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
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
• • 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
  • C23C8/02—Pretreatment of the material to be coated

Definitions

• the invention relates to a method for carburizing a thermoformed article or a stamped and bent article made of austenitic stainless steel with a wall thickness which is at least partially suitable for such articles.
• customary low wall thicknesses are below 2000 ⁇ m.
• Such stainless steel articles are made of very thin sheets by tensile or compression bending and sometimes take on very filigree structures.
• articles with varying or constant wall thickness can be produced, whereby they then have a wall thickness of less than 2000 ⁇ m, at least in regions or as a whole.
• filigree articles are used in a variety of fields of technology such. used as bearing covers in gearboxes, valve seats in ABS systems or as sample carriers for hazardous substances in high-precision measurements where they are exposed to extreme mechanical, thermal and chemical stresses.
• the demand for high hardness corrosion resistant materials is therefore correspondingly high.
• the US 6,461,448 shows a method for carburizing a steel article, wherein said steel article is treated in a Schmelzalkalibad.
• Such an aggressive type of treatment leads to filigree articles in the context of the invention due to the small wall thickness sometimes severe corrosion phenomena, which has a highly inhomogeneous edge layer result.
• liquid treatments in filigree articles due to incomplete surface wetting lead to unsatisfactory results.
• the EP 0 678 589 B1 discloses in this context a method of carburizing an austenitic metal.
• the metal is exposed to a fluorine-containing gas.
• Fluorine-containing gases are highly corrosive due to their reactivity and, as a result, aggressively affect the surface of the metal. While the resulting removal of surface is even desirable for articles with high wall thickness due to a corresponding material wealth, it can not be compensated for thin-walled thermoforming and stamping bending articles and leads to the irreversible destruction of the article.
• thermoforming and stamping bending articles With the invention, a method with mild conditions is proposed in an advantageous manner, which are tailored to the specifics of thin-walled thermoforming and stamping bending articles.
• the article is introduced into an oven for carrying out the method. It has been shown that in particular oxygen and water residues interfere with the surface hardening. To exclude these disturbing factors, the article is heated to a temperature which is above the boiling point of water. Preference is given here to a temperature of 110 ° C to 140 ° C, more preferably 120 ° C.
• the oxygen-containing atmosphere in the furnace is replaced in accordance with the invention by a first gas mixture.
• the furnace therefore advantageously has gas inlets and gas outlets.
• the furnace may be provided to flood the furnace with an inert gas before the introduction of the first gas mixture.
• the oxygen displacement is accelerated in an advantageous manner and a potentially existing hazard potential, resulting from the contact of the oxygen-containing normal atmosphere with the first gas mixture is lowered.
• the inert gas it is preferable to use known chemically unreactive gases such as, in particular, nitrogen or argon.
• Stainless steels include, among others, chromium as an alloying constituent. Upon contact with atmospheric oxygen, a passivating and corrosion-resistant chromium (III) oxide layer is formed on the surface of the material.
• the first gas mixture has reducing properties in order to avoid further oxidation of the chromium.
• this gas mixture already initiated the depassivation of the surface.
• the first gas mixture consists of at least one hydrogen-containing gas and a nitrogen-containing gas, and more preferably H 2 and N 2 . It has been found that this gas mixture, in particular in conjunction with the mild temperature of the first process step, exerts a particularly mild and advantageous effect on the chromium oxide layer without adversely affecting the morphology of the surface of the filigree articles.
• the oxygen concentration is measured continuously or at intervals by means of a sensor.
• a control unit connected to the sensor checks the actual value here continuously or at intervals with a freely selectable desired value and releases the oven in the case of an identity between actual and desired value for a second method step.
• the inventive method is thereby greatly simplified in an advantageous manner and minimizes in this way possible user-side sources of error.
• a second method step in which the article is heated to the target temperature, the second temperature, for the carburization.
• the second temperature is preferably chosen so that it is well below the recrystallization temperature of strongly cold-worked iron alloys (680 ° C). A possible change in the morphology of the surface is thereby effectively prevented, whereby the formation of a homogeneous surface layer is promoted.
• the second temperature is 450 ° C to 550 ° C, and more preferably 500 ° C.
• the heating phase serves in particular the careful and complete depassivation of the chromium oxide layer.
• the heating rate in a certain temperature range between 0.5 and 1 ° C / min, more preferably between 0.5 and 0.7 ° C / min and more preferably 0.5 ° C / min.
• the temperature range in which this low heating rate is selected is preferably 420 ° C to 550 ° C, more preferably 450 ° C to 500 ° C, and most preferably 480 ° C to 500 ° C.
• the first gas mixture is replaced by a second gas mixture in the second method step. It has been found that mild depassivation of the thin-walled deep-drawn parts during the heating phase to the second temperature preferably by a gas mixture at least consisting of a hydrogen-containing gas, a nitrogen-containing gas and a carbon-containing gas. Particularly in connection with the low heating rate, a particularly slow and therefore mild and readily controllable depassivation of the chromium oxide layer can be achieved.
• the article is treated with additives which selectively or completely dissolve the passive layer.
• additives which selectively or completely dissolve the passive layer.
• it means salt compounds and / or organic substances and acid generators, which are applied in solid or liquid form to the product or in the oven.
• the application is preferably carried out before the article is placed in the oven or during the second process step.
