EP3168314A1 - Procédé de traitement thermique de pièces métalliques - Google Patents

Procédé de traitement thermique de pièces métalliques Download PDF

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Publication number
EP3168314A1
EP3168314A1 EP15194562.3A EP15194562A EP3168314A1 EP 3168314 A1 EP3168314 A1 EP 3168314A1 EP 15194562 A EP15194562 A EP 15194562A EP 3168314 A1 EP3168314 A1 EP 3168314A1
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EP
European Patent Office
Prior art keywords
furnace
temperature
critical temperature
work piece
process gas
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
EP15194562.3A
Other languages
German (de)
English (en)
Inventor
Jens Mirschinka
Georg Lehmkuhl
Laurent Coudurier
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.)
Air Liquide Deutschland GmbH
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Original Assignee
Air Liquide Deutschland GmbH
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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 Air Liquide Deutschland GmbH, LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude filed Critical Air Liquide Deutschland GmbH
Priority to EP15194562.3A priority Critical patent/EP3168314A1/fr
Publication of EP3168314A1 publication Critical patent/EP3168314A1/fr
Ceased legal-status Critical Current

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Classifications

    • 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
    • C21D11/00—Process control or regulation for heat treatments
    • 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
    • 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
    • C23C8/80—After-treatment

Definitions

  • the method for heat treating metallic work pieces allows to perform a heat treatment of metallic work pieces while avoiding internal oxidation having a rather broad choice of process gases, in particular for use in atmospheric furnaces.
  • the method for heat treating at least one metallic work piece is subjected to a predetermined temperature time profile in a furnace, wherein at least intermittent a process gas is introduced into the furnace atmosphere to define the composition of said furnace atmosphere, wherein the introduction of the process gas is controlled regarding at least one of the following parameters: the volume of the process gas introduced into the furnace and the composition of the process gas in such a way that during at least one of the following operations: heating up and cooling down the at least one work piece while the temperature of the furnace is within a predetermined critical temperature range in which internal oxidation occurs within the metal of the work piece being defined by a lower critical temperature and an upper critical temperature the furnace atmosphere is low in oxygen whereas above said upper critical temperature the furnace atmosphere is defined independently of the oxygen content in the furnace atmosphere.
  • the term subjection of at least one work piece to a pre-determined temperature time profile is to be understood in such a way that the temperature of at least one work piece is controlled over time.
  • This can e. g. be performed in batch furnaces by varying the temperature of the furnace over time following a predetermined cycle, or in continuous furnaces having e. g. a plurality of zones of different temperatures through which the at least one metallic work piece is moved.
  • the furnace is a batch furnace.
  • the critical temperature range is defined by a lower critical temperature and an upper critical temperature.
  • the values of these critical temperatures depend on the alloying elements of the metal of the work pieces. E. g. for manganese as alloying element the lower critical temperature is about 700°C whereas the upper critical temperature is about 900°C. Outside the critical temperature range internal oxidation is negligible. Nevertheless, even below the lower critical temperature range the oxygen content of the furnace atmosphere has to be low as then surface oxidation can occur which is usually undesired as well.
  • An oxygen source is of course gaseous oxygen or humidity coming from air ingress but also water, whereas another one can be carbon oxides like CO or CO 2 .
  • An oxygen source can be oxides on the surface of the at least one work piece which are reduced during chemical reactions with e. g. hydrogen.
  • the method according to the present invention is used for carburizing and/or hardening.
  • the work pieces are preferably made of steel, preferably case-hardened steels and heat-treatable steels (quenched and tempered steels), preferably high-alloy case hardened steels.
  • the method according to the present invention is advantageously usable for steels alloyed with titanium, manganese, silicon and/or chromium,.
