DE1287401B - Process for the production of a firmly adhering coating of stainless steel on a steel strip or the like by sintering on a chromium-containing metal powder - Google Patents

Description

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The invention relates to a method carried out in the atmosphere at least during Production of a firmly adhering, even and the first heating stages the halogen-containing gas corrosion-proof Stainless steel coating is performed. The belt can be cooled in with at least 12% chromium on a steel strip in a halogen-free protective gas atmosphere, ζ. Β. one or the like by coating the surface of the tape 5 in a hydrogen atmosphere, with a chromium-containing metal powder, compacting the thickness, ductility and corrosion of the Powders with a reduction in the tape thickness by the resistance of the layer are greater, the smaller preferably 1 to 10% and sintering the compacted is the carbon content of the applied powder. Powder in a protective gas atmosphere. The decarburization measures can be avoided

The firmly adhering coating should generally be on the surface if a steel surface is used as the starting material of steel objects, such as B. ribbons, whose carbon content of the above applies Sheets, plates, rods, bars and wires, meets the maximum requirement, to be brought. If this method is applied to flat, rolled material

It is extremely difficult to apply material to thin objects such as strips, sheets or plates in the form of elongated ribbons, the coating can be placed on an or moderate alloy layer of chrome iron to be created on both sides, gen. Normal chromating processes, e.g. B. those, with further details go from execution two Chromium in a compound with a halogen play out the following in connection is used, with which the to be covered with the figures are explained in more detail, surrounding the object are for the treatment of ao Fig. 1 shows the reproduction of a photographic tape Material not satisfactory; because to see micrograph of a cross section of one with both or only one side of the band to be an iron-chromium alloy covered steel band; cover, the tape must if it is in the form of a coil F i g. 2 is the reproduction of a cellular unwound was to be settled. Then scan the X-ray intensity for chromium in the coating material applied and the alloy 25 of a rolled powder layer after sintering, which formed during the movement of the belt is determined by electron microscopy; or if the belt is in the stationary state F i g. 3 is a photograph of a cross section is covered, it must be as long as possible with that of a covered band, one end of the Coating is provided that a heating system of cross-section to expose the coating with acid inconvenient size is required; but when the 30 has been etched.

Layer is only formed in small sections, so in a characteristic example of the invention

if the long duration of the process becomes inhospitable, a band of unkilled steel, which

economic. decarburized to a carbon content of 0.003%

According to the invention, these difficulties are unwound from a roll. This is a

overcoming the fact that the content of 35 thin film of tridecyl alcohol with the help of rubber

effective or unbound carbon in the miroll is applied to both sides of the tape.

Steel belt for sintering to a maximum of 0.01%> and the belt then runs under a vibrating

Carbon content of the powder at the beginning of the sin-

terns is limited to a maximum of 0.25%, so that chrome powder (0.1 clear mesh size in millimeters)

In the sintered coating, a carbon content of 40 is uniformly distributed on the upper side of the belt.

at most 0.10% shows that a powder is brought with little. The composition of the powder is:

At least 20% chromium is used and the sintering time is 67.6% chromium, 31.4% iron, 0.79% silicon and

and sintering temperature are dimensioned so that 0.11% carbon. By bending the tape over

mutual diffusion of the desired coating without a role and reversing the direction of transport

Formation of harmful chromium carbides occurs. 45 as well as guiding the tape under a second vis

It is recommended that the sintering process in a brationsverteiler is ferrochrome powder on the still

Atmosphere of practically pure hydrogen and uncovered side of the tape applied,

at a temperature of at least 840 ° C through- The tape is then converted into a set of hard-polished

respectively. th rollers of 10 cm in diameter introduced where

In the method, a chromium-containing metal 50 can use the powder together with the metal strip at a

powders with iron and / or nickel can be used. Pressure is compressed, which to a 10 percent

Sufficient to limit the effective carbon content by reducing the strip thickness. After this in the steel belt to a maximum of 0.01 percent by weight leaving the rollers, the belt is on a Aufkann A tape can be used that has a carbide take-up roll wound on it. Before heat treatment non-ferrous forming metal such as titanium. 55 the compressed, rolled-up tape is unwound

