WO2018131993A1 - Procédé de cémentation à basse pression - Google Patents

Procédé de cémentation à basse pression Download PDF

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Publication number
WO2018131993A1
WO2018131993A1 PCT/MX2017/000002 MX2017000002W WO2018131993A1 WO 2018131993 A1 WO2018131993 A1 WO 2018131993A1 MX 2017000002 W MX2017000002 W MX 2017000002W WO 2018131993 A1 WO2018131993 A1 WO 2018131993A1
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WO
WIPO (PCT)
Prior art keywords
carbon
steel
temperature
carburization
minutes
Prior art date
Application number
PCT/MX2017/000002
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English (en)
Spanish (es)
Inventor
Niko MATTHIAS BOUSKA
Original Assignee
Thyssenkrupp Presta De México S.A. De C.V.
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 Thyssenkrupp Presta De México S.A. De C.V. filed Critical Thyssenkrupp Presta De México S.A. De C.V.
Publication of WO2018131993A1 publication Critical patent/WO2018131993A1/fr

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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
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces

Definitions

  • the present invention relates to the technical field of metalworking, materials science, fluid dynamics, the calculation of atmospheric pressures, thermochemistry and mechanical strength, since it provides a low pressure carburizing process.
  • Cementation or carburization is one of the oldest methods to produce a hardening on the surface of low carbon steel parts and low carbon alloy steels, generally from 0.08 to 0.25% C.
  • This process consists of supplying carbon to the surface of the steel so that it diffuses inside the piece.
  • This thermochemical treatment is carried out in an endothermic atmosphere plus an enrichment gas, to obtain a sufficient carbon potential, capable of enriching the carbon percentage layer and the time necessary to obtain the desired layer depth, tempering in oil to harden the layer and core of the piece.
  • a subsequent tempering to eliminate the tensions caused during tempering, and obtain that the surface has the resistance, hardness to the required wear and the ductile core.
  • the reactive (endothermic) atmosphere used in this process must protect the steel from oxidation and provide enough carbon to increase its surface content. This increase is based on the adsorption and subsequent diffusion of carbon in the steel at high temperatures, once the carbon penetration is desired, the part is removed by tempering it or normalizing it.
  • LPC low pressure carburation
  • Parts can be carburized between 930 and 1,000 ° C (1,700 and 1,830 ° F).
  • the carburization process can be summarized in the following steps:
  • the carburization can be liquid, solid or gas.
  • controlled fuel atmospheres are used. They are produced by mixing a carrier gas with a rich gas (fuel gas).
  • the latter is usually natural gas (methane), propane or butane.
  • a carrier gas is the endothermic gas, which is produced in an independent generator by mixing, in a certain proportion, a hydrocarbon gas (natural gas, propane or butane) with air. Subsequently, it decomposes at high temperature (1000 ° C) and in the presence of a catalyst in an oven. This is the principle of the endothermic atmosphere generator.
  • the carrier gas is a mixture of CO, H2, N2 and to a lesser extent CO2, CH4 and water vapor.
  • the types of furnaces for gaseous carburization can be divided into two categories: continuous ovens and batch type ovens.
  • batch ovens the pieces are loaded and unloaded from the oven in each batch. The most common are pit, horizontal and fluidized bed furnaces. In all of them, the pieces are placed in baskets or hung with wires, depending on their shape and size. Then, they are introduced into the oven through which the fuel gas circulates, generally agitated by a fan.
  • the oven lid is moved and the basket where the pieces are located is taken out to be taken quickly to another oven (which is at a lower temperature) and then the pieces are passed to the tempering bath.
  • some horizontal furnaces may have an integrated quenching system, in which it is not necessary to remove the part from the fuel atmosphere.
  • the pieces are taken from the oven to a hall that ends in an oil quenching pool. In this case, since the furnace atmosphere also flows into the lobby, oxidation of the pieces before tempering is avoided.
  • composition of the atmosphere As secondary variables can be named the content of alloys of the piece to be carbureted, and the degree of circulation of the oven atmosphere.
  • TEMPERATURE The maximum speed at which carbon can enter steel is limited by the diffusion rate of carbon in austenite. This diffusion rate increases sharply with increasing temperature. For example, carbon is incorporated into steel 40% faster by going from 870 ° C to 925 ° C.
  • a widely used carburization temperature is 925 ° C, for allowing a reasonably fast carburization rate without excessive deterioration of the interior of the oven. This temperature can be raised to 955 ° C and 980 ° C, shortening the carburization time for parts that require greater layer depth.
  • TIME The carburization time decreases if the temperature increases.
  • the graph was calculated assuming saturated austenite on the surface of the piece. In case of controlling the content of surface carbon, and that this is less than saturation, the layer depth will be less.
  • COMPOSITION OF ATMOSPHERE XA The atmosphere consists of an endothermic gas (produced from methane) that is enriched by the addition of methane, which is ultimately the source of carbon.
  • the main constituents of the resulting fuel atmosphere are: CO, N2, H2, CO2, H2O and CH4.
  • N2 is inert, acting only as a diluent.
  • the parameters that are monitored in order to control the fuel atmosphere are: water vapor content (measuring the dew point of the gas), CO2 content (by infrared gas analysis), amount of O2 (by zirconia sensors
  • the part to be treated is heated in a closed container (box) and in contact with a solid carburization compound.
  • this technique allows more options in terms of selective carburization techniques.
  • solid carburization does not provide flexibility or accuracy regarding the control of process variables and therefore, the final results.
  • the most commonly used commercial carbonization compounds or hardener powders are made up of charcoal, petroleum coke or tar, mixed with 10 to 20% barium carbonates, calcium and sodium.
