WO1983000168A1 - Method for producing a semi finished or finished product of metal material by thermoforming - Google Patents

Abstract

Semi-finished and finished products made of aluminum, copper, nickel and iron alloy with or without material dispersed by oxidation are produced by thermoforming, in which the forming takes place in a single operation at constant temperature or almost constant, very little lower than the solidus temperature of the alloy of the workpiece, at a relatively low deformation speed and under low specific deformation forces. The workpiece and the tool are maintained at least during the last longest phase of forming at the temperature, if possible the same temperature, maximum allowable near the solidus line. Preferably, a prior homogenization of the material at said maximum admissible temperature followed by cooling to ambient temperature before forming. Very good filling power of the mold.

Description

 Process for producing a semi-finished product or a finished part from a metallic material by hot shaping

The invention is based on a method for producing a semifinished product or a finished part according to the preamble of claim 1.

When it comes to the hot shaping of metallic materials, for economic reasons one tries to keep the number of process steps as low as possible, and on the other hand to get as close as possible to the final shape in order to limit the amount of costly machining that may be required. Known processes of this type are, for example, isothermal or quasi-isothermal forming (forming with heated tools), as has become established above all in forging (drop forging). Attempts are also being made to reduce the resistance to deformation and to improve the mold filling capacity by shaping the so-called superplastic state of the material - if such a state can be set at all (see: G. Schröder, isothermal and superplastic forming in drop forging, workshop and operation 113 / 1980/11, S. 765 - 770; GH Gessinger, Isothermal Forming - An Inexpensive Precision Forging Process, Technical Reports Metallurgical Processing Metalworking 11/78, pp. 954-957).

In the case of the forming processes described, the possibilities of inexpensive production are used only in an imperfect manner. Conventional isothermal deformation is usually carried out at temperatures that are comparatively low, i.e. have a considerable distance from the solidus temperature for safety reasons. At these temperatures, however

Ductility of the workpiece to be deformed leaves something to be desired and the necessary deformation forces and the deformation energy are relatively high. Superplastic forming, on the other hand, relies on an ultra-fine grain of the blank, which can only be achieved with certain alloy additives and complex thermomechanical processes. Certain materials do not show any superplasticity at all, so that due to these requirements with regard to the structure of the structure, the corresponding material limits are encountered again. There is therefore a great need to expand the possibilities of hot-forming metallic materials in general by refining and broadening the processes and to extend them to as many materials as possible.

The invention is based on the object of specifying a hot molding process for metallic materials which, with great simplicity, allows the production of semifinished or finished parts in as few work steps as possible and, thanks to good mold filling capacity, allows the design limits to be expanded. The process is said to possibly work on a variety of plants Substances may be applicable.

According to the invention, this object is achieved by the features of claim 1.

The main idea of the invention is to form the material as close as possible to below the solidus temperature, but to avoid local liquefaction in the best possible way. With this measure, the yield stress (deformation resistance) of the material is reduced considerably, so that optimum mold filling capacity is achieved.

The invention is described with reference to the following exemplary embodiments and an explanatory figure.

It shows:

the figure shows the working diagram of the method in the form of a time / temperature function.

In the figure, the abscissa represents the time axis, the ordinate the temperature axis. With the horizontal on the

Level 1 indicates the solidus temperature T _{sol of} the material (alloy) to be deformed, which must not be reached during the entire work process under any circumstances. Otherwise local melting would occur and the connection and controlled structure of the workpiece would be lost. 2 is the maximum temperature which - mostly at the end of the shaping - can be reached by the workpiece and tool at the same time. Depending on the alloy and type of workpiece, it must always remain below 1 (T _sol ) by a certain amount. 3 represents the comogenization system temperature of the workpiece, for which the same applies as for temperature 2, so that subsequent melting during the forming process can be avoided with certainty. 4 is the course of the workpiece temperature over time until the end of the shaping. This operation breaks down into the preheating phase 8 and the forming phase 9. 5 represents the course of the workpiece temperature during normal cooling to room temperature. 6 is the analogous course after shaping in the event that the latter is directly subjected to further additional heat treatment (e.g.

Warm aging, thermal hardening etc.) is connected. In most cases, you will not be able to avoid homogenizing the material beforehand. However, this is not an absolutely necessary prerequisite for the method according to the invention, but it means a preferred safety measure. The course of the temperature during the homogenization phase 10 is shown by the line 7.

Embodiment I: Die pressing of a radial compressor wheel made of an Al-Cu-Mg-Ni alloy.

