, the hydrogen dew point changes with the respective furnace temperature. During the reduction of iron and nickel oxides at .593 ⁰ C, the dew point was higher than -t.1 ° C. During the reduction of Cr ₂ O varied the output end of oven when measured dew point of -27 ⁰ C at the beginning of this reduction (about 1065 ° C) to -37 ° C at the end of which (1203 ° C), thus was the Gas suitable for reducing Cr ₂ O _{3 throughout this period.} Although the resulting 0.254 mm stainless steel wire contained some unreduced chromium oxide particles internally, its surface was of good quality and had corrosion resistance with reasonable mechanical properties commercially available for stainless steel wire. The mechanical properties and corrosion resistance can be seen in Table 2 below

TABLE 2

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Stainless grinding time Chemical
Steel ball mill composite Hours. Settlement Table 2 strain g / ccm Sintered
density Degree of corrosion
mm / month - Type Cr Ni 25.4 mm 5uvoii forge
material Head chef,
water ENT 6th 15.7 9.52 train
strength 6.82 304 ■ 6 15.7 9.52 kg / mm 18.4 6.82 86.4 (2)
0 0.03302 304 6th
annealed
commercial "
wire 15.7 9.52
(4) (4)
18-20 8-12 25.9 6.82
7.9 86.4 - - 304
(D
304 6th 15.4 - 58.8 15.2
(3)
55 - 86.4 (2)
0 0.02286 430 annealed
commercial
wire (4)
14-18 65.8 —— 7.7 - - - 109 (D
430 61.8
59.5 (3)
30th —— - - · - OO
co - 7/0683 5.25

(1) From Metals Handbook, Vol. 1, pp. 422-423.

(2) Calculated from the weight loss after 12 hours.

(3) elongation in 50.8 mm

(4) Nominal composition.

, cn oo

Example IV

Excellent austeitic (Hype 304) and ferritic (Type 430) stainless steel wires were made from a mixture of Fe ₂ O, NiO and a ferrochrome powder or of Fe ₂ O and ferrochrome powder. Both types of wire could be bent into a tight loop when sintered and had an impeccable microstructure, indicating an almost complete diffusion of nickel and chromium. Both types of stainless steel could be drawn from 0.3302 to 0.127 mm in diameter. Type 430 was drawn without intermediate annealing, while Type 304 required intermediate annealing at a diameter of 0.2286 mm. After sintering, both types had roughly the same elongation properties as the annealed wire made of forged stainless steel. Ductile Type 304 stainless steel tubes were also made from the Fe ₂ O 2, NiO and ferrochrome powder.

The following procedure was carried out in the manufacture of stainless steel wire using ferrochrome. Standard HCl iron oxide (Fe ₂ O ₃ ), nickel oxide and ferrochrome (68.1 Cr, 1.96 Si, 4.24 C and 0.029 N ₃ ) in powder form are placed in a ball mill with 203.2 mm diameter using Steel balls with about 22.2 mm

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Grind the diameter dry. The particle size of the used Ferrochrome powder was "minus 400 mesh" (ASTMX < 37 ^ u). The grinding time was 48 hours (longer than for similar Mixture required). The usual cooked starch binder was then added (2.5 g cooked starch on 22.7 g powder) and threads with a diameter of 0.4572 mm were applied using a pressure of .2016 up to 0.504 kg / mm extruded.

Reduction and sintering of the filaments obtained were carried out under a hydrogen atmosphere with a dew point of -40 ° C. or better. The hydrogen flow rate was 169.8961 / h (considerably less than required for the reduction of Cr ^ O-). The threads or Preßstränge were maintained for 10 minutes at 593 ° C, then heated gradually (3-4 hours) 1203 ⁰ C and kept at this temperature for 1,3 and 8 hours. After sintering at 1203 ° C for a given period of time, the resulting wire was rapidly cooled to room temperature by pulling it into the cold zone of the furnace. Both the 3 and 8 hour sintering at 1203 ° C produce a wire of good quality. After one hour at 1203 ^° C., the ferrochrome had not diffused into the fine structure. This wire

ι π ei fs ρ ■ "/ / η &

3 Usiiö / / Ub

had only a low ductility, as caused by the bending or Buckling test as well as the elongation test was proven. The average diameter of the sintered wire was 0.3175 mm.