  • Furnaces heated with coal, gas, fuel oil or electricity are used. In them, the cement boxes are placed, with the pieces and the cementitious mixtures inside. The joints of the boxes must be tightly closed, using mud or refractory clays.
  • the main characteristics that an oven must have to be used in solid carburization are: to provide good thermal capacity, temperature uniformity and to have adequate supports for the boxes.
  • carbon steel containers can be coated with aluminum
  • cast iron welded steel sheets
  • stainless steel Fe-Cr-Ni alloys
  • the function of aluminum as a coating of carbon steel is to extend the life of carbon steel. This significantly reduces the cost of the boxes.
  • the choice of material will depend on the amortization given. That is, the cheapest material could become a Fe-Cr-Ni alloy, with the largest initial investment, but amortized based on the number of years of use and continuity of the
  • the carburization in boxes has the same variables to control as those already mentioned in the carbonated gas: temperature, time and composition of the atmosphere. ⁇ 1 as in carbonated gas, the velocity of formation of the carbureted layer increases rapidly with temperature. The normal temperature range is 815 ° C to 955 ° C. However, in recent years the temperature of carburization has been raised up to 1095 ° C, due to improvements in the manufacturing processes of steel (fine grain practices). Some steels can keep the fine grain up to 1040 ° C. Above this temperature, grain growth would occur after a long enough time. Finally, the increasing improvement of the material of the boxes and the fine grain steels allow the use of a great variety of temperatures.
  • the layer depth at a given carburization temperature is proportional to the square root of time. In this way, the carburization rate is higher at the beginning of the process and gradually decreases over time.
  • the amount of nascent carbon in the generated atmosphere is directly increased by increasing the ratio of carbon monoxide to carbon dioxide. Therefore, the amount of carbon on the surface of the part is greater if energizers and carburization compounds are used that promote the formation of carbon monoxide.
  • liquid carburization the piece is immersed in a bath of carburizing salts at a temperature greater than Acl. Like solid carburization, liquid carburization no longer has the commercial importance it had in the past. This is mainly due to environmental issues, due to the difficulty and cost associated with the disposal of salts, especially those that contain cyanide. In addition, the removal of salts can be very difficult in some parts.
  • the piece Due to the characteristics of the thermal transfer of the salt bath to the piece, the piece heats up much faster and the liquid carburization takes place in less time than the soda. In general, the pieces are tempered after the bath, followed by a temper.
  • Cemented layers of 1 to 3mm are achieved. In general they are used in the range of 875 to 950 ° C. In some cases depths of up to 6mm can be achieved. The most important use of these salts is the rapid formation of 1 to 2mm layers.
  • the salts are arranged in crucibles that can be cast iron, sheet steel (embedded or welded) or refractory stainless steel.
  • the heating of the crucibles can be with coal, gas, gasoline or electricity.
  • a type of electric oven widely used consists of a group of electrodes that are submerged in the bathroom. As the molten salts are conductive, the electric current passes through them and the heat generated by the passage of this current is sufficient for heating the bath. Since solid salts are not conductive of electricity, commissioning is somewhat complicated. It begins by placing between two electrodes a piece of coke of appropriate size, which is pressed between them with an auxiliary iron bar to facilitate contact. The passage of the current heats the coal, which becomes red. Then, the salts around it begin to melt. Subsequently, the rest of the dough is heated and melted. The temperature is regulated with great accuracy by modifying the electrode voltage. Is It is necessary to have bells on the crucibles, to absorb the harmful vapors that are released.
  • the improved vacuum cementation method comprises a cementation treatment of work pieces made of steel material is heated to approximately 900 to 1100 ° C. Performed by introducing an ethylenee gas as a carburation gas at a vacuum of 1 to 10 kPa in a cement kiln chamber.
  • Another object of the present invention is to provide a suitable mixture of gases, the main advantage is the reduction of carbon remnants and therefore less pollution, preserving the original conditions of the carburizing chamber and achieving repeatability between batches.
  • the present invention describes a low pressure carburizing process, it is composed of the following steps:
  • Iv. Inject by means of nozzles, a mixture of gases to generate an atmosphere enriched with carbon, in a time range of 1 to 7 minutes, with a flow range of 75 to 300 liters per minute;
  • viii Cool the carbon steel load using nitrogen as a convective medium; ix. Maintain a temperature between 600 ° C and 700 ° C for a time range of 20 to 90 minutes, to refine the austenitic grain;
  • xii Transport the carbon steel load to the cooling chamber; and, xiii. Dip the carbon steel load in oil for at least 30 minutes.
  • Steps iv to vi are repeated as many times as necessary, to meet the specific specifications.
  • the gas mixture described in step iv is to generate an enriched enough to carburizing areas larger than 20m 2 carbon steels low carbon atmosphere.
  • Said mixture is composed of:
  • Acetylene and Ethylene are in a 3: 1 ratio in a temperature range between 900 ° C and 1000 ° C; and Hydrogen is in a 1: 3 ratio to Acetylene to maintain a clean reaction.
  • Acetylene is used as the main carbon carrier, and Ethylene will increase the efficiency of Acetylene.
  • the low carbon steel parts that are carburized are mainly intended for automotive applications.
  • An advantage of the gas mixture described above is that it allows the reduction of carbon remnants and therefore less pollution, preserving the original conditions of the carburizing chamber and achieving repeatability between lots, in less time, as well as, achieving volumes greater than 200 x 200 x 400 mm, modifying process flows and consumables for a carburizing area greater than 0.4 m 2 .

