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WO1998018978A1 - Composition et procede d'alliage par diffusion de materiaux ferreux - Google Patents

Composition et procede d'alliage par diffusion de materiaux ferreux Download PDF

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Publication number
WO1998018978A1
WO1998018978A1 PCT/US1997/019278 US9719278W WO9818978A1 WO 1998018978 A1 WO1998018978 A1 WO 1998018978A1 US 9719278 W US9719278 W US 9719278W WO 9818978 A1 WO9818978 A1 WO 9818978A1
Authority
WO
WIPO (PCT)
Prior art keywords
approximately
chromium
ferrochromium
components
recited
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US1997/019278
Other languages
English (en)
Inventor
Inna Isaakovna Zaetz
Lidia Omovna Chunayeva
Grigory Anatolyevich Tkach
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Jamar Venture Corp
Original Assignee
Jamar Venture Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Jamar Venture Corp filed Critical Jamar Venture Corp
Priority to EP97911922A priority Critical patent/EP0946784A4/fr
Priority to AU49188/97A priority patent/AU4918897A/en
Priority to CA002269735A priority patent/CA2269735A1/fr
Priority to US09/284,365 priority patent/US6197436B1/en
Publication of WO1998018978A1 publication Critical patent/WO1998018978A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/28—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes
    • C23C10/30—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes using a layer of powder or paste on the surface
    • C23C10/32—Chromising
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/28—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes
    • C23C10/30—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes using a layer of powder or paste on the surface

