KR20150003900A - Method for solution hardening of a cold deformed workpiece of a passive alloy, and a member solution hardened by the method. - Google Patents

Abstract

The present invention relates to a method for solution curing of a cold-formed workpiece of a passive alloy containing at least 10% of chromium,
A first step of dissolving at least nitrogen in said workpiece at a temperature (T1) which is higher than an available temperature for carbide and / or nitride and lower than the melting point of said passive alloy, and
Wherein the nitriding dissolution at temperature (T1) is performed to obtain a diffusion depth in the range of 50 [mu] m to 5 mm -
Cooling the workpiece at a temperature below the temperature of the nitride and / or carbide formed in the passive alloy after the dissolving step at the temperature (T1)
- the cooling step is carried out in an inert atmosphere which does not contain nitrogen -
/ RTI > The present invention also relates to a lock washer and a member for a nut or a security bolt manufactured through the method.

Description

A method for solution curing of a cold deformed workpiece of a passive alloy and a solution cured member by the method.

The present invention relates to a method for the formation of expanded austenite and / or expanded martensite by solution curing of a cold deformed workpiece of a passive alloy. The process provides a cured alloy substantially free of carbides and / or nitrides. The method also provides a corrosion resistant surface while retaining the core strength of the material resulting from cold deformation. The present invention also relates to a solution cured member by the above method. Such members are particularly relevant to the fields of medicine, food, automotive, chemical, petrochemical, pharmaceutical, marine, packaging, watches, cutlery / tableware, medicine, energy, pulp & paper, mining or wastewater technology.

Stainless steels and other passive alloys are typically materials that have excellent corrosion resistance but have relatively low lubricity properties, such as adhesion wear characteristics. To solve this problem, stainless steels and similar alloys can be surface hardened at low temperature (less than 450 to 550 DEG C) by dissolution of nitrogen and / or carbon, thereby forming a so- Get the zone of the siege. This zone is a supersaturated solution of carbon and / or nitrogen in austenite and / or martensite and is metastable to carbon / nitrogen formation. Such a low temperature process may be based on gas, plasma or molten salt, and the gas process requires the use of special activation techniques, whereas in the case of plasma and salt bath activation is achieved immediately and no special treatment is required. Thereby the surface zone is obtained from the material, which contains a large amount of nitrogen and / or carbon, which is due to the relatively low process temperature. Whereby the material is surface hardened and retains its corrosion resistance. However, most passive alloys, such as stainless steels, may not be solution cured directly by nitrogen and / or carbon because this passive alloy has an impermeable oxide layer, also referred to as a passive layer, For example, to prevent the dissolution of nitrogen and carbon. Therefore, a special technique for removing such a passive layer is required. Such techniques are known to those skilled in the art.

Most used technical components are used in the machined state, which means that the material is cold-deformed (plastic deformation) inhomogeneously. In many applications, such cold deformation is desirable from a component-strength-minded perspective: if the component does not have an increase in strength from the work hardening induced by cold deformation, the component will not work. This results in a significant problem when such cold machined components surface harden in a low temperature process such that the surface is changed to expanded austenite or martensite under the absorption of nitrogen and / or carbon. The presence of plastic deformation (defects in the microstructure) in the material is more easily caused by the reaction of nitride and carbide with alloying elements such as chromium (Cr) with nitrogen and carbon in the stainless steel. Consequently, a certain amount of Cr is removed from the solid solution and bound as chromium nitride / chromium carbide. This implies that the corrosion properties deteriorate because less chromium is available for the maintenance of the passive layer. Such Cr-depletion in the localized region can be noticeable and results in loss of corrosion protection at the surface of the localized region. Precipitation of the nitride / carbide is referred to as sensitization. Particularly in this phenomenon, the dissolution of nitrogen is very pronounced because chromium nitride is more stable than chromium carbide and can be formed at lower temperatures. This means that in a low temperature process the temperature must be (further) lowered to avoid sensitization, which is undesirable because the process proceeds more slowly. For extreme degrees of deformation in stainless steel, there is probably no lower limit for sensitization.

Cold Stressed Stainless Steel Workpiece In low temperature curing, sensitization will occur in relation to low temperature melting of nitrogen and / or carbon occurring at temperatures below 550 ° C. In order to solve the problem of sensitization in the cold-deformed material during low temperature surface hardening, the complete annealing of the components was made possible by a so-called austenitisation in a vacuum or hydrogen atmosphere. Complete annealing is a process performed at a temperature in excess of 1020 DEG C, typically in the range of 1020 to 1120 DEG C. Whereby the cold deformation of the material is nullified and low temperature dissolution can be carried out without risk of sensitization. However, this process presents the problem of reduced strength of the cold worked metal, which is referred to in the material as the so-called egg shell effect, i.e. when the workpiece is subsequently cured at low temperature, Softened with respect to the thin surface. By performing austenitization, the core strength of the material is reduced to the core strength of the annealed material, which requires that the core strength of the treated component be a less important design parameter.

Another possibility is to exploit the carburization process, in which the carbon is dissolved in the material at low temperature, i.e. the formation of carbon-expanded austenite. The sensitization is not as great for carbon dissolution as for nitrogen dissolution (nitrification and nitrocarburising), thus resulting in less effect on corrosion resistance. However, even for components with a strong degree of cold deformation, even this is considered harmful. Another disadvantage of using only carbon dissolution is that a lower surface hardness is obtained than for nitrogen dissolution and the composition profile (hardness) can not be adjusted in the same way (see, e. G. EP 1095170 B1 and WO 2006/136166 A1 Reference).

See, for example, Georgiev et al., Journal of Materials Science and Technology, Vol. 4, 1996; 4, pp. 28] and Bashchenko et al., Izvestiya Akademii Nauk SSSR. Metally, No. 4, 1985, pp. 173-178, nitrogen and / or oxygen can be dissolved in stainless steel at elevated temperatures (above about 1050 DEG C) under equilibrium conditions. By using high temperatures, it is possible to circumvent the problems of penetration of the passive layer of stainless steel, since this becomes unstable at such a high temperature. It is also explained that the available temperature for chromium carbide and chromium nitride is below this temperature. Consequently, carbides and / or nitrides are not formed at such high temperatures. However, the solubility of nitrogen / carbon is relatively limited and no actual surface hardening occurs for austenitic stainless steels; This applies in particular to carbon. Rapid cooling rates are required to avoid precipitation of carbide / nitride during cooling. For the martensitic stainless steel type, considerable hardening of the surface can be caused by rapid cooling, but the hardening effect is significantly lower than that obtained by the process for forming expanded austenite.

