JPH09310132A - Manufacture of extremely hard metallic material and its use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacture of an extremely hard, wear resistant metallic material having, even if the metallic material contains cobalt alone as residual element, characteristics comparable with those of cobalt alloy with respect to wear resistance and corrosion particularly in a nuclear environment and further capable of having wear resistance superior to that of cobalt alloy.

SOLUTION: A powder of metal alloy essentially containing, as element, at least one kind among iron, nickel, and chromium is subjected to hot isostatic pressing. At this time, the pressure, temp., and time of the isostatic pressing treatment are specified, respectively, in order to obtain a uniform and isotropic fine-grained material materially free from cracks and defects in volume.

COPYRIGHT: (C)1997,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for the production of very hard and wear-resistant metallic materials and the application of this method, in particular the coating and production of components which are rubbed during use, such as valve seats and sealing members. Regarding More particularly, the invention is used in structures for nuclear power plants and for obtaining coatings of wear-resistant alloys or parts made therefrom which must contain as little cobalt as possible.

[0002]

In nuclear power plants, parts that are highly stressed with respect to rubbing, such as valve seats or sealing members, pump parts for circulating liquids in the nuclear power station, latch arms or cores of control rod drive mechanisms. A support key located inside the reactor vessel is used. These parts may be made from materials such as stainless steel coated with an abrasion resistant coating, or may be made from the abrasion resistant material in bulk form. TIG
Producing wear resistant coatings on rubbing parts by melting and depositing the coating metal using the (tungsten inert gas) welding method, the TAP (transfer-arc plasma) method or by using a torch. It has been known. It is known to use cobalt-based alloys such as stellite to produce wear resistant coatings using one of the deposition methods described above. When cobalt-based alloy coatings are produced on rubbing components used in nuclear power plants, these coated components tend to release cobalt under the action of wear and corrosion, which causes the cobalt to come into contact with the rubbing component parts. It can be entrained by a liquid, such as a reactor refrigerant. The cobalt entrained by the reactor refrigerant passes through the reactor core, where it is activated. Cobalt then became one of the most important radioactive elements present in nuclear power plants, and as a result,
This cobalt is the major source of dose rate to which workers are exposed when performing repair or maintenance operations during nuclear reactor outages.

Therefore, it is very important to reduce or even eliminate the cobalt-based alloys used in nuclear power plants for the purpose of reducing the dose received by the nuclear power plant manager. Therefore, it has been proposed to use an alloy based on nickel or iron and containing chromium to replace the wear resistant cobalt alloy.
French patent application 2,405,306 discloses, for example, nickel-based alloys containing only cobalt as a residual element, which under certain conditions
It may have a hardness comparable to that of cobalt alloys such as No. 6. Such nickel alloys are especially suitable for TIG or TAP
It can be used in the form of powders, welding sticks or coated or flux cored wires for producing coatings using the method. However, French patent application No.
It has been found that the coatings obtained by these methods using nickel-based alloy No. 2,405,306 do not have wear resistance properties comparable to those of cobalt alloys. This also applies to bulk parts obtained by melting and shaping the alloy in an induction furnace. Generally, when they are used in the form of coatings obtained by methods such as the TAP method, in particular known nickel alloys containing chromium as the alloying element (the composition of the nickel alloy is adjusted to obtain high hardness). Does not have wear resistance properties comparable to those of cobalt alloys such as stellite. In particular, iron-based alloys containing chromium as an alloying element (the composition of which is adjusted to obtain high hardness) are difficult to use, and moreover they are used in environments such as the main refrigerant circuit of a pressurized water nuclear reactor. It generally has poor corrosion resistance when used as a substrate or coating to make the parts used.
Also, when it is possible to use cobalt alloys as wear resistant materials, it may be desirable to increase the hardness and wear resistance of these alloys.

[0004]

Therefore, it is an object of the present invention to determine the properties of cobalt alloys with respect to wear resistance and corrosion, especially in a nuclear environment, even if the metallic material contains only cobalt as a residual element. The object is to propose a method for the production of very hard and wear-resistant metallic materials which have comparable properties and which can also have wear resistance properties superior to cobalt alloys.

