JP2015514874A5 - - Google Patents

Description

Method for solution hardening of cold-deformed workpieces of passive alloys, and members solution-hardened by this method

The present invention relates to a method for solution hardening of a cold-deformed workpiece of a passive alloy. This method provides a hardened alloy that is substantially free of carbides and / or nitrides. This method also provides a corrosion resistant surface while maintaining the core strength of the material obtained by cold deformation. The present invention further relates to a member that has been solid solution hardened by the method. Such components are particularly relevant in the fields of medical, food, automotive, chemical, petrochemical, pharmaceutical, marine, package, watch, cutlery / tableware, medical, energy, pulp and paper, mining or wastewater technology. Yes.

Stainless steel and other passive alloys are typically materials that have good corrosion resistance but relatively unfavorable tribological properties, such as adhesive wear properties. To solve this problem, stainless steel and equivalent alloys can be surface hardened at low temperatures (below 450-550 ° C.) with nitrogen and / or carbon solubilization , so that so-called expanded austenite or alternatively expanded martensite Area is obtained. This region is a supersaturated solid solution of carbon and / or nitrogen in austenite or martensite and is metastable to carbide / nitride formation. Such low temperature processes may be based on gas, plasma or molten salt, and gas processes require the use of special activation techniques, but activation is achieved immediately for plasma and salt baths. No special processing is required. Thereby, a surface region containing a large amount of nitrogen and / or carbon is obtained in the material. This is due to the relatively low process temperature. The material is thereby surface hardened and retains its corrosion resistance. However, most passive alloys, such as stainless steel, have impermeable oxide layers, which are also referred to as passive layers (which are responsible for good corrosion properties, such as nitrogen and carbon solid solutions) . Cannot be immediately solid solution hardened by nitrogen and / or carbon. Therefore, special techniques for removing this passive layer are required. These techniques are known to those skilled in the art.

Most of the technical components used are used in the machined state, which means that the material is heterogeneously cold deformed (plastically deformed). In many applications, such cold deformation is desirable due to component-strength issues. The component will not function if there is no increase in strength due to work hardening induced by cold deformation. This creates a major problem when such cold machined components are surface hardened in a low temperature process, and as a result the surface is changed to expanded austenite or martensite by nitrogen and / or carbon uptake. . The presence of plastic deformation of the material (defects in the microstructure) means that nitrides and carbides are more easily generated by the reaction of nitrogen and carbon with alloy elements such as chromium (Cr) in stainless steel. Thus, the amount of Cr is removed from the solid solution and combined as chromium nitride / chromium carbide. This means that the corrosion properties are impaired because less chromium is available to maintain the passive layer. Such consumption of Cr becomes remarkable locally and the surface of the place cannot be corroded. Nitride / carbide precipitation is called sensitization. Chromium nitride is more stable than chromium carbide and can be formed at lower temperatures, so this phenomenon is very pronounced especially when nitrogen is in solid solution . This means that the temperature in the low temperature process must be (further) lowered to avoid sensitization (which is undesirable because the process proceeds more slowly). There is no lower limit to sensitization due to the extreme degree of deformation of stainless steel.

Sensitization occurs at low temperature hardening of cold deformed stainless steel workpieces with low temperature hardening of nitrogen and / or carbon (performed at temperatures below 550 ° C.). In order to solve the problems associated with the sensitization of cold deformed materials when the surface is cold-cured, complete annealing of the components is carried out, if possible, by so-called austenitization in a vacuum or hydrogen atmosphere. Also good. Complete annealing is a process performed at temperatures above 1020 ° C, typically in the range of 1020-1120 ° C. This prevents cold deformation of the material and allows low temperature solid solutions to be carried out without the risk of sensitization. However, this process raises the problem that the strength of the cold-worked metal is reduced-this is called the so-called egg shell effect of the material, i.e. the material becomes soft when the workpiece is subsequently cold-cured. Has a hard and thin surface. By performing austenitization, the core strength of the material is reduced to that of the annealed material, and this process requires that the core strength of the treated component is a relatively unimportant design parameter. And

Another possibility is to use a carburizing process in which only carbon is dissolved in the material at low temperatures, ie the formation of carbon expanded austenite. Sensitization is a solid solution of nitrogen (nitriding and nitrocarburizing (nitrocarburising)) not critical if enough solid solution carbon case, therefore, it does not affect significantly the corrosion resistance. However, even this is considered to be a hindrance for components that undergo severe cold deformation. Another inconvenience of using only carbon solid solution is that lower surface hardness is obtained than in the case of nitrogen solid solution and that the composition profile (hardness) cannot be adjusted in the same way (eg European Patent No. 1095170B1 and International Publication No. 2006 / 136166A1 pamphlet).

See, for example, Georgeev et al, Journal of Materials Science and Technology, Vol. 4, 1996, no. 4, pp. 28 and Bashchenko et al, Izvestiya Akademii Nauk SSSR. Metally, no 4, 1985, pp. In 173-178, it has shown that under equilibrium conditions can Rukoto is dissolved nitrogen and / or carbon into a stainless steel at high temperatures (about 1050 ° C. greater). It has been shown that by using high temperatures problems with the penetration of the passive layer of stainless steel can be avoided because it becomes unstable at these high temperatures. It is also described that the melting temperature of chromium carbide and chromium nitride is lower than this temperature. Accordingly, carbides and / or nitrides are not formed at these high temperatures. However, the solid solubility of nitrogen / carbon is relatively limited, and actual surface hardening does not occur for austenitic stainless steel. This is especially true for carbon. A rapid cooling rate is required to avoid carbide / nitride precipitation during cooling. For martensitic stainless steel types, significant surface hardening can occur due to rapid cooling. However, the effect of curing is at a much lower level than obtained by the process for the formation of expanded austenite.

  WO 2008/124239 proposes a carburizing hybrid process with rapid quenching in between, thereby providing carbide precipitates by subjecting the metal workpiece to both high and low temperature carburizing. The carbon-cured surface of the metal workpiece can be formed without forming a carbon, where, immediately after high temperature carburization, the workpiece is rapidly quenched to a temperature at which carbide precipitates are formed. Rapid quenching may be achieved by, for example, immersing the workpiece in water, oil or other coolant, such as gas or molten salt. WO 2008/124239 cannot recognize the problem of carbide and / or nitride formation during cold deformation and subsequent low temperature curing.

There is a need for a method that allows low temperature solid solution of nitrogen and / or carbon for the hardening of passive alloys such as stainless steel, where problems associated with sensitization and / or adjustment of the composition profile are solved.

