DE2155153A1 - Chromed ferrous metal item and the manufacturing process for this item - Google Patents

Description

DR. MOLLER-BORg DIPL-PHYS. DR. MANITZ DIPL-CHEM. DR. DEUFEL DIPL-INQ. FINSTERWALD DIPL-ING. GRÄMKOW

PATENT LAWYERS £ I O O I b J

Munich, November 5, 1971 Iiak / Sv - H 1117

HEAD WEIGHTSON AND GOiIPANY LIMITED

The Vfiarage, Yarm, Yorkshire, England

Chromed ferrous metal item and the manufacturing process for this item

The invention relates to an article made of chromium-plated ferrous metal and a manufacturing method for this article.

Chromed iron objects or iron parts have a surface layer which consists of an iron-chromium alloy, which as a result of the diffusion of chromium atoms into the Iron substrate is generated during a high temperature heat treatment. There are many methods of doing this Diffusion known, for example chromium-containing halogen gas can be caused to react with the iron to form Ciiromatome deposit that into the substrate at the temperature used

* ° can diffuse. Such chromium-containing halides can

co formed elsewhere and introduced into the furnace in ^ which the chrome plating takes place, or you can on site ° una place by reaction of a halide with a chromo rich powder can be produced in the furnace. The former

ho drive type ict usually as there :. "Gas" method known. σ>

Dr. Müller-Bor · Or. Manitz · Dr. Bag ■ DipL-lng. Fintierwald Dlpl.-Ing. Qrimkow Bfaunechwelg. Am BOreerparlc · · Munich 32, Robert-Koch-Straee 1 7 Stuttgart-Bad Cannitatt, Marktatrato Telephone (OKI) 73 * e7 Telephone (OHI) »3646, T.l.x 5-22080 mbpat T.lafon (0711) Μ72 · 1 Bank: -ZMttralkaaa · Bayer. Volkibankan, Munich, account number MS Poetecheck: Munich B5496

The latter type of process usually involves embedding a substrate to be chromed into a package comprising a chromium-rich particulate material and a refractory or contains a heat-resistant diluent that serves to prevent the ghrome particles from sintering together, and then heating the pack.

Furthermore, methods have been developed in which a porous layer of chromium-rich particulate material and halide is formed on the substrate, and the substrate thus coated is subjected to a heat treatment. Such procedures are particularly suitable for sheet metal or thin layers of steel and allow adjacent or adjacent Surfaces of the substrate are in contact, for example in a stack or a tight coil, during heating.

Processes of this type are described in British Patents 1,023,224 (U.S. Patent 3,382,085), 1,146,594 (U.S. Patent 3,589,92) and 1,184,183 (U.S. Patent 3,585,068) and in British patent application 28,929/70 (U.S. Patent Application 833 189).

It has been found that the resulting article, while having significantly improved corrosion resistance, is relatively has deteriorated mechanical properties. These disadvantageous properties result from the prolonged heat treatment, those inherent with the coating or I.1 attation process connected is. So a normal mild steel or a normal wrought iron suffers during the course of the heat treatment migration of carbon to the chromium-rich coating accompanied by substantial iron growth. As a bottom line results in an object with low strength and high stretchability or plasticity (ductility), but can due to of the coarse grain whose porriages are worse and the strength may be less than desired. Additionally Xarni is there a problem too? the embrittlement depending on

215515?

ability of the cooling rates or cooling speeds that applied during the coating process, and as well on the chemical composition of the coated material.

It has been found according to the invention that by selection of a particular type of metal as the substrate, an article can be made that is corrosion-resistant and has an increased has mechanical strength.

As a result, the invention provides an article made of chromium-plated ferrous metal (ferrous metal) having a substrate which has a diffused layer of a chromium-rich material on at least one surface, in which the substrate comprises a steel having a manganese content of 0.4 % to 5%, a carbide stabilizer content of 0.02% to 1%, a carbon content of 0.02% to 0.10% and the remainder iron with the exception of incidental, normally occurring impurities such as aluminum.

In practicing the invention, is preferred the manganese content in the range of 1 wt% to 5 wt%; the carbide stabilizer is in an amount of 0.02% by weight to 0.15% by weight, but can be in the range of 0.05% to 0.15%; and the carbon is present in the range of 0.02 wt% to 0.05 wt%.