The tape with the compacted metal powder can and rewound. During the recovery

up to the effective carbon content of wraps, spacer strips are inserted around a

at least 0.01 percent by weight in an atmosphere of the open-ply spool or roll. It

This is because water vapor and practically pure hydrogen are advantageously produced between the layers of the roll

be charred. 60 to keep a distance so that the atmosphere in the

In order to allow the powder to circulate freely on the belt to the sintering furnace and to effect possible can be prevented from welding adjacent layers on the tape, The powder is a thin layer of a volatile The exposed or open role is turned into an annealing liquid are applied, the z. B. at least oven used where it is in a dry Atmozum Part consists of tridecyl alcohol. The sintering 65 sphere of 100% hydrogen for 48 hours The powder is preferably heated in a halogen-temperature of about 900 ° C. After sintering containing gas containing inert gas atmosphere or brushed the tape with gloss brushes so as not to to remove sintered powder from the surface in a continuously flowing hydrogen.

3 4

The brushed product has light metallic color in terms of the application of the powder on the

Shine. Band can use methods other than those in the

Used in a modification of the above examples described above

Procedure will first be a steel band with the. Such methods can be used in electrical

same properties as in the previous example with 5 phoretic application or in the electrostatic

Tridecyl alcohol coated. The powder used spray technique or in any other method

is a mixture of iron and chrome powder with which the powder is effective on the belt

a fineness of about 0.1 mm clear mesh size. adheres.

In this example, the tape is raised vertically. Although it may be advantageous to

drive through a chamber with a fluidized bed of the powder io from one already before the process steps

guided. This hot bed is obtained by starting the invention decarburized steel, this is

through a porous filter at the bottom of the chamber just a matter of choice, as shown by the example

Pressing compressed air, whereby the forced stream is explained, in which an unkilled steel after

mung keeps the powder in the state of suspension. Compacting and decarburizing just before sintering.

The tape passes through a narrow opening in the filter 15. There is no limitation in the invention

and then through the fluidized bed. If it is the closed selection of the steel used as the basic

leaves the chamber at the top, it is of the same material as long as the effective carbon content of the

moderately covered with the powder. The covered band of base material kept below 0.01% during sintering

is rolled to compact the powder, under is.

as low tension as possible, wound around an ao Most metal powders contain some carbon

To avoid welding during sintering, fabric, and this carbon must be at a value

and then sintered at about 900 ° C for 48 hours. are kept, in which no harmful chromium

After brushing, the strip shows the same me- carbide in the final alloy cover-

metallic sheen as in the previous example. can stand. As previously stated, the

In a further modification of the method as the permissible amount of carbon, which with the powder in the

a band of cold-rolled non-killed steel is introduced no more than compacted matter

used as base material or underlay. After that 0.25% of the powder weight. In any case

Coating with tridecyl alcohol becomes a metal- should the total effective carbon content in the metal-

The powder mixture of about 0.1 mm clear mesh and powder must be sufficiently low that the

uniformly spread the resulting alloy coating on one side of the strip surface 30 after sintering

distributed with the help of a vibration distributor. The powder coherent, ductile and corrosion-resistant

is in this example a mixture of a chrome is.