• solids and / or liquids are used which form acid reaction products in conjunction with the reaction gases, which would give a pH ⁇ 7 when introduced into water, as the application of the substances has proven particularly advantageous directly on or in the article surface , As a result, local depassivation processes, which initiate and promote uniform depassivation earlier, occur even at low temperatures.
• carbon oxides saturated, unsaturated, aliphatic, cyclic, heterocyclic and / or aromatic hydrocarbons may preferably be added to the second gas mixture.
• unsaturated hydrocarbons in particular ethyne.
• elemental nitrogen As the nitrogen-containing component, elemental nitrogen, ammonia, amines, amides, imines, nitriles and / or nitrogen oxides may preferably be added to the second gas mixture. Particularly preferred here is the use of elemental nitrogen.
• the temperature is measured continuously or at intervals by means of a sensor.
• the control unit connected to the sensor checks the actual value here continuously or at intervals with a freely selectable setpoint value for the second temperature and releases the oven in the case of an identity between the actual and setpoint values for a third method step.
• the inventive method is thereby greatly simplified in an advantageous manner and minimizes in this way possible user-side sources of error.
• a third method step is provided in which the deep-drawn part is kept constant at the second temperature.
• the third step in this context serves to carburize the thin-walled deep-drawn part. It has been found that the second temperature advantageously allows a careful construction of the surface layer to be hardened. The diffusion of the carbon into the edge region of the deep-drawn part takes place slowly at these temperatures, is therefore easy to control and causes the formation of a homogeneous carbon-rich surface layer. Too high a temperature is to avoid in any case, as it comes to the formation of irregular layers and the formation of carbide particles due to the high diffusion rate and the high kinetic energy of the molecules involved.
• the second gas mixture is replaced by a third gas mixture, which is particularly suitable for gentle carburizing under mild conditions.
• a gas mixture which is composed of at least a hydrogen-containing gas, a nitrogen-containing gas and a carbon-containing gas. It can further be preferred to add to this gas mixture still another carbon-containing component, whereby the Forming a homogeneous carbon-rich surface layer by the two different carbon components is promoted in a synergistic manner.
• carbon oxides saturated, unsaturated, aliphatic, cyclic, heterocyclic and / or aromatic hydrocarbons may preferably be added to the second gas mixture.
• unsaturated hydrocarbons in particular ethyne.
• carbon oxides saturated, unsaturated, aliphatic, cyclic, heterocyclic and / or aromatic hydrocarbons may preferably be added to the second gas mixture.
• Particularly preferred here is the use of carbon oxides, in particular carbon monoxide.
• nitrogen-containing component elemental nitrogen, ammonia, amines, amides, imines, nitriles and / or nitrogen oxides may preferably be added to the second gas mixture.
• the individual concentrations of the gas components are measured continuously or at intervals by means of respective sensors.
• the control unit connected to the sensors checks the respective actual values continuously or at intervals with freely selectable desired values for the respective concentration of the gas component and compensates for changes within a fault tolerance continuously or at intervals.
• the process control is advantageously simplified and allows the provision of constant process conditions, which is for the construction of a homogeneous carbon-rich surface layer of crucial importance.
• the layer thickness of the carbon-rich surface layer can be adjusted over the gassing time.
• a period of 2 to 10 hours is required to generate a 10-40 microns thick edge layer.
• control unit which has a corresponding device for time detection, releases after the expiration of one Selectable carburizing free the oven for the fourth step.
• the inventive method is thereby greatly simplified in an advantageous manner and minimizes in this way possible user-side sources of error.
• a fourth method step is provided in which the deep-drawn part is cooled to a third temperature. It is hereby preferably provided to cool the deep-drawn part to a temperature of 50 ° C to 80 ° C and more preferably 60 ° C.
• the choice of atmosphere in the cooled is crucial for the formation of a homogeneous surface layer. It is therefore provided according to the invention to replace the third gas mixture by a fourth gas mixture.
• the choice of a slightly reducing gas mixture is considered advantageous.
• the fourth gas mixture consists at least of a hydrogen-containing gas and a nitrogen-containing gas. It is particularly preferred here that the fourth gas mixture of H 2 and N 2 is formed.
• the composition of the fourth gas mixture advantageously consists of 5% to 25% H 2 and 75% to 95% N 2 , more preferably 5% to 10% H 2 and 90% to 95% N 2 and especially preferably 5% H 2 and 95% N 2 . It has been found that the cooling according to the invention of the thin-walled deep-drawn part effectively prevents the escape of the carbon from the hardened edge layer.
• the invention relates to an edge-hardened thermoforming article with very small wall thicknesses.
• the deep-drawing article according to the invention has a soft, elastic core with a hardness of 350 to 400 HV1 and a hard carbon-rich surface layer.
• the surface layer is free of defects and / or particles, circumferentially completely closed and has a substantially planar surface.
• the thin-walled thermoforming article according to the invention has mechanical properties of unprecedented quality.
• the deep-drawing article according to the invention has in its edge region a carbon-rich layer having a hardness of 700 to 1000 HV0.01 and a layer thickness of 10 to 40 ⁇ m.
• the corrosion and abrasion resistance of the thermoforming article are better than those of the starting material.
• the former in particular, is surprising in that carburizing generally worsens the corrosion properties of a steel product.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Heat Treatment Of Articles (AREA)

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Citations (8)

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• 2013
  • 2013-12-06 PL PL13196076T patent/PL2881492T3/pl unknown
  • 2013-12-06 EP EP13196076.7A patent/EP2881492B1/fr active Active
• 2014
  • 2014-12-02 US US14/557,574 patent/US9738962B2/en active Active
  • 2014-12-04 CN CN201410737053.1A patent/CN104451534B/zh active Active

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