  • the critical temperature range is the temperature range in which internal oxidation takes place. Surprisingly, the depth of the internal oxidation in the final work piece is mostly depending on the availability of oxygen for promoting internal oxidation in a specific temperature range only. Therefore, the present invention is based on the application of a process gas allowing a low oxygen furnace atmosphere as defined above in the critical temperature range while heating, whereas above this critical temperature range a furnace atmosphere with a higher oxygen partial pressure can be applied. This allows above the critical temperature range to use e. g. an endogas (comprising hydrogen, nitrogen and carbon monoxide, optionally carbon dioxide and/or water) or a gas mixture comprising carbon monoxide and hydrogen as a process gas for controlling the furnace atmosphere above the critical temperature range.
  • an endogas comprising hydrogen, nitrogen and carbon monoxide, optionally carbon dioxide and/or water
  • a gas mixture comprising carbon monoxide and hydrogen
  • the furnace atmosphere comprises e. g. endogas or a mixture of carbon monoxide and hydrogen and, preferably, nitrogen and/or argon. Influence on the formation of oxides have beside the partial pressure of oxygen in the furnace atmosphere the temperature and the enthalpy of formation of the respective oxide which can be estimated according to the Ellingham diagram.
  • Possible oxygen sources for atomic oxygen can be impurities in the atmosphere, air ingress when work pieces are placed in the furnace or are taken out of the furnace. Further oxygen sources are leaks in the furnace through which ambient air can enter the furnace and carbon monoxide, carbon dioxide, oxygen and water in the furnace atmosphere.
  • the critical temperature range is defined as the temperature range in which internal oxidation takes place.
  • the critical temperature range is preferably defined depending on the alloying elements of the metal. Experiments of the applicant have revealed that outside this critical temperature range the tendency of usual alloying elements to form oxides is tolerable resulting in an acceptable layer thickness of the respective layer having internal oxides.
  • the process gas is oxygen free, in particular consisting of at least one inert gas, preferably nitrogen and/or argon, in particular nitrogen.
  • the process gas comprises at least one of the following gases:
  • a mixture of hydrogen and nitrogen is used to control the furnace atmosphere in the critical temperature range.
  • binary mixtures of hydrogen and nitrogen are used, preferably 30 Vol.-% [volume percent] to 50 Vol.-% hydrogen and 70 Vol.-% to 50 Vol.-% nitrogen, in particular 35 Vol.-% to 45 Vol.-% hydrogen and 65 Vol.-% to 55 Vol.-% nitrogen, in particular 40 Vol.-% hydrogen and 60 Vol.-% nitrogen.
  • the preferred range of 35 Vol.-% to 45 Vol.-% hydrogen in nitrogen has been found to be advantageous.
  • the hydrogen in the process gas is used to reduce the oxygen chemically bound in the oxides on the metallic work piece.
  • the preferred hydrogen content ensures a homogeneous carbon-profile of the work piece after the treatment. A lower hydrogen content was found to create inhomogeneous carbon profiles. A higher hydrogen content is possible but is usually undesirable from an economical point of view.
  • At least one hydrocarbon can be added to the process gas. This is advantageous in particular when it is desired to carburize the work piece.
  • a process gas including at least one hydrocarbon to generate a carburizing atmosphere in the furnace at temperatures above the critical range.
  • propane C 3 H 8
  • methane CH 4
  • the carbon activity can be adjusted by the amount of hydrocarbon in the process gas.
  • methane particular preferred to a mixture of hydrogen and nitrogen, as it has been found that soot formation is reduced compared to situations in which e. g. propane and/or acetylene have been added to a respective mixture. Therefore, the use of methane as a carbon source to present a carbon activity is advantageous for the quality of the final product.
  • the term at least for a temperature within the critical temperature range is to be understood in such a manner that even at temperatures below the lower critical temperature such a gas mixture can be used as a process gas.
  • the process gas comprises at least one of the following gases or gas mixtures:
  • An endogas is a gas mixture of hydrogen, nitrogen and carbon monoxide (CO).
  • CO 2 carbon dioxide
  • H 2 O water
  • a second option is a gas mixture of carbon monoxide and hydrogen.
  • Both process gases contain oxygen atoms in the form of CO which is available for reaction with alloying elements in the metal which is particularly preferred steel. Above the critical temperature range the risk for internal oxidation is significantly reduced allowing the use of oxygen-containing process gases above the critical temperature range.