In order to overcome the problems associated with low temperature nitridation and / or sensitization associated with carburizing of cold deformed workpieces, the prior art first anneals the material so that partial or complete recrystallization is obtained. Suggest to do. Or we propose only material recovery. This eliminates the cold deformation of the material and the strengthening obtained from the cold deformation, while the low temperature solid solution can be carried out without causing problems with sensitization. However, this solution cannot provide a component with high core strength.

Danish Patent Application No. PA201170208 discloses a method for solution hardening of cold-deformed workpieces of passive metals or alloys. The method includes a first step in which nitrogen and / or carbon is dissolved in the workpiece at a temperature above the melting temperature of the carbide and / or nitride former and below the melting point of the workpiece, and the carbide and / or And a subsequent second step in which nitrogen and / or carbon is dissolved at a temperature at which nitride formation does not substantially occur. The method may also include rapid cooling from the first temperature to the second temperature. Although the treatment of metals according to patent application PA201170208 provides superior properties compared to other processes of the prior art, it is believed that further improvements in the properties of the metals may be achieved.

It is an object of the present invention to provide a method that enables solution hardening of a product made and produced by cold deformation from a passive alloy, particularly stainless steel, without causing sensitization of the workpiece, and Thereby providing better corrosion resistance. A further objective is that the strengthening effect obtained may be equal to or greater than the strengthening effect obtained by cold deformation.

The present invention relates to a method for solution hardening of a cold deformed workpiece of a passive alloy containing at least 10% chromium, which method comprises:
- a step of Ru a solid solution at least nitrogen in the workpiece at a lower temperature T1 than the melting point of the higher passivating alloy than the dissolution temperature of the carbides and / or nitrides, to implement a solid solution of nitrogen at a temperature T1 50 m to Obtaining a diffusion depth in the range of 5 mm;
-Cooling the workpiece to a temperature below the temperature at which carbides and / or nitrides are formed in the passive alloy after the solid solution step at temperature T1, wherein the cooling step does not contain nitrogen. Performed in an active gas.

The method of the present invention may also be viewed as a method for solid solution hardening of a cold deformed workpiece of a passive alloy,
Lower than the melting point of the higher passivation alloy than the austenitizing temperature, the steps of Ru a solid solution at least nitrogen in the workpiece at a temperature T1,
Cooling the workpiece to a temperature below the temperature at which carbides and / or nitrides are formed in the passive alloy after the solid solution step, the cooling step being performed in an inert gas containing no nitrogen Steps.

In a preferred embodiment, the first solid solution step is performed in a gas containing N ₂ , for example, a gas such as substantially high purity N ₂ that has no gas other than unavoidable impurities, and also a cooling step. Moreover, it implements in the gas which is an inert gas (nitrogen-free inert gas) which does not contain nitrogen, and argon is especially preferable. In the context of the present invention, an “inert gas” is a gas that does not contain any substantial amount of molecules that interact with the elements of the alloy, and any inert gas or mixture of gases that does not contain nitrogen. Is considered. When inert gas is used in the cooling step, the workpiece that is Oite processed in the method of the present invention, when either using other cooling gas or cooling step, are performed using other methods It has been surprisingly found that it has a corrosion resistance that is even better than that obtained. In particular, nitrogen-containing gases are believed to promote the formation of nitrides when cooling is performed in a nitrogen-containing gas compared to cooling in an inert gas, and therefore use an inert gas. A more robust and flexible method with a cooling step is provided. The partial pressure of nitrogen during treatment at temperature T1 determines the solid solubility of nitrogen. Therefore, when the partial pressure of nitrogen during treatment at temperature T1 increases, the effect of cooling in an inert gas containing no nitrogen is obtained. Become more prominent. In addition, cooling in a nitrogen-free inert gas may have a cooling time longer than 60 seconds, but preferably the cooling is performed in a nitrogen-free inert gas in less than 30 seconds, for example, less than 10 seconds. To be implemented.

In certain embodiments, the method further results in the formation of expanded austenite and / or expanded martensite within the cold deformed workpiece of the passive alloy. Thus, the method is lower than the temperature at which carbides and / or nitrides are formed in the passivation alloy, subsequent to Ru a solid solution of nitrogen and / or carbon into the workpiece at a temperature T2 of at least 300 ° C. The Two steps may be further included.

First step of Ru is dissolved nitrogen to the workpiece at a temperature higher than the melting temperature of the nitride passivation, such as when compared to stainless steel which performs only recrystallization annealing of the material in front of the low temperature cure It significantly improves the core strength of the alloy. The high temperature solid solution of nitrogen is performed at a temperature above the austenitizing temperature of the alloy, such as at least 1050 ° C. or above and below the melting point of the alloy. This strengthening effect of high temperature nitriding is surprisingly sufficient to compensate for the loss of strength caused by the absence of cold deformation while the workpiece is maintained at a high temperature during nitriding. In addition, high temperature nitridation allows low temperature curing to be performed at temperatures higher than normal without the problems associated with nitride and / or carbide formation, and the passivity on the material in subsequent surface low temperature curing processes. It becomes easier to activate the surface. Therefore, formation of a hardened region is promoted. Furthermore, better corrosion properties are obtained because nitrogen is present in the solid solution.

A significant improvement in the hardening of the passive alloy can be obtained by performing low temperature nitriding, carburizing or soft nitriding after high temperature solid solution of nitrogen. Any passive alloy that may form expanded austenite or expanded martensite is suitable for the present invention, and stainless steel, particularly cold deformed austenitic stainless steel, is preferred.

The optional subsequent low temperature solid solution of nitrogen and / or carbon is performed at a temperature lower than the temperature at which carbides and / or nitrides are formed in the passive alloy, for example, below 450-550 ° C., depending on the process. Subsequent steps may be performed on a material that does not include plastic deformation but has the same level of strength as the plastically deformed workpiece. This means that the risk of sensitization is considerably reduced. The presence of nitrogen and optionally carbon in the solid solution of stainless steel increases the diffusion coefficient of nitrogen and carbon with increasing carbon / nitrogen content, so that it can be obtained using prior art methods. It has further been found that a fast low temperature process results. Thus, in certain embodiments, the passive alloy is stainless steel containing nitrogen and / or carbon.

