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
  • 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 present application relates to a method for heat treatment of a workpiece made of temperature-resistant steels, in particular of hot-work steels, wherein the workpiece is hardened and nitrided after mechanical processing and electrochemical treatment and wherein a reduction of the workpiece surface is carried out during curing without a pickling treatment before the subsequent nitriding must be performed.
• DE 3 633 490 discloses a rotor made of a steel alloy for a ring spinning machine.
• DE 1 933 439 discloses a nitriding process with two basic process steps.
• US 6,168,095 discloses a fuel injector for internal combustion engines with a nozzle body.
• Nozzle bodies for modern DI injection systems are increasingly being used at working temperatures up to 450 ° C. Accordingly, high demands are placed on the component strength and the wear resistance of the nozzle body.
• For the production of the nozzle body in particular nitrided hot working steels are therefore used.
• In the production of internal bores (pressure chamber) and for the rounding ECM procedures (Electro Chemical Maschining, electrochemical metalworking) are used.
• the ECM processes which are used for shaping and surface treatment of metallic workpieces, are used in an electrolyte solution performed, wherein the workpiece to be machined is usually connected as the anode and the tool as a cathode.
• the electrochemical metal working methods are used in particular for deburring, polishing, grinding and etching the surfaces of a workpiece.
• the surfaces resulting from the ECM process are largely passive and can only be treated very poorly by thermal-chemical diffusion methods, in particular nitriding, since more noble alloying elements such as Cr remain on the surface or oxidize alloying elements, with metal oxides and metal hydroxides Me x O y [OH] z are formed.
• the passive surfaces are currently pickled prior to nitriding, especially using hydrochloric acid.
• the pickling suffers from considerable disadvantages.
• stigmata may be produced.
• the results of the pickling can be reproduced very poorly, since, for example, the storage time between processing, heat treatment and nitriding can be different lengths.
• Pickling also creates significant additional costs, particularly due to the cost of the equipment used for pickling and the labor costs required.
• the stained workpieces must be cleaned after pickling using a very complex special cleaning technology. The disposal of pickling solutions is expensive.
• the pickling with acid to an undesirable burden on the environment and worsens the working conditions.
• the technical problem underlying the present invention is therefore to develop a method for the treatment of workpieces made of hot-work steels, in particular DI nozzle bodies, that in particular improves the nitridability of these workpieces without the need to pickle the workpieces, and therefore the stand known in the art, caused by the pickling disadvantages are avoided.
• the present invention solves the underlying technical problem by providing a method for producing a workpiece from a temperature-resistant steel, in particular hot-work steel, wherein the workpiece is hardened and thereby de-passivated, characterized in that the hardening step comprises a reduction treatment, in particular by means of hydrogen and nitriding the quenched workpieces with the more active surface in different steps under different gas atmospheres is then carried out, the nitriding initially under an atmosphere of ammonia and an oxidizing agent, in particular water vapor or air, and then under an atmosphere of ammonia and a carbon-containing gas , in particular endogas or a mixture with CO and / or CO 2 , is performed.
• the hardening step comprises a reduction treatment, in particular by means of hydrogen and nitriding the quenched workpieces with the more active surface in different steps under different gas atmospheres is then carried out, the nitriding initially under an atmosphere of ammonia and an oxidizing agent, in particular water vapor or air, and
• the method according to the invention is also considerably less expensive than the methods known in the prior art since the systems required for pickling and subsequent cleaning are eliminated and only devices for supplying hydrogen to the vacuum hardening system are required. Since no acids are used for pickling in the process according to the invention, this also leads to a significant relief of the environment, in particular to an improvement in working conditions.
• the workpiece is hardened from a temperature-resistant steel, in particular from hot-work steel, and thereby de-passivated, the hardening step comprising a reduction treatment.
• the reduction removes the metal oxide and / or metal hydroxide layers present on the surface of the workpiece, so that the subsequent nitriding is considerably improved without the need for pickling.
• the reduction treatment is carried out using hydrogen.
