HIGH-TEMPERATURE FORMING TOOL

Abstract

A high-temperature forming tool is formed at least partly of a molybdenum-based alloy having a fraction of molybdenum of 90 wt. %. The molybdenum-based alloy is in a pressed-and-sintered state and in the pressed-and-sintered state has a thermal shock resistance of at least 250 K. The thermal shock resistance is defined as the quotient of R.sub.eH/(.Math.E), where R.sub.eH is the yield point at room temperature in MPa, a is the thermal expansion coefficient in 1/K and E is the elasticity modulus in MPa.

Claims

1-15. (canceled)

16. A high-temperature forming tool, comprising: a body being formed at least partly of a molybdenum-based alloy having a fraction of molybdenum of 90 wt. %, said molybdenum-based alloy being in a pressed-and-sintered state and in the pressed-and-sintered state having a thermal shock resistance of at least 250 K, the thermal shock resistance being defined as a quotient of R.sub.eH/(.Math.E), where R.sub.eH is a yield point at room temperature in MPa, is a thermal expansion coefficient in 1/K and E is an elasticity modulus in MPa.

17. The high-temperature forming tool according to claim 16, wherein said molybdenum-based alloy has the yield point R.sub.eH at room temperature of at least 400 MPa.

18. The high-temperature forming tool according to claim 16, wherein said molybdenum-based alloy has a relative density of between 90% and 97%.

19. The high-temperature forming tool according to claim 16, wherein said molybdenum-based alloy has an elongation at break at room temperature of at least 8%.

20. The high-temperature forming tool according to claim 16, wherein said molybdenum-based alloy has a plane-strain fracture toughness K.sub.IC at room temperature of greater than or equal to 10 MPa.Math.m.sup.1/2.

21. The high-temperature forming tool according to claim 16, wherein a ductile-brittle transition temperature of said molybdenum-based alloy, ascertained in a bending test, is 60 C.

22. The high-temperature forming tool according to claim 16, wherein said molybdenum-based alloy has said fraction of molybdenum being 99.0 wt. %, a boron fraction B of 3 ppmw and a carbon fraction C of 3 ppmw.

23. The high-temperature forming tool according to claim 22, wherein said molybdenum-based alloy has said fraction of molybdenum being 99.93 wt. %, said boron fraction B being 3 ppmw and said carbon fraction C being 3 ppmw, a total fraction B+C of said carbon and said boron being in a range of 15 ppmwB+C50 ppmw.

24. The high-temperature forming tool according to claim 22, wherein said molybdenum-based alloy has an oxygen fraction O is in a range of 3 ppmwO20 ppmw.

25. The high-temperature forming tool according to claim 22, wherein said molybdenum-based alloy has said fraction of molybdenum being 99.93 wt. %, said boron fraction B being 3 ppmw and said carbon fraction C being3 ppmw, a total fraction B+C of said carbon and said boron being in a range of 15 ppmwB+C50 ppmw and an oxygen fraction O being in a range of 3 ppmwO20 ppmw.

26. The high-temperature forming tool according to claim 16, wherein said molybdenum-based alloy has a mean grain aspect ratio, expressed as GAR value, formed as quotient of a grain length by a grain width, of less than 1.5.

27. The high-temperature forming tool according to claim 16, wherein said body is formed wholly of said molybdenum-based alloy.

28. The high-temperature forming tool according to claim 16, wherein said body has embodied therein at least one facility for introducing a cooling medium.

29. A method for producing a product, which comprises the steps of: providing a high-temperature forming tool according to claim 16; and using the high-temperature forming tool for producing tubes or profiles.

30. A process for producing a high-temperature forming tool, which comprises the following steps of: pressing of a powder mixture of molybdenum powder and boron- and carbon-containing powders, to give a green compact; and sintering the green compact an oxidation-proof atmosphere with a residence time of at least 45 minutes at temperatures in a range of 1600 C.-2200 C., to afford a sintered blank of the high-temperature forming tool.

31. The process for producing the high-temperature forming tool according to claim 30, which comprises: working the green compact for approximation to a final shape of the high-temperature forming tool; and final working of the sintered blank.

Description

[0131] FIG. 1: shows a perspective view of an exemplary embodiment of a high-temperature forming toolpiercing plug as example

[0132] FIG. 2: shows a side view of a piercing plug

[0133] FIG. 3: shows a piercing plug in cross section

[0134] FIGS. 4a, 4b show views of a further exemplary embodiment of a high-temperature forming tooldie as example

[0135] FIGS. 5a, 5b show views of a further exemplary embodiment of a high-temperature forming toolpunch as example

[0136] FIG. 6 shows schematically the production route for a high-temperature forming tool, using a piercing plug as example

[0137] FIG. 7 shows a diagram relating to the ductile-brittle transition temperature

[0138] FIG. 8 shows a scanning electron micrograph of a Mo material according to the prior art

[0139] FIG. 9 shows a scanning electron micrograph of a molybdenum-based alloy of a high-temperature forming tool of the invention

[0140] FIG. 1 shows schematically a high-temperature forming tool of the invention, which in this exemplary embodiment is embodied as a piercing plug 1. The piercing plug 1 has a tip portion 2 and a rear portion 3. At the rear portion 3, the piercing plug 1 is typically carried by a plug rod (not shown), for which a receiver is embodied.