According to the invention, low temperature hardening of passive materials, and in particular stainless steel, and more strongly cold deformed components, can be carried out without causing material sensitization and without loss of strength. Cold deformed materials treated by the method of the present invention can obtain significantly better corrosion resistance than untreated materials. The experiments carried out, the carbon by nitrogen and optionally at elevated temperature in a stainless steel, the strength obtained by Rukoto typically a solid solution at 1050 ° C. than is may result in (core) strength or substrate bearing capacity It shows that while heating and maintaining at high temperatures during nitridation, cold deformation is sufficient to compensate for the strength reduction that occurs when recrystallization is removed. That is, the strength obtained from cold deformation is reduced, but this reduction is compensated by the strength obtained by solid solution hardening with nitrogen and optionally carbon. Even relatively small amounts of nitrogen cause a significant increase in strength and provide bearing capacity, which is necessary for wear resistant expanded austenite.

  The method of the present invention provides a manufacturing member that has at least the same strength as a cold deformed member and at the same time has better corrosion resistance, and further provides the advantage of less time to implement.

The solid solution at temperature T1 and at optional temperature T2 may be performed using any suitable technique. For example a solid solution in and the temperature T2 at the temperature T1, in a gas process, a gas containing, for example, nitrogen, such as ammonia, preferably may be carried out using N _2. Solid solution may also be performed using ion implantation, salt bath or plasma. The solid solution at temperatures T1 and T2 is preferably carried out using a gas because it is an inexpensive and efficient solution, and all types of geometries are uniformly distributed. It can be processed and has good temperature uniformity. Furthermore, the use of a gas process means that it is within the framework of the laws of thermodynamics, which means that there are very well controlled processing conditions. Furthermore, surprisingly, the use of gas is an advantage since the high temperature process of the present invention has been found to make it easier to activate the surface using gas in the low temperature process. It is therefore easier to remove the impermeable oxide layer (passive layer) found on the passive material after high temperature solid solution . This is believed to be due to the presence of nitrogen and optionally carbon that is dissolved at high temperatures.

An optional low temperature process may be performed immediately after the high temperature process, but this is not required. It is also possible to implement two processes with time and location shifts. If these processes are carried out immediately after having a cooling step between the first and second solid solution steps, surface passivation can be avoided and thus low temperature process Prior activation is unnecessary. Therefore, the present invention also relates to an embodiment in which there is no surface passivation / activation between the implementation of the high temperature process and the low temperature process and the solid solution at temperature T2 takes place immediately after cooling from temperature T1. This may be done in the same furnace. When using a gas, the relevant gas containing nitrogen and / or carbon for use in a low temperature process may be supplied as soon as the material is cooled to temperature T2. However, the cooling is advantageously performed using argon with no nitrogen present during cooling. The advantage of using gas processing is that a gas that does not activate the surface at temperature T2 in a low temperature process can be used. Another advantage of this embodiment is that it makes the curing process cheaper and faster.

An advantage of the method of the present invention is that better corrosion properties are obtained because nitrogen is present in the solid solution. The solid solution of carbon does not change the corrosion characteristics. If the component is fully saturated with nitrogen, the material may be considered a nitrogen-containing alloy. This is often the case for thin-walled workpieces, for example for workpieces having a material thickness of up to 4 mm, for example 2-4 mm, which are treated by the method of the invention. Thus, stainless steel workpieces processed by the method of the present invention have much better corrosion resistance compared to workpieces that are only processed by a low temperature process (see Examples). Aspects of the invention relate to cold-deformed metal or alloy thin-walled components or workpieces processed by the method of the invention.

  For thin-walled components, the material may be fully saturated with nitrogen by a high temperature process. In thick materials, surface areas up to several millimeters, for example up to about 5 mm, may be obtained where nitrogen is in solid solution. In both cases, the bearing capacity of the material is increased and is comparable to the bearing capacity that may be obtained by cold deformation. In embodiments of the invention, it allows a workpiece having a thickness of up to about 10 mm to be fully saturated with nitrogen, so that a particularly strong workpiece is obtained. Generally, this method allows an expanded austenite or expanded martensite thickness of at least 5 μm to be obtained in the workpiece, wherein the expanded austenite or expanded martensite region has a hardness of at least 1000 HV, for example greater than 1050 HV. is there.

The method may further include a step in which the solid solution at the temperature T2 is performed without generating surface passivation immediately after cooling from the solid solution at the temperature T1. In a particular embodiment, the cooling is particularly rapid after the first solid solution process at temperature T1 in the temperature intervals where the related alloys are most prone to sensitization and formation of precipitates, such as nitrides and / or carbides. For example, the time is 60 seconds or less. For stainless steel, this has been found to occur at intervals between 900 ° C. and 700 ° C., particularly when the material must be cooled rapidly. In one embodiment, the workpiece is cooled from 900 ° C. to 700 ° C. in less than 60 seconds. In a preferred embodiment, the workpiece is cooled from 900 ° C. to 700 ° C. in less than 30 seconds. This is an advantage because carbide and / or nitride formation is thereby substantially avoided and these can react with alloying elements in stainless steel such as chromium. The consumption of alloying elements from the solid solution and their bonding as nitrides and / or carbides are suppressed and the corrosion resistance is maintained.

In general, the features of the method of the invention may be freely combined and all such combinations are contemplated in the present invention. For example, all features and variations discussed for the first solid solution step at temperature T1 are valid even when the method includes a second solid solution step at temperature T2. Similarly, lower than the temperature at which carbides and / or nitrides are formed in the passivation alloy, all of the features discussed for the subsequent step of Ru is dissolved nitrogen and / or carbon into the workpiece at temperature T2 It is reasonable for any combination of features for the first solid solution step at temperature T1 and cooling in an inert gas.

In another aspect, the invention relates to a member that has been solid solution hardened by the method of the invention. Any workpiece may be Oite processed in this way, but this, since the resultant member is fully saturated with nitrogen, the workpiece preferably has a thickness of up to about 10 mm. The member that has been solid solution hardened by the method of the present invention may be used in any technical field. Specific relevant fields are for use in the technical areas of medicine, food, automobile, chemical, petrochemical, pharmaceutical, marine, package, watch, cutlery / tableware, medical, energy, pulp and paper, mining or wastewater technology Including the member. Specific purpose components include valves (butterfly valves, ball valves, control valves), steering bolts, nuts, washers, fasteners, nozzles, pumps, mechanical parts, semiconductor ASML, ferrule parts, ball bearings and bearing gauges, pneumatic pressure Includes parts, membranes, etc.

In a further aspect, the present invention relates to a member solid solution hardened by the method according to the present invention, wherein the member is a valve component or a component used in a valve.

In a further aspect, the present invention relates to a member which has been solid solution hardened by the method according to the present invention, wherein the member is a clip, sign board, holder, box lid, cutlery, watch or handle for holding paper or note paper. To form a design target outer surface area, such as a plate attached together with, or a plate that forms part of a lamp.