WO 2008/124239 proposes a hybrid carburization process with intermediate rapid quench wherein the carbon hardened surface in a metal workpiece is treated with both high and low temperature carburization to form carbon precipitation And immediately after mixing the hot carbon, the workpiece is rapidly quenched to a temperature below which it forms carbon precipitation. The rapid quenching can be performed, for example, using a dipping of the workpiece into water, oil, or other cooling medium such as gas or molten salt. WO 2008/124239 does not recognize the problem of the formation of carbides and / or nitrides and the cold-deformation during subsequent low temperature curing.

There is a need for a method that allows low temperature melting of nitrogen and / or carbon for curing of passive alloys, for example stainless steels, wherein the problem of adjusting the sensitization and / or composition profile is solved.

In order to overcome the problem of sensitization in relation to low temperature nitridation and / or carburization of the cold deformable workpiece, the prior art first proposes to anneal the material to obtain partial or complete recrystallization; Alternatively, only the recovery of the material is obtained. This negates the reinforcement obtained from the cold deformation and the cold deformation in the material, but on the other hand, the low temperature dissolution can be carried out without any problem due to sensitization. However, this solution does not provide a component with high core strength.

Danish patent PA2011 70208 discloses a process for solution curing of cold-formed products of passive alloys or passive metals. The method includes a first step of dissolving at least nitrogen in the workpiece at a temperature (T1) that is higher than an available temperature for the carbide and / or nitride and lower than the melting point of the passive alloy, and wherein the carbide and / And a subsequent second step of dissolving nitrogen and / or carbon in the workpiece at a temperature (T2) lower than the temperature at which it is formed. The method also provides fast cooling from the first stage to the second stage. It is contemplated that treatment of the metal according to PA 2011 70208 provides superior properties as compared to the prior art steps, which would enable an improvement in the properties of the metal to be obtained.

It is an object of the present invention to allow for the formation of expanded austenite or expanded martensite by cold nitriding and / or carburizing of products formed from cold deformation without sensitization occurring in the workpiece and made from passive alloys, in particular stainless steels , Wherein the reinforcing effect obtained may be comparable to or even greater than the reinforcing effect obtained by cold deformation.

A method for solution curing of a cold-formed workpiece of a passive alloy containing at least 10% of chromium,

A first step of dissolving at least nitrogen in said workpiece at a temperature (T1) which is higher than an available temperature for carbide and / or nitride and lower than the melting point of said passive alloy, and

Wherein the nitriding dissolution at temperature (T1) is performed to obtain a diffusion depth in the range of 50 [mu] m to 5 mm -

Cooling the workpiece at a temperature below the temperature of the nitride and / or carbide formed in the passive alloy after the dissolving step at the temperature (T1)

- the cooling step is carried out in an inert atmosphere which does not contain nitrogen -

/ RTI >

The present invention also relates to

A first step of dissolving at least nitrogen in the workpiece at a temperature (T1) higher than the austenitizing temperature and lower than the melting point of the passive alloy, and

Wherein the nitriding dissolution at temperature (T1) is performed to obtain a diffusion depth in the range of 50 [mu] m to 5 mm -

Cooling the workpiece at a temperature below the temperature of the nitride and / or carbide formed in the passive alloy after the dissolving step at the temperature (T1)

- the cooling step is carried out in an inert atmosphere which does not contain nitrogen -

/ RTI >

In a preferred embodiment, the first dissolving step is carried out with substantially pure N2 without a gas, for example a gas containing N2, such as, for example, unavoidable impurities, and the cooling step is also preferably carried out in a first dissolving step Which can be the same gas as the gas. However, an inert gas (nitrogen-free inert gas) in which the gas in the cooling step does not contain nitrogen is preferable, and argon is particularly preferable. In the context of the present invention, "inert gas" is a gas that does not contain any substantial amount of molecules interacting with the elements of the alloy, and any inert gas or mixture of gases that does not contain nitrogen is contemplated by the present invention. It is believed that when the inert gas is used in the cooling step, the workpiece treated in the method of the present invention has better corrosion resistance than that obtained with other cooling gases, or even better than when the cooling step is carried out using other methods It was announced. In particular, it is believed that when cooling is carried out in a gas containing nitrogen compared to cooling in an inert gas, it is believed that the nitrogen containing gas accelerates the formation of nitride, so that a more robust and flexible method is used, Lt; / RTI > Cooling in a nitrogen-free inert gas may also allow a cooling time longer than 60 seconds, but preferably cooling is carried out in a nitrogen-free inert gas for less than 30 seconds, for example less than 10 seconds.

A particular embodiment is a method of providing expanded austenite and / or expanded martensite formations in a cold formed product of a passive alloy. Thus, the method further comprises a subsequent second step of dissolving nitrogen and / or carbon in the workpiece at a temperature (T2) of at least 300 DEG C lower than the temperature at which the carbide and nitride are produced in the passive alloy.

The present invention relates to a process for the formation of expanded austenite and / or expanded martensite by solution curing of a cold-deformed workpiece of a passive alloy. / RTI > and / or a subsequent second step of dissolving carbon. The temperature T2 is lower than the temperature at which carbides and / or nitrides are formed in the passive alloy.

The first step of dissolving nitrogen in the workpiece at a temperature higher than the available temperature for the nitride significantly improves the core strength of the passive alloy, for example stainless steel, compared to recrystallization annealing of the material prior to cold hardening. The high temperature dissolution of nitrogen is carried out at a temperature above the austenitizing temperature of the alloy, for example at least 1050 ° C or above 1050 ° C, and below the melting point of the alloy. This reinforcing effect of high temperature nitrification is surprisingly sufficient to compensate for the loss of strength caused by the nullification of the cold deformation while the workpiece remains at high temperature during nitriding. Moreover, high temperature nitriding can be performed at a higher temperature than normal, without causing problems due to the formation of nitrides and / or carbides, and that low temperature hardening is more likely to activate the passive surface on the material in the subsequent low temperature surface hardening process It is easy to allow. Thus, the formation of the curing zone is accelerated. Moreover, improved corrosion properties are obtained, since nitrogen is present in the solid solution.