In a preferred embodiment, the manganese content is 5.5%, the content of carbide stabilizer 0.1% and the Carbon content 0. OJ%.

The carbide stabilizer can be niobium, vanadium, titanium, zircon, Tungsten or Molybdenum, or quantities of two or more of the CCR materials can be used.

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The chrome-plated metal article according to the invention can be made by any of the known chrome-plating processes. These include packed, gas and salt bath processes of the type described in the patents referenced above. In all these methods ist'es necessary that the substrate is heated to a temperature of at least 75O ⁰ C.

According to the invention a process for the preparation of the above-defined object is also provided in which a Subfe strat a suitable composition of a chromium diffusion Värmebehandlung is subjected at a temperature of at least 75O ⁰ C.

More in detail is a method of making the above Chromed ferrous metal object provided, in which at least one surface of the object has a layer a particulate chromium-rich material is deposited and subjecting the coated article to a heat treatment in a protective atmosphere in the presence of a halide to induce the formation of a diffused chromium layer on the object.

ψ One method of the types mentioned above is described in British patent specification 1 O2J 224. Thereafter, first a substrate in the form of a steel strip, which has a manganese content of 0.4 % to 5%> a carbide stabilizer content of 0.02% to 1%, a carbon content of 0.02 % to 0.10 % and the rest of iron with the exception of accidental, normally occurring contamination, first cleaned and after cleaning thoroughly moistened or wetted evenly on both sides. The moistening operation is carried out by immersion in a bath containing a liquid with a low surface tension or, alternatively, by applying such a liquid in a spray operation.

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Chromium-rich powder is then deposited on the strip, for example by spraying in an electrostatic field, and the strip is dried so that the powder adheres firmly to the strip. For drying, the strip is subjected to a roller operation to turn the powder into a continuous Layer to compact and then _{rolled up} or coiled.

The rolled or coiled strip is then heated in an oven to induce diffusion of the chrome in the stems.

Another method for the preparation of the object-plated metal is described in British Patent 1,146,594. According to this process, the above-mentioned steel strip is cleaned and then coated or coated with a powder rich in chromium. The coating can contain other metals such as nickel, aluminum, silicone, or any combination of these, but preferably the coating contains at least 50 % chromium.

The coating can be made by any of the known methods which involves an electrolytic deposition of chromium from known chromium plating solutions, a plasma or Flame spraying a chromium-rich powder or wire and compaction by a roller technique of a previously spread on the surface or surfaces of the strip include chromium-rich powder.

The coated strip is then subjected to a first stage of heating in an oven, which is a non-oxidizing one Has an atmosphere containing a hydrogen halide. In order to maintain a non-oxidizing atmosphere, it is preferred the furnace is cleaned of oxygen before the heating operation is started by passing a non-oxidizing gas therethrough. The non-oxidizing gas can

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Hydrogen or argon or can be other inert gases. The hydrogen halide can be introduced into the furnace atmosphere are either directly as anhydrous, gaseous acid or by passing the non-oxidizing component of the atmosphere through an aqueous solution of the acid is passed and then the gas stream is dried before it enters the furnace. Alternatively, the halide can be introduced into the furnace with hydrogen. The hydrogen halide, on the other hand, can can be generated by a mixture that dissociates upon heating to form a hydrogen halide. For example, in the Furnace charge may contain ammonium or another halide, which decomposes on heating to give a hydrogen halide. The hydrogen halide used is preferably hydrogen chloride or hydrogen bromide.

The temperature at which the first heating step is carried out is that at dex a reaction occurs between the hydrogen halide and the coating and / or the exposed iron on the surface of the strip, but below that at which any appreciable amount of metal halides formed therefrom would be removed by evaporation. In practice it has been found according to the invention that this temperature is usually in the range from 400 ° to 700 ° C, preferably around 600 ° C, although it may be necessary where aluminum is contained in substantial amounts in the initial coating, To use temperatures as low as 180 ⁰ C in order to minimize the loss of aluminum shark ο benefit from the furnace. The furnace is held at this temperature while the bubbling of non-oxidizing gas continues with the addition of a hydrogen halide. The amount of hydrogen halide in the gas stream and the rate of passage of the gas stream through the furnace are preferably adjusted so that little or no hydrogen halides are contained in the furnace exhaust gases.

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The introduction of hydrogen halide into the furnace atmosphere continues until enough halogen has been fixed to the surface of the strip to ensure that a sufficient chrome plating speed is achieved.