The elongation or tensile properties of the wire were good in comparison with the typical properties of forged stainless steel wire described in the literature, but not of the ημΓ sintered wire for 1 hour, which is too low Showed ductility (see Table 3) (because of the insufficient diffusion of the chromium).

The chemical compositions of the sintered wire were as follows:

Type
stainless stole Composition in %
Cr Ni 9.59 C. 304 18.8 9-12 0.063 304 (commercial .) 18-20 -! - 0.08 (max. 430 16.1 _— 0.013 430 (commercial .) 14-18 0.12 (max.

109887/0683

-OXj-

Tabel

Type condition

Wire-Dürch- Tensile Strength- Elongation Remarks knife speed _n %

mm

kg / mm

sintered 0.32258

0.31750 0.32258 0.32512 0.32258

304
304

304

4§0

drawn 0.21082 0.22352

drawn 0.12192 0.11430 0.12192 0.12192 0.12192

0.31496 0.32512 0.32004 0.32004 0.32004

Annealed Ö, 05ÖS-Ö, 508 customary

liiifif »» * 'ft. ItQROA

sintered

tiuiiuv,

Under
sintered

t 430 pulled
sintered

0.39624 0.31750

Ö, 32258 Ö, 32ÖÖ4

0.09652 0.09652 0.09651

0.33174

430

Annealed imter 0, §9624 customary

59.3

68.2 54.8 60.2 63.8

135.1 143.5

166.0 176.0 170.0 153.0 154.8

49.7 58.0 39.9 63.7 64.6.

73.5-101.5

52.5-73.5 35.3

41.4 40.2

111.0 108.0 105.0

36.6 37.9

4S, 5 - 59.5

46

34
57

4.1 5.0

7.8 6.4 4.5 7.6 2.8

50

63
3Ö-S5

7.5

16.7 18.3

1 * 4 1.8

1.7

Sintered for 8 hours

Sintered for 3 hours

(D type values

1 hour * sited

untypical UTerte

AUs Ghrömituti ^ NiGk ^ i StaiiiliBSg Steel Data Book, internätiohäi

Nickil Gö _M Ine * '-Seetiöa 1, Bulletia Ä, päg ^ Ö,

ASTM itänääri Ä 493-63 for Siainless-iteel Cibld JHeädihi

1ÖIS8T / Oil U

Example V

To clarify the advantages of reducing shrinkage when elemental iron metal particles are added to the iron oxide powder HCl iron oxide particles, which were calcined and ground in a ball mill for 3 hours (cf. particle size in Table A) with iron powder (thermally decomposed iron carbonyl), which has a particle size of essentially below 10 / U, mixed.

A plasticizer / binding agent was added to the mixtures ( ₂ g, pregelatinized starch, 14 ml H 2 O and 3.6 nil HCl to 100 g of the mixture consisting of iron oxide and iron), which was then introduced into the die chamber and extruded into threads (10.5 ml kg / mm) "were all yarn strands were reduced during 5 minutes at a temperature of about 593 ⁰ C in hydrogen atmosphere and then sintered for 5 minutes at about 1177 ⁰ C.

The results are shown in Table 4 below:

1098 87/0683

Table 4

sample Iron particles sintered strand- sintered shrinkage No. density pressed strength '"■ % strength 7 » mm mm

1 20th Weight -% 95 4th O, 508 0, 3302 35 2 0 % 99 3 0, 508 0, 3048 40

Example 6

In order to demonstrate the advantages of the method according to the invention by using lower temperatures, lower sintering times and temperatures, HCl oxide powder was calcined, ground in the ball mill for three hours (see Table A for particle size) and then with a plasticizer / binder (2g pregelatinized starch, 14 ml H ₂ O and 3.6 ml HCl to 100 g iron oxide) mixed, whereupon the mixture is introduced into a pressing chamber and a pressing

2
pressure of approx. 10.5 kg / mm for strands of thread with 0.4064 mm

Diameter were pressed.

All samples were reduced for 5 minutes at 593 ° C, while the sintering temperatures from 705 to 1159 ° C

109887/0683

were varied. The sintering conditions, sintered rods, and tensile or elongation properties of the wire samples are given in Table 5 below. The wire sintered at 705 and 760 ° C was too brittle for tensile tests. After sintering at 815 ^° C., the tensile strength was quite high. Sintering at 983, 1092 and 1159 ° C gave good properties; the best properties were obtained by sintering at 1092 ⁰ C after this series of experiments.