[0005]

For this purpose, a powder of a metal alloy mainly containing the elements iron and nickel and at least one of chromium is subjected to high temperature isostatic pressing, the pressure, temperature and A time period is specified to obtain a uniform and isotropic particulate material that is substantially free of cracks and defects in volume.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The method of the present invention may be used, inter alia, to produce wear resistant coatings on parts such as stainless steel parts. In order to clearly understand the present invention, some of the methods of the present invention are used with reference to the drawings, in particular for producing abrasion resistant coatings on rubbing components used in nuclear power plants. A non-limiting example description of an embodiment of To carry out the process according to the invention and according to a preferred embodiment, powders of alloys containing mainly iron or nickel, as well as chromium, are used. The composition of the iron and / or nickel and chromium alloys can vary depending on the hardness properties and, in particular, the high temperature hardness properties desired for the product made from the alloy powder. In all cases, the powders are produced, for example, by atomization in a jet of an inert gas of an alloy produced in liquid form in a furnace. The properties of the metal powder can be adjusted by adjusting the parameters for atomization.
It can also be obtained by sieving.

The method consists of subjecting the metal powder to a high temperature isostatic press. Such hot isostatic pressing takes place in a furnace, in which the powder is subjected to high temperatures and very high pressure in contact with an inert gas such as argon. The powder is isostatically pressed in a deformable mold that is inserted into an isostatic pressing chamber in the furnace. For the manufacture of bulk parts using the method of the invention, the mold is completely filled with metal powder. In the case of the production of coatings on parts, the powder is contained in the space between the part to be coated and the mold. in this case,
It is known to pre-treat the surface of the part to be coated in order to promote the bonding of deposits on the part. In general,
The powder may be for a period ranging from 1 hour to several hours, eg 1
A pressure of about 1000 bar to 1500 bar and a temperature of 0.8 to 1 times the solidus temperature are applied over a period of ~ 5 hours.
The pressure, temperature and duration of the isostatic press are determined so that the material has good structural homogeneity, so that it consists of fine particles and is substantially free of cracks and defects in its volume. In addition, the material obtained by isostatic pressing is completely isotropic. Some examples of materials produced using the method of the present invention are set out below in a non-limiting manner, and these iron and / or nickel based materials have different compositions.

Example 1 A metal powder is produced from an alloy belonging to the first group of nickel-based alloys containing chromium, boron and silicon and having a relatively low carbon content. This group of nickel-based alloys themselves is subdivided into a first subgroup represented by the letter A and a second subgroup represented by the letter B. The implementation of the method of the invention using a subgroup A alloy is described below in the form of Example 1a, and the implementation of the method of the invention using a subgroup B alloy is also illustrated.
It is described in the form of 1b. Example 1a A powder is produced from a nickel alloy belonging to subgroup A by the method described above. Subgroup A alloys are specified by the weight content of the alloying elements below. -Carbon 0.2 to 0.6%, Silicon 1.25 to 3.50%, Boron 2 to 3%, Chromium 7 to 14%, Iron 1.25 to 3.25%, The balance of the alloy is unavoidable impurities (of which cobalt is 1%).
(With a content of less than or equal to wt.%) Apart from nickel.

The alloys of the first subgroup A are known commercially in particular by the names "Colmonoy 4", "Deroro 40" and "TY 15.40", or by the symbol RNiCr-A according to the standard AWS.5.13. Corresponds to the displayed alloy. Hot isostatic pressing of the alloy powder is carried out at a temperature of 900 to 980 ° C. for several hours at a pressure of about 1000 to 1500 bar. Isostatic pressing is preferably carried out at a temperature of 920 ° C. The hardness of the material obtained by hot isostatic pressing is greater than 40 HRC (Rockwell hardness), which may be preferable compared to the hardness of the material obtained from the same type of alloy using prior art coating methods. unknown. In fact, if the coating is produced using one of the above alloys by prior art methods, for example the TAP method, the Rockwell hardness of the resulting coating is 38-45.

Example 1b Alloys belonging to the second subgroup B are specified by the weight content of the following alloying elements: -Carbon 0.3 to 0.8%, silicon 3 to 5%, boron 2 to 4%, chromium 10 to 16%, iron 2 to 5%, the balance of the alloy is nickel and unavoidable impurities (of which,
Cobalt has a weight content of less than 1%). A hot isostatic press at a temperature of 900 to 980 ° C, preferably 920 ° C for several hours at a temperature of about 1000 bar to 15
At a pressure of 00 bar. The hardness of the resulting alloy is at least 50 HRC, which is the hardness of the coating obtained using prior art methods applied to second subgroup B alloys, for example the TAP method (in this case The resulting hardness is 46-54
HRC) and may be preferable. Typical alloys of Group B consist of alloys commercially known by the names "Colmonoy 5", "Delloro 50" and "TY12.50" or designated by the symbol RNiCr-B according to standard AWS.5.13. .