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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)
  • Resistance Heating (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)

Abstract

La présente invention concerne un procédé de cémentation à basse pression qui, au moyen d'un mélange adéquat de gaz, permet que les résidus de carbone issus de chaque procédé n'imprègnent pas toute la surface des chambres dans lesquelles le procédé de cémentation est effectué, lesdites chambres étant composées de graphite, autant en termes d'isolation thermique que pour les éléments de chauffage (résistances en graphite). L'invention permet d'éviter la contamination des chambres et de maintenir celles-ci dans de bonnes conditions, ce qui a pour effet d'empêcher l'apparition de variations importantes dans les résultats obtenus, et de réduire la consommation d'énergie.
PCT/MX2017/000002 2017-01-13 2017-01-13 Procédé de cémentation à basse pression WO2018131993A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
MXMX/A/2017/000565 2017-01-13
MX2017000565A MX2017000565A (es) 2017-01-13 2017-01-13 Proceso de carburizado a baja presión.

Publications (1)

Publication Number Publication Date
WO2018131993A1 true WO2018131993A1 (fr) 2018-07-19

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MX (1) MX2017000565A (fr)
WO (1) WO2018131993A1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1264914A2 (fr) * 2001-06-05 2002-12-11 Dowa Mining Co., Ltd. Procédé et installation de cémentation
WO2004035853A1 (fr) * 2002-10-21 2004-04-29 Seco/Warwick Sp. Z O.O. Melange d'hydrocarbure gazeux pour la carburation sous pression de l'acier
ES2392595T3 (es) * 2007-04-02 2012-12-12 Seco/Warwick S.A. Método y medición para el control de una superficie de carga activa en el procedimiento de cementación a baja presión

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1264914A2 (fr) * 2001-06-05 2002-12-11 Dowa Mining Co., Ltd. Procédé et installation de cémentation
WO2004035853A1 (fr) * 2002-10-21 2004-04-29 Seco/Warwick Sp. Z O.O. Melange d'hydrocarbure gazeux pour la carburation sous pression de l'acier
ES2392595T3 (es) * 2007-04-02 2012-12-12 Seco/Warwick S.A. Método y medición para el control de una superficie de carga activa en el procedimiento de cementación a baja presión

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Publication number Publication date
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