Iron alloy (70% chromium) with about 10% han- The expression "effective carbon content" is common nickel powder. The powder is compacted by pulling itself onto the carbon in the base metal using rollers with a thickness of 10 cm. The 35 or layer that is wound up to form chromium after rolling is unwound carbide is available. When these carbides are limped in and are present in sufficient quantity prior to sintering, they make the spacers wound up again. The band drum coating becomes brittle and limit the deformability mel with the spacers is in an annealing furnace of the covered product. In addition, a coating containing chromium used and because of the carbon content of 40 carbide-containing coating has a lower corrosion resistance of 0.06% of a decarburization treatment in a wet corrosion resistance than a carbide-free coating.
Hydrogen atmosphere (dew point 35 ° C or 5.5 if the strength properties of a volume percent) are subjected. The decarburization of the carbon steel in the coated tape is carried out at 676 ° C for 5 hours. If you want to maintain the tape, it is possible and brings the carbon content to 0.01% or 45 a tape greater than 0.01 % Less carbon. After decarburization, the wet will turn when a carbon-defining substance removes the hydrogen atmosphere and is present in the band through practically like titanium. When titanium is replaced in pure, dry hydrogen gas so that there is an amount sufficient to virtually prevent oxidation. The compacted, decarburized entire carbon of the band binds, so the band is annealed (sintered). It prevents carbon diffusion into the 900 ° C for 24 hours. Coating during sintering and the formation of un-

While the invention in the foregoing desires chromium carbides in the same. Other

Examples as a method of producing a carbide former that are used to fix the carbon

Alloy plating of chrome iron on one can be used are chrome and niobium. if A metal object in the form of a steel strip contains a carbide former to fix the carbon in it

it is easy to see that the bands are being used in this way, it is

Invention the same application possibilities with the important that the unbound effective carbon,

Production of such layers on steel sheets which is dissolved in the strip, d. H. free to react

or has plates. with the chromium of the compacted powder, under one

When applying the invention to sheet metal 60 limit of 0.01% is kept,
As an example of the freedom of choice in terms of steps, namely applying the powder, compacting the steel grade for the base material and sintering, the same main process is used, with the only sub-20 gauge cold-rolled strip of a titanium stabilizer mechanical handling of the countered steel used as the starting material. The stand. For example, metal sheets after the 65 band had a content of 0.30% titanium and 0.06% rollers to compact the powder so into the total carbon. This amount of titanium binds prak-annealing furnace are used that a welding table all the carbon with the formation of sta is avoided during sintering. bile titanium carbides.

As in the previous examples, the tape is coated with alcohol and a metal powder evenly distributed on both sides of the strip. A ferrochrome alloy with 70.0% is used as powder Cr, 27.5% Fe and 0.08% C were used. The entire powder passes through a network of 0.1 mm clearer Mesh size, about half that of about 0.075 mm clear mesh size.

The tape covered with powder is pulled through the compaction roller, in which the powder and the stapled powder are about a factor of 2 Tape to be squeezed. The rolled product 100 g / sqm will be increased to the number given above, is then sintered at 927 ° C for 24 hours. The following table shows numerical values

As the bulk of the carbon is listed in the volume of a number of experiments. they show has been determined by titanium and less than the amounts of alcohol and powder as well as the 0.01% carbon to diffusion in the excess 15 ratios. In some examples were related is available, the coating obtained is achieved peaceful layers, while with others free from harmful

100 g / m² of supporting tape area is applied, the results are quite satisfactory; these Amount is already held on the tape by a very thin film of tridecyl alcohol. Heavier ones 5 or lighter powder coatings can be used. The amount depends to some extent on the desired chromium distribution and the thickness of the sintered layer. Using a thicker alcohol film, the amount of

of harmful chromium carbides, the pores, brittleness and low corrosion resistance in Alloy layer of this type can cause. The coated product resists therefore, even after a bend through 180 °, the attack of boiling 20 percent by volume nitric acid.

"Generally a spotty or soiled Steel belt with a cleaning agent such as a liquid hydrocarbon or an alkaline one Detergent, to be cleaned.

The adhesive that is applied to the tape in the form of a thin skin and temporarily Serving as an adhesive for the powder can be a liquid with the appropriate viscosity, volatility and bond strength - as mentioned above - but should not leave any carbon residues on the steel strip and also meet industrial safety regulations. The metal powder can

the amount of alcohol or powder so large to produce a uniform layer was.

attempt alcohol powder
(-150 mesh) Together
hanging the same g / sqm g / sqm moderate shift 1 0.65 92 Yes 2 0.85 111 Yes 3 1.40 156 Yes 4th 1.90 181 Yes 5 2.50 185 Yes 6th 3.46 219 no 7th 4.00 256 no

However, application of such a liquid skin is viewed as more advantageous, as this includes the process steps of powder application and compaction gives more effectiveness.