In a further aspect, the invention relates to a member that has been solid solution hardened by the method according to the invention, wherein the member is a part of a bearing, for example a part of a ball bearing, a part of a roller bearing or a bearing cage.

In a further aspect, the present invention relates to a member solid solution hardened by the method according to the invention, wherein the member is a medical device, or a medical device, or a dental device, or a part of a dental device, or a medical device. Or a dental instrument.

In a further aspect, the present invention relates to a member solid solution hardened by the method according to the present invention, wherein the member is part of a formulation device such as a plate, nozzle, shim, tube or grid.

In a further aspect, the present invention relates to a member that has been solid solution hardened by the method according to the invention, wherein the member is a part of a vehicle, such as a plate, an exhaust part, a filter part, an engine part, an equipment, a handle, or a decorative surface. It is a part having.

FIG. 1 shows a constant temperature transformation diagram (TTT diagram) of nitrogen-containing austenitic stainless steel. FIG. 2a shows a set of lock washers. FIG. 2b shows a set of lock washers with bolts and nuts. FIG. 3 shows photomicrographs of lock washers processed in two prior art methods. FIG. 4 shows micrographs of lock washers processed in two prior art methods. FIG. 5 shows micrographs of samples of AISI 316 processed in two prior art methods. FIG. 6 shows micrographs of samples of AISI 304 processed in two prior art methods. FIG. 7 shows the hardness profile of stainless steel treated in the prior art method and by the method of the present invention. FIG. 8 shows a lock washer treated in the method of the present invention and in the prior art method. FIG. 9 shows micrographs of samples of AISI 316 processed in the prior art method (right) and by the method of the present invention (left).

Definitions In the context of the present invention, the terms “expanded austenite” and “expanded martensite” describe austenite or martensite, respectively, which is nitrogen (for nitride or carbide formation) or nitrogen and carbon. Supersaturated. Expanded austenite and expanded martensite may be defined as nitrogen expanded or carbon expanded, or expansion may be defined as nitrogen expanded and carbon expanded. However, in the context of the present invention, “expanded austenite” and “expanded martensite” generally refer generally to austenite or martensite expanded with nitrogen, carbon or any combination of nitrogen and carbon, respectively. An overview of expanded austenite can be found in T.W. L. Christiansen and M.M. A. J. et al. Provided by Somers (2009, Int. J. Mat. Res., 100: 1361-1377), the contents of which are incorporated herein by reference. Any alloy in which “expanded austenite” or “expanded martensite” may be formed is contemplated for the method of the present invention. Expanded austenite or expanded martensite may form on the surface of the alloy when the alloy is subjected to solid solution of nitrogen or carbon, or nitrogen and carbon, and expanded austenite or expanded martensite may be expanded austenite or expanded. It may also be referred to as a “region” of martensite. The term “region” in the context of the present invention is to be understood in relation to the thickness of the material being processed, and “region” is comparable to the thickness of expanded austenite or expanded martensite. The method of the present invention ensures that a thickness of expanded austenite or expanded martensite of at least 5 μm is obtained in the workpiece. That is, the thickness of expanded austenite or expanded martensite may be up to about 50 μm or more.

From the perspective of the present invention, “alloy element” may refer to a metal component or element in an alloy or any component in the analysis of the alloy. In particular, the alloys associated with the method of the present invention include elements that may form nitrides and / or carbides with each of the nitrogen and carbon present. The method of the present invention advantageously provides a surface free of nitrides and carbides of alloying elements. However, it is also contemplated in the present invention that the alloy may include only single metal elements that can form nitrides and / or carbides. The alloy may also contain other elements such as metalloid elements, intermetallic elements, or non-metallic elements. The alloying elements that can form nitrides and / or carbides may typically be metallic elements that provide corrosion resistance to the alloy for the formation of a passive oxide layer with the alloying elements. The terms “nitride” and “carbide” when used in the context of the present invention refer to nitrides and carbides formed between an alloying element and nitrogen and carbon, respectively. Typical nitrides are chromium nitride, CrN or Cr ₂ N, but the terms “nitride” and “carbide” are not limited to chromium nitrides and carbides.

  By the term “passive” associated with an alloy or metal, an alloy having an oxide layer on the surface must be understood. The alloy can either be self-passivated or passivated as a result of the process in which the alloy is subjected. Belonging to the group of self-passivating alloys are alloys that have a strong affinity for oxygen (eg Cr, Ti, V), including alloys containing such alloy elements (eg, essentially, Stainless steel which is an Fe-based alloy containing at least 10.5% Cr).

  By the term “cold deformation” (also referred to as “cold working”), plastic deformation induced in the material by external forces at temperatures below the recrystallization temperature of the material must be understood. Cold deformation may be provided by actual plastic shape changes such as forging, extrusion, shaping, stretching, pressing, or rolling, and also for example turning, milling, stamping, grinding or polishing etc. It may be caused by machining or a combination of these processes.

  By the term “sensitization”, nitrogen or carbon reacts with one or more alloying elements that are otherwise utilized to form an oxidation protection film on the surface, such as chromium in stainless steel, for example. Should be understood to form nitrides and carbides, respectively. When sensitization occurs, the free content of alloying elements such as chromium in the solid solution is reduced to a level that is no longer sufficient to maintain a complete oxidation protection film, which means that the corrosion properties are impaired.

  By the term “carbide and / or nitride dissolution temperature”, the temperature at which the nitride / carbide is not stable and the nitride / carbide already formed must be understood is understood. In general, alloys containing metal alloy elements that can form nitrides and / or carbides have a temperature interval in which nitrides and / or carbides may form when nitrogen and carbon are present, respectively. . Therefore, when this temperature interval is exceeded, nitrides and carbides are not formed, and nitrides / carbides already formed are dissolved. When nitrides or carbides are present, ie when sensitization occurs, these carbides can generally only be removed by exposing the sensitized metal to temperatures above the austenitizing temperature. Furthermore, such alloys have temperatures below this temperature interval at which nitrides and carbides are not formed, but nitrides or carbides already formed in the alloys cannot be removed at low temperatures.

  “Austenitizing temperature” is typically the temperature used when heat treating an alloy to dissolve carbides, and thus “austenitizing temperature” may correspond to “carbide melting temperature”. At the austenitizing temperature, the alloy is in the austenitic phase. The temperature at which the alloy steel changes phase from ferrite to austenite is typically at or below the austenitizing temperature.

