EP0248431B1 - Method of producing outer coating layers on heat and corrosion resistant austenitic steels - Google Patents
Method of producing outer coating layers on heat and corrosion resistant austenitic steels Download PDFInfo
- Publication number
- EP0248431B1 EP0248431B1 EP19870108108 EP87108108A EP0248431B1 EP 0248431 B1 EP0248431 B1 EP 0248431B1 EP 19870108108 EP19870108108 EP 19870108108 EP 87108108 A EP87108108 A EP 87108108A EP 0248431 B1 EP0248431 B1 EP 0248431B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- heat
- corrosion resistant
- layer
- coating layers
- outer coating
- 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.)
- Expired - Lifetime
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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
- C23C8/02—Pretreatment of the material to be coated
Description
Die Erfindung betrifft ein Verfahren zur Herstellung einer Diffusionsdeckschicht mit erhöhten physikalisch-chemischen Eigenschaften, die durch einen chemisch-thermischen Prozess in einer Gasatmosphäre durch Nitrieren, an Elementen aus hitzebeständigem Stahl bzw. korrosionsfestem Stahl erhalten wird. Die Erfindung betrifft insbesondere Stahl mit austenitischer Struktur.The invention relates to a method for producing a diffusion cover layer with increased physico-chemical properties, which is obtained by a chemical-thermal process in a gas atmosphere by nitriding, on elements made of heat-resistant steel or corrosion-resistant steel. The invention relates in particular to steel with an austenitic structure.
Im Zusammenhang mit hoher Verwandschaft des Chroms zu Sauerstoff, passivieren sich diese Stähle oberflächig mit einer Oxid-Schicht, besonders von Chromoxid. Die Passivierung kann sowohl bei den Aussentemperaturen als auch während der thermisch-chemischen Behandlung erfolgen, z.B. sogar unter den Bedingungen des spurenweisen Anfeuchtens der Gasatmosphäre des dissozierten Ammoniaks. Diese Oxid-Schicht, besonders die des Chromoxids ist sehr passiv und diffusionsundurchdringlich.In connection with the high relationship between chromium and oxygen, these steels passivate on the surface with an oxide layer, especially chromium oxide. The passivation can take place both at the outside temperatures and during the thermal-chemical treatment, e.g. even under the conditions of trace wetting of the gas atmosphere of the dissociated ammonia. This oxide layer, especially that of chromium oxide, is very passive and diffusion-impermeable.
Die bisher bekannten Verfahren zur Herstellung von äusseren Deckschichten an den diesartigen Stählen bestehen in der Durchführung der Depassivierung der Stahlflächen, die weiter eine effektive Durchführung des Gasnitrierens ermöglichen. Die Depassivierung der Flächen ist mechanisch durchzuführen z.B.durch Abstrahlen, elektromechanisch in Bädern bzw. durch chemische Zersetzung der Oxidschicht mit den in die Gasatmosphäre des Prozesses eingeführten Depassivatoren.The previously known methods for the production of outer cover layers on this type of steel consist in carrying out the depassivation of the steel surfaces, which further enable an effective implementation of gas nitriding. The surfaces are to be de-passivated mechanically, e.g. by blasting, electromechanically in baths or by chemical decomposition of the oxide layer with the de-passivators introduced into the gas atmosphere of the process.
Im Hinblick auf die sekundäre Passivierung der Flächen werden die Depassivatoren beim Nitrieren in der Gasatmosphäre am Anfang des Prozesses zugegeben. Meistens werden Halogenidverbindungen wie z.B. HF, HBr, bzw. NH₄Cl benutzt.With regard to the secondary passivation of the surfaces, the depassivators are added when nitriding in the gas atmosphere at the beginning of the process. Halide compounds such as HF, HBr or NH ,Cl are mostly used.