A significant improvement in the curing of the passive layer can be obtained by high temperature melting of nitrogen followed by low temperature nitriding, carburizing or nitrocarburising. Any passive alloy in which expanded austenite or expanded martensite can be formed relates to the present invention, and stainless steels, especially cold deformed austenitic stainless steels, are preferred.

Subsequent low-temperature dissolution of nitrogen and / or carbon, occurring at a temperature below the temperature at which the carbides and / or nitrides are formed in the passive alloy, for example at a temperature of less than 450 to 550 ° C depending on the process, Which does not include plastic deformation but has the same level of strength as the plastic 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 has been found to provide a lower temperature process than can be achieved using prior art methods because the diffusion coefficient of nitrogen and carbon is increased by the carbon / As well. Thus, in certain examples, the passive alloy is stainless steel containing nitrogen and / or carbon.

The present invention makes it possible to perform low temperature curing of passive materials, especially stainless steels, of even strongly cold deformed components without the occurrence of sensitization of the material and without loss of strength. The cold deformed material treated by the method of the present invention can even obtain significantly better corrosion resistance than untreated material. The tests carried out are typically carried out when the cold strain is removed by recrystallization while the temperature is maintained at a high temperature during the nitriding and the strength obtained by dissolving nitrogen and optionally carbon in the stainless steel at high temperatures above 1050 DEG C (Core) strength or substrate support capacity sufficient to compensate for the loss of strength. That is, although the strength obtained from low temperature deformation is lost, this loss is compensated by the strength obtained from solution curing with nitrogen and optionally carbon. Even a relatively small amount of nitrogen provides a sufficient increase in strength to provide the bearing capacity needed for abrasion-resistant expanded austenite.

The method of the present invention provides a manufactured member having at least the same strength and at the same time improved corrosion resistance as the cold deformed member and further provides the advantage of taking less time to perform.

Dissolution at temperature (T1) and at temperature (T2) can be performed using any suitable technique. For example, the dissolution at the temperature (T1) and the temperature (T2) can be carried out in a gas process using a gas containing, for example, nitrogen, for example ammonia, preferably N2. Dissolution can also be performed using ion implantation, salt bath or plasma. Dissolution at temperature T1 and temperature T2 is carried out using gas because this dissolution is an inexpensive and efficient solution and all types of geometries can be treated uniformly and good temperature uniformity desirable. Moreover, the use of a gas process means that the process is within the framework of the thermodynamic law, which means that there are very well controlled process conditions. Surprisingly, there is an additional advantage of using gases since it has been found that the high temperature process of the present invention makes it easier to activate the surface with gas in the low temperature process. This makes it easier to remove the impermeable oxide layer (passive layer) found on the passive material after high temperature dissolution. It is assumed that this is due to the presence of nitrogen and optionally carbon dissolved at high temperatures.

The low temperature process may be performed immediately after the high temperature process, but this is not mandatory. It is also possible to perform two processes by offset in time and place. If the process is carried out immediately after each other, for example by a cooling step between the first and second dissolving steps, it is possible to avoid the passivation of the surface from occurring, thus requiring no activation prior to the low temperature process . Accordingly, the present invention also relates to an example in which dissolution at temperature T2 occurs immediately after cooling from temperature T1 without passivation / activation of the surface in between the execution of the high temperature process and the low temperature process. This can be done in the same furnace. An associated gas containing nitrogen and / or carbon for use in a low temperature process when using gas can be supplied immediately when the material is cooled to temperature (T2). However, cooling is advantageously performed using argon without any nitrogen present during cooling. The advantage of using the gas treatment employed is that it is possible to use a gas which does not activate the surface at the temperature T2 in the low temperature process. Another advantage of this example is that the curing process can thereby be made cheaper and faster.

A further advantage of the process of the invention is that better corrosion properties are obtained, since nitrogen is present in the solid solution. Dissolution of carbon does not change the corrosion properties. If the component is fully saturated with nitrogen, the material may be considered to be a nitrogen-containing alloy. This is often the case for workpieces with thin walls which are processed by the method of the invention, for example with a material thickness of up to 4 mm, for example from 2 to 4 mm. Thus, the stainless steel workpieces processed by the method of the present invention have a much better manner than the workpieces processed by the low temperature process (see for example). Embodiments of the present invention relate to thin walled components or workpieces of cold deformed metal or alloy treated according to the method of the present invention.

For thin-walled components, the material may be sufficiently saturated with nitrogen by a high temperature process. A surface area of up to several millimeters, for example up to about 5 mm, can be obtained from thick materials of nitrogen-solubilized. In both cases the bearing capacity of the material will increase and is similar to what can be obtained by cold deformation. In the example of the present invention, the dissolution of nitrogen at a temperature (T1) is carried out by obtaining a diffusion depth in the range of 50 [mu] m to 5 mm, whereby the workpiece with a thickness of up to about 10 mm is sufficiently filled with nitrogen Allow to be saturated. In general, the method is characterized in that the thickness of the expanded austenite or expanded martensite of at least 5 [mu] m is obtained in the workpiece and the hardness of the expanded austenite zone or expanded martensite zone is at least 1000 HV, Or more.

The method further comprises an intermediate step of cooling the workpiece to a temperature below the temperature at which the carbide and / or nitride is formed into a passive alloy after the dissolving step at a temperature (T1), wherein in the specific example of the invention, Dissolution occurs immediately after cooling from dissolution at temperature T1 without occurrence of surface passivation. In certain examples, cooling after the first melting step at temperature T1 is particularly rapid, for example in the period of less than 60 seconds, the greatest tendency is to sensitize the alloys concerned and to form precipitates such as nitrides and / or carbides Occurs in the temperature range. In the case of stainless steels, this is known to occur, in particular, in the 900 to 700 ° C range where the material must be cooled rapidly. In one embodiment, the workpiece is cooled from 900 占 폚 to 700 占 폚 in less than 60 seconds. In a preferred embodiment, the workpiece is cooled from 900 DEG C to 700 DEG C in less than 30 seconds. Thereby, the formation of carbides and / or nitrides is substantially avoided, which is useful because they can react with alloy elements in stainless steel, for example chromium. As the nitride and / or carbide, the depletion of the alloying elements from their bonding and solid solution is suppressed and the corrosion-resistant properties are maintained.

