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
  • C23C8/24—Nitriding
  • C23C8/26—Nitriding 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
  • C21D1/06—Surface hardening
• • 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
  • 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
  • C21D1/76—Adjusting the composition of the atmosphere
• • 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
  • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
  • C21D3/02—Extraction of non-metals
  • C21D3/08—Extraction of nitrogen

Definitions

• the present invention relates to a method for nitriding a component made of a metallic material.
• nitriding inevitably produces a hard, but brittle bonding layer in the areas closest to the surface, with a significantly higher nitrogen content. This layer can flake off in particular at notch loads, which can lead to failure of the component as well as consequential damage caused by released particles.
• DE 102005049534 AI it is known from DE 102005049534 AI to subsequently remove the compound layer electrochemically. For more complex part geometries this is not always possible.
• DE 102009045878 A1 discloses to limit the thickness of the bonding layer to an optimum already during the nitriding process
• Nitrogen supply an initially thick compound layer can be subsequently reduced again.
• Another prior art is DE 102009002985 AI to call.
• the component is heated in a first Nitrierphase to at least 450 ° C, and it is on its surface a nitrogen-emitting process gas and / or
• the bonding layer is dissolved in a first degradation phase by heat treatment.
• Imperfectly nitrided areas in the component surface develop during operation to weak points at which the component preferably fails under repeated vibration load. Due to the formation of the bonding layer, first of all the disadvantage is accepted that it has a significantly lower vibration resistance. By the subsequent dissolution of the compound layer in the mining phase, this disadvantage disappears.
• the metallic material contains at least one other
• the further metallic element may in particular be an alloying element of the metallic material.
• the invention expressly refers not only to higher alloyed materials, but also to low alloyed and unalloyed materials.
• the duration of the first nitriding phase, the temperature of the component during the first nitriding phase and / or the supply of nitrogen on the surface of the component are advantageously selected such that the connecting layer has a thickness of at most 10 ⁇ m, preferably between 2 ⁇ m and 6 ⁇ , is formed. This range is preferred in the sense that the actual nitration is uniformed, but that no pore space is yet formed in the compound layer by the recombination of atomic to molecular nitrogen. These pores could not be removed by simply removing the iron nitride; they only could be removed by, for example mechanical or electrochemical, removal of the bonding layer.
• a second nitration phase and a second degradation phase are connected to the first phase of degradation.
• the parameters of the second nitriding phase do not have to match the parameters of the first nitriding phase.
• the parameters of the second phase of dismantling do not have to match the parameters of the first stage of dismantling.
• Two (or more) nitration phases with intermediate decomposition phase have the advantage that overall a higher nitration depth can be achieved without being too thick at any time
• Connecting layer is formed and thereby forms, for example, a pore space.
• the nitriding depth increases additively with each nitriding phase, while the thickness of the connecting layer always begins again at zero due to the preceding reduction phase.
• Bonding layer increases with increasing treatment temperature.
• the component is heated to temperatures of up to 580 ° C for the formation of the special nitride. According to the prior art had to be worked at significantly lower temperatures, so as not to form a bonding layer
• X-ray microscope or by means of energy-dispersive X-ray spectroscopy (EDX) are detectable, are correlated with early failures of the treated components.
• the connecting layer initially formed is therefore advantageously completely dissolved so that it is no longer recognizable at least in a light microscope.
• XRD X-ray diffractometry
• Process gas mixture is changed so that less nitrogen is offered for nitriding. This measure can be carried out, for example, for a batch of a variety of different components, which are in disordered form as bulk material in a treatment chamber, in one operation.
• the nitrogen-emitting process gas may in particular be ammonia. It is also possible to use a mixture of, for example, ammonia with nitrogen and / or hydrogen. Then, by changing the
• the nitrogen supply for the nitration be changed without the pressure in the treatment chamber must be changed.
• the nitrogen supply at the component surface can also be reduced without changing the gas composition solely by further heating of the component and / or the gas or gas mixture: the higher the temperature, the faster ammonia dissociates at the component surface and the faster atomic nitrogen diffuses from the component surface path.
• the gas composition is changed, then as an intermediate step, advantageously, the treatment chamber can be evacuated to the whole
• the component for dissolving the connecting layer to not more than 1000 ° C, preferably not more than 600 ° C, further heated.
• the metallic material of the component is austenitic by the nitrogen introduced on its surface. This is not desirable in nitriding because the component warps, its core is too high annealed and / or its lattice structure could be changed at the edge.
• many nitriding are limited to operating temperatures up to 700 ° C; at higher temperatures, the service life of the furnace materials can be greatly reduced, which can cause more distortion.