When the desired amount "of halogen" introduced into the furnace has been stopped, the flow of gases therethrough, preferably in such a way that the furnace is under a low positive pressure or "overpressure remains in order to reduce the possibility of air leakage into it to a minimum, which can cause an oxidation of the chromium or the chromium and iron halides.

The temperature of the furnace is then increased to a temperature of at least 750 ° C, at which the chrome plating takes place, and held at that elevated temperature for as long as necessary to keep all in the to alloy the chromium contained in the initial coating with the ferrous metal and to apply an alloy coating of the desired thickness form. For any given amount of chromium deposited on the strip, it is possible to obtain alloy coatings that Gradually transition from thin alloys with high chromium content to thick alloys with low chromium content.

When the chrome plating has been carried out to the desired extent, the remaining halogen mixtures in the Oven atmosphere can be removed from the oven by kneeling with a non-oxidizing gas before cooling the furnace. Alternatively, you can let the oven cool down and the rest of them Halides from the surface of the treated strip Washing, for example with water, remove. The treated strip has a chromium / iron alloy surface, the Depth and chromium content with the pre-chromium plating conditions used varies.

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Another method that can be used is described in British Patent 1,184-183. In this pail the above-mentioned steel strip is cleaned and then with a chromium-rich powder by any suitable method, for example as described herein, coated or overdrawn.

An adherent metallic, halide-containing coating is then applied to the chrome-rich coating on the strip. The halide-containing coating is preferably one which is a Metal halide such as an iron halide, in particular contains an Fe halide (ferrous halide), however, can other metal halides can also be used.

A plurality of strips coated in this way are combined into one Stack or coil formed with the coated surfaces in contact with each other or with each other Spaced apart and heated in an oven to cause the chrome-rich plating with the strip surfaces diffused and thereby a chrome plating of the strip surfaces is effected.

During the heating the furnace is followed cleaned with a stickstoffhalti- ™ gen gas by cleaning with hydrogen, the temperature of the furnace is typically raised above 75O ⁰ C in the order of 1000 ⁰ C to cause a chrome plating.

Another method that can be used is described in British Patent Application 28929/70. When using This procedure cleans the above mentioned strip first and then puts it on at least one surface an adhesive film is applied in the form of a vaporizable liquid which wets the surface and which is a binder may contain. The adhesive can contain a halogen-containing pathogen (energiser), for example an iron halide (iron

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halide), in which ball, due to the adhesive properties of the pathogen, the inclusion of a binding agent is not essential needs to be.

On the "wetted strip with or without the pathogen is then a Coating of chrome-rich powder applied. This coating is in a known manner, for example by spraying in a Get electrostatically charged deposition zone. The strip so formed is then heated to remove the liquid from the Evaporation of the coating to obtain an adherent coating on the strip without the need for compaction.

A multitude of coated strips are then either in Single form, or in stacks or in a coiled form in one Furnace heated in a protective atmosphere to initiate the formation of a chromium diffusion layer thereon.

If the adhering film has the halogen-containing pathogen, the stacked or coiled strips become with their face in contact with each other during the heating process arranged. However, if the adhering film does not contain the halogen-containing agent, the agent may at the time of chrome plating to be added. So the pathogen can be in dry powder form, as a solution or a gas by any known procedure can be added. In this case are the strips are spaced apart or are in an open helical shape or coil shape and it is for example a halogen-containing gas in the furnace chamber at the time of chrome ens led.

In a suitable heat treatment cycle, air is replaced with nitrogen and then the nitrogen atmosphere with a protective atmosphere containing hydrogen or a mixture of hydrogen and inert gas, and the strips are reduced to about. 370-425 ⁰ O, preferably ^{heated to about 400 0} C, while the protective

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atmosphere is passed through the furnace to remove volatile components. This temperature can be maintained for about 5 to 20 hours, preferably for about 10 hours. After the cleaning is completed, the temperature is up to about 840 ° - 1010 ⁰ C preferably at about 940 - 95O ⁰ C and raised Verchromungstemperatur this is held for a period of time sufficient to chrome to the strip surfaces. For example, the chrome plating temperature can be maintained for 10 to 80 hours and preferably for about 20 to 40 hours. During this period of time, the furnace is not cleaned and the atmosphere is maintained at a positive pressure of about 1-2 inches of water. The atmosphere in the furnace can be pure hydrogen or a mixture be an inert gas such as argon or helium and hydrogen. During the chrome plating step, the exciter provides halogen between the adjacent layers of strip material in the array, and more particularly, closest to the strip material. As is known, the halogen aids and promotes chrome plating of the adjacent surface in a minimal period of time.