Generally, the configurations of the present invention are freely combinable, and all such combinations are contemplated by the present invention. By way of example, the features and variations discussed in the first melting step at temperature T1 apply even when including the melting process at temperature T2. Likewise, all the functions discussed for the subsequent step of dissolving nitrogen and / or carbon in the workpiece at the temperature T2, which is lower than the temperature at which the passive alloy is formed to form carbides and / or nitrides, and the first dissolving process and the inert gas It is suitable for any combination of cooling functions.

In another aspect, the invention relates to a solution cured member by the method of the first aspect or the above-mentioned further aspect. Although it is desirable for the workpiece to have a thickness of up to about 10 mm, any workpiece can be treated in this manner, as this will provide sufficient saturation of the resulting element with nitrogen. The solution-cured member according to the method of the first aspect or the further aspect can be used in any technical field. Particularly relevant fields are those for use in the technical fields of medicine, food, automotive, chemical, petrochemical, pharmaceutical, marine, packaging, watches, cutlery / tableware, medicine, energy, pulp & paper, mining, Member. Particularly important members are valves (diaphragm valves, ball valves, control valves), steering bolts, nuts, washers, fasteners, nozzles, pumps, mechanical components, semiconductor ASML, ferrule parts, ball bearings and bearing gauges , Pneumatic components, membranes, and the like.

In a further aspect, the invention relates to a solution cured member by a method according to the first aspect or a further aspect, wherein said member is a valve part or a part used in a valve.

In a further aspect the present invention relates to a solution cured member by a method according to the first aspect or a further aspect wherein the member is selected from the group consisting of an outer surface area of the object of design such as a clip for fixing the paper or note, A holder of a box, a cover of a box, a cutlery, a watch, or a plate-formed part of a plate or lamp mounted with a handle.

In a further aspect, the invention relates to a solution cured member by a method according to the first or further aspect, wherein the member is part of a bearing, for example a part of a ball bearing, a part of a roller bearing, to be.

In a further aspect, the invention relates to a solution cured member by a method according to the first aspect or a further aspect, wherein the member is a part of a medical device, or a medical device, or a dental device, a dental device, Mechanism.

In a further aspect the present invention relates to a solution cured member by the method according to the first aspect or a further aspect wherein the member is a part of a pharmaceutical equipment, such as a plate, nozzle, shim, It is a grid.

In a further aspect, the invention relates to a solution cured member by a method according to the first aspect or a further aspect, wherein the member is part of a vehicle, for example a plate, a part in an exhaust system, a filter part, A fixture, a handle, and a decorative surface.

Figure 1 shows isothermal transformation (TTT plots) for nitrogen-containing austenitic stainless steels.
Figure 2a shows a set of lock washers.
Figure 2b shows a set of lock washers with bolts and nuts.
Figure 3 shows a microscope photograph of a lock washer (left) treated with a prior art method and a lock washer (right) treated by the method of the present invention.
Figure 4 shows a microscope photograph of a lock washer (left) treated with a prior art method and a lock washer (right) treated by the method of the present invention.
Figure 5 shows a micrograph of a sample of AISI 316 processed by the prior art method (left) and the inventive method (right).
Figure 6 shows a micrograph of a sample of AISI 304 processed by the prior art method (left) and the inventive method (right).
Figure 7 shows the hardening profile of the stainless steel treated by the prior art method and the method of the present invention.
Figure 8 shows the lock washers processed in two different embodiments of the method of the present invention.
Figure 9 shows a micrograph of a sample of AISI 316 treated by the prior art method (right) and the inventive method (left).

Justice

The terms "expanded austenite" and "expanded martensite " in the context of the present invention describe austenite or martensite supersaturated by nitrogen or carbon or nitrogen and carbon respectively (for nitride or carbide formation) do. The expanded austenite and the expanded martensite may be specified as nitrogen-swellable or carbon-swellable, or the swell may be specified as nitrogen- and carbon-swellable. However, in the context of the present invention, the terms "expanded austenite" and "expanded martensite" refer generally to austenite or martensite expanded in any combination of nitrogen, carbon or nitrogen and carbon, respectively . A review of expanded austenite is presented in T. El. TL Christiansen and M.A.J. (MAJ Somers (2009, Int. J. Mat. Res., 100: 1361-1377), the contents of which are incorporated herein by reference. Any alloy capable of forming "expanded austenite" or "expanded martensite" is contemplated for the process of the present invention. Expanded austenite or expanded martensite may be formed on the surface of the alloy when the alloy is subjected to a solution of nitrogen or carbon, or nitrogen and carbon, and the expanded austenite or expanded martensite may also be an expanded austenite or Quot; zone "of the expanded martensite. The term "zone" in the context of the present invention should be understood to relate to the thickness of the treated material, and "zone " is similar to the thickness of the expanded austenite or expanded martensite. The method of the present invention may result in at least 5 占 퐉 of expanded austenite or expanded martensite in the workpiece and the thickness of the expanded austenite or expanded martensite may be up to about 50 占 퐉 or more.

According to the present invention, "alloy element" can refer to a metal component or element, or any component, in an alloy upon analysis of the alloy. In particular, in the process of the present invention, the relevant alloys comprise elements which are capable of forming nitrides and / or carbides by the presence of nitrogen and carbon, respectively. The method of the present invention advantageously provides a nitride and carbide free surface of the alloy element. However, it is also contemplated in the present invention that the alloy may comprise a single metal element that can only form nitrides and / or carbides. The alloy may also include other elements, such as semi-metallic elements, intermetallic elements, or non-metallic elements. Alloying elements capable of forming nitrides and / or carbides can be metal elements, which typically provide corrosion resistance to the alloy by the formation of a passive oxide layer with alloy elements. The terms "nitride" and "carbide ", as used in the context of the present invention, refer to nitrides and carbides formed between the alloying elements and nitrogen and carbon, respectively. Although the terms "nitride" and "carbide" are not limited to nitride and carbide with chromium, exemplary nitrides are chromium nitride, CrN or Cr2N.

The term "passive" in the context of alloys or metals should be understood as alloys having an oxide layer on the surface. The alloy may be passivated by itself or passivated as a result of the process in which the alloy is treated. Belonging to the group of self-passivating alloys are those having a strong affinity for oxygen (e.g., Cr, Ti, V) and such alloying elements (e.g., iron containing essentially at least 10.5% Cr - < / RTI > stainless steel as a base alloy).