Chemical Abstracts Teil 85, Nr 4/79, S.229, Zusammenfassung Nr 501920q beschreibt ein Verfahren, in welchem Trichloräthylen als Depassivator verwendet wird. In dem beispielsweise beschriebenen Prozess,wird das Trichloräthylen in der Menge von 3% in die 50% endothermischer Gase und 50% NH₃ aufweisende Gasatmosphäre während der ersten 5 Minuten des Prozesses zugeführt. Das Nitrieren wird bei einer Temperatur von 570°C eine Stunde lang durchgeführt. Das Trichloräthylen unterliegt einer Pyrolyse zu Chlor,das die Chromoxide aus der Stahlfläche entfernt. Die insbesondere in der Gasatmosphäre auftretenden Verbindungen charakterisieren sich durch eine hohe Giftigkeit, was über die technisch-ökologische Anwendbarkeit des Prozesses entscheidet. Ausserdem verursachen die in die Gasatmosphäre eingeführten Depassivatoren auch die Depassivierung der inneren Flächen der Anlage, vor allem der Retorte, in der der Prozess verläuft.Chemical Abstracts Part 85, No. 4/79, p.229, abstract No. 501920q describes a process in which trichlorethylene is used as a depassivator. In the process described for example, the trichlorethylene in the amount of 3% in the 50% endothermic gases and 50% NH₃ gas atmosphere is supplied during the first 5 minutes of the process. The nitriding is carried out at a temperature of 570 ° C for one hour. Trichlorethylene is subject to pyrolysis to chlorine, which removes the chromium oxides from the steel surface. The compounds that occur particularly in the gas atmosphere are characterized by a high level of toxicity, which determines the technical and ecological applicability of the process. In addition, the depassivators introduced into the gas atmosphere also cause the depassivation of the inner surfaces of the system, especially the retort in which the process takes place.
Sie lagern sich ausserdem in Installationen an Stellen mit einer Temperatur niedriger als 300°C ab, was eine Veränderung der Verläufe und eine Unstabilität des Prozesses verursacht.They also deposit in installations at locations with a temperature lower than 300 ° C, which causes a change in the course and an instability of the process.
Es ist auch das Verfahren zum Sulfonitrieren bekannt, in dem der Zusatz von Schwefeldämpfen in die Atmosphäre des teilweise dissoziierten Ammoniaks auf die Passivität der Oxidschicht reduzierend wirkt, was die Stickstoffdiffusion in das zu behandelde Element erleichtert. Dieses Verfahren ist aber für austenitische Stähle wenig erfolgreich anwendbar.The method for sulfonitriding is also known, in which the addition of sulfur vapors to the atmosphere of the partially dissociated ammonia has a reducing effect on the passivity of the oxide layer, which facilitates nitrogen diffusion into the element to be treated. However, this method is not very successfully applicable to austenitic steels.
In der FR-A-1.453.876 wird ein Verfahren dargestellt, welches eine thermische Nachbehandlung von chemisch oder galvanisch beschichteten Substraten bei einer Temperatur von über 700°C in einer Schutzgasatmosphäre beinhaltet, wobei die Substrate bzw. Schichten aus den Elementen der Ordnungszahlen 23-28, 41-46, 73-78 und 91-96 des Periodensystems ausgewählt sein Können, und das unter anderem mit der die Herstellung von oberen Schichten in den korrosions - und abnutzungsfesten Konstruktionsstählen betreffenden Lösung illustriert wurde. Es beruht auf galvanischem Abscheiden einer Chromschicht auf ein Element aus Konstruktionsstahl und einstündigem Tempern bei einer Temperatur von 900°C in der 75% Stickstoff und 25% Wasserstoff und weniger als 10% Wasserdampf enthaltenden Gasatmosphäre.Das Tempern des Elementes soll zur Diffusion zwischen dem Chromüberzug und dem Stahlkern führen, wodurch das Element in der Flächenzone zwei Schichten erreichen soll. Die untere Schicht weist 10 bis 50% Chrom auf; die obere Schicht bildet eine Interkristallinphase mit hoher Härte. Die Wirksamkeit der Stickstoffdiffusion aus der Gasatmosphäre ist unter diesen Bedingungen sehr niedrig,weil die Fläche des Elementes mit Chromoxiden passiviert werden kann.FR-A-1.453.876 describes a process which includes a thermal aftertreatment of chemically or galvanically coated substrates at a temperature of over 700 ° C. in a protective gas atmosphere, the substrates or layers consisting of the elements of atomic numbers 23- 28, 41-46, 73-78 and 91-96 of the Periodic Table, and which was illustrated, among other things, with the solution relating to the production of upper layers in the corrosion and wear resistant structural steels. It is based on the electrodeposition of a chrome layer on an element made of structural steel and annealing for one hour at a temperature of 900 ° C in a gas atmosphere containing 75% nitrogen and 25% hydrogen and less than 10% water vapor lead to diffusion between the chrome plating and the steel core, whereby the element in the surface zone should reach two layers. The lower layer has 10 to 50% chromium; the upper layer forms an intergranular phase with high hardness. The effectiveness of nitrogen diffusion from the gas atmosphere is very low under these conditions because the surface of the element can be passivated with chromium oxides.