  • the use of these gases allows e. g. the use of the carbon in the gases e. g. from the dissociated alcohol like in particular methanol for carburizing of the metal.
  • the above-identified process gases used above the upper critical temperature allow in particular to control the processes in the furnace and in particular its furnace atmosphere using oxygen sensors and/or lambda sensors.
  • a dry inert gas like argon or nitrogen, preferably nitrogen before changing to the afore-mentioned process gas, preferably a mixture of nitrogen and/or argon and hydrogen.
  • the change of the process gas to said mixture of nitrogen and/or argon and hydrogen is preferably performed at a temperature of 750 °C and above.
  • the upper critical temperature is 900°C, whereas the lower critical temperature is 700°C. This is particularly advantageous if the relevant alloying element is manganese.
  • the process gas is at least one inert gas which is introduced into the furnace atmosphere after equipping the furnace with the at least one work piece for a predetermined time or until a predetermined purge temperature is reached.
  • the purging action with at least one inert gas allows a quick reduction of the oxygen level in the furnace atmosphere.
  • the work piece is carburized at a carburizing temperature above the upper critical temperature while a carburizing atmosphere is maintained in the furnace for a carburizing time.
  • this carburizing step it is possible to control the furnace atmosphere based on the signal of at least one oxygen sensor and/or lambda sensor.
  • the temperature at which the carburizing atmosphere is created in the furnace is depending on the metal quality, alloying elements and the desired time of carburizing Usually, said temperature is at 900 °C or above limited by undesired changes in the material structure of the metal of the work piece.
  • the furnace atmosphere during carburizing comprises particularly one of the following gas mixtures:
  • the carburizing atmosphere during carburizing provides carbon for the carburizing process i. e. includes carbon sources and has a significant carbon activity. Usually, the carbon activity is between 0,8 to 1,1 % carbon.
  • the duration of the carburizing time, the carburizing temperature and the contents of the furnace atmosphere during carburizing are preferably determined based upon the metal of the work piece, in particular depending on the alloying elements in the metal, the surface of the at least one work piece and/or the desired carbon (profile) to be reached by the carburizing process.
  • the at least one metallic work piece is quenched after carburizing after the furnace temperature has been lowered to a hardening temperature.
  • the at least one work piece is made of one of the following materials:
  • the at least one work piece is made of high-alloy case hardened steel.
  • the method according to the invention is preferably usable with steels having titanium, chromium, silicon and/or manganese as alloying elements.
  • Fig. 1 a schematic temperature time profile 1 for a method for heat treating at least one metallic work piece according to an embodiment of the present invention in a batch furnace is depicted.
  • the temperature T is drafted against the time t both in arbitrary units. Both axes are not to scale but merely schematic.
  • the furnace Prior to equipping the furnace with the work pieces the furnace is purged with nitrogen until a dew point of -15°C is reached.
  • the temperature of the furnace is either room temperature or a temperature significantly above room temperature, i. e. above 800°C or the like. Even in the latter case the furnace temperature will significantly drop due to the introduction of the comparatively cold work pieces having a large thermal capacity. Therefore, in the following a low temperature (room temperature) is depicted when starting the process but it is understood that this could be a higher temperature as well.
  • a furnace is provided with one or more metallic work pieces in a first step of equipping 10.
  • the furnace is open and in fluid communication with the ambient atmosphere.
  • an oxygen free gas e. g. with nitrogen and/or argon during the step 10 of equipping. This can improve the safety of the process as the furnace is further inertized and a reaction with burnable gases can be avoided.
  • the surfaces of the work pieces that are to be hardened have to be accessible for the atmosphere inside the furnace to allow a reaction of atoms or molecules in furnace atmosphere with atoms or molecules within the work pieces.
  • the temperature of the furnace is not the ambient temperature as assumed above but is at a certain temperature level, e. g. in the range of 860° C.
