DE2226876A1 - PROCESS TO INCREASE THE WEAR AND CORROSION RESISTANCE OF HIGH TEMPERATURE COMPONENTS - Google Patents

Description

Process to increase the wear and corrosion resistance high temperature "he claims components

The present invention relates to © in herfahren sur increase the wear and corrosion resistance hochtemperaturbeaiisprucliter Bauteil® ;, from materials based on iron or nickel-based ,, hochtempsraturbaan = spruchbare Such materials often do not meet öen wear "* and Korrosionsbeanspruchungea" boi operating temperatures higher than 500 ⁰ G .

To achieve such properties, uniräsa dorsrtigo base pieces are coated with order gaseiiwsiasstS'ä or cletoaatioasgQspritstsa layers »These sent have a ®ia hard metal structure, ie embedded in a ductile matrix s ± n & T & iiGhQH of very high hardness. Such a Gseits® has the great advantage that thermal stresses can be relieved relatively easily. The disadvantages of this technique are the mixing up of the basic material in a welded layer, the relatively large size of the day before guests and the relatively high costs.

It was therefore the task

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Process for such components © to not adhere to parts and with ä®m g to coat parts made of materials with high thermal expansion coefficients. This means _a öass such see alternating stresses tob the sight old

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so that a loosening of the connection between the pushes and the base material is to be feared. In order to solve this problem, it is assumed that protective layers grown on are used

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Expansion coefficient {& £ less than 120. 10 ~ ') limited. With regard to the creep rupture strength and a sufficient resistance to thermal shock, the layer thickness must be kept relatively small even in these cases, in GegensstE to d n former auftragegeschweißten layers have grown such Schichtw a homogeneous structure,

The solution of the problem consists in the present invention is that dia lioclvSsmperatiirbeanspruchten components with a grown layer eiligstene "'of a metal to be provided subsequently by ■ on the one below 900 ⁰ C taking place Slüiiprc ^ ESS sine Eindiffüsioi. This material along the Eorngrenzen of Sriffiäffiaierials and Further diffusion of nitrogen, carbon or silicon causes a hard metal image within a cuctile matrix made of unconverted layer material. Metals from the fourth, fifth and seaworthy main groups of the periodic system can preferably be used as the grown layers, as well as copper, nickel and silver and outside of the Kerareaktorteohziik also cobalt.

Through this process, the material of the grown soil will first diffuse into the base material along the grain boundaries and thereby anchor itself 'Ι® allgeasinen wii'd thereby a diffusion depth of about 10D ^ * gantigen, through subsequent diffusion of nitrogen, carbon or silicon becomes a part The layer that grows next to the material is converted to nitrides, carbides or suicides, these substances are known as hard materials and are therefore carriers of the wear resistance but also the corrosion resistance of the components protected with them.

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With the help of this procedure it is in contrast to the "known" methods mentioned above are possible to and / or anti-corrosion layers on workpieces for operating temperatures higher than 500 C and with a thermal

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Coefficients of expansion o (= 120. 10 apply. Such Components exposed to high temperatures consist of high-temperature-resistant materials such as austenitic steels, Kiekel-based and cobalt based alloys. Examples of such components are valve spindles, valve seats and cones in steam turbines, Exhaust valves of diesel engines, hot pressing dies and stamps, structural parts for gas or liquid metal-cooled nuclear reactors and others. Pure components of nuclear reactor technology however, cobalt-based alloys come because of the risk of forming very long-lived radioactive alloys Isotopes not in imprint.

After this process has been carried out, the applied layers have an inhomogeneous structure - analogous to the structure of a Carbide - that from a metallic ductile matrix with non-metallic hard wear-resistant inclusions consists. Matrix and inclusions should be corrosion-resistant under the intended operating conditions. Under certain circumstances, the breakdowns occurring in such components can a also with ductile inclusions in a wear-resistant the matrix surrounding the embedding sufficiently wide be dismantled. The wear-resistant structural components preferably consist of compounds of the diffused substances nitrogen, carbon or silicon with one or more components of the base material or which diffused into the base material surface zone Layered metals. The ductile parts of the structure are made up of the components that do not react with the substances mentioned of the base material or the diffused layer metals. The occurrence or non-occurrence of the reactions the diffused substances nitrogen, carbon or silicon is determined by the size of the free enthalpy of formation which of these compounds is determined.

Selection criteria for the combination of suitable materials are the thermal expansion coefficient of the basic

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Material, as well as the layer metals, the desired microhardness, the oxidation and corrosion resistance of the coating, the diffusion properties of the grown layer materials and the temperature required for this with regard to a desirable diffusion rate of more than 5 / t per hour. Here be noted in particular that the diffusion temperatures should not exceed 900 ⁰ G, so that grain enlargement and reduced strength of the base materials ale so small held possible. The same also applies to default. In general, carbides are harder and often more wear-resistant than suicides, but these are often more resistant to oxidation and corrosion. Nitrides can generally only be used up to operating temperatures of about 550 C and are less resistant to oxidation and corrosion, but can be formed at lower diffusion temperatures than, for example, carbide layers.

Layer materials are used in accordance with these selection criteria Chromium, for example, but also manganese, molybdenum, niobium, vanadium, tantalum, titanium and zirconium are embossed. Copper, nickel, Silver and, outside of nuclear reactor technology, cobalt are also used.

In summary, it can be said that carbides are preferred for wear protection layers, only in a few cases Sitride in embossing. Pure wear protection layers in corrosive Media or suicides for wear and corrosion protection layers.

Pure wear protection layers on heat-resistant, austenitic Chromium carbide is best suited for steels. Manganese, vanadium, zircon, titanium, niobium and tantalum carbides can also be used Molybdenum carbide is less favorable.