A radial compressor wheel with a diameter of 180 mm was produced in one operation by isothermal high-temperature pressing from a disc-shaped cylindrical blank. The aluminum alloy used complied with US AA standard 2618 and had the following composition:

Si = 0.10 - 0.25% by weight

Fe = 0.9 - 1.3% by weight

Cu = 1.9-2.7% by weight Mg = 1.3-1.8% by weight

Ni = 0.9-1.2% by weight Zn = 0.10% by weight

Ti = 0.04-1.10% by weight AI = rest

A disc in the form of a rod section was used as the starting material. The rod itself was made from a section of a larger diameter press stud produced by extrusion by extrusion. In the case of larger blank dimensions (disc with a diameter of more than 200 mm), workpieces produced by open-die forging can also be used as preforms. The shape of the compressor wheel to be produced had 18 radially standing blades, slightly curved on the circumference in the tangential direction, of approximately 30 mm depth, which had a wall thickness of approximately 4 mm at the base and one of approximately 2 mm at the head. The disk-shaped wheel body had an axial wall thickness of approx. 6 mm on the circumference.

Practical tests have shown that it is completely impossible to manufacture a body of such a complicated geometry by conventional pressing or forging. The actual shape deviates considerably from the target values due to insufficient mold filling capacity.

The starting material was subjected to a homogenization annealing at a temperature of 520 ° C. for 20 hours before the shaping. This measure serves to avoid local melting or local pore formation when the maximum temperature is subsequently passed during the shaping process. The latter was carried out as an isothermal high-temperature die press on a specially designed hydraulic press equipped with inductive workpiece and tool heating. The press was set up for low stamp speeds of 0.05 - 5 mm / s, which could be changed as desired during the pressing. Furthermore, the pressing force could also be kept constant over a longer predetermined period of time after a predetermined limit value had been reached. The table and stamp were provided with a cooling device. The inductive heating system consisted of an induction coil for heating the workpiece blank as well as the tools (dies) made of hot-work steel. Precise temperature control and temperature control was ensured via thermocouples in the tool and via buttons on the workpiece blank. A specially designed device was used to transport the workpiece into the heating zone or into the area of the tool, as well as to eject it from the tool after it had been formed and transported to storage.

The workpiece blank in the form of a disc was first continuously heated to a temperature of 480 ^ο + 10 ^ο C by inserting it into the associated induction coil. Then the blank was ^ο out in the 480 - 520 ^ο C heated

Die inserted. Now the pressing speed was set to an average value of approx. 0.5 - 1 mm / s. During this first phase of upsetting, in which the workpiece temperature adapts to the tool temperature, the pressing force rose only slightly (from 0 to approx. 500 kN). The blades were then shaped in a second phase, the punch speed being reduced to 0.05-0.1 mm / s and the pressing force increasing steadily until it reached its maximum (approx. 3000 kN). The pressing force was now kept constant in order to completely fill the mold during this third phase, which lasted about 5-10 minutes. The pressing time for such a compressor wheel was approx. 10-20 min. the mean pressing pressure was approximately 120 MPa.

When pressed here Al-Cu-Mg-Ni alloy, the solidus temperature is at 549 ° C, the solution treatment at 530 ^{ο ο} C. At 520 C exists in this alloy still undissolved intermetallic compound FeNiAl ₉ as a separate phase. It prevents uncontrolled grain growth during high temperature shaping. The deformation temperature of 480 ^ο - 520 ^ο C was optimally chosen in this regard and local pore formation due to melting was also not to be feared.

Compared to the invention for punching, the forming is according to the conventional forging technology, which for the aforementioned aluminum alloy in the temperature range of about 410 - 450 ^° C is carried out, Wesent lent favorable. Experience has shown that the pressures here are between 200 and 500 MPa, which requires heavier and stronger presses. The mold filling capacity is significantly poorer, so that the blades do not reach the target dimension (rib wall thickness 2 - 4 mm) by far and one with rib thicknesses of approx. 8 - 10 mm in the first

Operation must be satisfied. This requires at least a few additional work steps, including additional costly machining.

Embodiment II: Die pressing of a turbine blade made of a precipitation-hardenable nickel-based superalloy.

A turbine blade 150 mm long and 35 mm wide was cut in one operation due to isothermal high temperatures door presses made from a bar section. The alloy used with the trade name Nimonic-80A had the following composition:

Cr = 19.5% by weight Co = 1.0% by weight

Ti = 2.25% by weight

AI = 1.4% by weight

Fe - 1.5% by weight

C =. 0.05% by weight Cu = max. 0.10 wt

Ni = rest

A section from a rolled bar was used as the starting material. In order to provide a homogeneous structure for the shaping, the primary material was first annealed under protective gas at a temperature of 1080 ^o C for 8 hours and then quenched in water. In principle, the hydraulic press provided for carrying out the operation was constructed similarly to that described in Example I. It had an adjustment range for the stamp speed of 0.05 - 25 mm / s. In addition, it was encapsulated in such a way that operation under protective gas or vacuum was possible. Dies were used as tool from the well-known molybdenum alloy TZM, which allow operating temperatures up to over 1200 ^ο C. The inductive heating was designed in the same way as that in example I. In addition to the transport system for the workpiece, there were lock chambers, which enabled the transition between the press room and the outside world.