Although the amount of adhesive liquid applied and the grain size of the metal powder are not is critical, it is useful to control both. The adhesive is said to be a fairly thin film

When compacting the powder on the belt, the goal is to create a uniform metal "crust" on it

even without creating a liquid with the upper metal base in which the individual named properties are applied; the powder particles are welded together and the immediately the substrate metal opposite particles pressed into the surface of the same are. An excellent compression was achieved with chromium-40 containing metal powders by a roller pressure, which reduces the thickness of the backing metal by 1 to 10%. These numbers are not meant to be Limitation, rather than guide values, since one applies the pressure to adapt to differences that is just sufficiently thick, 45 borrowed working conditions can vary. Such In order to ensure good adhesion of the powder particles, differences in the hardness of the Afford. An excess of liquid can cause poor substrate metal, the size of the rollers, the granularity consist of slipping and insufficient size of the powder, etc., result in sealing during rolling. The compacted "crust" of metal powder is from

When choosing a special adhesive liquid 50 nature porous, and this turns out to be the nachist care should be taken that this does not include carbon in subsequent sintering step as an advantage. While leaves the compacted metal, which has a warm-up time prior to sintering Could cause brittleness. Petroleum is a volatile oily adhesive material that evaporates and Adhesive fluid that has been used with success. escapes through the pores of the compacted layer. Transformer oil and washing oil are also mixed. If it were not porous, it would pass through during sintering but turned out to be less effective - the vapors lifted off.

The sintering temperature should preferably be between about 844 and 1038 ° C and at least 12 Hours can be sustained, although significantly 60 longer times depending on the degree of required Alloy formation may be desirable. The upper limit for the alloy temperature is only dictated by practical considerations. The minimum time is reversed above 844 ° C value size of the particles depends somewhat on the type 65 shortened.

of the liquid film used and of the me- If the decarburization immediately before sintering

mechanical application method of the powder. is carried out in the annealing room, the holding

When the powder is in an amount of 80 to temperature between 620 and about 788 ° C.

sam proved to be tridecyl alcohol and petroleum. Other oils that can be used are those based on naphthol with a Seybold universal viscosity of 90 to 110 seconds at 38 ° C.

A metal powder that passes through a sieve with a mesh size of about 0.1 mm has proven to be Proven very useful, although larger particles can be used. The desired

For example, a decarburization time of 12 hours at a minimum temperature of 620 ° C for strips with 0.08% carbon are generally sufficient. The reliable time-temperature cycle is illustrated by an example in which a band of the Caliber 20 made of non-killed steel with a carbon content of 0.002% wetted with alcohol and with a powder of 50% H-iron (99.2% Fe reduced with hydrogen) and 50% electrolyte chromium was covered. After compaction of the powder on the belt, the product was at about 1010 ° C Annealed in a pure hydrogen atmosphere for 12 hours. After cooling, the abbreviated in this one Alloy coating obtained from the sintering process subjected to an electron microscopic examination. The results of the analysis showed about 12% chromium at the interface between the layer and the steel base and an increasing chromium gradient towards the layer surface where the Chromium content was 24.0%.

The powder compositions suitable for the invention are those with chromium alone, iron and chromium as well as iron, chromium and nickel, with chromium being present in sufficient quantities is to form chromium iron alloy in the surface of the final product. This description Corresponding metal powders are: Iron — chromium alloyed, a mixture of iron and chromium, commercially available Chrome powder, iron — chrome alloy plus nickel and a mixture of the powders of iron, Chrome and nickel. In the case of alloy powders, iron, chromium or nickel powder can be added if necessary will.

The term "chromium-containing metal powder" used in the claims refers to a Powder sufficient to form an iron-chromium alloy in the coating of the final product. The powder can also be iron or nickel or a non-reactive material or other Contain substances that do not have a harmful effect on the process.