Definitions

  • the present invention relates to a composition and method for diffusion coating ferrous metals, and more particularly to a method for diffusion coating ferrous metals using a pulverous coating composition including chromium and ferrochromium.
  • Carbon steels are frequently used in various industries due to their high plasticity, that is, their ability to deform inelastically without rupture at high stresses. This high plasticity, in turn, makes carbon steels relatively easy to machine, process and treat.
  • compositions have been proposed for the diffusion coating of ferrous base metals.
  • One such composition has the following components: Chromium 50 wt% Aluminum Oxide 43-45 wt%
  • the diffusion coating of carbon-containing ferrous base metals with this composition produces a surface layer comprising a solid solution of chromium in iron with a discontinuous chromium carbide phase.
  • Such surface layers have been found to be susceptible to fracture, leading to a relatively short coating life. This is believed to be due to the failure of the coating.
  • Such surface layers also have been found to be insufficiently resistant to corrosion, especially in weak acidic or chloridic solutions at high temperatures.
  • Another proposed diffusion coating composition uses ferrochromium:
  • the wear resistance of ferrous base metals diffusion-coated with this composition is very low.
  • German Patent No. 36 04 309 proposed the following composition for use in diffusion coating metal:
  • microadditives tend to enhance the formation of a continuous upper surface carbide layer and thereby meaningfully increase the corrosion resistance and wear resistance of the finished part.
  • coatings formed on carbon-containing ferrous base metals from chromium-based compositions including boron or molybdenum microadditives lack sufficient resistance to aggressively corrosive solutions such as calcium chloride, sulfur-containing petroleum and mineral oil.
  • prior art coating compositions have required relatively large amounts of these relatively expensive microadditives (from approximately 2-5 wt%) which significantly increased the cost of the coatings.
  • Tantalum carbide which is synthesized by the direct carbidization of tantalum powder and soot, or by the reaction of tantalum oxide with carbon at 1900°C in an inert gas atmosphere, is known to possess high hardness and high resistance to corrosion except at elevated temperatures.
  • Tantalum metal is widely used in sheet form in the manufacture of different kinds of apparatus including vessels, heaters, steam condensers and pipe heat exchangers. Tantalum is rarely used for coating other metals, however. Though tantalum coatings might be formed by explosion or by precipitation from the vapor phase, these processes are expensive and do not guarantee sufficiently continuous, unbroken coverage of the base metals.
  • German Patent No. 42 38 220 proposed a composition for the diffusion coating of ferrous metals such as cast iron: Chromium 50-60 wt%
  • the present invention provides a composition and method for use in diffusion protection of ferrous workpieces.
  • the composition or mixture comprises both chromium and ferrochromium in combination with an ammonium halide and aluminum oxide.
  • a preferred form of the composition also includes between 0.75 wt% and 1.35 wt% of microadditives selected from the group consisting of vanadium, tantalum, their alloys and mixtures thereof.
  • the composition comprises:
  • the preferred ammonium halide is ammonium chloride.
  • the invention also provides a relatively simple coating method which can be performed using conventional equipment.
  • the components, in powdered form, are weighed and mixed in a container.
  • the workpieces are preferably degreased, for example in a weak acid solution, and then placed in the container. Careful cleaning or scouring of the workpiece is not required.
  • the container is hermetically sealed and heated to a temperature of 1000°-1050°C. No protective atmosphere is required.
  • the workpieces and the composition are kept at that temperature for a predetermined period, on the order of forty-five minutes or longer, of sufficient duration to permit a surface layer of desired thickness to form.
  • the container is then cooled in a conventional cooling chamber and the workpieces are removed.
  • the diffusion coating of workpieces of carbon steel or cast iron with the preferred coating composition forms a protective surface layer having mechanical properties akin to those of highly alloyed steels, with improved plasticity characteristics. More specifically, the preferred coating composition serves to form an ultra-hard surface layer. As a result of chemical and thermal processing of the base metal, the surface acquires high wear and corrosion resistance characteristics to satisfy the requirements for long-term performance in various environments.
  • the composition and method of the invention are preferably applied to high carbon and medium carbon steels. While less preferred, the composition and method of the invention do provide coatings with desirable properties on low carbon steels.
  • the inclusion of both chromium and ferrochromium in the composition of the present invention is believed to be unique.
  • the waste products of metallurgical smelting typically include 68-70 wt% ferrochromium.
  • the use of such waste products as a source of ferrochromium is believed to result in significant cost savings.
  • the mixture of ferrochromium with chromium improves the alloying characteristics of the composition and provides for a better treatment of the base metal. If the percentage of ferrochromium added is less than approximately
  • the composition does not produce a pore-free carbide layer which reduces the protective capability of the coating. If the percentage of ferrochromium is greater than approximately 37 wt% (or if the total percentage of chromium and ferrochromium exceeds the preferred limits of the invention), oversaturation occurs and the resulting surface is brittle and prone to fracture.
  • tantalum carbide in the range of 0.40-0.65 wt% increases the wear resistance of the surface layer.
  • vanadium in the range of 0.35-0.70 wt% improves the plasticity properties of the surface layer. If insufficient amounts of tantalum carbide and vanadium are used, the composition does not produce a pore-free surface layer. If excessive amounts of the microadditives are used, the cost of the composition is increased without significantly improving the properties of the surface layer.
  • the structure of the surface layer is formed by the diffusion of tantalum carbide and chromium carbide into vacancies in the surface.
  • the vanadium fills the space between the carbides to form a continuous layer.
  • the chromium carbides diffuse farther into the matrix of the base metal and fill deeper vacancies.
  • the carbides making up the solid, pore-free coatings produced by the composition and method of the invention have low diffusion mobility at room temperature.
  • the diffusion mobilities of chromium carbides and tantalum carbides are on the order of magnitude often times lower than the diffusion mobilities of pure chromium and tantalum in the crystalline structure of metal.
  • the chromium and tantalum carbides formed on the workpiece surface as a result of the diffusion treatment are not inclined to diffuse into the structure of the base metal once the surface layer is formed.
  • composition and method of the present invention are effective to form on carbon steels and cast irons diffusion coatings having Vickers hardnesses up to approximately 2200-2500 kg/mm 2 with porosities less than 0.1%. Further increases in hardness are possible, but may lead to undesirably low plasticity.
  • Workpieces of any geometric shape may be treated by the method of the invention.
  • the only practical size limitation on the parts which can be treated by the method of the invention is the size of the furnace.
  • the preferred surface layer thickness, 8-500 ⁇ m, is independent of the dimensions of the workpiece.
  • the diffusion coating method of the present invention is believed to be cheaper than electrodeposition methods. Unlike electrodeposition methods, the diffusion coating method of the present invention does not generate significant fumes harmful to workers or the environment.
  • One significant advantage of the method of the invention is that the coating composition may be continuously refreshed and recycled, and the process may be operated so as to generate practically no waste.
  • the coating process of the present invention is believed to be applicable in many fields, including the engineering, chemical, oil and gas, agricultural, automotive, shipbuilding, electronics and communications industries. The process may also find application in the construction and consumer goods industries. Therefore, it is one object of the invention to provide a composition and method for diffusion coating ferrous base metals to form surface layers having good wear and corrosion resistance while maintaining desirable plasticity characteristics.
  • the invention will be further described in conjunction with the following detailed description. Detailed Description of the Preferred Embodiment The invention will be further explained in conjunction with the following examples which are included as being illustrative of the invention and should not be construed to limit the scope of the invention.
  • EXAMPLE 1 A mixture of the following components was weighed out and placed in a sealed container with a prismatic workpiece (65 cm x 15 cm x 3 cm) of carbon steel and three test samples of the same steel:
  • the container was heated in a furnace at a temperature of 1050°C for ninety minutes and then placed in a cooling chamber.
  • the test samples with the newly-formed protective surface layers were tested by means of (1) X-ray structural analysis and (2) Vickers micro-hardness analysis.
  • the thickness of the diffused carbide layer was 12 ⁇ m.
  • An upper portion of the surface layer was comprised of tantalum carbide, chromium carbide and vanadium.
  • a lower portion of the surface layer was comprised of chromium carbides and a solid solution of chromium in iron.
  • the microhardness of the surface layer was 1900 kg/mm 2 Vickers. A scratch test using different degrees of pressure revealed the absence of cracks and showed that the surface possessed good wear resistance and plasticity characteristics.
  • the porosity of the surface layer was determined by placing a sheet of filter paper saturated in Vokker's reagent, a mixture of
  • EXAMPLE 2 Additional ferrous workpieces were coated according to the method of Example 1 using various pulverous coating compositions. The results are shown in Table 1 below:
  • C-42 Low Alloy Steel includes 13.5 wt% chromium, 0.6 wt% silicon and 0.6 wt% manganese.
  • test results set forth in Table 1 showed the desirable properties of surface layers formed on carbon steels and cast irons by the method and composition of the invention.
  • Tests Nos. 1, 2, 4-11, 13 and 14 the method of the present invention resulted in surface layers having Vickers hardnesses of 1550 kg/mm 2 or greater without porosity or brittleness.
  • the test results set forth in Table 1 also showed the significance of the chromium/ferrochromium composition on the properties of the coating.
  • the coating in Test No. 3 formed using a composition including 50 wt% chromium, 39 wt% ferrochromium, and microadditions was brittle.
  • the coating in Test No. 12 formed using a composition including 45 wt% chromium, 22 wt% ferrochromium, 0.38 wt% tantalum carbide, and 0.35% vanadium was porous and relatively soft.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)