Example 2 A nickel-based alloy belonging to the second group of alloys having a high chromium content and a high carbon content is prepared. Such nickel-based alloys belonging to the second group are described, for example, in French patent application No. 2,405,306 and are known commercially under the name "PY150". The second group of alloys may be identified by the weight content of the alloying elements below. -Carbon 1.4 to 2.5%, Silicon 0 to 2%, Chromium 25 to 33%, Molybdenum 6 to 15%, The balance of the alloy is unavoidable impurities (in which cobalt is 1%).
%, Which must have a weight content of less than or equal to%). Typically, the second group of alloys will have the following composition: -Carbon 1.65%,-Si 1.1%,-Chromium 29%,-Molybdenum 7.8%,-Iron less than 1%, the balance of the alloy is nickel and inevitable impurities (among them,
Cobalt has a weight content of less than 1%). Hot isostatic pressing the powder at a temperature above 1000 ° C, preferably at 1100 ° C for about several hours over 1000
At bar pressure. The hardness of the obtained alloy is at least
36 HRC, which is the hardness of a product obtained from a second group of alloys using prior art methods, such as a coating obtained by TAP or a molded bulk part, whose hardness is between 30 and 35 HRC) is preferred.

Example 3 A third group of very hard alloys consists of iron-based alloys with high chromium content and relatively low carbon content. This third group of alloys may be identified by the weight content of the alloying elements below. -Chromium 22-30%,-Nickel 7-25%,-Carbon 0.2-0.5%,-Manganese about 2%,-Molybdenum 6-12%,-Silicon about 2%,-Tungsten 1-4%,-Vanadium about 1%, the balance of the alloy consisting of iron and unavoidable impurities, of which cobalt has a weight content of less than 1%. Typical alloys of the third group are those commercially known by the name "Cenium Z 20". Hot isostatic pressing is carried out at temperatures above 1000 ° C., preferably at 1100 ° C. for several hours at a pressure of about 1000 bar. The hardness of the obtained alloy is greater than 45 HRC.

Example 4 A fourth group of cobalt-free very hard alloys consists of iron-based alloys having high chromium and carbon contents. This fourth group of alloys may be identified by the weight content of the alloying elements below. -Chromium 22 to 30%,-Nickel 0 to 10%,-Carbon 1 to 3%,-Manganese 0.3 to 15%,-Vanadium about 4%, The balance of the alloy is unavoidable residual impurities (of which cobalt is 1 (With a weight content of less than%) apart from iron. An example of such an alloy belonging to the fourth group is the alloy known commercially under the name "Norem". Hot isostatic pressing is carried out at temperatures above 1000 ° C., preferably at 1100 ° C. for several hours at a pressure of about 1000 bar. The hardness of the resulting alloy is at least 45 HRC. When performing an isostatic press, the pressure and duration parameters of the process are related to each other.
Thus, increasing the pressure can limit the pressing time, or conversely, increasing the pressing time can limit the pressure. The temperature maintained by the furnace during isostatic pressing should be within the solidus temperature of the alloy, ie, 0.8-1 times the initial melting point of the alloy when the temperature is raised from the solid state. is necessary. Thus, the temperature during hot isostatic pressing is below the temperature at which the alloy burns.

The conditions for carrying out the isostatic pressing are specified in particular to preserve as much as possible the fine-grained structure of the powder in the alloy after isostatic pressing. In other words, the isostatic pressing method should not result in the coalescence of powder particles initially introduced into the mold. In the case of ferrous alloys, after isostatic pressing,
By adjusting the cooling operation of the alloy, for example,
It is preferable to cool at a rate of 400 ° C./hour. After isostatic pressing, heat treatment may be considered to improve the properties of the alloy. Hard materials produced using the method of the present invention and prior art
Comparative Wear Testing of Surgical Materials A pin-on-disk type wear test was performed on materials made using the method of the present invention and materials made using prior art methods. Abrasion tests are performed by rubbing a hard material coated disk with a Stellite 12 cobalt alloy pin. Test at 300 ° C for 10
10 mm / with bearing pressure between 0 MPa pin and disk
At a rubbing speed of seconds. Wear rate is measured by weight loss measurements on coated specimens.