With a powder composition of 20% chromium and 80% iron, a coating of the stainless steel type is obtained which withstands _{a boiling 20% by volume nitric acid solution based on 100% HNO 3.} With a chromium content above the previous 20% example and up to 100%, a coating that is resistant to 20% nitric acid is also obtained. Other mixtures corresponding to the nitric acid test, in which the chromium content is at least 20%, are:

Chrome and nickel,
Chrome iron alloy and nickel,
Chrome, nickel, iron.

The coating resulting from the invention generally has a thickness between 0.025 mm and 0.075 mm and is a real alloy of chromium and iron or of chromium, iron and nickel.

The iron-chromium or iron-chromium-nickel content of the alloy does not only depend on the quantity and composition of the powder, but also on the sintering time and temperature.

For the implementation of the process it is not decisive to what extent the chromium content of the applied coating is above the minimum value of 12%, ie the process can be carried out with powders with a low chromium content as well as with powders with a high chromium content. The chromium content of the powder, however, has a decisive influence on the properties of the coating produced.
With a chromium content of the powder of at least 20%, a coating of the stainless steel type can be produced which contains at least about 12% chromium in the entire layer and is characterized by a sharp interface between the alloy coating and the base metal. Below the interface, the chromium content of the steel drops rapidly to zero.

The mechanism of formation of this stainless alloy layer can be assumed as follows will:

The compacted metal powder coating is sintered by diffusion of iron and chromium atoms. This diffusion initially causes bonds or bridges of connected metal between

ao see individual powder particles and also between the particles and the steel backing. This effect causes voids between the particles. With As the diffusion proceeds, the area of the vacancies is reduced until it becomes very small or disappears completely. If the chromium content of the layer is greater than about 12%, the structure is of the sintered compact layer body-centered-cubic or ferritic, at all temperatures between room temperature and diffusion temperature. Below about 12% chromium is the Structure face-centered-cubic or austenitic at the diffusion temperature of 870 ° C, however body-centered cubic at room temperature. Diffusion is faster at any temperature Ferrite than in austenite.

The gradient of the chromium content of the alloy layer and the thickness thereof can be varied as desired.
With a short sintering time, e.g. B. 5 hours at 955 ° C, the chromium content runs from 12% at the interface to about that of the applied powder on the outer surface, and the interface is only slightly below the original surface of the steel base.

With longer sintering times, more iron migrates to the outer surface of the object, whereby the The chromium content of the alloy layer is consistently more uniform, while the interface is somewhat deeper goes, d. H. the thickness of the alloy layer increases somewhat. When the sintering times are abnormally extended eventually the stainless alloy layer disappears, i.e. i.e., the diffusion of Iron and chromium continues until the chromium content of the outer layer is less than 12%. That would however, require so long sintering times that are far beyond anything compatible with practical operation Time lie.

The following example illustrates one type of stainless coating that can be produced by the process can be produced.

A steel belt with a carbon content of 0.003% is moistened with alcohol and with a Layer of chromium-iron alloy powder, which is 0.025mm thick and contains 70% chromium, covered.

The covered strip is passed through rollers and when the layer is compacted by 10% in the Reduced thickness. The covered tape is sintered at 955 ° C for 48 hours. A microanalysis of the

909503/1484

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The tape showed that the tape was covered with a rustproof pad. Because of this, it can occur with property-iron-chromium alloy was covered, whose chromium of oxygen in the sintering atmosphere required analysis through the scanning line in FIG. 2 is shown. be a means to free the chrome powder from In another example, a tape was applied with its oxide, so that the chromium is with 0.003% carbon content diffuse in the same way with the iron and both into the substrate a powder of the composition 75% Cr, 25% can and also in the powder itself, if this Ni covered. After rolling and sintering at 955 ° C contains iron.