  • the temperature within the furnace drops significantly below 700° C.
  • the ingress of atomic oxygen sources cannot be avoided even by purging with at least one inert gas as e. g. the surface of the work piece comprises oxides acting as oxygen sources as well as gaseous oxygen bound to the surface by adhesion or the like.
  • the furnace After equipping 10 the furnace is heated up to a furnace temperature equal to a upper critical temperature T U of a critical temperature range being critical for internal oxidation in a step of heating 20.
  • the lower critical temperature T L for internal oxidation is in this example with manganese as the predominant alloying element 700°C and is in general determined depending on the metallic material of the work pieces to be heat treated. Different concentrations c M of alloying elements that are dissolved in the lattice or between grains of the raw material contribute to an increased or decreased lower limit temperature T L .
  • the current furnace temperature is monitored via one or more temperature sensors allowing an exact process control. Already during said primary heating 20 a process gas low of oxygen has to be fed to the furnace, as even if there is no internal oxidation surface oxidation could occur which is undesired as well.
  • a process gas is fed into the furnace while the furnace temperature is further increased to a diffusion treatment temperature T D .
  • the process gas comprises hydrogen and nitrogen, preferably between 35 to 45 Vol.-% hydrogen in nitrogen.
  • the oxides on the surface of the furnace and/or the at least one work piece are reduced generating water in the atmosphere. This water vapor is then purged by the process gas entering the furnace, thereby reducing the dew point of the furnace atmosphere.
  • methane (CH 4 ) may be additionally fed to the furnace in order to act as a further carbon (C) donator.
  • the diffusion treatment temperature T D is in the range from 900 °C to 950 °C. Similar as the lower limit temperature T L the diffusion treatment temperature T D is increased or decreased depending on different concentrations c M of alloying elements in the raw material.
  • the furnace atmosphere is changed by changing the composition of the process gas to a carburizing atmosphere.
  • the process gas is fed to the furnace in a step of feeding process gas 50.
  • This process gas is an endogas consisting of a mixture of 20% carbon monoxide (CO), 40% hydrogen (H 2 ) and 40% nitrogen (N 2 ).
  • the carbon monoxide (CO) acts as a carbon donator or carbon source. The respective carbon atoms adhere at the surfaces of the work pieces and diffuse into the work pieces.
  • a step of diffusion treatment 60 the furnace temperature is kept constant at the diffusion treatment temperature T D (or carburizing temperature) in order to yield reproducible results.
  • T D diffusion treatment temperature
  • the surface areas of the work pieces are carburized.
  • the carbon (C) atoms dissolve in the lattice of the raw material and are deposited at interstitials of the lattice (hexagonal spaces in the face-centered cubic austenite lattice).
  • the diffusion treatment time t D is commonly in the range of 3 h to more than 8 h.
  • the furnace atmosphere can be changed again by changing the process gas entering the furnace at a later stage of the diffusion treatment 60.
  • a process gas consisting of a mixture of nitrogen (N 2 ), and methanol (CH 3 OH) can be introduced into the furnace about 1 h to 2 h before the end of the total diffusion treatment time t D .
  • the furnace is provided with a process gas comprising only nitrogen and/or argon and hydrogen in a cooling step 70, while the furnace temperature is reduced to a lower hardening temperature T H .
  • the temperature T H is about 840 to 880 °C for a hardening step 80.It is possible to add an amount of a source of carbon e. g. by adding a hydrocarbon or the like to the furnace atmosphere during the diffusion treatment step 60.
  • a step of quenching 90 is applied.
  • the work pieces are rapidly quenched in oil from the lower temperature T H of 840 to 880°C to a quenched temperature T Q , which is between 20 °C and 200 °C depending on the raw material and the desired grain structure. Due to the rapid cooling the carbon (C) atoms have no time to diffuse out of their interstitials and to build carbon grains at grain boundaries of the iron matrix.
  • the mechanical properties may be further adapted to the intended purpose of the work pieces by additional processes like tempering, etc. Thereby, the high stiffness may for example be reduced and the toughness further increased.
  • the method according to the present invention allows heat treatment processes with a significantly reduced internal oxidation while allowing a broad choice of process gases for temperatures above the upper critical temperature T U .