The term "cold deformation" (also referred to as "cold working") should be understood as a plastic deformation that is induced in the material by an external force at a temperature below the recrystallization temperature of the material. The cold deformation can be provided by an actual plastic shape change such as forging, extrusion, molding, drawing, pressing, or rolling, and also machining, for example turning, milling, punching, Grinding or polishing, or the like, or by a combination of these processes.

The term "sensitization" refers to the formation of nitrides and carbides, respectively, by reaction of nitrogen or carbon with one or more alloying elements, otherwise utilized as chromium in stainless steel to form a protective oxide layer on the surface . When sensitization occurs, the free constituents of the alloying elements, such as chromium, in the solid solution are lowered to a level no longer sufficient to maintain a complete protective oxide layer, which means that the corrosion properties are degraded.

The term "available temperature for carbides and / or nitrides" should be understood as the temperature at which the nitride / carbide is not stable and the already formed nitride / carbide is dissolved. Generally, an alloy comprising a metal alloy element capable of forming nitride and / or carbide will have a temperature interval at which nitride and / or carbide can form when nitrogen and carbon are present, respectively. Therefore, beyond this temperature interval, nitride and carbide will not be formed and the already formed nitride / carbide will dissolve. When a nitride or carbide is present, i. E. When sensitization occurs, this carbide can generally only be removed by exposing the sensitized metal to an overtemperature of the austenitizing temperature. Moreover, although such nitrides or carbides already formed in the alloy may not be removed at low temperatures, such alloys have temperatures below the temperature range during which nitride and carbide are not formed.

The "austenitizing temperature" is typically the temperature used when the alloy is heat treated to dissolve the carbide, and the "austenitizing temperature" may accordingly correspond to the "available temperature for the carbide ". At the austenitizing temperature the alloy is an austenite phase. The temperature at which the steel alloy changes from ferrite to austenite is typically a temperature somewhat lower than the austenitizing temperature.

Temperatures at which carbides and / or nitrides as well as austenitizing temperatures are formed in passive alloys are generally well known to those skilled in the art. Likewise, temperatures below which no nitride or carbide is formed are generally known to those skilled in the art. Moreover, the melting temperatures of the alloys are generally known to those skilled in the art. The temperature can depend on the composition of the passive alloy and for any given composition such temperature is more easily determined experimentally by those skilled in the art.

The stated alloy content is expressed in weight percents. With regard to the composition of the alloy or gas, inevitable impurities may also naturally exist, even if this is not specifically mentioned.

Further description of the invention

FIG. 1 shows an example of an isothermal transformation curve (TTT diagram) for nitrogen-containing austenitic stainless steels, and the stainless steel has the composition Fe-19Cr-5Mn-5Ni-3Mo-0.024C-0.69N (J. W. Simmons, Ph.D., Oregon Graduate Institute of Science and Technology, 1993). In Fig. 1, the temperature range at which nitrogen starts to be formed is denoted by "Cr2N ". In the method of the present invention, the step of dissolving nitrogen in the passive alloy is thus carried out at a temperature (T1) above the austenitizing temperature and the second step of dissolving nitrogen and / or carbon is to form a nitride and / (T2) which is less than the predetermined temperature range. The temperature T1 is therefore higher than the temperature T2. It is preferred that the workpiece is cooled to a temperature below the temperature at which the carbide and / or nitride is formed in the passive alloy after the first dissolving step at a temperature (T1) within a time interval of, for example, 60 seconds. The passive alloy of the workpiece will thus be stabilized against the formation of nitrides and / or carbides, and the second dissolving step can then be carried out as desired. The austenitization temperature may also be referred to as "high" temperature in the context of the present invention. In addition, 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 comprises dissolving nitrogen and / or carbon in the passive layer. The step of dissolving nitrogen may also be referred to as "dissolving nitrogen" or "nitriding ", and likewise the carbon dissolving step may be referred to as" dissolving carbon " When both nitrogen and carbon are dissolved in the same process step, they can be referred to as "softening."

In certain embodiments, the invention relates to a member that is solution cured by the method of the present invention. "Treated" in the context of the present invention should be understood broadly. In particular, the term "treated" means that the method of the present invention is utilized in the manufacture of a member. Accordingly, the present invention also relates to members made using the method of the present invention, and the terms " treated in "and" manufactured using "are used interchangeably. The method of the present invention may be the last step in the manufacture of the member, or the member processed by the method may also undergo further processing steps to provide a final member.

In the context of the present invention the "thin wall component" is a component of a size that allows the component to be sufficiently saturated with nitrogen and / or carbon in the process of the present invention. Thus, a "wall-thinned component" may be a layer of the smallest dimension, including, for example, up to about 10 mm and about 10 mm, for example, a thickness in the range of about 2 mm to about 4 mm, A thickness ranging from 0.4 mm to 6 mm, a thickness ranging from 0.5 mm to 5 mm, or a thickness ranging from 1.5 mm to 4.5 mm. The method can be used with any thin-walled component.

A novel and unique way in which one or more of the above objects is accomplished is by providing a method for the formation of expanded austenite and / or expanded martensite by solution curing of a cold-deformable workpiece of a passive alloy,

A method for solution curing of a cold formed product of a passive alloy containing at least 10% of chromium, characterized in that it comprises the steps of: (a) heating at a temperature (T1) above the melting temperature of the passive alloy, A first step of dissolving at least nitrogen in the workpiece, and

Wherein the nitriding dissolution at temperature (T1) is performed to obtain a diffusion depth in the range of 50 [mu] m to 5 mm -

Cooling the workpiece at a temperature below the temperature of the nitride and / or carbide formed in the passive alloy after the dissolving step at the temperature (T1)

- the cooling step is carried out in an inert atmosphere which does not contain nitrogen -

Lt; / RTI >

And a subsequent second step of dissolving nitrogen and / or carbon in the workpiece at a temperature (T2) of at least 300 DEG C lower than the temperature at which carbide and nitride are produced in the passive alloy.

The invention is particularly suited to stainless steels and similar alloys, wherein expanded austenite or martensite can be obtained in a low temperature melting process. In general, iron, nickel and / or cobalt based alloys comprising chromium are involved in the process. The chromium content can be varied and can, for example, be up to about 10%. In another example, the chromium content may be about 10% or at least 10%. Thus, in one example, the invention relates to a method for solution curing of a cold deformable workpiece of stainless steel. Nitrogen and optionally also carbon can be dissolved in the stainless steel at a temperature higher than the austenitizing temperature of the stainless steel, for example, the temperature of the carbides and / or nitrides to existing alloying elements such as chromium. Even a relatively small amount of nitrogen provides a significant increase in strength to provide the load bearing capacity needed for abrasion-resistant expanded austenite. In one embodiment of the present invention, the hardness of the expanded austenite zone or the expanded martensite zone is at least 1000 HV.