When the Verchromungsstufe has been completed, the temperature is lowered to about 340-400 ⁰ C or below, and the hydrogen-containing protective atmosphere may be replaced with gaseous nitrogen. When the temperature has been further lowered to about 150-210 ⁰ C or below, the furnace can be opened and the chrome-plated sheet metal material to be removed. The chromed strip material is subjected to washing with water, spraying and / or brought in contact with the mechanically driven brush to remove residual chemicals and inert UIlermittel E ^1, if present, to be removed. The chrome-plated strip material is then brushed or subjected to mechanical treatment in order to produce a shiny finish, or it is tempered by rolling.

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Another method of manufacturing an article of chromium-plated Fe metal according to the invention, particularly in the case when the article is in the form of a small workpiece such as a bolt, is embedded in a package containing the chromium-rich powder and a heat-resistant diluent such as aluminum hydroxide (alumina) or magnesia or magnesium oxide, which serves to prevent the chromium particles from sintering together, and the packing is heated ^{up to 900 0} O or more, usually in the region of 1000 ^{0 C.}

Experiments have shown that by applying a chromium-rich Powder coupled to a low carbon steel substrate by any of the methods discussed above with a manganese content that is higher than normal, and an addition of a carbide stabilizing element, the resulting End product has mechanical properties that are more favorable compared to those of mild steel substrates.

For example, when using a steel with a carbon content of 0.03 %, a manganese content of 3.5% and a niobium content of 0.1%, it has been found possible to

_. or .fine-grain chrome-plated strips chromed fine-grain strips / with a tensile strength of et \ ^ a

6000 kg / cm (40 tons / sq.inch.). It is believed, that the improved property of the coated substrate is a combined effect which is that some of the Carbon is retained as niobium carbide in the substrate, thus resisting grain growth, and that together with the effect of manganese the ferrite is solidified.

Furthermore, experiments have shown that the improved properties of the coated substrate discussed above become evident as a more or less continuous change when the Proportions of manganese and niobium or another carbide stabilization element increase.

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To illustrate the finding that the improved mechanical Properties of a chrome-plated steel substrate are evident when the proportions of the manganese and the carbide stabilizer are increased are the following examples with reference to niobium as the carbide stabilizer.

A steel with a manganese content of about 0.3% and no Üfiob additive has the following mechanical properties after chrome plating on:

1 050 - 1340 kg / cm ² 0.2% test stress / 15,000 - 19,000 psi)

Specific tensile strength 2 100 - 2 460 kg / cm ² (Ultimate Tensile Strength) (30,000 - 35,000 psi)

Transition temperature 15 - 25 ° C

The term "transition temperature" can be defined as the temperature at which a brittle crystal fracture (brittle crystalline fracture) is obtained when the coated material is subjected to a dynamic cupping test of the type which is used in the typing of color coatings (DEF.1053 method 17A).

Example 2

A steel with a manganese content of 0.56% and a niobium content of 0.02% has the following mechanical properties after chrome plating:

0.2% test stress 1 400 - 1 550 kg / cm ²

(20,000 - 22,000 psi)

Specific tensile strength 3 250 - 3 300 kg / cm ²

(46,000 - 47,000 psi)

Transition stone temperature - '} ° U - -17 ⁰ E

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A comparison of the two examples shows that with a higher than normal manganese content in the steel substrate plus the addition of a small amount of niobium, improved mechanical properties are obtained after chrome plating. Furthermore, the transition temperature has been lowered to about 30 ⁰ G as compared to Example 1 in Example 2. FIG. With respect to the latter, when carrying out the method of the invention, it was observed on a large number of standard mild steel strips of various origins that none of them caused ^{a transition temperature below 0 ° C after chrome plating.} As a result, it appears from the tests carried out that the small amount of niobium in the substrate enables sufficient "grain-demanding" cores in the form of niobium carbides or nitrides to be retained, thereby avoiding the coarse grain size that is customary associated with the chrome plating process. As a result, along with the presence of a larger than usual amount of manganese in the ferrite, the strength is increased and the transition temperature is decreased. In order to explain this, it is shown in the following example that by further increasing the manganese and niobium compared to Example 2, the improved mechanical effect and the reduction in the transition temperature become even more noticeable.