a coating resulted over 48 hours, which was found to result from the introduction of a

an iron-chromium-nickel alloy with a carbon-containing material in the furnace atmosphere fuel content of 0.05%. Microanalysis io diffusion of chromium in iron, and vice versa, very much

on chrome was about the same as in FIG. 2. accelerated when unavoidable oxygen

It can be seen from these examples that it is possible to clean the oven. The halogens is, on a steel strip a coating of a and also the halogen compounds act as an iron-chromium alloy to generate its accelerator by removing the oxygen film from the times a chromium content of about 12% and a carbon 15 chromium particle and a contact oxygen content is less than 0.10% carbon and allow the metals. The usage the rustproof, ductile and metallurgical with the support of a halogen-containing material accelerates the diflage connected is. A rustproof coating of this type has such a rate of fusion that one in some withstands a boiling 20% by volume water-based cases, sintering time of 4 hours. Extraordinary Solution of nitric acid. The resistor 20 can dem in the presence of a halogen or against Boiling 20 percent nitric acid is a logenids with a higher carbon content in the standard ver sealed powders can be approved for testing the corrosion behavior. The one in one a chrome iron alloy of the "rustproof" industrial furnace with the addition of an accelerator type. The coatings provided were found to be significantly

The sintered coating has a dull gray appearance that is more attractive than that in the absence of accelerators,

nending surface without metallic luster. In a case where a halogen-containing accelerator

covered tape can be used in this state or ger has been used as the final product, a

by brushing or polishing in its surface - chromium alloy coating on a low carbon

appearance to be improved. Usually one gives steel strip, on a stretching roll up to a whole Strip another surface rolling with 1 to 30 th reduction in cross-sectional area by about

2% stretching to achieve the mechanical properties 80% or from a thickness of 1.42 mm to 0.29 mm

to improve. When the covered tape is decorated, rolled. Without the use of accelerators

If you want, a combination of which can reduce the product by no more than 50% is advantageous

Surface rolling with polished rollers and brushes.

sten, buffing leather and other means to shine. 35 After reducing the thickness of the covering used to create a surface with high tensile tape in the range of 5 to 80% To create shine. the malleability has decreased to a degree,

The sintering must take place in a protective atmosphere or in which the use of the product

environment that practically fertilize freely with a minimum of deformation

of carbon, oxygen and nitrogen. Too much is limited. If additional formability is

For this purpose, one of the noble gases can be desired as the surrounding environment, so the product can after the cold

Atmosphere to be used; however, rolling is equivalent to annealed to restore ductility

an atmosphere of pure hydrogen will be better.

practical requirements. Hydrogen has a halogen or a hazard as an accelerator The advantage of using the halogen compound during the process 45 is that the oxides formed during the sintering process are temperature-reduced or volatile below like. On the other hand, sintering in such an accelerator may be preferable to that of relatively complete or a partial vacuum at low temperature are introduced in gaseous form Essence of hydrogen or noble gases take place. can, because then the speed and amount exactly

That can be controlled to create a reduced atmosphere 50. Among other halogen Hydrogen gas used in the sintering furnace should preferably contain gases or vapors, can also be 100% pure in the form of chlorine. But also when practically using hydrogen gas and hydrogen fluoride gas pure hydrogen is used, it will still be possible. Suitable halogenated substances in solid Certain impurities in the furnace atmosphere, mold can be used in the furnace and when especially in larger systems due to leaks in which 55 or near the sintering temperature are volatile System, from the furnace walls or other parts, among other things, ammonium chloride, chromium fluoride and the facility or with the hydrogen. Ammonium bifluoride. Chlorine gas was considered special Chromium has a strong affinity for carbon, found beneficial when it is in gaseous form in what-nitrogen and oxygen, which is introduced, for example, as an impurity in the sintering furnace, get into the sintering furnace. The main source of interference 60 The following examples illustrate the use of for the sintering process is oxygen. halogenated material in the manufacture of a

Explained in more detail at the sintering temperature and even a considerable amount of the stainless steel coating,

the highly active chromium powder reacts under it. A roll weighing 18 kg and 7.5 cm wide

with any small amount of oxygen in the atmosphere, decarburized unkilled steel became with a fungus