  The austenitizing temperature and the temperature at which carbides and / or nitrides are formed in the passive alloy are generally known to those skilled in the art. Similarly, temperatures below which no nitrides or carbides are formed are generally known to those skilled in the art. Furthermore, the melting temperature of the alloy is generally known to those skilled in the art. The temperature may depend on the composition of the passive alloy, and furthermore, for any given composition, these temperatures are readily determined experimentally by those skilled in the art.

  The alloy content is expressed in weight percent. Inevitable impurities to the alloy composition or gas composition may also be present, even if not specifically mentioned.

Further Description of the Invention FIG. 1 shows an example of a constant temperature transformation diagram (TTT diagram) of a nitrogen-containing austenitic stainless steel. Stainless steel has the composition Fe-19Cr-5Mn-5Ni-3Mo-0.024C-0.69N (from JW Simmons, PhD thesis, Oregon Graduate Institute of Science and Technology 1993). The temperature interval at which nitride may begin to form in FIG. 1 is indicated by “Cr ₂ N”. In the method of the present invention, the step of Ru nitrogen is a solid solution passivation alloy is thus carried out at a temperature T1 greater than the austenitizing temperature, the workpiece, passivating alloy in an inert gas containing no nitrogen At a temperature lower than the temperature at which carbides and / or nitrides are formed. The method may include the second step of Ru is dissolved is carried out at a lower temperature T2 than the temperature interval nitrides and / or carbides may be formed, nitrogen and / or carbon. Therefore, the temperature T1 is higher than the temperature T2. The workpiece is cooled to a temperature lower than the temperature at which carbides and / or nitrides are formed in the passive alloy, for example within a time range of 60 seconds after the first solid solution step at temperature T1, for example. . Thus, the passive alloy of the workpiece is stabilized against nitride and / or carbide formation, and then an optional second solid solution step may be performed if desired. An austenitizing temperature may also be referred to as a “high” temperature in the context of the present invention. Similarly, temperatures below the temperature at which carbides and / or nitrides are formed are also referred to as “low” temperatures.

The method of the present invention comprise Ru a solid solution of nitrogen and / or carbon passivation alloy. Further, the step of Ru is dissolved nitrogen may be called a "solid solution of nitrogen" or "nitride", similar steps Ru is solid-dissolved carbon is called a "solid solution of carbon" or "carburizing" May be. When both nitrogen and carbon are dissolved in the same process, the step may be referred to as “soft nitriding”.

In a particular embodiment, the present invention relates to a member that has been solid solution hardened by the method of the present invention. In the context of the present invention, “processed” should be broadly understood. In particular, the term “treated” means that the method of the invention has been used in the manufacture of parts. Thus, the present invention also relates to components manufactured using the method of the present invention, and the terms “processed in” and “manufactured using” may be used interchangeably. The method of the present invention may be the last step in the manufacture of the member, or the member processed by this method may also be subjected to further processing steps to provide the final member.

  A “thin component” in the context of the present invention is a component of a size that allows the component to be fully saturated with nitrogen and / or carbon in the process of the present invention. Thus, a “thin component” is, for example, in its smallest dimension, a material thickness of up to about 10 mm (including), for example a thickness of about 2 mm to about 4 mm or a thickness in the range of 0.2 mm to 8 mm, or 0 It may have a thickness in the range of 4 mm to 6 mm, or a thickness in the range of 0.5 mm to 5 mm, or a thickness in the range of 1.5 mm to 4.5 mm. The method may be used with any thin component.

A novel and unique method that provides one or more of the above objectives provides a method for solution hardening a cold deformed workpiece of a passive alloy containing at least 10% chromium This method obtained by
- a step of Ru a solid solution at least nitrogen in the workpiece at a lower temperature T1 than the melting point of the higher passivating alloy than the dissolution temperature of the carbides and / or nitrides, to implement a solid solution of nitrogen at a temperature T1 50 m to Obtaining a diffusion depth in the range of 5 mm;
-Cooling the workpiece to a temperature below the temperature at which carbides and / or nitrides are formed in the passive alloy after the solid solution step at temperature T1, wherein the cooling step does not contain nitrogen. Performed in an active gas. This method is lower than the temperature at which carbides and / or nitrides are formed in the passivation alloy, subsequent second step of Ru is dissolved nitrogen and / or carbon into the workpiece at a temperature T2 of at least 300 ° C. May further be included.

The present invention is particularly suitable for stainless steel and equivalent alloys, where expanded austenite or martensite can be obtained in a low temperature solid solution process. In general, chromium-containing iron, nickel and / or cobalt-based alloys are associated with this method. The chromium content may vary, for example up to about 10%. In other examples, the chromium content may be about 10% or at least 10%. Accordingly, the present invention, in one embodiment, relates to a method for solid solution hardening of a stainless steel cold deformed workpiece. Carbon by nitrogen and optionally also at temperatures higher than the austenitizing temperature of the stainless steel, for example, it may be dissolved in a stainless steel at a temperature higher than the melting temperature of the carbides and / or nitrides of the alloying elements such as chromium . Even a relatively small amount of nitrogen results in a significant increase in strength resulting in load bearing capacity, which is necessary for wear resistant expanded austenite. In an embodiment of the present invention, the hardness of the expanded austenite region or the expanded martensite region is at least 1000 HV.

In the embodiment of the present invention, the stainless steel is an austenitic steel. This material is relatively soft compared to, for example, martensitic stainless steel. Therefore, it is particularly advantageous for this material that nitrogen and optionally carbon are dissolved in the high temperature process. Thereby, the austenitic steel has sufficient core strength to compensate for the strength loss that occurs when cold deformation is prevented, and then without problems due to precipitation of nitrides and / or carbides, etc. it is possible to Rukoto is dissolved nitrogen and / or carbon at low temperature. In a further embodiment of the invention, the passive alloy is selected from the group comprising stainless steel, austenitic stainless steel, martensitic stainless steel, ferritic stainless steel, precipitation hardenable (PH) stainless steel or ferrite-austenite stainless steel. Ferritic-austenitic stainless steel may also be referred to as duplex stainless steel.

The content of nitrogen and optionally carbon dissolved in stainless steel in high temperature processes is typically less than 1% by weight, but can be higher if necessary. This is in the form of a higher partial pressure of for example N ₂ in gas process, it may be obtained by applying a higher nitrogen and optionally by a carbon activity. The nitrogen and / or carbon content obtained in stainless steel in low temperature solid solution may be as much as 14% by weight and 6% by weight, respectively.