• a hot-work steel is understood to mean a steel which, during its use, is constantly exposed to an elevated temperature, in particular a temperature of more than 200 ° C. During use, no structural changes may occur in hot-work steel, but the structure must be sufficiently stable and resistant to attack. Depending on the desired use, hot working steels must have different properties. Important desired properties are in particular hardness and strength, which in turn determine the wear resistance.
• Hot work tool steels must meet some special performance requirements, such as hot strength, especially achieved by molybdenum, tungsten and grain fine vanadium, tempering resistance produced by chromium, which together with molybdenum, nickel and manganese enhances hardenability, and hot wear resistance the heat resistance of the matrix and by the type and amount of special carbides is determined.
• hot strength especially achieved by molybdenum, tungsten and grain fine vanadium
• tempering resistance produced by chromium which together with molybdenum, nickel and manganese enhances hardenability
• hot wear resistance the heat resistance of the matrix and by the type and amount of special carbides is determined.
• DI nozzle bodies made of hot-work steel must have a very high wear resistance.
• the workpiece made of a temperature-resistant steel, in particular hot-work steel, machined before curing and an electrochemical Processing, ie, running in electrolyte solution ECM process for shaping and surface treatment.
• electrochemical Processing ie, running in electrolyte solution ECM process for shaping and surface treatment.
• the workpiece in particular deburred, polished; be ground and / or etched.
• internal bores can be produced with an ECM process, which are subsequently rounded.
• the workpiece is subjected to a cleaning step in an aqueous cleaning medium, in particular a neutral cleaner.
• the cleaning step according to the invention prevents the formation of thick Me x O y [OH] z layers on the surface of the workpiece.
• the workpiece is dried. Subsequently, the workpiece can be hardened immediately.
• the workpiece if it is to be stored for a longer period after ECM processing, first conserved using suitable methods and after storage, immediately before curing, again cleaned in a liquid cleaning medium ,
• the curing which leads to a structural change of the hot-work steel described above, takes place in a single-chamber or multi-chamber vacuum furnace.
• the hardening involves first a convective heating of the workpiece under nitrogen.
• the convective heating of the workpiece is carried out under a nitrogen pressure of more than 0.8 bar.
• the workpiece can also be heated in a vacuum.
• the workpiece is heated at least up to the hardening temperature of the hot working steel.
• the hardening temperature of hot-work steel is around 1040 ° C.
• the nitrogen atmosphere or the vacuum is replaced by hydrogen.
• the introduced hydrogen which serves as a reducing agent for reducing the metal oxide and / or metal hydroxide layers present on the tool surface, is introduced according to the invention at a temperature of at least 400.degree.
• the temperatures at which hydrogen is introduced are in the range of the hardening temperature.
• the hydrogen partial pressure is about 1 to 100 mbar.
• the flow rate for the hydrogen to be added is 100 to 2000 Nl / h.
• the austenitization is preferably carried out over a period of 10 to 40 minutes.
• the gas exchange takes place pulsating over a period of 1 to 10 minutes. That is, the pressure build-up of the hydrogen partial pressure is pulsed over a period of 1 to 10 minutes in exchange with vacuum. In this way, a better gas exchange, especially for workpieces with blind holes, achieved according to the invention.
• the hydrogen is pumped off before ending the austenitization in order to avoid contamination of the gas used in the subsequent quenching step with hydrogen.
• the quenching of the austenitized workpiece in nitrogen at a pressure of 1 to 10 bar is carried out after holding to hardening temperature.
• the workpiece is subjected to at least one annealing step.
• the workpiece is tempered at a temperature of up to 650 ° C, wherein the tempering of the workpieces takes place either in a nitrogen atmosphere or under a nitrogen-hydrogen atmosphere.
• a nitrogen-hydrogen atmosphere this contains up to 5% hydrogen.
• the tempering of the workpiece takes place in a vacuum oven or an evacuatable tempering furnace. The annealing step according to the invention is carried out for about 1 to 2 hours.