Sphere, and the resulting chromium oxide can be converted from tridecyl alcohol by means of a roller coater

completely surround exposed parts of the powder particles. covered. The coated tape was through a

The formation of the oxide film on the particles is prevented. Fluidized bed of low-carbon ferrochrome powder

changes the normal diffusion of chromium into the steel (0.08% C ₃ 70.7% Cr, 0.43% Si, 0.50% Mn, remainder

Claims (15)

11 12 Fe) in order to achieve a uniform coverage and cooling of 25.5 cbm per hour during the strip with powder. Then it was sintered at 8.5 cbm per hour.
Compaction of the powder by means of a tempering roller According to the above process, transfers can be made and then produced using deductions, which are rewound evenly and evenly. The open-ended 5 mm thick and an average thickness of 0.05 mm, wound roll was made together with a container containing 50 g samples of the covered tape withstand co-ammonium chloride powder in chender 20% nitric acid,
a retort was used. After ensuring the tight seal of the retort because of the toxicity and corrosive nature of the halogens, suitable precautionary measures must be taken for a retort furnace with a diameter of 40 cm to be hit. To do this, use the existing chloride batch for 24 hours at 927 ° C. During the heating-up time and during the ventilations on the sintering furnace.
During the 24-hour sintering period, hydrogen was initiated in the care must also be exercised in handling the halogens system at the bottom of the retort at a rate of 4151 per hour. Prevent at the end of the mixture with hydrogen. For example, in the sintering period, the charge was cooled to room temperature in the American "Bureau of Cooled and Nine", Bulletin No. 503, entitled "Limits of Hydrogen, passed through the retort". Flammability of Gases and Vapors' stated that In order to determine the effect of the hydrogen chloride gas as an explosive mixture of chlorine and hydrogen forming an accelerator, a test was carried out if the chlorine content of the mixture was above 11.0% with eight samples of a steel strip from. However, there is never a need to make 0.003% C. The pieces of 10 x 25 square cm in our process, a halogen-containing substance and 1.44 mm thick, were loaded with tridecyl alcohol to use in such large quantities. Although layered and covered with low-carbon ferrochromium powder, the acceleration effect did not have an upper limit (70.5% Cr, 0.04% C, 0.45% Si). The halogen powder to be used in the process was made by passing the metal sheets through a quantity, a satisfactory result is compacted with 10 cm rollers, the reduction holding when the halogen quantity in the sintering atmosphere was about 10%. Then the sheets were sphere between 0.25 and 1%,
inserted into the retort of a retort furnace and heated to 927 ° C by a stream of hydrogen in the 30th, although it is based on a theory. This temperature, which the success of the method according to the invention was maintained for 24 hours and could be clarified, is not intended, but hydrogen and hydrogen chloride can be proven continuously by analysis that they have been initiated again. The introduction of the chlorine water-generated layer completely from a chromium-iron substance corresponded to 0.5% of the total atmosphere, the alloy or, if nickel was also used as the initial hydrogen rate was 4151 per material, from an iron-chromium hour. After 24 hours the hydrogen chloride was made up of nickel alloy. turned off and the batch reduced to room temperature- This assumption is supported by metallographic, cools. During the cooling, the water was subjected to X-ray diffraction and electron microscope analysis Maintain material flow. 40 confirmed. It is believed that the alloy At the end of the run, the pieces were covered by intermetallic diffusion of iron and uniform layers of a thickness of about chromium or of iron, chromium and nickel 0.038 mm provided. The layers were uniform, so that when the sintering process was completed, a and extremely ductile. Coating of an iron-chromium alloy with at least In another example, a 2700 kg 45 at least 12% chromium was created. The metallographically heavy roll of 90 cm wide decarburized strip - see the structure of the sintered product - is applied in the steel in a roller coater with tridecyl alcohol drawing in FIG. 1, in which "α" represents the overcoated and then in a fluidized bed with a simplex train and "&" represents the base. The in Fig. 1 ferrochrome powder covered. The composition pattern shown was etched in Nital and is shown in the powder was 71.3% Cr, 0.01% C and 1.46% 50 × 250.