In a preferred embodiment, the above solid solution of nitrogen and / or carbon is performed at temperature T1 using a gas containing nitrogen and optionally carbon, but it is also performed by ion implantation, plasma assistance or a salt bath. May be. In a preferred embodiment, a nitrogen containing gas such as N ₂ is used. The pressure of the gas may be up to several bars but may also be less than 1 bar, for example 0.1 bar. It is advantageous to use gas because all types of geometric shapes may be treated uniformly and there is sufficient temperature uniformity.

In the embodiment of the present invention, the solid solution is performed at the temperature T1 and the temperature T2 using a gas. The gas contains nitrogen and / or carbon, and the gas used in the cooling step is an inert gas that does not contain nitrogen. In certain embodiments, the solid solution at temperature T2 is performed in a method selected from the group comprising gas-based methods, ion implantation, salt baths or plasmas.

In an embodiment of the invention, a diffusion depth of 50 μm to 5 mm is obtained by solid solution of nitrogen and optionally carbon at temperature T1. This results in both a hard surface of the material and a reinforcement of the core. This may result in complete hardening of the thin-walled component having a material thickness that is equal to or about twice that of the solid solution depth, since the solid solution usually occurs from both sides of the workpiece. It is. For thicker components, a relatively thick surface area is obtained with nitrogen and optionally carbon in solid solution. This provides a support for the expanded austenitic layer that is formed on the surface in a subsequent low temperature process. For thin workpieces, complete nitriding / carburizing / soft nitriding of the workpiece may thus be obtained. Even if this is not fully achieved, this solid solution is significant especially for thin-walled workpieces, since these are greatly improved in the method of the present invention if the stringent requirements for corrosion resistance and bearing capacity are reasonable. Is an advantage.

In embodiments of the present invention, the temperature T1 is greater than 1000 ° C., such as at least 1050 ° C., or it may be at least 1100 ° C., such as 1120 ° C. or 1160 ° C., at least 1200 ° C., or at least 1250 ° C. The upper temperature limit is lower than the melting point of the material being processed. For stainless steel, the melting point is about 1600 ° C. In embodiments of the present invention, the temperature T1 is less than 1600 ° C, such as less than 1500 ° C, or less than 1400 ° C, such as less than 1350 ° C. In an embodiment of the present invention, the temperature T1 is in the range of 1050 to 1300 ° C., for example about 1150 ° C. It is important that the temperature is higher than the melting temperature of the relevant carbides and / or nitrides that may possibly form in the material, but lower than the melting point of the material being processed. When gas is used for solid solution at temperature T1, the temperature used may be selected taking into account the gas mixture and the applied gas pressure.

In another embodiment of the present invention, carbon is dissolved at temperature T2, which is less than 550 ° C, preferably in the range of 300-530 ° C during carburization.

In yet another embodiment of the invention, nitrogen is dissolved at temperature T2, which is less than 500 ° C. during nitridation, such as less than 470 ° C., preferably in the range of 300-470 ° C.

In yet another embodiment of the invention, nitrogen and carbon are dissolved at temperature T2, which is less than 500 ° C. during soft nitriding, for example less than 470 ° C., preferably between 300 and 470 ° C.

In embodiments of the invention, the high temperature solid solution is at temperature T1 for at least 20 minutes, such as at least 30 minutes, or at least 1 hour, or at least 1.5 hours, or at least 2 hours or at least 3 hours, or at least 4 hours, or Performed for at least 5 hours, or at least 10 hours or at least 15 hours. Since nitride or carbide is not formed at temperature T1, there is basically no upper limit on time. Depending on the thickness of the further processing, the material may be saturated with nitrogen and optionally carbon, ie completely nitrided or soft nitrided.

In an embodiment of the invention, the method includes cooling the material to ambient temperature after solid solution at temperature T1. It is particularly preferable that the second solid solution step at the temperature T2 is performed immediately after the cooling step. This avoids the passivation of the workpiece, i.e. the formation of an oxide layer. In an embodiment of the invention, the cooling is carried out under high pressure, for example in the range of 6 to 10 bar, for example at 7 bar or at 8 bar or at 9 bar. Cooling can be performed in an inert gas that does not contain nitrogen, for example, a noble gas such as helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), or radon (Rn), or Argon is particularly preferred although it is carried out in any of these mixtures. In another embodiment, the cooling is carried out at high pressure, for example in the range 4-20 bar, for example in the range 6-10 bar, for example 7 or 8 bar, or in 9 bar argon.

The present invention further relates to a stainless steel lock washer (see FIGS. 2a and 2b) for securing bolts and nuts that is solid solution hardened using the method of the present invention. The lock washer is relatively thin, so that significant and necessary improvements in both the strength and corrosion resistance of the lock washer are achieved by curing the lock washer using the method of the present invention. In the embodiment of the present invention, the lock washer has a first surface having radial teeth, the other surface on the opposite side, and a cam surface having a cam. The lock washer is used by attaching the cams in contact with each other to obtain a key lock effect. They are particularly suitable for effectively tightening bolt assemblies that are exposed to extreme vibrations or dynamic loads and corrosive environments such as salt water. Therefore, there are strong requirements for the strength and corrosion resistance of these washers.

The present invention is particularly suitable for stainless steel and equivalent alloys, where expanded austenite or martensite can be obtained in a low temperature solid solution process. However, the invention is inclusive in nature and is a high temperature solid solution process having nitrogen and optionally carbon in a passive alloy, such as an iron-based alloy, cobalt-based alloy, nickel-based alloy or chromium-based alloy, It provides strength and also provides an improved low temperature solid solution process for corrosion, processing speed and strength.

  The following examples and prior art examples illustrate the invention in more detail in conjunction with the accompanying drawings.

Prior art example 1
Hardening of cold deformed austenitic stainless steel, AISI 316 key lock washer by two prior art methods Two identical key lock washers of cold deformed austenitic stainless steel AISI 316L were hardened. FIG. 2 shows a key lock washer set 1 of the key lock washer 2 and illustrates their use. Each washer 2 has a first surface 3 having radial teeth 4 and an opposite cam surface 5 having a cam 6. While using the key lock washer set 1, the washer 2 is positioned such that the cam surfaces 5 are shown facing each other. The two key lock washers were solid solution hardened using nitrogen and carbon at a temperature of 440 ° C. One washer is cured by the method disclosed in patent application PA201170208, i.e. in a high temperature process and subsequently in a low temperature process, while the other washer is directly applied by the same low temperature process, i.e. a prior art low temperature process. Surface cured. The washer was analyzed by light microscopy. The box on the left side of FIGS. 3 and 4 shows a washer that has only been surface hardened by a soft nitriding process performed using nitrogen and carbon containing gases at a temperature of 440 ° C. for 16 hours at atmospheric pressure. The outer surface of the nitrogen-containing region appears to be partially sensitized (chromium nitride precipitation). The deformed substrate appears to be strongly deformed and is clearly affected by the etchant used, resulting in a microstructure. FIG. 4 shows an enlargement of FIG.