• Niobium nitride and chromium nitride are examples of special nitrides, which are up to about 1000 ° C
• the component temperature is kept below the temperature at which
• the supply of atomic nitrogen at the component surface can not only be reduced but completely reduced to zero, for example by evacuating the treatment chamber or by introducing only an inert gas, such as, for example, molecular nitrogen or argon, onto the component surface.
• an inert gas such as, for example, molecular nitrogen or argon
• Bonding layer bound nitrogen is driven from the surface of the component.
• the well-known teacher diagram exemplifies in which combinations of temperature, nitriding index and nitrogen supply an iron nitride layer forms or dissolves or whether the iron will transform into an austenitic structure.
• the process that led to the formation of the compound layer then preferably proceeds backwards.
• Embodiment is in this map area the Sonderitrid thermodynamically stable. It then remains in full.
• the component temperature is selected from a characteristic field range in which the nitrogen, which is more strongly bound in the special nitrides, remains in the surface of the component. Then the decisive for the fatigue strength actual nitriding is fully retained, and it is only the
• the degradation phase provided according to the invention in this embodiment is particularly advantageous with respect to the vibration resistance.
• the process gases or process gas mixtures can, for example
• the treatment chamber controlled by the coefficient of coal control. But you can also be supplied as a solid gas amount of the treatment chamber, for example.
• the general functioning of the invention does not depend on the fact that the process gases or process gas mixtures are supplied regulated in a certain way.
• the component By carbon number controlled feed, the component can be simultaneously nitrided and carburized. This changes the structure of the connection layer. Alternatively or in combination with this, the nitration effect can be increased by means of oxidation-parameter-controlled feed.
• the component consists of a highly alloyed with chromium steel.
• the process is carried out under atmospheric pressure. Then the treatment chamber does not have to be pressure-resistant.
• the method but also in low pressure, ie with a lower pressure than that
• Pressure difference can be prevented, for example, escape process gases in case of a leak from the treatment chamber.
• the mean free path for diffusion at a lower pressure is greater.
• the method may also be performed under plasma nitriding conditions with or without active screen support. This will be the
• Bonding layer has the side effect that tools with which this surface is subsequently machined mechanically, less quickly
• simulation models can be used that calculate the diffusion of nitrogen and the formation of the special nitrides as a function of time, temperature and material composition. Otherwise, the process parameters can be fine tuned in a known manner by making a series of coupons and inspecting metallographic cuts.
• Iron matrix is already greatly reduced during nitriding by effusion and diffusion in the edge region. How much nitrogen is allowed to
• the originally formed, later dissolved compound layer is detectable metallographically by a modified Aniser .
• Figure 1 Course of the temperature T over the time t in one embodiment of the method according to the invention.
• FIG. 2 micrograph of a sample nitrated according to the prior art (a) and a sample (b) nitrided by the process according to the invention.
• FIG. 3 GDOES depth profile analysis of the nitrogen concentration n over the edge distance d for the sample according to FIG. 2a (curve a) and the sample according to FIG. 2b (curve b).
• Figure 4 Effect of nitration with bonding layer thicknesses of ⁇ 1 ⁇ and 5 ⁇ on the fatigue strength.
• Figure 5 Effect of nitration according to an embodiment of the invention on the fatigue strength.
• Figure 1 shows an example of the process control for an embodiment of the method according to the invention.
• the continuous curve indicates the course of the temperature T over the time t.
• sections AI to F are defined in which different activities take place.
• the component 6 is first brought from room temperature to a temperature of 420 ° C.
• the heating rate is constant.
• the treatment chamber in which the process is carried out is filled with an inert gas, such as nitrogen or argon, with an overpressure of 20 to 100 mbar above atmospheric pressure.
• Temperature equalization phase Bl the treatment temperature is kept constant at about 420 ° C. During the heating phase AI and the temperature equalization phase Bl is thereby no oxygen-containing
• the temperature equalization phase Bl is followed by a
• Preoxidation phase C with an oxygen-containing process gas is provided.
• the treatment chamber for example, air, nitrous oxide, synthetic
• an inert gas such as nitrogen or argon is fed isobarically to the treatment chamber to exchange the gas atmosphere.
• an inert gas such as nitrogen or argon is fed isobarically to the treatment chamber to exchange the gas atmosphere.
• Heating rate until a treatment temperature of about 540 ° C is reached is followed by the second
• a nitrogen donor gas 7 for example, an ammonia-nitrogen mixture or an ammonia-nitrogen-hydrogen mixture. Due to a sufficiently high supply of ammonia, the metallic components 6 contained in the treatment chamber are nitrided, and a bonding layer V is formed.
• the nitrogen supply is lowered by the treatment chamber isobaric an ammonia-nitrogen mixture or an ammonia-nitrogen-hydrogen mixture with a lower
• the nitrogen supply is increased again to the level of the nitration phase Dl.
• further Sonderitride form while again forms a connecting layer in its surface next to the surface. This is completely degraded in the subsequent mining phase E2, in which the nitrogen supply is lowered back to the level of the first degradation phase El.
