EP1649071A1

EP1649071A1 - Titanium or titanium alloy contacting surface

Info

Publication number: EP1649071A1
Application number: EP04786015A
Authority: EP
Inventors: Gérard Raisson; Dominique Cauvin; Didier Guichard
Original assignee: Aubert and Duval SA
Current assignee: Aubert and Duval SA
Priority date: 2003-08-01
Filing date: 2004-07-30
Publication date: 2006-04-26
Also published as: FR2858331A1; WO2005012586A1; CN1829814A; US20050161124A1; CA2534070A1; JP2007501326A; FR2858331B1

Abstract

The invention mainly concerns the use of a weakly alloyed steel, substantially nickel-free, non-stainless, for making at least one surface of an article designed to be contacted with titanium or a titanium alloy, as well as a method for making at least the surface of such an article. In particular, the invention concerns the use of said alloy for making at least the contact surface of a mould for hot forming in solid state titanium-based alloys or titanium alloy, or for making at least the contact surface of tools for densifying or forming solid alloys or powders of titanium or of titanium alloy. The invention also enables the manufacture of articles designed to be in contact with titanium or a titanium alloy.

Description

Surface in contact with titanium or a titanium alloy DESCRIPTION: The present invention essentially relates to the use of a low alloy steel, substantially nickel-free, non-stainless, for the manufacture of at least the surface of an article intended to be brought into contact with titanium or a titanium alloy in the solid state, as well as a process for manufacturing at least the surface of such an article with said steel.

STATE OF THE ART:

It is known to produce parts of titanium-based alloy or of titanium alloy using hot forming molds, or tools, made with various types of steel. Until now, at least the parts of the molds or tools in contact with titanium and titanium alloys have been made of selected steel to avoid reactions sensitive to surface diffusion with titanium and titanium alloys. In this context, the steels used are carbon steels prepared by Powder Metallurgy (MdP), austenitic stainless steels for recoverable mold elements (MdP), maraging steels, and refractory steels with high nickel content for forming. isothermal, possibly superplastic. However, these steels do not make it possible to sufficiently limit the surface diffusions with titanium and titanium alloys. In these two cases, there is a diffusion particularly of iron with possible formation of intermetallic zones, which leads to degradations of the surface properties. Superficial changes in the microstructure are also observed. To correct it, it is necessary to resort to costly additional operations such as anti-diffusion coating, chemical dissolution of the surface of the parts. Other categories of steel are also used for the manufacture of molds in contact with titanium alloys. These highly alloyed steels, in particular chromium and molybdenum, but without nickel, do not react with titanium. However, these alloys are of the stainless type, which is different from those produced by the present invention.

GOALS OF THE INVENTION:

The main object of the present invention is to solve the new technical problem consisting in the selection for the surfaces in contact with titanium and titanium alloys, of a non-stainless steel capable of avoiding any sensitive (measurable) reaction in surface diffusion. of a component of this steel, and in particular of iron, with titanium and titanium alloys. Another object of the invention is to solve this technical problem according to a simple, inexpensive solution which can be used on an industrial scale for shaping titanium or a titanium alloy in the solid state.

SUMMARY AND DETAILED DESCRIPTION OF THE INVENTION:

The invention makes it possible to solve for the first time these new technical problems stated above, in a simple, inexpensive, reliable and reproducible manner, usable on an industrial scale. According to a first aspect, the present invention relates to the use of a low-alloy steel, substantially nickel-free, non-stainless, for the manufacture of at least the surface of an article intended to be brought into contact with titanium or a titanium alloy for solid state shaping of said titanium or titanium alloy for example either for the densification and / or the forming of titanium or titanium alloy powders, or for the formation of solid titanium or '' a massive titanium alloy. According to a first embodiment of the invention, said steel is used for the manufacture of at least the surface in contact with a hot forming mold in the solid state of titanium or of a titanium alloy . According to a second embodiment of the invention, said steel is used for the manufacture of tools for the densification and / or the forming of titanium or titanium alloy powders. According to a third embodiment of the invention, said steel is used for the manufacture of tools for the solid state forming of solid titanium or of a solid titanium alloy. Advantageously, the forming is not limited to the forming of "final" parts, but can also be the forming of blanks for example, possibly followed by another operation, such as forging, stamping or rolling. Advantageously, a low-alloy steel is used comprising less than 10% by weight of alloying elements, in particular, the steel comprises, in percentage by weight: - nickel less than or equal to 2.5%, preferably less than or equal to 0.5%, - chromium: between 0.5 and 4%, preferably between 0.8% and 2%, - carbon less than or equal to 1, preferably less than or equal to 0.4%; - balances iron and unavoidable impurities. According to an advantageous embodiment, the use is characterized in that the steel comprises from 0.1 to 4% by weight of molybdenum, preferably 0.1 to 2% by weight of molybdenum, even better from 0.15 1% by weight of molybdenum. According to yet another advantageous embodiment, the use according to the invention is characterized in that the steel comprises from 0.05 to 4% by weight of vanadium, preferably from 0.05 to 2%, even better 0.1 to 1%, by weight of vanadium. According to yet another advantageous embodiment of the invention, the use according to one of the preceding claims, characterized in that the steel is a steel of grade 18CD4. According to yet another advantageous embodiment of the invention, the use according to one of the preceding claims, characterized in that the steel is a steel of grade 15CDV6. According to a second aspect, the present invention also covers a method of manufacturing at least the surface of an article intended to be brought into contact with titanium or a titanium alloy for shaping in the solid state of said titanium. or titanium alloy for example, either for the densification and / or the formation of titanium powders or of titanium alloy, or for the formation of solid titanium or of a solid titanium alloy, characterized in that it comprises the manufacture of said surface with a low alloy steel, substantially nickel free, non-stainless, as defined above and in the following description, including the examples which form an integral part of the invention, unless otherwise indicated. This makes it possible in particular to avoid any sensitive (measurable) reaction in surface diffusion of a component of this steel, and in particular iron, with titanium and titanium alloys in the solid state. The steel of the present invention makes it possible in particular to avoid sticking and diffusion in the titanium or the titanium alloys of the constituent elements of the steel of the invention. The surface microstructure is not modified, contrary to what is observed for steels of the prior art. The steel of the present invention advantageously makes it possible to obtain no measurable contamination of the titanium or of the titanium-based alloy in the solid state with the elements of the article of the invention. According to a first embodiment of the invention, the manufacturing process comprises manufacturing at least the surface in contact with a hot forming mold in the solid state of titanium or a titanium alloy. . According to a second embodiment of the invention, the manufacturing process comprises the manufacture of tools for the densification and / or the forming of titanium or titanium alloy powders. According to a third embodiment of the invention, the manufacturing process comprises the manufacture of tools for the solid state forming of solid titanium or of a solid titanium alloy. According to a particular embodiment of these two aspects, the method according to the invention is characterized in that the hot molding is carried out at a temperature at least equal to 500 ° C and less than 1000 ° C, preferably less than about 980 ° C. According to a particular embodiment, the method is characterized in that one carries out the molding of titanium parts of TA6V grade. According to yet another particular embodiment, the method according to the invention is characterized in that pump impellers are produced from a titanium-based alloy, in particular from a shade alloy TA6V, using tools made of said low alloy steel produced by turning or milling. According to a fourth aspect, the present invention also covers articles comprising a surface in contact intended to be brought into contact with titanium or a titanium alloy for shaping in the solid state of titanium or titanium alloy> for example , either for the densification and / or the formation of titanium or titanium alloy powders, or for the formation of solid titanium or of a solid titanium alloy, characterized in that at least said surface in contact with the the article is produced with a low-alloy steel, substantially nickel-free, non-stainless, in particular as previously defined and in the following description, including the examples which form an integral part of the invention, unless otherwise indicated, or as obtained by the method as previously defined and in the following description, including the examples which form an integral part of the invention, unless otherwise indicated. According to a fifth aspect, the present invention also covers tools for the densification and / or the forming of titanium powder or of titanium alloy, characterized in that at least the surface of the tool intended to be brought into contact with the titanium or titanium alloy in the solid state, is made of a low alloy steel, non-stainless, as previously defined and in the following description, including the examples which form an integral part of the invention, except otherwise indicated, or as obtained by the process as previously defined and in the following description, including the examples which form an integral part of the invention, unless otherwise indicated. According to a sixth aspect, the present invention also covers tools for the solid state forming of solid titanium or of an alloy. solid titanium, characterized in that at least the surface of the tool intended to be brought into contact with titanium or titanium alloy in the solid state, is made of a low-alloy steel, non-stainless, as previously defined and in the following description, including the examples which form an integral part of the invention, unless otherwise indicated, or as obtained by the process as previously defined and in the following description, including the examples which form part integral of the invention, unless otherwise indicated. According to a seventh aspect, the present invention also covers molds for hot forming in the solid state of titanium or of a titanium alloy, for example either for the densification and / or the forming of powders of titanium or titanium alloy, either for the formation of titanium, solid or of a massive titanium alloy, characterized in that at least the surface of the mold intended to be brought into contact with titanium or the titanium alloy, the solid state is made of a low-alloy, non-stainless steel, as defined above and in the following description, including the examples which form an integral part of the invention, unless otherwise indicated, or as obtained by the process as previously defined and in the following description, including the examples which form an integral part of the invention, unless otherwise indicated. Advantageously, the invention relates to tools for maintaining heat treatment. According to a particular embodiment, this steel has a chromium content of between 0.5 and 4% by weight, with a nickel content of less than 2.5% by weight and a carbon content of less than 1% by weight. The steel in the use of the present invention can be implemented by forging, rolling, followed by machining or grinding or by cast steel. Preferably, this steel is in the annealed state to improve dimensional reproducibility. Other objects, characteristics and advantages of the invention will become apparent to a person skilled in the art in the light of the description of the use made with reference to several currently preferred examples of the invention given simply by way of illustration. and which therefore cannot in any way limit the scope of the invention. In the examples, the percentages are given by weight and the temperatures in degrees Celsius or it is ambient temperature, the pressure is atmospheric pressure, and the atmosphere is air, unless otherwise indicated. EXAMPLES:

Examples 1 to 7: STEEL TESTS OF THE INVENTION AND COMPARISONS

The following mild and low-alloy steels respectively of the invention (EX 1, EX 2A and EX 2B) and of the prior art (EX 3A, EX 3B, EX 4 and EX 5), commercially available (in particular the grade 15CDV6, is available from the company THYSSEN FRANCE SA MANUFACTURERS, grade 18 CD4 from the company ASCOMETAL, grade 100HLES from the company TECPHY FIRMINY), will be subjected to the tests of Example 8, and present the chemical analyzes following, in percentage by weight, reported in Table I, the balance being iron and unavoidable impurities.

<

LD EXAMPLE 8- TEST ON TESTS FROM STEELS IN EXAMPLES 1 TO 7 LISTS IN TABLE I

A Test on test pieces

A.1 Test pieces machined by milling

Test specimens were produced from a cylindrical container approximately 50 mm in diameter and approximately 70 mm in height. The containers were filled with standard TA6V powder and within the powder parallelepiped inserts, obtained by milling 20 * 10 * 10 mm were placed made of mild steels of grades XES, XC18 (lot 23729), 18CD4 ( lot A4791), 15CDV6 (lot 78384) and 100HLES (lot R2417). The characteristics of the materials are given respectively in Table I for the steel inserts, and in Table II for the titanium alloy powder of standard TA6V. The containers were densified by hot isostatic compression with a 4 hour plateau at 920 ° C. and OOMPa. The steel was removed by dissolving in nitric acid. After densification, the following investigations were carried out:> on the micrographic section: micrographic examination and determination of the diffusion profiles at the TA6V-steel interfaces with the EDAX probe using a scanning microscope. • After dissolution of the steel inserts in nitric acid: determination of the diffusion profile in TA6V, examination of the surface geometry with a scanning microscope and measurement of the roughness. Table II - Characteristics of TA6V powders Elemental analysis (% by weight)

Production

• rotating electrode spray • sieving: 315 μm

The results of the exams are as follows:

1. XES insert (prior art A4) • continuous intermetallic layer of approximately 5 μm. Diffusion of Fe in TA6V over approximately 0.3mm - roughness: Ra = 15μm • significant indentation of powder grains in steel • surface modification of the microstructure

2. insert in XC18 (prior art A3A and A3B) • continuous intermetallic layer of approximately 5 μm. Diffusion of Fe in TA6V over approximately 0.3mm • roughness: Ra = 9 to 12 μm • significant indentation of grains of powder in steel

3. 18CD4 insert (invention II) • absence of an intermetallic layer. No diffusion of element of the steel in the TA6V "• roughness: Ra = 5 μm • limited indentation of the powder in the steel with formation of diamond points at triple points. • no surface modification of microstructure

4. 15CDV6 insert (invention I2A and I2B) - absence of an intermetallic layer. No diffusion ', of element of the steel in the TA6V • roughness: Ra = 3 to 4 μm • weak indentation of the powder in the steel without formation of diamond points at triple points. • no surface modification of microstructure

5. 100HLES insert (prior art A5) • irregular intermetallic layer from 0 to 20 μm depending on the location. Diffusion of Fe in TA6V up to 0.3 mm. • Roughness: Ra = 2 to 3 μm "Weak indentation of the powder in the steel.