The right box in FIG. 3 and FIG. 4 shows the washer processed by the method disclosed in the patent application PA201170208. The washer was exposed to a nitrogen-containing atmosphere (N ₂ gas) at a temperature above 1050 ° C. and then rapidly cooled in the same gas. Thereby the material was fully austenitic and the material was completely saturated with nitrogen. The washer is then surface hardened by a soft nitriding process performed using nitrogen and carbon containing gas at a temperature of 440 ° C. for 16 hours at atmospheric pressure, whereby the surface of the region where the expanded austenite has a thickness of at least 5 μm Formed. The soft nitrided nitrogen-containing region was not sensitized and the substrate was clearly not cold deformed. However, the base washes (260-300 HV0.5) and surface hardness (1200-1400 HV0.005) of the two washers are almost the same. The washer corrosion resistance (exposure time in salt spray chamber (ISO 9227)) using the method disclosed in the patent application PA201170208 was many times better than the corrosion resistance of the washer that was only surface cured. (Time in the room until corrosion is observed). The washer treated by the method disclosed in patent application PA201170208 showed no corrosion after 400 hours, whereas the directly cold-cured washer is clearly visible already after 20 hours. Showed corrosion. Rather than exposing the washer to a nitrogen-containing atmosphere (N ₂ gas) at a temperature above 1050 ° C. and then cooling in a nitrogen-containing atmosphere, by rapidly cooling in an inert atmosphere that does not contain nitrogen, for example argon. Further improvements in corrosion resistance can be obtained while retaining other advantageous properties.

Prior art example 2
Hardening of cold deformed austenitic stainless steel, AISI 316 by the prior art method and the method disclosed in patent application PA201170208. Two identical components of cold deformed austenitic stainless steel AISI 316 ( The rear ferrule) was solid solution hardened using nitrogen and carbon at a temperature of 440 ° C. One component was cured by the method disclosed in patent application PA201170208, ie in a high temperature process and subsequently in a low temperature process, and the other component was directly surface cured by the same low temperature process. The box on the left side of FIG. 5 shows the fines analyzed by optical microscopy of components that were only surface hardened by a soft nitriding process performed using nitrogen and carbon containing gases at a temperature of 440 ° C. for 12 hours. The structure is shown. The outer surface of the nitrogen-containing region appears to be partially sensitized by the obvious precipitation of CrN on the outermost surface. The right box in FIG. 5 shows a component that has been processed by the method disclosed in the patent application PA201170208. This component was exposed to a nitrogen-containing atmosphere (N ₂ gas) at a temperature above 1050 ° C. and then rapidly cooled in the same gas. The surface of the component was then cured by a soft nitriding process in a low temperature process performed using nitrogen and carbon containing gas at a temperature of 440 ° C. for 12 hours. The soft nitrided nitrogen-containing region was not sensitized. However, the substrate hardness (260-300 HV0.5) and surface hardness (1200-1400 HV0.005) of the two components are almost the same. The total layer thickness of the expanded austenite region is about 20 μm in both cases. The outermost layer is nitrogen expanded austenite and the innermost layer is carbon expanded austenite. The corrosion resistance of both components was tested in a 14% by weight sodium hypochlorite solution. The component treated by the method disclosed in patent application PA201170208 showed no corrosion after 24 hours, while the directly cold-cured component showed obvious corrosion after only 10 minutes. Therefore, the components used in the method disclosed in the patent application PA201170208 differ in that they exhibit significantly better corrosion resistance than directly soft-nitrided workpieces. Rather than exposing the ferrule to a nitrogen-containing atmosphere (N ₂ gas) at a temperature in excess of 1050 ° C. and then cooling in a nitrogen-containing atmosphere, rapidly cooling in a nitrogen-free inert atmosphere, such as argon. Thus, further improvements in corrosion resistance can be obtained while retaining other advantageous properties.

Prior art example 3
Hardening of Cold Deformed Austenitic Stainless Steel AISI 304 Plate by Prior Art Methods and Methods Disclosed in Patent Application No. PA201170208 Cold Rolled (Deformed) Austenitic Stainless Steel Plate, AISI 304 The two identical components were solid solution hardened using nitrogen and carbon at a temperature of 440 ° C. One component was cured by the method disclosed in patent application PA201170208, ie in a high temperature process and subsequently in a low temperature process, and the other component was directly surface cured by the same low temperature process. The box on the left side of FIG. 6 shows a component that has only been surface hardened by a soft nitridation process performed using nitrogen and carbon containing gas at a temperature of 440 ° C. for 20 hours, but then for 70 minutes. Corrosion testing was performed by exposure to a 14 wt% sodium hypochlorite solution. The right box in FIG. 6 shows a component cured by the method disclosed in Patent Application No. PA201170208. The components were exposed to a nitrogen-containing atmosphere (N ₂ gas) at a temperature of 1150 ° C. for 30 minutes and then rapidly cooled in the same gas. The components were then surface hardened by a soft nitridation process performed using nitrogen and carbon containing gases at a temperature of 440 ° C. for 20 hours. Finally, the component was subjected to a corrosion test by exposing it to a 14% by weight sodium hypochlorite solution. The surface appeared to be unaffected by the corrosion test even after 16 hours of exposure. There is a clear attack of corrosion after a short exposure / corrosion test (70 minutes) in the directly cured component. Therefore, the components used in the method disclosed in the patent application PA201170208 are different in that they have much better corrosion resistance. Rather than exposing the components to a nitrogen-containing atmosphere (N ₂ gas) at temperatures above 1050 ° C. and then cooling in a nitrogen-containing atmosphere, rapidly cooling in an inert atmosphere that does not contain nitrogen, such as argon By doing so, further improvement in corrosion resistance can be obtained while maintaining other advantageous properties.