Das erfindungsgemässe Verfahren gemäß Anspruch 1 eliminiert die dargestellten technologischen Nachteile.The inventive method according to
Zu diesem Zwecke, unmittelbar nach der Stahldepassivierung, die im Bad vorzugsweise elektrochemisch durchgeführt wird, werden die Flächen, auf welchen die äusserste Deckschicht gebildet werden soll, galvanisch mit einer Eisenschicht beschichtet.For this purpose, immediately after the steel passivation, which is preferably carried out electrochemically in the bath, the surfaces on which the outermost cover layer is to be formed are galvanically coated with an iron layer.
Das weiterhin ausgeübte Gasnitrieren wird in der Atmosphäre ohne Depassivierungszusätze durchgeführt.The continued gas nitriding is carried out in the atmosphere without depassivation additives.
Die beschichtete Eisenschicht bildet während der thermisch-chemischen Behandlung eine den Sauerstoff auffangende Scheidewand, und sie besitzt eine homogen durchdringbare Struktur für die Stickstoffdiffusion. Im Ergebnis gewinnt man eine vergrösserte Diffusionsgeschwindigkeit vom Stickstoff im Stahl, die Wiederholbarkeit der Parameter von den hergestellten Elementen, und eine verminderte Feuchtigkeitsempfindlichkeit der Gasatmosphäre - was günstige Bedingungen für die Verwendung in der Serienfertigung bildet.The coated iron layer forms an oxygen-collecting partition during the thermal-chemical treatment, and it has a homogeneously penetrable structure for nitrogen diffusion. The result is an increased rate of diffusion of nitrogen in the steel, the repeatability of the parameters of the elements produced, and a reduced sensitivity to moisture in the gas atmosphere - which creates favorable conditions for use in series production.
Das Verfahren ist ungiftig und ermöglicht die Erreichung der äusseren Deckschicht am ganzen Element bzw.gewählten Flächen des Elementes .The process is non-toxic and enables the outer cover layer to be reached on the entire element or selected areas of the element.
Das Verfahren gemäss der Erfindung wird durch die Beschreibung des beiepielsweisen Prozesses zur Herstellung der nitrierten Schicht am Schaft des Auslassventiles eines Verbrennungsmotors näher dargestellt.Das Ventil ist aus austenitischem Stahl der Type 50H21G9N4 ausgeführt. Nach der endgültigen mechanischen Behandlung des Schaftes wird das entfettete Ventil der elektrochemischen Depassivierung in einem Natriumglukonatbad unterworfen. Dann wird das galvanische Beschichten des Ventilschaftes mit Eigen zwecks Erreichung eines Eisenüberzuges mit einer Dicke von 0,002 mm durchgeführt. Die folgende Operation nach Trocknung des Ventils ist die chemisch-thermische Behandlung des Gasnitrierens.
Das Ventil wird in einer Retorte, die mit der Gasanlage des Ammoniaks hermetisch verbunden ist, angeordnet. Das Ofentempern bei einer Temperatur von 575°C während 2 Stunden verursacht die Herstellung der verschleiss- und schmierbeständigen Schicht am Schaft,und der Ventilteller wird mit einer Oxidschicht überzogen,welche die Diffusion unmöglich macht.The method according to the invention is illustrated in more detail by the description of the exemplary process for producing the nitrided layer on the stem of the exhaust valve of an internal combustion engine. The valve is made of austenitic steel type 50H21G9N4. After the final mechanical treatment of the shaft, the degreased valve becomes the electrochemical depassivation subjected to a sodium gluconate bath. Then the galvanic coating of the valve stem is carried out by the customer to achieve an iron coating with a thickness of 0.002 mm. The next operation after the valve has dried is the chemical-thermal treatment of gas nitriding.
The valve is placed in a retort hermetically connected to the ammonia gas system. The oven tempering at a temperature of 575 ° C for 2 hours causes the wear and smear-resistant layer to be produced on the shaft, and the valve disk is coated with an oxide layer, which makes diffusion impossible.
Das ist günstig in Hinsicht auf die Nichtsenkung der Tellerfestigkeit im Hinblick auf die Korrosionswirkung des Abgases während des Ventilbetriebes.This is favorable with regard to the non-lowering of the plate strength with regard to the corrosion effect of the exhaust gas during valve operation.