A.2 Inserts produced using techniques other than tool machining (turning or milling) The influence of the method of obtaining steel inserts has been studied for the following combinations: * standard TA6V - 18CD4 (lot A4791) machined by water jet cutting standard TA6V - 25CD4 molded in lost wax TA6V ELI-15CDV6 ( lot 1470) machined by EDM

(wire cutting). The densification was carried out by Hot Isostatic Compression, known as CIC, (920 ° C, 100 MPa, 4h). The steel-TA6V interfaces were the subject of a micrographic examination to highlight a possible diffusion between the two materials. No diffusion was detected for the first two combinations. On the other hand, a diffusion in places was highlighted on the TA6V ELM5CDV6 combination machined in EDM.

B Tests on parts

Bl. ISOPREC ^® process: The ISOPREC ^® process makes it possible to obtain shaped parts with good dimensional accuracy, at least part of the surfaces of which is produced without a finishing machining operation. The part is produced by densification by CIC (Hot Isostatic Compression) of pre-alloyed stainless powders in a non-stainless steel mold comprising a cavity whose dimensions are calculated to obtain the desired final geometry. The mold or tool is removed by machining and dissolved in nitric acid. Pump impellers were produced using the ISOPREC ^® process from TA6V and steel tools produced by turning and milling. The following combinations have been achieved: standard TA6V- XC18 lot 69181 standard TA6V- 18CD4 lot A4791 (invention II) TA6V ELI- 18CD4 lot A4791 (invention II), TA6V ELI- 15CDV6 lot 78384 (invention I2A) TA6V ELI- 15CDV6 lot 1470 (invention I2B)

It is recalled that the characteristics of the materials used are given in Tables I and IL After densification by CIC (920 ° C, 100 MPa, 4h) and, elimination of the steel tools by dissolution in nitric acid, the surfaces were characterized in roughness and iron contamination (detection limit 0.25%). The results obtained on test pieces have been fully confirmed. We can just note a slightly greater dispersion of roughness due to a particle size distribution of the powders when filling the containers.

B2. Manufacture of a half-sphere by a holding tool for heat treatment:

This process concerns the maintenance of a standard TA6V half-sphere of diameter 550 mm, having a thickness of 5 mm. This half-sphere is brought for one hour to approximately 870 ° C. under vacuum, maintained by a tool having in hollow the same geometry produced in 18CD4. After this treatment, the results obtained show that there is an absence of deformation and surface contamination by iron. This confirms that this steel can be used to make a holding tool for heat treatment, in order to suppress diffusion reactions, by iron in particular.

B3. Process for manufacturing a blank by densification of powder then forging:

The production of a blank was carried out by densification of powder and then forging of this blank. This blank was produced by densification by hot isostatic compression (CIC) of a cylindrical container according to FIG. 1 (for example at 920 ° C; 100 Mpa, for 4 hours). The cylindrical container (1) comprises a central core (10), an external container (20), as well as elements (40, 41) allowing the ends to be sealed. This cylindrical container (1) has a hollow (30) for collecting a filling material, such as a powder (50), for example. The thickness of the outer container (20) was 3 mm. It was produced, by way of illustration from this cylindrical container (1), after CIC, a cylinder having an outside diameter of 50 mm, an inside diameter of 30 mm, and a length of 200 mm. The central core was in 18CD4 and the outer container, in XC18. This container was filled with standard TA6V powder. The cylinder obtained was peeled to a diameter of 45 mm so as to eliminate the XC18 container and the diffusion zone created during densification. The blank thus obtained was forged at around 900-920 ° C by crushing the diameter between the plates to a height of 35 mm. The central core in 18CD4 was removed by dissolution in nitric acid. The results showed that the section presented: - regular material deformation; - a total absence of diffusion on the surface of the cylinder in TA6V previously in contact with the core in 18CD4. This also makes it possible to confirm the use of 18CD4 for the manufacture of tools or molds intended to be in contact with TA6V in order to eliminate the diffusion reactions. The invention includes all the technical means constituting technical equivalents of the means described in the description taken as a whole. In addition, any characteristic which appears new compared to any prior art forms an integral part of the invention and is claimed as such and in its generality or its function.

Claims

1. Use of a low-alloy steel, substantially nickel-free, non-stainless, for the manufacture of at least the surface of an article intended to be brought into contact with titanium or a titanium alloy for shaping in the solid state of said titanium or titanium alloy, for example either for the densification and / or the formation of titanium or titanium alloy powders, or for the formation of solid titanium or of a solid titanium alloy.