The blank was first heated to a temperature of 1100 ^o + 20 ^o C in the associated induction coil then placed in the TZM die heated to 1150 ° - 1200 ° C. The stamp was then pressed against the lower half of the die at a pressing speed of approx. 4 mm / s (phase I). After the beginning of the pressing force rose, it was then deformed at a pressing speed of approx. 0.1 mm / s for the purpose of filling the burr section (phase II). After reaching the maximum force, this value was reached for about 5 minutes until the mold was finally filled. kept constant (phase III). Depending on the shape and material, this phase can last approx. 1 - 10 min. The total pressing time for such a turbine blade can be approximately 2-15 minutes. The mean pressing pressure in the present case reached approximately 200 MPa.

The present nickel-based superalloy has a solidus temperature of approx. 1360 ^o C and a solution annealing temperature of approx. 1080 ^o C. In the temperature range of 1150 ^ο - 1200 C ^ο what a sufficiently large distance from the solidus to prevent incipient melting speaks ent, there are still unresolved metal carbides in finely divided form. These prevent uncontrolled grain growth during high-temperature deformation, which could also be determined by comparing metallographic micrographs.

In conventional forging / pressing under hammers and high-speed screw presses, the pressures are comparatively considerably higher and would reach values of 500 - 1000 MPa in the present example. In addition to the required size of such machines, the limits of the temperature-material strength (risk of surface cracks) of the die materials are also reached. There are mold filling capacities the same disadvantages as described in example I.

Working example III:

High temperature presses of a turbine blade made of an oxide dispersion hardened stainless ferritic steel.

A turbine blade of 200 mm in length and 50 mm in width was produced in one operation by isothermal high-temperature presses from a rod section. The iron alloy used had the following composition:

Cr = 12.5% by weight

Ti = 3.5% by weight

Mo = 1.5% by weight

C = 0.02% by weight

Y ₂ O ₃ = 0.5% by weight

TiO ₂ = 1.0% by weight

Fe = rest

A section of an extruded rod was used as the starting material. The alloy itself was produced in a known manner by powder metallurgy by mechanical alloying and subsequent compression by extrusion. The blank was first homogenized at a temperature of 1150 ^° C. for 15 minutes and cooled again to room temperature. The further process steps were carried out in a manner analogous to that described in Example II. The workpiece temperature after preheating 1150 ^ο C, that of TZM tools (swaging and base) 1150 ^ο 1200 ^ο C. All other parameters were adhered to in a similar way to Example II (deformation hare I-III). The submicroscopic form and distribution of the oxidic dispersoids Y ₂ O ₃ and TiO ₂ are thermally stable up to over 1200 ° C and reliably prevent uncontrolled grain growth during the operations. A finished part made in this way from a dispersion alloy is characterized by maximum density, ie absolute freedom from pores compared to the conventional type of workpiece directly produced by powder metallurgy (pressing + sintering, hot isostatic pressing).

Working example IV:

High-temperature extrusion / hot extrusion of semi-finished and finished parts made of a Cu / Al / Ni memory alloy with oxide dispersoid.

A round rod of 5 mm in diameter was extruded from a press bolt by isothermal high-temperature extrusion

Made 20 mm diameter. The shape memory alloy used had the following composition:

AI - 13 wt. -%

Ni - 3% by weight

Al ₂ O ₃ - 0.4 wt. -%

Cu - rest

A precompacted ingot produced by mechanical alloying from a Cu / Ni pre-alloy and aluminum with Al ₂ O _{3 was} used as the starting material, which served as a press bolt. The press bolt was first homogenized at 950 ^° C for 1 h and cooled again to room temperature. Thereupon it was heated to a temperature of 850 ^° C. and at a temperature of 850 ^{° to} 950 ^° C. by means of a matrix made of a nickel-based alloy (trade name IN-100) to form a strand of 5 mm in diameter. The presence of the Al ₂ O ₃ dispersoid in an ultrafine distribution prevents inadmissible grain growth during the pressing process.