Die beigelegte Aufnahme stellt den metallographischen Schliff des Ventilschaftes in 500 facher Vergrösserung dar.Die Diffusionsschicht 1 mit einer Dicke von 0,026 mm, welche die nitrierte Eisenschicht 2 umfasst, befindet sich über der Unterlageschicht 3 mit verschwindenden Diffusionsspuren. Die vorgenommenen Messungen der Härte ergaben folgende Werte :
Claims (1)
- A method for the production of external surface layers on heat restant and corrosion resistant, particularly austenitic, steels by depassivating of the steel surfaces, preferably in an electrochemical bath, and gas nitriding, characterised in that, directly after the depassivation, the surfaces, on which the outermost surface layer is to be formed, are coated electrolytically with a layer of iron, and that thereafter pacticed gas nitriding is carried out in an atmosphere without depassivating additives.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PL259905 | 1986-06-04 | ||
PL25990586A PL147547B1 (en) | 1986-06-04 | 1986-06-04 | Method of producing superficial layers on heat-resisting and stainless steels in particular austenitic ones |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0248431A2 EP0248431A2 (en) | 1987-12-09 |
EP0248431A3 EP0248431A3 (en) | 1990-01-31 |
EP0248431B1 true EP0248431B1 (en) | 1993-10-06 |
Family
ID=20031520
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19870108108 Expired - Lifetime EP0248431B1 (en) | 1986-06-04 | 1987-06-04 | Method of producing outer coating layers on heat and corrosion resistant austenitic steels |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP0248431B1 (en) |
CS (1) | CS274730B2 (en) |
DD (1) | DD263308A5 (en) |
DE (1) | DE3787672D1 (en) |
PL (1) | PL147547B1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6086684A (en) * | 1997-06-04 | 2000-07-11 | Japan Science And Technology Corporation | Electric discharge surface treating method and apparatus |
WO2004007789A2 (en) * | 2002-07-16 | 2004-01-22 | Danmarks Tekniske Universitet-Dtu | Case-hardening of stainless steel |
EP1850619A1 (en) | 2006-04-28 | 2007-10-31 | Motorola, Inc. | Capability update during call |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH07119420A (en) * | 1993-10-27 | 1995-05-09 | Fuji Oozx Inc | Method for treating surface of titanium or titanium alloy made engine valve |
US6547888B1 (en) * | 2000-01-28 | 2003-04-15 | Swagelok Company | Modified low temperature case hardening processes |
US7751320B2 (en) * | 2006-09-30 | 2010-07-06 | Alcatel-Lucent Usa Inc. | Admission control of sessions with preference lists |
CN111826654A (en) * | 2020-07-06 | 2020-10-27 | 安徽省赛威输送设备有限公司 | Processing method for improving corrosion resistance of elevator shell |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR1453876A (en) * | 1965-05-13 | 1966-07-22 | Ct Tech De L Ind Horlogere | Process for the treatment of parts with metal coatings of great hardness and with high protection against corrosion and parts with metal coatings obtained by this process |
JPS5114837A (en) * | 1974-07-27 | 1976-02-05 | Tokyo Heat Treating | Sutenresukono shintanaruiha nanchitsukashorihoho |
US4326898A (en) * | 1978-11-13 | 1982-04-27 | Massachusetts Institute Of Technology | Method for forming material surfaces |
-
1986
- 1986-06-04 PL PL25990586A patent/PL147547B1/en unknown
-
1987
- 1987-06-04 EP EP19870108108 patent/EP0248431B1/en not_active Expired - Lifetime
- 1987-06-04 CS CS411987A patent/CS274730B2/en unknown
- 1987-06-04 DE DE87108108T patent/DE3787672D1/en not_active Expired - Fee Related
- 1987-06-16 DD DD30385487A patent/DD263308A5/en not_active IP Right Cessation
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6086684A (en) * | 1997-06-04 | 2000-07-11 | Japan Science And Technology Corporation | Electric discharge surface treating method and apparatus |
WO2004007789A2 (en) * | 2002-07-16 | 2004-01-22 | Danmarks Tekniske Universitet-Dtu | Case-hardening of stainless steel |
WO2004007789A3 (en) * | 2002-07-16 | 2004-03-18 | Univ Danmarks Tekniske | Case-hardening of stainless steel |
EP1850619A1 (en) | 2006-04-28 | 2007-10-31 | Motorola, Inc. | Capability update during call |
Also Published As
Publication number | Publication date |
---|---|
CS274730B2 (en) | 1991-10-15 |
EP0248431A3 (en) | 1990-01-31 |
PL147547B1 (en) | 1989-06-30 |
DD263308A5 (en) | 1988-12-28 |
EP0248431A2 (en) | 1987-12-09 |
DE3787672D1 (en) | 1993-11-11 |
CS411987A2 (en) | 1991-02-12 |
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