2. Use according to claim 1, characterized in that said steel is used for the manufacture of at least the contact surface of a hot forming mold in the solid state of titanium or an alloy of titanium.

3. Use according to claim 1, characterized in that said steel is used for the manufacture of tools for the densification and / or the forming of titanium or titanium alloy powders.

4. Use according to claim 1, characterized in that said steel is used for the manufacture of tools for the solid state forming of solid titanium or of a solid titanium alloy. 5. Use according to claim 1, characterized in that the low alloyed steel comprises less than 10% by weight of alloying elements, in particular, the steel comprises, in percentage by weight: - nickel less than or equal to 2, 5%, preferably less than or equal to 0.5%, - chromium: between 0,

5 and 4%, preferably between 0.8% and 2%, - carbon less than or equal to 1, preferably less than or equal to 0.4%; - balance: iron, as well as unavoidable impurities.

6. Use according to claim 1 or 2, characterized in that the steel comprises from 0.1 to 4% by weight of molybdenum, preferably 0.15 to 2% by weight, even better from 0.15 to 1% by weight of molybdenum.

7. ' Use according to one of the preceding claims, characterized in that the steel comprises from 0.05 to 4% by weight of vanadium, preferably from 0.05 to 2% by weight of vanadium, even better from 0.1 to 1% by weight of vanadium.

8. Use according to one of the preceding claims, characterized in that the steel is a steel of grade 18CD4.

9. Use according to one of the preceding claims, characterized in that the steel is a steel of grade 15CDV6.

10. Method for manufacturing at least the surface of an article intended to be brought into contact for shaping in the solid state of said titanium or titanium alloy, for example with titanium or a titanium alloy either for densification and / or forming of titanium or titanium alloy powders, either for the formation of solid titanium or of a solid titanium alloy, characterized in that it comprises the manufacture of said surface with a weak steel alloyed, substantially nickel-free, non-stainless, as defined in any one of claims 1 to 9.

11. The manufacturing method according to claim 10, characterized in that it comprises the manufacture of at least the surface in contact with a hot forming mold in the solid state of titanium or an alloy of titanium.

12. The manufacturing method according to claim 10, characterized in that it comprises the manufacture of tools for the densification and / or the forming of titanium or titanium alloy powders.

13. The manufacturing method according to claim 10, characterized in that it comprises the manufacture of tools for the solid state forming of solid titanium or of a solid titanium alloy.

14. The method of claim 10, characterized in that the hot molding is carried out at a temperature at least equal to 500 ° C and less than 1000 ° C, preferably less than about 980 ° C.

15. The method of claim 10 or 11, characterized in that one carries out the molding of titanium parts of TA6V grade.

16. Method according to one of claims 10 to 15, characterized in that one manufactures pump impellers in titanium-based alloy, in particular in alloy of TA6V grade, using tools made of said steel low alloy made by turning or milling.

17. Method according to one of claims 10 to 16, characterized in that an annealing of the steel is carried out to improve the dimensional reproducibility.

18. Article comprising a surface in contact intended to be brought into contact with titanium or a titanium alloy for shaping in the solid state of said titanium or titanium alloy for example either for the densification and / or the forming of powders of titanium or titanium alloy, either for the formation of solid titanium or of a solid titanium alloy, characterized in that at least said surface in contact with the article is produced with a low alloy steel, substantially nickel free, non-stainless as defined in any one of claims 1 to 9 or as obtained by the process according to any of claims 10 to 17.

19. Tool for densification and / or forming of titanium powder or titanium alloy, characterized in that at least the surface of the tool intended to be brought into contact in the solid state with titanium or the titanium alloy, is made of a low alloy steel, not stainless steel as defined in any one of claims 1 to 9 or as obtained by the process according to any one of claims 10 to 17. '20. Tools for forming solid titanium or a solid titanium alloy , characterized in that at least the surface of the tool intended to be brought into contact in the solid state with titanium or the titanium alloy, is made of a low alloy steel, non-stainless as defined in any one of claims 1 to 9 or as obtained by the process according to any one of claims 10 to 17. 21. Mold for hot forming in the solid state of titanium or an alloy of titanium for example, either for the densification and / or the forming of titanium or titanium alloy powders, or for the forming, of solid titanium or of a solid titanium alloy, characterized in that at least the surface of the mold intended to be brought into contact with titanium or the titanium alloy in the state solid is made of a low-alloy, non-stainless steel as defined in any one of claims 1 to 9 or as obtained by the process according to any one of claims 10 to 17.