Abstract

Procédé de durcissement de revêtement par diffusion de pièces métalliques contenant du fer tels que l'acier au carbone et la fonte, ce procédé consistant à peser et mélanger les composants suivants, se présentant sous forme de poudre: chrome 40 à 50 % en poids, ferrochrome 25 à 37 % en poids, carbure de tantale 0,40 à 0,65 % en poids, vanadium 0,35 à 0,70 % en poids, halogénure d'ammonium 4 à 5 % en poids, le reste étant de l'oxyde d'aluminium. Ces pièces sont de préférence dégraissées, puis placées dans un réceptacle avec le mélange de composants. Le réceptacle est fermé hermétiquement et chauffé à une température comprise entre 1000 et 1050 °C. Les pièces et la composition sont maintenues à cette température sur une durée prédéterminée, de l'ordre de 45 minutes au moins, de façon à permettre la formation d'une couche superficielle d'une épaisseur désirée. Le réceptacle est ensuite refroidi dans une chambre de réfrigération traditionnelle et les pièces sont retirées. Ce procédé permet de produire des revêtements présentant une bonne résistance à l'usure et à la corrosion.
PCT/US1997/019278 1996-10-25 1997-10-23 Composition et procede d'alliage par diffusion de materiaux ferreux Ceased WO1998018978A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
EP97911922A EP0946784A4 (fr) 1996-10-25 1997-10-23 Composition et procede d'alliage par diffusion de materiaux ferreux
AU49188/97A AU4918897A (en) 1996-10-25 1997-10-23 Method and composition for diffusion alloying of ferrous materials
CA002269735A CA2269735A1 (fr) 1996-10-25 1997-10-23 Composition et procede d'alliage par diffusion de materiaux ferreux
US09/284,365 US6197436B1 (en) 1997-10-23 1997-10-23 Method and composition for diffusion alloying of ferrous materials