Pure wear protection layers on nickel-based alloys the carbides mentioned but also molybdenum carbide are suitable.

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As already mentioned, the layers are applied to the surface by electroplating or with the aid of the CVD method (Chemical Tapomr Desposition) or, under certain circumstances, also diffused in on the same side. It is expedient or necessary to carry out these diffusion processes within a protective gas atmosphere or in a yakwim.

The hard metals forming the elements nitrogen, carbon and silicon are preferably used as gaseous thermally disoziierende hydride or halide © © © büd TeBp - temperatures below 800 ⁰ C in contact with the zti schlt £ © brought surface. They react preferentially with the alloy components of the grown Schielite, oil carbides etc. have the largest free enthalpy of formation and then diffuse into the surface area. This diffusion is accompanied by further reactions of this kind, while other alloy components a, whose carbide © etc. have lower enthalpies, do not react and the ductile matrix or the ductile matrix. The course of these reactions can be influenced not only by the temperature but also by the pressure and by the naisohexs of hydrogen or inert gas.

To further explain the process according to the invention and to identify the lrg © teisse aeiea that can be achieved with it briefly described some application examples.

A. It should have a chromium carbide wear protection layer of high-temperature steel material no. 1.4981 ", a wear resistance test body (hollow cylinder 40 mm long, 28 mm outside and 18 mm inside diameter) made of diesel" steel and two ball-head friction pins © with 8.2 bd diameter were galvanically chrome-plated (50 ^) and then at 900 ⁰ C 24 Diffusion annealed for hours in a vacuum of 10 ~ ^{2 ϊογγ.} The enriched on average by $ 65 chrome surface zone of 100/4, strength wurä © 900 ⁰ C for a period of 30 hours eat a H®than material mixture 1:50 carburized "With a hardness of

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Material Yon 180 kgf / mm had the Chrcmkarbi & itself formed thereby verschleißsohicht a microhardness of 1000 kp / "The ö dry at 700 ° C and tested at 600 ⁰ under liquid sodium riding wear resistance corresponded to that of stellite 3P6. After the annealing treatment, the base material now showed an essentially substantial increase in grain size.

B «An impact-resistant chrome carbide wear protection element should be used on high-resistance steel material no. 1.4-981 * A test body and friction pins were designed as under A. and galvanically 50 / * chrome-plated. AnechlieSeM they were strongly μ nickel 30 and at 900 ⁰ C

-2 36 hours l Kg at a vacuum of 1o Torr diffusionsgeglüirfc "The enriched with chromium and nickel in this manner and 150 μ, strong Oberfläohensone of the material was aufßökcfilt at 900 G ⁰ 40 Stunöoa hours in a Metkanwasserstoffgemisch of 1:50. Ms UhroE &d.r'bidschicht with the nickel inclusions liatte eir-s micro hardness of 950 kp / mm compared to the SrunÄ ^ srkstoff of 180 kp / aiii ⁴ ". The Efci & wear-resistantkait tested dry at 700 C: 'he layer corresponded as in example A. the same - ^ & Sttillit SP6. In the ball impact vsrsüök according to ΓίΙΪΓ 5115 !? the layer remains completely free of cracks in contrast to a similarly thick Sellit layer.

G. A chrome carbide wear protection layer on nickel-based alloy Yakumelt-iiTS-290-G should be created. First, a Yerschleißbeständigkeitsprüfkörper and Reibstifte eat the dimensions of Example A., however, from Valcuaelt-ASS ~ 290-G in a powder pack from 20 parts by weight of chromium powder 5i, SO wt _e -5 * Aluisiniuisoxid, 0.2 wt .- ^ Annealed barium chloride for 1G hours at 1100 ^° C. The 100 Å thick surface zone, enriched with chromium, was carburized in a methane-hydrogen mixture for 1s50. The micro-hardness of the chromium carbide _{layer with nickel inclusions was 1000 kgf / mn t and} the friction wear resistance of the layer, tested dry at 700 ⁰ G, corresponded in turn to that of stellite Sf6. Also in the ball impact test

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according to DIN 51155, the layer remained free of cracks in contrast to a stellite layer of approximately the same thickness.

These examples show how it can be done with the help of the choice of matrix materials as well as the process management is possible, the desired corrosion and corrosion in a relatively simple manner Wear properties of high-temperature base materials achieve. The thermal stresses that occur during thermal cycling are reduced by the ductile ones Matrix materials largely degraded. The additional matrix formers such as copper, nickel and silver are then included Recommended if, in addition to particularly good impact resistance, the ductility of the wear-resistant layer is particularly important Requirements are made.

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Claims (4)

Claims - t - VPA 72/9434 1. A method for increasing the wear and corrosion resistance to high temperatures stressed components made of materials based on iron or nickel-based, characterized in that it is provided with at least a ductile metal with a grown layer, followed by a below 900 ⁰ C taking place Grlühprozeß a diffusion of these substances along the grain boundaries of the base material and by further diffusion of nitrogen, carbon or silicon, a hard metal formation is triggered within a ductile matrix of unconverted layer material. 2. The method according to claim 1, characterized in that as a layer, preferably metals from the fourth, fifth or the sixth main group of the periodic system are used, for example by galvanic means or with the help of the GVD process (Chemical Vapor Deposition) can be applied to the components. 3. The method according to claim 1, characterized in that the diffusion of the grown layer to a depth of about 100 / * - is carried out. 4. The method according to claim 2, characterized in that as an additional former of a ductile matrix copper, Nickel, silver and outside of nuclear reactor technology also cobalt is used. 30a8bU / U7Ü