In one example of the present invention, the stainless steel is an austenitic steel. These materials are relatively soft compared to martensitic stainless steels, for example. Thus, it is particularly useful for these materials that nitrogen and optionally carbon are dissolved in a high temperature process. Thereby, austenitic steels receive sufficient core strength to compensate for the loss of strength that occurs when cold deformation is negated, and then nitride and / or carbides at low temperature, without the problem of precipitation, such as nitride and / Whereby it becomes possible to dissolve the carbide. In a further example of the present 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 ferritic-austenitic stainless steel , Ferritic-austenitic stainless steels may also be referred to as dual stainless steels.

The content of nitrogen and optionally carbon dissolved in the high temperature process in stainless steel may typically be less than 1% by weight, but may be higher if desired. This can be achieved, for example, by applying a higher nitrogen and optionally carbon activity in the form of a higher partial pressure of N2 in the gas process, for example. The content of nitrogen and / or carbon obtained in stainless steel at low temperature dissolution may be as high as 14% by weight and 6% by weight respectively.

In a preferred embodiment, the dissolution of nitrogen and / or carbon above is generated at a temperature (T1) using a nitrogen and optionally a carbon containing gas, but may also be performed by ion implantation, plasma aiding or bathing. In a preferred example, a nitrogen-containing gas, such as N2, is used. The pressure of the gas may be several bars, but the pressure of the gas may also be less than 1 bar, for example 0.1 bar. There is an advantage of using gas because all geometric configurations are uniformly processed and good temperature uniformity.

In the example of the present invention, the dissolution is carried out at a temperature (T1) and a temperature (T2) using a gas. The gas contains nitrogen and / or carbon. In certain instances, the dissolution at temperature T2 is performed in a process selected from the group comprising gas-based processes, ion implantation, salt baths, or plasma.

In the present example, a diffusion depth of 50 [mu] m to 5 mm is obtained by dissolving nitrogen and optionally carbon at temperature T1. This provides both a reinforcing and hard surface of the core of the material. This makes it possible to obtain a complete cure of thin walled components with a material thickness of up to about twice the depth of diffusion or up to about twice the depth of the diffusion since dissolution typically occurs from both sides of the workpiece. For thicker components, a relatively thick surface area is obtained in which nitrogen and optionally carbon are in solid solution. This provides a support for the expanded austenite layer formed on the surface in a subsequent low temperature process. In the case of thin-walled workpieces, complete nitrification / carburization / softening of the workpiece can be obtained accordingly. Although this is not completely achieved, the dissolution will have a considerable advantage, especially for thin-walled workpieces, where stringent requirements for corrosion resistance and for bearing capacity are involved, which is a considerable improvement in the method of the present invention .

In an example of the present invention, the temperature T1 may be greater than 1000 degrees Celsius, such as at least 1050 degrees Celsius, or the temperature T1 may be at least 1100 degrees Celsius, such as 1120 degrees Celsius or 1160 degrees Celsius, at least 1200 degrees Celsius or at least 1250 degrees Celsius . The upper limit for temperature is below the melting point of the treated material. In the case of stainless steel, the melting point is about 1600 ° C. In the present example, the temperature T1 is less than 1600 占 폚, for example less than 1500 占 폚, or less than 1400 占 폚, for example less than 1350 占 폚. In the present example, the temperature T1 is in the range of 1050 占 폚 and 1300 占 폚, for example, about 1150 占 폚. It is important that the temperature is potentially higher than the available temperature for the associated carbides and / or nitrides that can be formed in the material but can be formed below the melting point of the treated material. The temperature used when the gas is used for dissolution at temperature (T1) can be selected in consideration of the gas mixture and the applied gas pressure.

In another example of the present invention, the carbon is dissolved at a temperature (T2), and the temperature (T2) is less than 550 占 폚, preferably 300 to 530 占 폚, during carburization.

In another example of the present invention, nitrogen is dissolved at a temperature (T2) and the temperature (T2) is less than 500 占 폚 during nitriding, for example, less than 470 占 폚, preferably 300 to 470 占 폚.

In another example of the invention, nitrogen and carbon are dissolved at a temperature (T2) and the temperature (T2) is less than 500 占 폚 during softening, e.g., less than 470 占 폚, preferably between 300 and 470 占 폚.

In the present example, the high temperature dissolution is carried out for at least 20 minutes, for example 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 5 hours, or at least 10 hours, or at least 15 hours. In principle, there is no time limit because no nitride or carbide is formed at temperature T1. In the extended treatment, the material may be saturated with nitrogen and optionally carbon, depending on its thickness, i.e. it may be completely nitrided or softened.

In an example of the present invention, the method includes an intermediate step of cooling the workpiece after the dissolving step at temperature (T1) to a temperature below the temperature at which the carbide and / or nitride is formed in the passive alloy, Lt; / RTI > to < RTI ID = 0.0 > ambient temperature. It is particularly preferred that the second dissolving step at temperature (T2) is carried out immediately after the cooling step, which will avoid the passivation of the workpiece, i. E. The formation of an oxide layer. In the present example, cooling is generated in the gas which is cooled by the same gas as the solution, for example under high pressure, for example by N2 in the range of 6 and 10 bar, for example 7 bar or 8 bar or 9 bar. The cooling may be performed using an inert gas containing no nitrogen such as rare gas such as He, Ne, Argon, Krypton, Xe or Radn, Or any mixture thereof, and argon is particularly preferred. In another example, cooling occurs in argon at a high pressure, for example in the range of 4 to 20 bar, for example in the range of 6 and 10 bar, e.g. 7 bar or 8 bar, or 9 bar.

The present invention relates to a stainless steel lock washer (see Figs. 2A and 2B) for fixing bolts and nuts, which is melt-cured using the method of the present invention. The lock washers are relatively thin in wall, so that a significant and necessary improvement in both strength and corrosion resistance of the lock washers is achieved by curing the lock washers using the method of the present invention. In one embodiment of the present invention, the lockwasher has a first side with a radially toothed portion and a facing opposite side with a cam, cam side. The lock washers are used as pairs mounted by cams against each other to obtain a key lock effect. Lock washers are particularly suited for effectively securing bolt assemblies that are exposed to corrosive environments such as extreme vibration or dynamic loads and salt water. There is therefore a strict requirement for the strength and corrosion resistance of such a washer.