Example 1
Hardness profile of cold deformed stainless steel treated by the prior art method and the method of the present invention Two identical components of cold deformed austenitic stainless steel are used in the prior art method and by the method of the present invention. Processed. Samples are exposed to a nitrogen-containing atmosphere (N ₂ gas) or to an atmosphere of hydrogen (H ₂ ) at temperatures above 1050 ° C. and then rapidly in argon (for N ₂ treated samples) or H ₂ gas Cooled down. The component surface was then cured by soft nitridation in a low temperature process performed using nitrogen and carbon containing gas at a temperature of 440 ° C. for 12 hours. The soft nitrided region was not sensitized. The hardness profile of the sample was analyzed and the results are shown in FIG. Samples treated at high temperature in a nitrogen-containing atmosphere (“EXPANITE ON HTSN”) retained the core strength of the material, but the core strength was lost during high temperature annealing in hydrogen (“EXPANITE ON ANNEALED”). It is clear from FIG.

Example 2
Argon cooling after high temperature solution hardening using nitrogen A cold deformed austenitic stainless steel, AISI 316L lock washer described in Example 1 of the prior art and illustrated in FIG. Exposure to a nitrogen-containing atmosphere (N ₂ gas) followed by rapid cooling to ambient temperature in either the same atmosphere or an argon atmosphere. The sample was not subjected to further surface hardening. The corrosion resistance of the components was tested in a 14% by weight sodium hypochlorite solution. FIG. 8 shows three typical lock washers (left side) cooled in argon and three lock washers (right side) cooled in nitrogen. The lock washer cooled with argon had much better corrosion resistance than the lock washer cooled in nitrogen, showing clear evidence of corrosion.

Example 3
Hardening of Cold Deformed Austenitic Stainless Steel, AISI 316 Component According to Prior Art Methods and Methods of the Invention The corrosion resistance of cold deformed austenitic stainless steel AISI 316 treated according to the present invention is And compared to similar components processed by the method. The corrosion test was performed by immersing the two surface hardened components in a 14 wt% sodium hypochlorite solution for 18 hours.

  The box on the left side of FIG. 9 shows the components that have been processed according to the present invention, i.e., processed in a high temperature process and then cooled in argon in a low temperature process, and other components in the right box. Was directly surface hardened only by a low temperature process.

  The surface of the component treated according to the present invention does not appear to be affected by the corrosion test even after 18 hours of exposure. In the components treated according to the prior art, corrosion attack was observed after a short exposure (7 minutes). Therefore, the components in which the method of the present invention is used differ in that they have much better corrosion resistance.

Claims (20)

In a method for the solution treatment of cold deformed workpieces of iron-based, nickel-based and / or cobalt-based alloys containing at least 10% chromium,
-At least nitrogen is dissolved in the workpiece at a temperature T1 higher than about 1020 ° C and lower than the melting point of the alloy , the solid solution of nitrogen being performed at the temperature T1 to achieve a diffusion depth in the range of 50 µm to 5 mm. Obtaining step;
The step of cooling the workpiece to a temperature below 550 ° C. after the solid solution step at temperature T1 , the cooling from 900 ° C. to 700 ° C. being carried out in less than 60 seconds, Performing the step in an inert gas containing no nitrogen. The method of claim 1, further comprising a subsequent second step of solid solution of nitrogen and / or carbon into the workpiece at a temperature T2 of at least 300 ° C and less than 550 .   3. The method according to claim 1, wherein the inert gas is helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), or radon (Rn), or these. A method characterized in that it is selected from any mixture of   4. A method according to any one of claims 1 to 3, characterized in that the inert gas is argon except for inevitable impurities. 5. A method according to any one of the preceding claims, characterized in that nitrogen and carbon are dissolved at temperature T1. 6. The method according to any one of claims 1 to 5, wherein the alloy is stainless steel, austenitic stainless steel, martensitic stainless steel, ferritic stainless steel, precipitation hardened (PH) stainless steel or ferrite-austenite. A method characterized in that it is selected from the group comprising stainless steel. The method according to any one of claims 1 to 6, wherein the solid solution at the temperature T1 is performed using a gas containing nitrogen. The method according to any one of claims 2 to 7, wherein the solid solution at the temperature T2 is carried out in a method selected from the group comprising a gas system method, an ion implantation, a salt bath or plasma. how to. 9. The method according to any one of claims 1 to 8, characterized in that the solid solution at temperature T1 and temperature T2 is carried out using a gas. 10. A method according to any one of the preceding claims, characterized in that the temperature T1 is in the range from 1050C to 1300C . 11. A method according to any one of claims 2 to 10, characterized in that the carbon is solid-solved at a temperature T2 and the temperature T2 is in the range of 300 to 530 [deg.] C. The method according to any one of claims 2 to 10, wherein nitrogen is solid-solved at a temperature T2, and the temperature T2 is in the range of 300 to 470 ° C. The method according to any one of claims 2 to 10, wherein nitrogen and carbon are solid-solved at a temperature T2, and the temperature T2 is in the range of 300 to 470 ° C. 14. A method according to any one of claims 2 to 13, characterized in that expanded austenite or expanded martensite thickness of at least 5 [mu] m is obtained in the workpiece. 15. The method according to any one of claims 2 to 14, wherein the hardness of the expanded austenite region or the expanded martensite region is at least 1000 HV. 16. The method according to any one of claims 2 to 15, wherein the solid solution at the temperature T2 is performed without generation of surface passivation immediately after cooling from the solid solution at the temperature T1. ,Method. In a method for producing a corrosion-resistant material of an iron-base, nickel-base and / or cobalt-base alloy containing at least 10% chromium, the material has a thickness of up to 10 mm, the method comprising:
Providing a cold deformed workpiece of iron-base, nickel-base and / or cobalt-base alloy containing at least 10% chromium, the workpiece having a thickness of up to 10 mm;
A solid solution of at least nitrogen in the workpiece at a temperature T1 higher than about 1020 ° C. and lower than the melting point of the alloy, the nitrogen being dissolved at the temperature T1 and a diffusion depth in the range of 50 μm to 5 mm. And getting the steps
The step of cooling the workpiece to a temperature below 550 ° C. after the solid solution step at temperature T1, the cooling from 900 ° C. to 700 ° C. being carried out in less than 60 seconds, The step is performed in an inert gas containing no nitrogen;
A method comprising the steps of: 18. A method according to any one of claims 1 to 17,
Method, characterized in that the workpiece or the corrosion-resistant material is a stainless steel lock washer for fixing a fixed part. The method of claim 18, wherein
The method, wherein the lock washer has a first surface having radial teeth and the other surface on the opposite side having a cam. 18. A method according to any one of claims 1 to 17,
The workpiece or the corrosion-resistant material is a valve, a design target outer surface area, a bearing part, a medical equipment part, a dental equipment part, a medical equipment, a dental equipment, a pharmaceutical equipment part, or an automobile part. A method, characterized in that it is a part used in