Example 3

A steel with a manganese content of 3.5 % and a niobium content of 0.05 % has the following mechanical properties after chrome plating:

0.2% test stress 4 780 kg / cm (68,000 psi)

Specific tensile strength 6100 kg / cm ² (87 000 psi) transition temperature below -78 ⁰ C.

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Thus it can be seen that by raising it, even a small one Amount, the manganese content and by adding niobium to the steel forming the substrate a much improved chrome-plated Material is achieved.

The above-mentioned examples show that the properties after chrome plating are improved due to the use of niobium as the carbide stabilizing element; however, similar results can be obtained using other carbide stabilizing elements such as vanadium, titanium, zirconium, tungsten or molybdenum can be obtained. Do this with the following example with reference to titanium given as the carbide stabilizer.

Example 4

A steel with a manganese content of about 0.4 % and a titanium content of 0.32 % has the following mechanical properties like chrome plating:

0.2 % test stress 1 550 kg / cm ² (22,000 psi) Specific tensile strength 3 160 kg / cm (45,000 psi) Transition temperature -52 ⁰ G

Instead of a steel strip, steel in the form of a sheet can be used in the same way.

- Claims 209820/0726

Claims (16)

Claims ΤΊ Object made from a chromium-plated Fe metal a substrate with a diffusion layer of a chromium on at least one of its surfaces, characterized in that the substrate is a steel with a manganese content of 0.4% to 5%> a carbide stabilizer content from 0.02% to 1%, a carbon content of 0.02% to 0.10% and the rest with Iron with the exception of incidental, normally occurring impurities such as aluminum. 2. Article according to claim 1, characterized in that the manganese content is in the area from 1% to 5% by weight. 3 · Object according to claim 1 or 2, characterized in that the Garbidstabilisierungselement in is present in an amount from 0.02% to 0.15% by weight. 4. The object of claim 3 »characterized in that that the carbide stabilizer is present in an amount of from 0.05% to 0.15% by weight. 5. Article according to one of the preceding claims, characterized in that the carbon content is in the range of 0.02 wt% to 0.05 wt%. 6. Article according to claim 1, characterized in that that the manganese content 3> 5% »the carbide stabilizer content 0.1% and the carbon content is 0.03%. 7. Article according to one of the preceding claims, characterized in that the carbide stabilizer is selected from niobium, vanadium, titanium, zirconium, tungsten and molybdenum, or amounts of at least two of these Materials. 209820/0726 8. A process for producing an article according to any one of the preceding claims, characterized in that a substrate of suitable composition of a chromium diffusion heat treatment is subjected at a temperature of at least 75O ⁰ C. 9. The method according to claim 8, characterized in that on at least one surface of the Subject a layer of particulate rich chromium Material is deposited and that the coated object is heat treated in a protective atmosphere in the presence of a halide, so that the formation of a diffused chromium layer on the object is set in motion. 10. The method according to claim 9 »marked thereby e t that the object is moistened or wetted prior to the deposition of the particulate chromium-rich material. 11. The method according to claim 10, characterized in that that the object is wetted or moistened with an adhesive containing a binder. 12. The method according to claim 10, characterized in that that the object is wetted or moistened with an adhesive containing the halide. 13. The method according to claim 11 or 12, characterized in that the objects during the heat treatment are in surface contact with one another or are provided in close spiral formation. 14 ·. Method according to claim 10 or 11, characterized in that the objects spaced apart or provided in an open spiral formation and that the halide is on this is applied during the heat treatment. 2 09820/0726 15 · The method according to any one of claims 9 to 14 ·, characterized marked that the particulate chromium-rich layer is compacted after application to the object. 16. The method according to any one of claims 9 "to 15 or 15j characterized in that the halide is an Fe halogen. 17 · A method for producing an object according to any one of claims 1 to 7 »characterized in that a liquid solution containing a Pe halide is applied to the object, that the object is coated with a particulate, chromium-rich powder, that the coated object is dried and that the object is arranged in a tight spiral arrangement or a plurality of objects are stacked in contact with adjacent surfaces, and that the counter /? or the counter / l. m heating an inert atmosphere in the range of 840 ° C to 1010 ⁰ C or be. 209820/0726