FIG. 1 shows the wear rate of the coating obtained by the hot isostatic pressing method (HIP method) of the present invention using various alloys and, for comparison, the stellite 6 cobalt alloy obtained by using the TAP method. It is a diagram showing the wear rate of the coating. In FIG. 1, points for coatings obtained using the method of the present invention are indicated by ▪, while points for Stellite 6 coatings obtained using TAP are indicated by □ for comparative points. Along the x-axis, the normalized name of the alloy used to make the coating is plotted. By way of comparison, Stellite 6 coatings were produced on the one hand using the TAP method and on the other hand using the HIP method of the invention. The wear rate of the coating obtained using the prior art TAP method is 1, while the wear rate of the coating obtained using the HIP method of the present invention is 0.6. Therefore, Stellite 6
The wear rate in the case of cobalt alloys was actually halved by using the HIP method of the present invention. In addition, results were presented for coatings obtained using the method of the invention using powders from the first group of nickel alloys belonging to the first subgroup A and the second subgroup B, respectively. The alloys of the first subgroup A are designated by the standardized name RNiCr-A, and the powders of the alloys of the second subgroup B are designated by the standardized name RNiCr-B. Standardized display RNiC
rA and RNiCr-B are derived from the American Welding Society standard AWS 5.13 for the definition of welding consumables and hard coatings.

The coatings obtained from materials of the first subgroup A of nickel alloys have a wear rate of about 0.4, which means that the HI
Even lower than the wear rate of the Stellite 6 coating obtained using P, which is 0.6. A coating made from a material from subgroup B has a wear rate less than 0.3 that of a coating made from a material from the first subgroup A.
Has a wear rate of. With reference to FIG. 2, in the case of a coating obtained using TAP from a material from the first subgroup (RNiCr-A), the cured phase 1 appears black in the micrograph of FIG.
It can be seen that are distributed in the layer, during which the material exhibits a very wide area 2 free of hardening precipitates. This results in a limited hardness and limited abrasion resistance of the coating material. Figure 3 shows the microstructure of a coating of material (RNiCr-A) from the first subgroup obtained using the HIP method. The magnification obtained with the microscope is 6 times greater in the case of FIG. 3 than in the case of FIG. The high magnification micrograph of Figure 3 clearly shows that the hardening phase 3 forms very fine precipitates which are evenly distributed in the coating material. This leads to a high hardness and a very good abrasion resistance in the case of coatings obtained using the method of the invention using an isostatic press.
In addition, the material obtained using the method of the invention does not contain internal defects, such as cracks or defects in the volume, which appear in the usual way (TIG, TAP or torch). This is because hot isostatic pressing prevents the appearance of internal defects such as those that appear during the forming or welding of metallic materials.

It was also possible to show that when a molded or welded part is subjected to a hot isostatic pressing operation, small internal defects due to forming or welding tend to be close up. Therefore, hot isostatic pressing has a healing effect in the case of materials obtained using molding or welding. In addition, one of the advantages of the hot isostatic pressing method is that it allows to form alloys that are difficult to make using conventional methods such as forging and rolling. The static press provides a material that is completely uniform in structure and isotropic in nature. Due to the uniform structure of the materials, they have excellent resistance to general and local corrosion due to the uniform distribution of chromium. Despite their high hardness, the products obtained using the process of the invention are not very brittle and have a considerable ductility (1% elongation at 20 ° C. and 1.5% elongation at 350 ° C.). ). This results in a product obtained using the method of the invention having improved heat shock resistance.

The invention is not limited to the embodiments described. Thus, hot isostatic pressing may be performed under pressure, temperature and duration conditions other than those shown. The properties of the alloy powder used, for example the particle size distribution and the particle shape of this powder, may be varied and adapted for the intended use. The method of the present invention may be practiced by using iron alloy or nickel alloy powder having a composition other than that described above.

[Brief description of drawings]

FIG. 1 is a diagram showing the wear rates of different composition materials obtained using the method of the present invention and materials obtained using prior art coating methods.

FIG. 2 is a photomicrograph of a prior art coating material obtained using an electron microscope.

FIG. 3 is a photomicrograph of a hard material produced by the method of the present invention, obtained using an electron microscope.