The extrusion and also the hot extrusion at these relatively high temperatures just below the solidus line allows, thanks to the better mold filling capacity, more complicated shapes and transitions with smaller radii of curvature. In this way, thin-walled fins (e.g. on finned tubes) can also be produced, which is particularly important for heat exchangers (aluminum or copper alloys).

von 0 bis 10s^-1 betragen, wobei

v = Werkzeuggeschwindigkeit h = WerkstückhδheThe invention is not restricted to the above exemplary embodiments. Both the workpiece and the tool are to be brought to a temperature for the deformation process which is between 5 Kelvin and at most 0.15 T _sol in degrees Kelvin (T _sol = solidus air temperature in degrees Kelvin) lower than T _sol . The temperature difference in the workpiece cross-section and over the entire time of the isothermal / quasi-isothermal shaping should not exceed 50 ^° C and the rate of deformation

from 0 to 10s ^-1 , where

v = tool speed h = workpiece height

Before shaping, the workpiece is advantageously homogenized for 0.1 to 100 h at a temperature which corresponds to the highest effective deformation temperature, in order to avoid local melting and pore formation, and is cooled again to room temperature. The cooling after shaping can can also be done by quenching to room temperature in water or oil. Quenching, similar to thermal hardening, can also be carried out to a temperature above room temperature in a metal or salt bath with subsequent aging. In principle, hot forming can be drop forging, hot pressing, hot extrusion or hot extrusion. Advantageously, the hot forming should be carried out in a temperature range in which, in addition to a first phase as the main structural component, there is also a second phase which inhibits grain growth at least during the entire shaping time. The latter can preferably consist, for example, of an oxidic dispersoid, such as Y ₂ O ₃ , TiO ₂ , Al ₂ O ₃ etc., or of an ordinary oxide or of a carbide. In this way, for example, aluminum alloys, copper alloys (in particular Cu / Al / Ni), nickel-based super alloys, nickel-based dispersion alloys and nickel alloys of the Ni / Ti type (memory alloys) or Ni / Ti / Cu can be formed. The method can also be applied to heat-resistant, rustproof ferritic, ferritic-austenitic and austenitic steels, in particular oxide-dispersion-hardened steels. The raw material can also be in the raw state as a porous sintered body or as a green, cold-pressed body made of a sintered material, which is compressed, sintered and converted into the intended shape at the same time during the shaping process.

Claims

Patent claims 1. A method for producing a calf or a finished part from a metallic material by hot forming, characterized in that a workpiece initially present as a cast ingot, rolled ingot or forging blank is heated to a temperature which is 5 degrees Kelvin to a maximum of 0.15 T _sol in degrees Kelvin below the solidus temperature of the material, the workpiece is then brought into contact with a tool whose temperature is kept constant and by 5 degrees Kelvin to 0.15 T _sol in degrees Kelvin is lower than the solidus temperature of the material but higher than the preheating temperature of the workpiece, and that the workpiece with a rate of deformation

is deformed isothermally or quasi-isothermally based on the change in cross-section from 0 to 10s in such a way that the temperature difference across the entire workpiece cross-section and over the entire time of the shaping is a maximum of 50 ^° C, whereby

the following dimensions are defined:

v = tool speed h = workpiece height T _sol = solidus temperature in degrees Kelvin, and that the workpiece is finally subjected to cooling. 2. The method according to claim 1, characterized in that the workpiece before heating for hot shaping during 0.1 to 100 h at a temperature which corresponds to the highest effective deformation temperature, in order to avoid subsequent local melting and pore formation, the mixture is then cooled again to room temperature. 3. The method according to claim 1, characterized in that the cooling of the workpiece consists in quenching the deformation temperature to room temperature in water, oil or to a temperature above room temperature in oil, metal or salt bath and that the workpiece is then at room temperature or at is outsourced to a temperature above room temperature. 4. The method according to claim 1, characterized in that the hot forming in a drop forging, Hot pressing, hot extrusion or hot extrusion exists. 5. The method according to claim 1, characterized in that the hot deformation is carried out in a temperature range of the material in which, in addition to a first phase as the main structural component, there is a second phase which inhibits grain growth at least during the total time of the deformation. 6. The method according to claim 5, characterized in that the grain growth inhibiting phase from one Oxide dispersoid such as Y ₂ O ₃ , TiO ₂ or consists of an oxide or a carbide. 7. The method according to claim 1, characterized in that the material to be deformed is an aluminum alloy. 8. The method according to claim 7, characterized in that the aluminum alloy has the following composition: 1.9-2.7% Cu 1.3-1.6% Mg 0.9 - 1.2% Ni rest AI. 9. The method according to claim 1, characterized in that the material to be deformed is a copper alloy of the Cu / Al / Ni type. 10. The method according to claim 1, characterized in that the material to be deformed is a nickel-based Super alloy or a nickel-based dispersion alloy or a nickel alloy of the Ni / Ti or Ni / Ti / Cu type. 11. The method according to claim 1, characterized in that the material to be deformed is a heat-resistant stainless ferritic, ferritic-austenitic or austenitic steel. 12. The method according to claim 11, characterized in that the material to be deformed is a ferritic oxide-hardened steel. 13. The method according to claim 1, characterized in that the material to be deformed is a raw sintered material as a porous sintered body or as a green, cold pre-pressed body, which at the same time compresses, sintered and converted into the intended shape during the shaping process.