• the workpiece is subjected to not only one but several annealing steps.
• the workpiece is a first annealing step, which takes about 1 to 2 hours and is heated to a temperature of 520 ° C, and then subjected to a second annealing step, which also takes about 1 to 2 hours and wherein is heated to a temperature of 610 ° C, subjected.
• the workpiece is nitrided immediately after tempering.
• the nitriding leads to a hardening of the hot working steel, from which the workpiece consists. This is due to a diffusion of nitrogen into the steel. This leads to the incorporation of nitrogen on interstitial sites and formation of nitrides and nitrogen deposition on carbides to form carbonitrides. Nitriding produces hard surface layers which increase the hardness, wear resistance and fatigue strength of the hot work tool steel.
• the workpiece is transferred immediately after curing and tempering in a nitriding.
• the nitriding furnace used in accordance with the invention is preferably a purged chamber furnace or an evacuable retort furnace.
• the oxidizing agent used in step 1 is preferably 0.5 to 10% by volume of water vapor or up to 15% of air.
• the carbon support used in step 2 is preferably 1 to 10% by volume of endogas. Endogas, which is obtained by endothermic reaction of hydrocarbons, such as propane, is a mixture of 23.7 vol .-% CO, 31.5 vol .-% H 2 and 44.8 vol .-% N 2 . In a further preferred embodiment, CO and / or CO 2 in equivalent proportions can also be used as carbon carriers.
• the nitriding in step 2 is referred to as gas oxycarbouration and, according to the invention, lasts more than 4 hours, preferably about 10 to 60 hours.
• Gasoxicarburleiters reaction which lasts longer than four hours according to the invention, already has a uniform nitriding on formed the surface of the workpiece.
• a treatment under ammonia or a gas additive to reduce the nitriding characteristic takes place in order to limit the connection layer growth.
• the flow rate of the gases during the nitriding is dependent on the volume of the furnace space and is preferably three times the volume of the furnace space in Nl / h.
• the workpieces are cooled after nitriding using nitrogen.
• the workpiece treated and produced using the method of the invention may then be hard worked using conventional methods.
• the inventive method can be used in particular for the production of temperature-resistant DI nozzle body made of hot working steels, wherein the nozzle body made of high-strength and temperature-resistant hot working steels, in particular the steel brands X40CrMoV51 and X38CrMoV51.
• the pressure chamber is further processed in a production cycle comprising the soft machining, ECM processing and subsequent directly concatenated cleaning in an aqueous cleaning medium, but according to the invention, no pickling treatment is carried out.
• the DI nozzle body in a vacuum oven in the temperature range between 1000 ° C and 1070 ° C under a pulsed hydrogen partial pressure of 1 to 100 mbar hardened and then quenched in a nitrogen gas stream at a pressure of 1 to 10 bar.
• the annealing is carried out at a temperature of up to 650 ° C in a nitrogen or nitrogen-hydrogen atmosphere.
• the subsequent nitration is preferably carried out at 510 to 590 ° C for a period of 10 to 60 hours using the above-described gas oxinitrocarburization process in a chamber furnace or evacuable retort furnace.
• treated heat-resistant DI nozzle body have more favorable consolidation properties, since the nitriding layer is uniform and accounts for the Beiznarben described in the prior art.

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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)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Heat Treatment Of Articles (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=7700199

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• 2001
  • 2001-09-25 DE DE10147205A patent/DE10147205C1/de not_active Expired - Lifetime
• 2002
  • 2002-09-24 EP EP02776699A patent/EP1432841B1/de not_active Expired - Lifetime
  • 2002-09-24 JP JP2003530909A patent/JP2005503488A/ja active Pending
  • 2002-09-24 BR BRPI0206051-5A patent/BR0206051B1/pt active IP Right Grant
  • 2002-09-24 US US10/432,751 patent/US7108756B2/en not_active Expired - Lifetime
  • 2002-09-24 WO PCT/DE2002/003582 patent/WO2003027349A2/de active IP Right Grant

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