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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)
EP15194562.3A 2015-11-13 2015-11-13 Procédé de traitement thermique de pièces métalliques Ceased EP3168314A1 (fr)

Priority Applications (1)

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EP15194562.3A EP3168314A1 (fr) 2015-11-13 2015-11-13 Procédé de traitement thermique de pièces métalliques

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EP15194562.3A EP3168314A1 (fr) 2015-11-13 2015-11-13 Procédé de traitement thermique de pièces métalliques

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107065707A (zh) * 2017-06-14 2017-08-18 合肥易美特建材有限公司 一种基于无线通信的沼气发酵管控系统
CN113981186A (zh) * 2021-09-23 2022-01-28 浙商中拓集团(浙江)新材料科技有限公司 一种防脱碳、增碳的气氛保护热处理工艺

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4175986A (en) * 1978-10-19 1979-11-27 Trw Inc. Inert carrier gas heat treating control process
US4322255A (en) * 1979-01-15 1982-03-30 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Heat treatment of steel and method for monitoring the treatment
US4992113A (en) * 1987-11-17 1991-02-12 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Process for heat treatment under a gaseous atmosphere containing nitrogen and hydrocarbon
EP0662525A1 (fr) 1994-01-08 1995-07-12 Messer Griesheim Gmbh Procédé pour empêcher l'oxydation superficielle pendant la carburation des aciers
US20040231753A1 (en) * 2001-06-25 2004-11-25 Michel Gantois Method for carburizing and carbonitriding steel by carbon oxide
US20080149225A1 (en) * 2006-12-26 2008-06-26 Karen Anne Connery Method for oxygen free carburization in atmospheric pressure furnaces
WO2012048669A1 (fr) * 2010-10-11 2012-04-19 Ipsen International Gmbh Procédé et dispositif de carburation et carbonitruration de matériaux métalliques

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4175986A (en) * 1978-10-19 1979-11-27 Trw Inc. Inert carrier gas heat treating control process
US4322255A (en) * 1979-01-15 1982-03-30 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Heat treatment of steel and method for monitoring the treatment
US4992113A (en) * 1987-11-17 1991-02-12 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Process for heat treatment under a gaseous atmosphere containing nitrogen and hydrocarbon
EP0662525A1 (fr) 1994-01-08 1995-07-12 Messer Griesheim Gmbh Procédé pour empêcher l'oxydation superficielle pendant la carburation des aciers
US20040231753A1 (en) * 2001-06-25 2004-11-25 Michel Gantois Method for carburizing and carbonitriding steel by carbon oxide
US20080149225A1 (en) * 2006-12-26 2008-06-26 Karen Anne Connery Method for oxygen free carburization in atmospheric pressure furnaces
WO2012048669A1 (fr) * 2010-10-11 2012-04-19 Ipsen International Gmbh Procédé et dispositif de carburation et carbonitruration de matériaux métalliques

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107065707A (zh) * 2017-06-14 2017-08-18 合肥易美特建材有限公司 一种基于无线通信的沼气发酵管控系统
CN113981186A (zh) * 2021-09-23 2022-01-28 浙商中拓集团(浙江)新材料科技有限公司 一种防脱碳、增碳的气氛保护热处理工艺
CN113981186B (zh) * 2021-09-23 2023-08-15 浙商中拓集团(浙江)新材料科技有限公司 一种防脱碳、增碳的气氛保护热处理工艺

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