Time,
Minutes Table 5 . tensile strenght
kg / mm ² strain
%. - · - 5 too brittle __ Sintering temp.,
⁰ C 10 % of theor
Density (t 3%) too brittle - 705 5 83 too brittle --- 705 5 92 40.5
40.0
4g; 3
Middle ¥ Ϊ7ϋ 3
3
4th 760 5 92 23.4
24a
23 _V 8
Medium 2372 " 4th
3
6th
¥, 3 815 5 96 iäö i ö
34.0
38iÖ
Middle Whfi 12th
22nd 872 S. 97 1; 1 El
22nd 983 ■ tra 98 Medium Hftt
3i! S 13 "
IS
if 1Ö92 1159 m

middle

Claims (16)

Claims P a) a compactable agglomerate of a particulate Metal compound with a plasticizer or Binder is produced, the metal compounds having a standard free reaction energy with hydrogen in the formation of elemental metal of less than "-, - · + 15 kilocalories per gram atom of hydrogen for the Have reaction temperature and at least 35 wt of the metal compound particles have a grain size of less than 10 / uj ► ■; ■. ' ■■■■■■■■■■ '■ -' ■ '■■■' ■■ '■■ ^: ■■■ ^:: ■' b) the agglomerate is corrugated; c) the compact under a reducing atmosphere is subjected to a temperature which is below ungs- derSublimationsoder melting temperatures of the metal and the metal compound and above Her evaporator or decomposition temperature of all the non-metallic compounds, for a time sufficient, so that a major part of the particles is reduced and 109807/0683 d) the compacted agglomerate until the sintering through the reduction of the particles of elemental metal obtained is heated. 2. The method according to claim 1, characterized in that the reducing atmosphere consists at least in part of carbon monoxide. 3. The method according to claim 1 or 2, characterized in that the compacting is done by extruding the agglomerate into wire-shaped threads or tubes with a thickness or wall thickness of not more than about 0.762 mm. 4. The method according to claim 1, characterized in that the agglomerate is extruded into an elongated shape and zvecks reduction of the metal compounds contained therein and sintering of the resulting metals continuously through a reducing hot gas zone and then through a hot protective gas zone suitable for sintering, which no contains substances reacting with the metal particles, is carried out so that the reduction zone and the sintering zone are designed so that the reduction of the metal compounds or sintering of the reduced metal particles within 109887/0683 the period is effected in that each cross section of the mold is in the reduction zone and sintering zone and that the elongated shape between reduction and sintering zone ¹ with no reactive atmosphere \ substances is exposed. 5. The method according to claim 4, characterized in that the gäcennzei Agglomerate consists essentially of iron oxide, elongated wire-like or is tubular in shape and that the Reduktkmszone to 498 up to 649 ° C and the sintering zone is heated to 815-1262 ⁰ C. 6. The method of claim 1 to 5, characterized ,, that the particles of metal compounds are not greater on average than 6 m. 7. The method according to claim 4, characterized in that at least 25% by weight of the particles have a size of not more than 2.5 , η . 8. The method of claim 1 to 7, characterized in that the metal compounds -that a mean apparent particle size of \ v ^r ess than 1 / U have " 109887/0683 9. The method according to claim 8, characterized in that the extruded wires or tubes are dimensioned so that they have a thickness or wall thickness of no greater than about 0.508 mm after sintering. 10. The method according to claim 8, characterized in that the wires or tubes from the reduction zone directly into the . Sintering zone are performed. 11. The method according to claim 1 to 10, characterized in that a mixture of iron ^ chromium and nickel compounds is used as the metal compound. 12. The method according to claim 1 to 11, characterized in that particles of at least one metal, which is the same as the metal of the metal compound, are mixed with the metal compound before the agglomerate is compacted. 13. The method according to claim 12, characterized in that the particulate metal compound is iron oxide and the mixture contains up to 65 wt .-? O particles of elemental iron. 14, method according to claims 1 to 3, 6 and 7, characterized in that the metal compound is made of hematite iron ore 109887/0683 ordered or contains this. 15. The method according to Angruch 2, characterized in that the reducing atmosphere contains hydrogen. fe 16. The method according to claim 1, dadur ch p; e indicates that it is carried out essentially according to one of the examples described.