• an inert gas such as nitrogen or argon is supplied isobarically to the treatment chamber to exchange the gas atmosphere.
• an inert gas such as nitrogen or argon is supplied isobarically to the treatment chamber to exchange the gas atmosphere.
• the nitriding of the metallic components 6 is terminated.
• the treatment chamber and the metallic components 6 are then cooled to room temperature.
• Nitrogen supply Dl, D2 two degradation phases with lower nitrogen supply El, E2 and a cooling phase F is limited.
• connection layer V does not reach a very great thickness, in which it forms pores P. These would not be removed in the degradation phase El.
• FIG. 2 illustrates the comparison of a sample nitrided according to the prior art (FIG. 2 a) with a sample nitrided in accordance with the process procedure shown in FIG. 1 (FIG. 2 b) in a sectional drawing.
• the nitrogen donor gas 7 was in each case on the surface 8 of the component 6 from the metallic
• the normal structure is also in the area that is closest to the surface 8 of the component 6, continued without breakage.
• the undesired pores P which extend in FIG. 2 a to a depth of approximately 4 ⁇ m are absent in the surface 8 of the component 6.
• connection layer V shows a stronger Aniser compared to a connection layer-free nitration from the outset and therefore appears darker on microscope images of metallographic cuts.
• the material of the samples sketched in FIG. 2 is X40CrMoV5-l, which in addition to iron as the base metal contains the following further alloying elements in the following percentages by mass: carbon 0.39, silicon 1.10, manganese 0.4, chromium 5.20, molybdenum 1.40 , Vanadium 0.95.
• FIG. 3 shows a GDOES depth profile analysis of the components 6 shown in FIG. 2.
• Curve a relates to the component 6 sketched in FIG. 2a.
• Curve b relates to the component 6 sketched in FIG. 2b.
• the nitrogen concentration n is plotted in mass percent M in each case % over the edge distance (depth) d in ⁇ .
• depth depth
• curve b in the case of the component 6 sketched in FIG. 2b, the entire surface 8 near its surface is nitrided very uniformly.
• the nitrogen concentration n in the component 6 according to FIG. 2a also converges to the nitrogen concentration n in the component 6 according to FIG. 2b.
• FIG. 4 shows results of a durability test of notched, cylindrical components 6 (tensile specimens) with respect to the fatigue strength. All components 6 were remunerated. A part of the components 6 was not further heat-treated while the rest of the components 6 were nitrided. Before the zugschwellenden claim all components 6 were reworked in the clamping area. The notches were not reworked. Non-nitrided components 6, components 6 with an approximately 5 ⁇ m thick bonding layer V and components 6 with a bonding layer V thicker than 1 ⁇ m were tested.
• the amplitude q of the voltages applied to the components 6 is plotted in N / mm 2 over the number z of vibrations to which the components 6 were exposed.
• the type of symbol indicates whether component 6 passed the test (hollow symbol) or failed (filled symbol).
• the measurements refer.
• a square lying on its edge indicates a measured value which was obtained on a non-nitrided component 6.
• a square standing on a point indicates a measuring point which has been recorded on a component 6 with 5 ⁇ thick bonding layer V.
• a circle indicates a measuring point which thickens on a component 6 with a diameter of less than 1 ⁇ m
• a compensation curve (la, 2a, 3a) is set, indicating for which combinations of voltage amplitudes q and repetition numbers z each one
• Compensation curve corresponding to 50% probability of failure The letter b indicates the curve corresponding to 90% failure probability.
• the letter c indicates the curve corresponding to 10% failure probability.
• the non-nitrided components 6 cut the worst from a failure probability of 50%.
• the components 6 with a less than 1 ⁇ thick compound layer V show the highest sustainable voltage amplitude based on a failure probability of 50%.
• Connection layer V are in a comparable range, is the
• the material of the samples investigated in FIG. 4 is 50CrMo4, which, in addition to iron as the base metal, has the following further alloying elements in the following
• Embodiment of the invention nitrided components 6 (circles as symbols, curves designated by number 4) and other non-nitrided components 6 (squares as symbols, curves designated by number 5) compared.
• the inclination of the curves 4a, 4b and 4c in the time-strength range is comparable to the inclination of the curves 5a, 5b and 5c.
• the curves 4a, 4b and 4c approach the curves 5a, 5b and 5c in the time-strength range. This can be spoken of a comparable time stability.
• the voltage amplitude is increased by about 24% based on a failure probability of 50%.
• the advantage of the method according to the invention manifests itself in particular in the fact that the scattering of the components 6 nitrided according to this method is similar in comparison with the non-nitrided components 6 and no early failures occur with small numbers z of load changes.
• the material of the samples investigated in FIG. 5 is 8CrMol6, which, in addition to iron as the base metal, has the following further alloying elements in the following

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Citations (8)

• 2015
  • 2015-07-13 DE DE102015213068.1A patent/DE102015213068A1/de not_active Withdrawn
• 2016
  • 2016-06-29 WO PCT/EP2016/065124 patent/WO2017009044A1/de active Application Filing
  • 2016-06-29 CN CN201680041599.0A patent/CN107849678A/zh active Pending
  • 2016-06-29 BR BR112017028323A patent/BR112017028323A2/pt active Search and Examination
  • 2016-06-29 EP EP16733080.2A patent/EP3322833B1/de active Active

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