The invention is particularly suited to stainless steels and similar alloys, wherein expanded austenite or martensite can be obtained in a low temperature melting process. However, the present invention is a high temperature melting process with nitrogen and optionally carbon in a passive alloy, such as an iron based alloy, a cobalt based alloy, a nickel based alloy, or a chromium based alloy, in a substantially comprehensive manner, Providing an improved low temperature melting process for strength.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention.

Conventional Example  One

Curing of key lock washers of cold deformed austenitic stainless steel, AISI 316, by prior art methods and by the method of the present invention.

Two identical key lock washers of cold deformed austenitic stainless steel AISI 316L were cured. Fig. 2 shows the key lock washer set 1 of the key lock washer 2 and illustrates their use. Each washer 2 has a first side 3 with a radial tooth 4 and another facing cam side 5 with a cam 6. During use of the key lock washer set 1, the washer 2 is disposed as shown by the cam side portions 5 facing each other. The two key lock washers were solution cured by nitrogen and carbon at a temperature of 440 ° C. One washer was cured by the method of PA 2011 70208, i.e. it was cured in a high temperature process and subsequently in a low temperature process, and the other washer was surface hardened directly, for example by the same low temperature process of the prior art. The washer was analyzed by an optical microscope. Figures 3 and 4 show the washer in the left panel, which was only surface hardened with the softening process performed with gas containing nitrogen and carbon at a temperature of 440 캜 for 16 hours at atmospheric pressure. In the nitrogen containing zone, the outer surface appears to be partially sensitized (chromium nitride precipitation). The deformed substrate appears to be strongly deformed and is definitely affected by the etching liquid used to generate the microstructure. Fig. 4 is an enlarged view of Fig.

Figures 3 and 4 show the washers processed by the method of PA 2011 70208 in the right panel. The washer was exposed to a nitrogen-containing atmosphere (N2 gas) at temperatures above 1050 DEG C and subsequently rapidly cooled in the same gas. Whereby the material was completely austenitized and the material was completely saturated with nitrogen. The washer was then surface hardened by a softening process carried out with a gas containing nitrogen and carbon at a temperature of 440 DEG C for 16 hours at atmospheric pressure, whereby the expanded austenite was subjected to a zone having a thickness of at least 5 mu m Lt; / RTI > The softened nitrogen-containing zone was not sensitized and the substrate was not cold-deformed reliably. However, the substrate hardness (260-300 HV0.5) and the surface hardness (1200-1400 HV0.005) are actually the same in the two washers. The corrosion resistance of the washers (exposure time (ISO 9227) in salt spray chambers) using the method of PA 2011 70208 is several times better than the corrosion resistance of only the surface hardened washers (time within the chamber until corrosion is observed). The washer treated by the method of PA 2011 70208 showed no corrosion after 400 hours, whereas the washer which had been directly cold-cured showed clear visible corrosion already after 20 hours.

Conventional Example  2

Curing of cold-deformed austenitic stainless steel, AISI 316, by the method of the prior art and the method of PA 2011 70208.

Two identical components (back ferrule) of cold-deformed austenitic stainless steel AISI 316 were solution cured with nitrogen and carbon at a temperature of 440 ° C. One component was cured by the method of PA 2011 70208, that is, in the high temperature process and subsequently in the low temperature process, and the other components were surface hardened directly by the same low temperature process. Figure 5 shows the microstructure analyzed by the optical microscope of the components in the left panel, which shows that the microstructure was only produced by the softening process carried out using a gas containing nitrogen and carbon at a temperature of 440 [deg.] C for 12 hours Surface hardening. The outer surface in the nitrogen containing zone appears to be partially sensitized by reliable deposition of CrN at the outermost surface. Figure 5 shows the components processed by the method of PA 2011 70208 in the right panel. The components were exposed to a nitrogen-containing atmosphere (N2 gas) at a temperature above 1050 DEG C and subsequently rapidly cooled in the same gas. The component surfaces were then cured by a softening process in a low temperature process carried out using a gas containing nitrogen and carbon at a temperature of 440 DEG C for 12 hours. The softened nitrogen containing zone was not sensitized. However, the substrate hardness (260-300 HV0.5) and the surface hardness (1200-1400 HV0.005) are actually the same in the two components. The total layer thickness of the expanded austenite zone is about 20 占 퐉 in both cases. The outermost layer is nitrogen expanded austenite and the innermost layer is carbon expanded austenite. Corrosion resistance for both components was tested in 14 wt% sodium hypochlorite solution. The components treated by the method of the present invention did not show any corrosion after 24 hours, whereas the components that had been directly cold cured showed definite corrosion only after 10 minutes. The components used in the method of PA 2011 70208 are therefore different in that they have considerably improved corrosion resistance than the directly softened workpiece.

Conventional Example  3

Curing of cold-deformed austenitic stainless steel AISI 304 plates by the method of the prior art and the method of PA 2011 70208.

Two identical components of the cold rolled (modified) austenitic stainless steel plate, AISI 304, were solution cured by nitrogen and carbon at a temperature of 440 ° C. One component was cured by the method of PA 2011 70208, i.e. in the high temperature process and subsequently in the low temperature process, and the other components were surface hardened directly by the same low temperature process. 6 was just surface hardened by the softening process performed with nitrogen and carbon containing gas at a temperature of 440 DEG C for 20 hours in the left panel and subsequently exposed to 1 wt% sodium hypochlorite for 70 minutes . Figure 6 shows the components cured by the method of PA 2011 70208 in the right panel. The components were exposed to a nitrogen-containing atmosphere (N2 gas) at a temperature of 1150 DEG C for 30 minutes and subsequently rapidly cooled in the same gas. The components were then surface hardened by a softening process performed with nitrogen and carbon containing gas at a temperature of 440 DEG C for 20 hours. Finally, the components were exposed to the corrosion test by exposure to a 14 wt% sodium hypochlorite solution. The surface appears to be unaffected by the corrosion test even after 16 hours of exposure. In direct low temperature cured parts a clear corrosion attack is shown after a short exposure / corrosion test (70 minutes). The components in which the method of PA 2011 70208 is used are therefore different in that they have a much better corrosion resistance.