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Claims (20)

[Claims] 1. A powder of a metal alloy mainly containing elemental iron and nickel and at least one of chromium is subjected to high temperature isostatic pressing, and the pressure, temperature and period of the isostatic pressing treatment substantially cause cracks and defects in the volume. A method for producing a very hard and wear-resistant metallic material, characterized in that it is specified in order to obtain a uniform and isotropic fine granular material which is not included in. 2. The method according to claim 1, wherein the metal powder comprises a nickel-based alloy and / or an iron-based alloy containing only cobalt as a residual element. 3. A method according to claim 2, characterized in that the metal alloy is nickel-based and contains boron and silicon, and a small amount of carbon. 4. The metal alloy comprises 0.2 to 0.6% by weight of carbon, 1.
25-3.50 wt% silicon, 2-3 wt% boron, 7-
Characterized by containing 14% by weight of chromium and 1.25-3.25% by weight of iron, the balance of the alloy consisting of nickel and unavoidable residual impurities, in which there is cobalt with a weight content of less than 1%. The method according to claim 3. 5. A metal alloy containing 0.3 to 0.8% by weight of carbon, 3
-5% by weight of silicon, 2-4% by weight of boron, 10-16% by weight of chromium and 2-5% by weight of iron, the balance of the alloy being unavoidable residual impurities (of which 1% cobalt is present). The method according to claim 3, characterized in that it consists of nickel apart from (present in the following weight contents). 6. A hot isostatic press 900
Process according to any of claims 4 and 5, characterized in that it is carried out at a temperature of from ~ 980 ° C, preferably 920 ° C, for several hours at a pressure of from about 1000 bar to 1500 bar. 7. A metal alloy containing 1.4 to 2.5% by weight of carbon, 0
~ 2 wt% silicon, 25-33 wt% chromium and 6-15
A method according to claim 2, characterized in that it comprises nickel by weight, the balance of the alloy being nickel apart from the unavoidable impurities, of which cobalt has a weight content of less than 1%. 8. The metal alloy comprises approximately 1.65% carbon and 1.1% carbon.
Silicon, 29% chromium, 7.8% molybdenum and 1%
8. The method according to claim 7, characterized in that it comprises less than iron and the balance of the alloy consists of nickel apart from unavoidable impurities, of which cobalt has a weight content of less than 1%. 9. Hot isostatic press 1000
Above ℃, preferably about 1100 ℃ for several hours
Process according to any of claims 7 and 8, characterized in that it is carried out at a pressure of 1000 bar. 10. A metal alloy containing 22 to 30% by weight of chromium, 7
~ 25 wt% nickel, 0.2-0.5 wt% carbon, about 2
Wt% manganese, 6-12 wt% molybdenum, about 2 wt% silicon, 1-4 wt% tungsten and about 1 wt% vanadium, the balance of the alloy being iron and unavoidable impurities (in which , Cobalt having a weight content of 1% or less). 11. A hot isostatic press 10
A temperature of more than 00 ° C, preferably 1100 ° C, at a pressure of about 1000 bar for several hours.
The method described in. 12. Metal alloy containing 22 to 30% by weight of chromium, 0.
~ 10 wt% nickel, 1-3 wt% carbon, 0.3-15
% Manganese and about 4% vanadium by weight,
The balance of the alloy is unavoidable impurities (of which cobalt is 1
The method according to claim 2, characterized in that it consists of iron apart from having a weight content of less than or equal to%). 13. Isostatic press at a temperature of 1000 ° C. or higher, preferably 1100 ° C. for about 1000 hours over several hours.
Method according to claim 12, characterized in that it is carried out at a pressure of bar. 14. The method of claim 1, wherein the hot isostatic pressing is carried out at a temperature in the range of 0.8 to 1 times the solidus temperature of the alloy. 15. The method according to claim 1, wherein the hot isostatic press is performed under an atmosphere of argon. 16. The method according to claim 11, wherein the metallic material is cooled at a rate of 300 to 400 ° C./hour after hot isostatic pressing. 17. Use of the method according to claim 1 for the production of wear resistant coatings on metal parts. 18. Use of the method according to claim 1 for the manufacture of bulk parts made of metal alloys. 19. A rubbing part in which a coated metal part or a metal alloy part is used in a nuclear power plant, such as a valve seat or a sealing member, a pump component, a latch arm of a control rod drive mechanism or a nuclear power plant. Use according to any of claims 17 and 18, characterized in that it is a key inside the reactor. 20. Use according to claim 19, characterized in that the metal alloy contains only cobalt as residual element.