[0141] The same is also evident from FIG. 2, which shows the piercing plug 1 in a side view. In the exemplary embodiment, the piercing plug 1 is implemented as rotationally symmetrical with respect to an axis of symmetry L.

[0142] FIG. 3 shows the piercing plug 1 in a cross section. Represented here is an optional facility 4 for cooling and/or instrumentation of the piercing plug 1. In the example, the facility 4 is implemented as a drilled hole.

[0143] FIGS. 4a and 4b show views of a further exemplary embodiment for a high-temperature forming tool of the invention, here, as an example, of a die 1 for metal forming. FIG. 4a here shows a perspective view, FIG. 4b a cross section.

[0144] Dies of the kind shown here are employed, for example, in the extrusion of high-alloy steels. Naturally, the die 1 may take on different shapes and, in particular, different cross-sectional shapes.

[0145] FIGS. 5a and 5b show views of a further exemplary embodiment for a high-temperature forming tool of the invention, here, as an example, of a punch 1 for metal forming. FIG. 5a here shows a perspective view, FIG. 5b a cross section. A facility 4 may be embodied for introducing a cooling medium. In the present example, the facility 4 is also configured as a receiver.

[0146] Punches of the kind shown here are employed, for example, in the backwards flow moulding of high-alloy steels. Naturally, the punches may also take on shapes which differ from the shape shown here.

[0147] FIG. 6 shows schematically the production route for a high-temperature forming tool of the invention, in the example of a piercing plug 1. In step a), a powder mixture of molybdenum powder and boron- and carbon-containing powders is compressed to give a green compact G.

[0148] The optional step b) shows the working of the green compact G for approximation to a final shape of the piercing plug 1.

[0149] In step c), the green compact G is sintered, to afford a sintered blank R of the piercing plug 1.

[0150] After the sintering, in step d), the piercing plug 1 is obtained through the sintered blank R. There may optionally be working of the sintered blank R.

[0151] FIG. 7 shows a diagram relating to the ductile-brittle transition temperature for various materials which are in principle candidates for high-temperature forming tools.

[0152] The variables plotted are bending angles in [ ] of three-point bending samples as the x-axis, against the temperature in [ C.] as the y-axis. The bending angles indicate the plastic bending of the sample at the onset of fracture.

[0153] In this diagram, the right-hand curve (dotted, labelled Mo) marks a typical profile of the fracture behaviour of pure molybdenum in the pressed-and-sintered state. It is seen that the material exhibits a pronounced ductile behaviour only beyond about 140 C.

[0154] Somewhat more favourable is the profile of the middle curve (dashed, labelled TZM), which shows the profile of the ductile-brittle transition for TZM in the pressed-and-sintered state. The profile is shifted slightly towards lower temperatures, which characterizes a somewhat more docile behaviour.

[0155] The two right-hand profiles (Mo and TZM) correspond to the prior art.

[0156] The left-hand curve (solid, labelled MoB15) shows a typical profile of a ductile-brittle transition for a molybdenum-based alloy of the kind which is proposed as particularly preferred for a high-temperature forming tool and has a molybdenum fraction of 99.0 wt. %, a boron fraction B of 3 ppmw and a carbon fraction C of 3 ppmw.

[0157] The advantages are achieved as soon as, according to one development, the base material of the high-temperature forming tool has a ductile-brittle transition temperature of 60 C. In the example presently shown, the ductile-brittle transition temperature, defined by plastic bending of 20 bending angle, is in fact well below 60 C., specifically around 30 C.

[0158] Also drawn in is an auxiliary line at a bending angle of 20. Bending of the sample on fracture at a bending angle of 20 is employed in the context of this application as the stipulation of the ductile-brittle transition temperature. Where the plastic bending experienced is 20, it is possible for technological purposes to assume a ductile behaviour of the material. Test parameters employed in the three-point bending test were as follows: an initial force of 20 N [newtons], a test velocity of 10 mm/min, a supporting width of 20 mm. The radius of the bearing rollers was 1.5 mm, as was the radius of the bending punch. The sample dimensions were 6635 mm.

[0159] FIG. 8 shows a scanning electron micrograph of a molybdenum material according to the prior art. The molybdenum material is in a recrystallized state. The micrograph shows a fracture surface of a tensile sample tested at room temperature. A striking feature is the presence of what is called an intercrystalline fracture, referring to a fracture with predominant separation of material along grain boundaries. A grain boundary detachment of this kind is marked by way of the inserted arrow. In the case of such an intercrystalline fracture event, the ductility is determined by the grain boundary strength.

[0160] FIG. 9 shows a fracture face of a molybdenum-based alloy of the kind suitable and proposed preferentially for the production of a piercing plug of the invention. The alloying strategy is based on an improvement in the grain boundary strength and is achieved in particular if the molybdenum-based alloy has a molybdenum fraction of 99.0 wt. %, a boron fraction B of 3 ppmw and a carbon fraction C of 3 ppmw. The fracture event here is transcrystalline, meaning that a fracture runs through the grains. This fracture event is due to a substantially increased grain boundary strength and is associated macroscopically with a substantially higher ductility.