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US2916396P 1996-10-25 1996-10-25
US60/029,163 1996-10-25

Publications (1)

Publication Number Publication Date
WO1998018978A1 true WO1998018978A1 (fr) 1998-05-07

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PCT/US1997/019278 Ceased WO1998018978A1 (fr) 1996-10-25 1997-10-23 Composition et procede d'alliage par diffusion de materiaux ferreux

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Country Link
EP (1) EP0946784A4 (fr)
AU (1) AU4918897A (fr)
CA (1) CA2269735A1 (fr)
WO (1) WO1998018978A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002002843A3 (fr) * 2000-06-29 2002-05-30 Borgwarner Inc Articles en acier revetus de carbure et procede de fabrication
RU2379376C2 (ru) * 2008-01-22 2010-01-20 ГОУВПО Кубанский государственный технологический университет Способ обработки поверхности стальных изделий
RU2481936C1 (ru) * 2011-09-13 2013-05-20 Александр Александрович Веселовский Способ восстановления изношенного слоя на рабочих поверхностях зубьев чугунных зубчатых колес
US9080235B2 (en) 2012-04-17 2015-07-14 Jamar International Corporation Composition and method for diffusion alloying of ferrocarbon workpiece

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IT202300011172A1 (it) 2023-05-31 2024-12-01 Rina Consulting Centro Sviluppo Mat S P A Rivestimenti anticorrosivi ottenuti tramite alluminizzazione per componenti in acciaio

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4234668A (en) * 1978-04-20 1980-11-18 General Electric Company Composite sulfur electrode container and method of manufacture
GB2206898A (en) * 1987-07-01 1989-01-18 Electric Power Res Inst Chromized coatings containing vanadium
US4963395A (en) * 1988-06-24 1990-10-16 Combustion Engineering, Inc. Method of chromizing large size articles
DE4238220C1 (en) * 1992-11-12 1993-05-27 Inna Isaakowna Sajez Mixt. for diffusion coating ferrous material - contains chromium@, tantalum carbide, ammonium chloride, and alumina

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB906884A (en) * 1960-05-04 1962-09-26 Deutsche Edelstahlwerke Ag The use of a steel for the production of smooth-surfaced parts which are to be chromised
DE1278741B (de) * 1964-06-09 1968-09-26 Deutsche Edelstahlwerke Ag Verwendung eines nickelhaltigen Stahles fuer Chromierungszwecke
US4099993A (en) * 1973-01-26 1978-07-11 Hermann Muller Process for producing an extremely hard mixed carbide layer on ferrous materials to increase their resistance to wear

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4234668A (en) * 1978-04-20 1980-11-18 General Electric Company Composite sulfur electrode container and method of manufacture
GB2206898A (en) * 1987-07-01 1989-01-18 Electric Power Res Inst Chromized coatings containing vanadium
US4963395A (en) * 1988-06-24 1990-10-16 Combustion Engineering, Inc. Method of chromizing large size articles
DE4238220C1 (en) * 1992-11-12 1993-05-27 Inna Isaakowna Sajez Mixt. for diffusion coating ferrous material - contains chromium@, tantalum carbide, ammonium chloride, and alumina

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP0946784A4 *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002002843A3 (fr) * 2000-06-29 2002-05-30 Borgwarner Inc Articles en acier revetus de carbure et procede de fabrication
US6582765B2 (en) 2000-06-29 2003-06-24 Borgwarner, Inc. Carbide coated steel articles and method of making them
RU2379376C2 (ru) * 2008-01-22 2010-01-20 ГОУВПО Кубанский государственный технологический университет Способ обработки поверхности стальных изделий
RU2481936C1 (ru) * 2011-09-13 2013-05-20 Александр Александрович Веселовский Способ восстановления изношенного слоя на рабочих поверхностях зубьев чугунных зубчатых колес
US9080235B2 (en) 2012-04-17 2015-07-14 Jamar International Corporation Composition and method for diffusion alloying of ferrocarbon workpiece

Also Published As

Publication number Publication date
AU4918897A (en) 1998-05-22
EP0946784A4 (fr) 2002-01-30
CA2269735A1 (fr) 1998-05-07
EP0946784A1 (fr) 1999-10-06

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