Example  One

The hardness profile of the cold-deformed stainless steel treated by the method of the present invention and by the methods of the prior art.

Two identical components of a cold-deformed austenitic stainless steel were treated according to the methods of the prior art and the present invention. The sample was exposed to a nitrogen containing atmosphere (N2 gas) at a temperature greater than 1050 DEG C or to an atmosphere of hydrogen (H2) and subsequently rapidly cooled in argon (N2-treated sample) or H2 gas. The component surfaces were then cured by softening in a low temperature process carried out using a gas containing nitrogen and carbon at a temperature of 440 DEG C for 12 hours. The softening zone was not sensitized. The hardness profile of the samples was analyzed and the results are shown in FIG. It is evident that the sample treated at high temperature in a nitrogen-containing atmosphere ("EXPANITE ON HTSN ") retained the core strength of the material while the core strength was extinguished at high temperature annealing (" EXPANITE ON ANNEALED "

Example  2

The argon cooling followed by curing the hot solution by nitrogen.

The cold washer stainless steel AISI 316L lock washer as described in prior art example 1 and illustrated in figure 2 is heated to a temperature above 1050 DEG C before rapidly cooling to ambient temperature in the same atmosphere or in an atmosphere of argon And exposed to a nitrogen-containing atmosphere (N2 gas). The sample was not subjected to further surface hardening. The corrosion resistance of the components was tested in a 14 wt% sodium hypochlorite solution. Figure 8 shows three exemplary lock washers (left) cooled in argon and three lock washers cooled in nitrogen (right). Argon cooled lock washers have much better corrosion resistance than nitrogen cooled lock washers that show clear signs of corrosion.

Example  3

Austenitic stainless steels cold-deformed by the methods of the prior art and of the present invention, AISI 316, curing of the components.

The corrosion resistance of the cold-deformed austenitic stainless steel AISI 316 treated according to the present invention was compared to similar components treated with prior art processes. The corrosion test was carried out by dipping two surface hardened components into 14 wt% sodium hypochlorite for 18 hours.

Figure 9 shows components processed in the left panel according to the present invention, i.e., in a high temperature process and subsequently in a low temperature process, and the other components were surface hardened directly in the right panel only by a low temperature process.

The surface of the treated component according to the present invention appears to be unaffected by the corrosion test even after 18 hours of exposure. In the components that had been treated according to the prior art, the corrosion attack was observed after a short-term exposure (7 minutes). The components in which the method of the present invention is used are therefore different in that they have significantly improved corrosion resistance.

Claims (21)

A method for solution curing of a cold-formed workpiece of a passive alloy containing at least 10% chromium,
A first step of dissolving at least nitrogen in said workpiece at a temperature (T1) which is higher than an available temperature for carbide and / or nitride and lower than the melting point of said passive alloy, and
Wherein the nitriding dissolution at temperature (T1) is performed to obtain a diffusion depth in the range of 50 [mu] m to 5 mm -

Cooling the workpiece at a temperature below the temperature of the nitride and / or carbide formed in the passive alloy after the dissolving step at the temperature (T1)
- the cooling step is carried out in an inert atmosphere which does not contain nitrogen -
/ RTI >
The method according to claim 1,
And a subsequent second step of dissolving nitrogen and / or carbon in said workpiece at a temperature (T2) of at least 300 DEG C lower than the temperature at which carbide and nitride are produced in the passive alloy.
3. The method according to claim 1 or 2,
Wherein the inert gas is selected from He, Ne, Argon, Krypton, Xe, or Radn, or mixtures thereof.
The method according to any one of claims 1 to 3,
Wherein the inert gas is argon except for unavoidable impurities.
5. The method according to any one of claims 1 to 4,
Nitrogen and carbon are dissolved at a temperature (T1).
6. The method according to any one of claims 1 to 5,
Wherein said passive alloy is selected from the group consisting of stainless steel, austenitic stainless steel, martensitic stainless steel, ferritic stainless steel, precipitation hardenable (PH) stainless steel or ferritic-austenitic stainless steel.
The method of any one of the preceding claims,
Wherein the dissolution at temperature (T1) is carried out using a nitrogen-containing gas, preferably N2.
8. The method according to any one of claims 2 to 7,
Wherein the dissolution at temperature (T2) is carried out in a process selected from the group comprising gas-based processes, ion implantation, salt bath or plasma.
The method of any one of the preceding claims,
Wherein the dissolution at a temperature (T1) and a temperature (T2) is carried out using a gas.
The method of any one of the preceding claims,
Wherein the temperature (T1) is in a range of at least 1050 ° C, for example, 1050 ° C to 1300 ° C.
The method of any one of the preceding claims,
Wherein cooling from a temperature of 900 [deg.] C to 700 [deg.] C is performed for less than 60 seconds.
The method according to any one of claims 2 to 11,
Wherein the carbon is dissolved at a temperature (T2) and the temperature (T2) is less than 550 占 폚, preferably 300 to 530 占 폚.
12. The method according to any one of claims 2 to 11,
Wherein the nitrogen is dissolved at a temperature (T2) and the temperature (T2) is less than 500 占 폚, preferably 300 to 470 占 폚.
12. The method according to any one of claims 2 to 11,
Nitrogen and carbon are dissolved at a temperature (T2), and the temperature (T2) is less than 500 DEG C and preferably in the range of 300 to 470 DEG C.
15. The method according to any one of claims 2 to 14,
Wherein a thickness of expanded austenite or expanded martensite of at least 5 占 퐉 is obtained in said workpiece.
16. The method according to any one of claims 2 to 15,
Wherein the expanded austenite zone or the expanded martensite zone has a hardness of at least 1000 HV.
17. The method according to any one of claims 2 to 16,
The dissolution at temperature (T2) occurs immediately after cooling from dissolution at temperature (T1) without the occurrence of passivation of the surface, preferably dissolution at temperature (T2) occurs in the same furnace as dissolution at temperature , Way.
A member cured by a solution according to any one of claims 1 to 17.
19. The method of claim 18,
Wherein the workpiece has a thickness of up to about 10 mm.
20. The method according to claim 18 or 19,
Said member being a lock washer of a stainless steel for securing a fixing part, for example a bolt and / or a nut.
21. The method of claim 20,
Wherein the lock washer has a first side with a radially-inlaid portion and an opposite side with a cam.

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