Si. The powder was applied to the strip with a temperature in that the coating consists of a material different from the base roller with a diameter of 70 cm and less than 2% reduction is shown in FIG. 3 Verrung compressed. Before the annealing process, an oven was shown which reproduces a photo with 15-fold winding by inserting spacers between enlargement. The backing material see the layers of the roll made. The coil 55 was etched away with 20 percent nitric acid at one end, then in a Lee-Wilson oven along with the piece, leaving the coating unattached to a container of 36 kg of chromium fluoride (CrF ₃ x 3Va. 3 H ₀ O) used in tablet form. The tablets have a thickness, malleability and corrosion resistance at a diameter between 1.25 to 2.5 cm. Easily recognized by the layer.
The batch with the nickel and the container was 60 covered by an alloy steel jacket. About the claims:
A Lee-Wilson furnace with gas 1. Method for the production of a firmly adhered heated radiant tube was placed in the casing and the batch was gradually heated to 927 ° C. After 32 hours of heating made of stainless steel with at least duration, the furnace was removed and the batch with 65 12% chromium on a steel belt or the like was cooled through the casing. During the heating, coating of the surface of the strip with one of the sintering and cooling, was- chromium-containing metal powder, compression of the pulsed substance was constantly fed into the furnace, during the heating, the strip thickness was reduced by preferably 1 to 10% and sintering the compacted powder in a protective gas atmosphere, thereby characterized in that the content of effective or unbound carbon in the Steel band for sintering to a maximum of 0.01% and the carbon content of the powder at the beginning of sintering is limited to 0.25% or less, so that there is a carbon content in the sintered coating of at most 0.10% shows that a powder with at least 20% chromium is used and the sintering time and sintering temperature so be dimensioned so that the desired coating without the formation of harmful chromium carbides are formed. 2. The method according to claim 1, characterized in that the sintering process in an atmosphere is carried out by practically pure hydrogen. 3. The method according to any one of the preceding claims, characterized in that the Sintering process is carried out at a temperature of at least 844 ° C. 4. The method according to any one of the preceding claims, characterized in that chromium-containing Metal powder with iron and / or nickel is used. 5. The method according to any one of the preceding claims, characterized in that for Limitation of the effective carbon content in the steel strip to a maximum of 0.01 percent by weight a tape containing a non-ferrous carbide-forming metal such as titanium is used. 6. The method according to any one of the preceding claims, characterized in that the Tape with the compacted metal powder up to the effective carbon content of at most 0.01 percent by weight in an atmosphere of water vapor and practically pure hydrogen is decarburized. 7. Method according to one of the preceding Claims, characterized in that the sintering process is carried out for at least 12 hours will. 8. The method according to any one of the preceding claims, characterized in that on the Before applying the powder, tape a thin layer of something that makes the powder stick volatile liquid is applied. 9. The method according to claim 8, characterized in that a liquid is used which consists at least in part of tridecyl alcohol. 10. The method according to any one of the preceding claims, characterized in that the Sintering is carried out in a protective gas atmosphere containing a halogen-containing gas. 11. The method according to claim 10, characterized in that a protective gas atmosphere with at least 0.25 percent by volume of a halogen-containing gas is used. 12. The method according to claim 10 or 11, characterized in that the halogen-containing Gas hydrogen chloride, ammonium chloride or chromium fluoride is used. 13. The method according to claims 10 to 12, characterized in that the cooling of the Tape is made in a halogen-free protective gas atmosphere. 14. The method according to claim 13, characterized in that the cooling of the strip in a hydrogen atmosphere. 15. The method according to claims 10 to 14, characterized in that the sintering in a continuously flowing hydrogen atmosphere is carried out in the at least the halogen-containing gas is introduced during the first heating stages, and that the heated Tape in a continuously flowing halogen-free hydrogen atmosphere to a temperature is cooled from at least 260 ° C. 1 sheet of drawings