EP0069421B1 - Process for manufacturing semi-finished or finished articles from a metallic material by hot-shaping - Google Patents

Abstract

The semi-finished and finished products of an aluminum, copper, nickel and iron alloy with or without oxydic dispersoids are obtained by thermoforming, wherein the forming is carried out isothermally or quasi-isothermally in a single step, at a temperature which is just lower than the temperature of the solidus of the alloy of the work piece, at a relatively low deformation rate and under low specific deformation forces. The workpiece and the tool are maintained at least during the last, longer face of the forming at the maximum allowable temperature nearest to the solidus line. Preferably, a previous homogenisation of the material at said maximum allowable temperature followed by a cooling to the surrounding temperature before the forming. Very good filling power of the mold.

Description

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 extent of the costly machining that may be required. Known methods of this type are e.g. isothermal or quasi-isothermal forming (forming with heated tools), as has become the norm in forging (drop forging). Attempts are also being made to reduce the resistance to deformation and to improve the mold filling capacity by shaping in the so-called superplastic state of the material - if such a state can be set at all (see: G. Schröder, isotherms and superplastic forming in drop forging, workshop and operation 113 / 1980/11, pp. 765 - 770; GHGessinger, isothermal forming - a cost-effective precision forging process, technical reports metallurgical practice metal processing 11/78, pp. 954-957).

In the forming processes described, the possibilities of cost-effective production are only used 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, the 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 that 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, one again hits the corresponding material limits.

US-A-3 975 219 describes a method for the thermomechanical treatment of nickel superalloys. Starting from encapsulated and hot-compacted powder, a superplastic state in the range below the y 'solution annealing temperature is initially sought. The hot pre-compacted blank is subjected to a gradual cooling down to room temperature via a salt bath and then reheated and an extrusion process just below the y'-solution annealing temperature. Disks are cut from the extruded material and subjected to further hot forming by isothermal forging within a temperature range which is below, but at most 120 ° C lower than the ys' solution annealing temperature. The deformation should be at least 10% (example 1: 83% decrease in height) and the rate of deformation should not exceed 0.017s- ^1- (example 1: 0.0017s- ¹ ). The workpiece shaped in this way is then zone-annealed under a temperature gradient of approx. 1 ° C./mm and a temperature at the end of the workpiece which lies between the y'-solution annealing temperature and the solidus temperature in order to set a coarse grain structure.

This process, which is specifically aimed at superalloys and the achievement of a coarse grain in the longitudinal direction of the workpiece, requires a superplastic condition beforehand and is characterized by numerous complex process steps.

There is therefore a great need to expand the possibilities of hot-shaping metallic materials in general by refining and broadening the processes and to extend them to as many materials as possible.

The invention has for its object to provide a hot-forming process in general for metallic materials, wherein a workpiece initially made as a cast ingot, rolled ingot, forged blank or powder-metallurgically manufactured blank made of a metal alloy, except for a nickel-based superalloy which has been brought into the superplastic state, in as few steps as possible can be converted into a semi-finished or finished part. Thanks to the good mold filling capacity of the workpiece, the process should allow for great simplicity to expand the design limits and be applicable to a large number of materials.

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

The guiding principle of the invention is to deform the material as close as possible below the solidus temperature, but to avoid local liquefaction with the greatest care. This measure considerably reduces the yield stress (deformation resistance) of the material, so that optimum mold filling capacity is achieved.

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

• die Figur das Arbeitsdiagramm des Verfahrens in Form einer Zeit/Temperatur-Funktion.

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 at level 1, the solidus temperature T _{sol of} the material (alloy) to be deformed is identified, which under all circumstances during the whole Work process must not be achieved. Otherwise local melting would occur and the connection and controlled structure of the workpiece would be lost. 2 is the maximum temperature which - usually 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 homogenization 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 with normal cooling to room temperature. 6 is the analogous course after the shaping in the event that the latter is subjected to further additional heat treatment (eg heat 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 requirement 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.

• Gesenkpressen eines Radialverdichterrades aus einer AI-Cu-Mg-Ni-Legierung.

Example 1:

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

• Si = 0,10 - 0,25 Gew.-%
• Fe = 0,9 - 1,3 Gew.-%
• Cu = 1,9 - 2,7 Gew.-%
• Mg = 1,3 - 1,8 Gew.-%
• Ni = 0,9 - 1,2 Gew.-%
• Zn = 0,10 Gew.-%
• Ti = 0,04 - 1,10 Gew.-%
• AI = Rest

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 corresponded to 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, in turn, was made from a section of a larger diameter press stud made 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 raw 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 deformation process. The latter was called isothermal. High-temperature die presses carried out 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 required during the pressing. Furthermore, the pressing force could also be kept constant over a longer predetermined period of time after reaching a predetermined limit value. 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 for transporting the workpiece into the heating zone or into the area of the tool, as well as for ejecting it from the tool after forming and transporting it to storage.

The workpiece blank in the form of a disk was first continuously heated to a temperature of 480 ° ± 10 ° C by being pushed into the associated induction coil. The blank was then placed in the die heated to 480 ° - 520 ° C. 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 steadily increasing at the same time 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 to 10 minutes. The pressing time for such a compressor wheel was approx. 10-20 min average pressing pressure was about 120 MPa.

In the case of the pressed Al-Cu-Mg-Ni alloy, the solidus temperature is 549 ° C, the solution annealing temperature is 530 ° C. At 520 ° C, the undissolved intermetallic compound FeNiAl ₉ still exists as an independent phase in this alloy. It prevents uncontrolled grain growth during high temperature shaping. The deformation temperature of 480 ° - 520 ° C was optimally chosen in this regard and local pore formation due to melting was also not to be feared.

In comparison to the die press according to the invention, the shaping according to conventional forging technology, which is carried out for the aforementioned aluminum alloy in the temperature range of approximately 410-450 ° C., is considerably less favorable. Experience has shown that the pressures here are between 200 and 500 MPa, which requires heavier and more powerful presses. The mold filling capacity is significantly worse, so that the blades do not reach the target dimension (rib wall thickness 2 - 4 mm) by far and you have to make do with rib thicknesses of approx. 8 - 10 mm in the first work step. This requires at least a few additional work steps, including additional costly machining.

• Gesenkpressen einer Turbinenschaufel aus einer ausscheidungshärtbaren Nickelbasis-Superlegierung.

Working example II:

• Die pressing of a turbine blade made of a precipitation hardenable nickel-based superalloy.

• Cr = 19,5 Gew.-%
• Co = 1,0 Gew.-%
• Ti = 2,25 Gew.-%
• AI = 1,4 Gew.-%
• Fe = 1,5 Gew.-%
• C = 0,05 Gew.-%
• Cu = max. 0,10 Gew.-%
• Ni = Rest

A turbine blade 150 mm long and 35 mm wide was produced in one operation by isothermal high-temperature pressing from a rod 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% by weight
• 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 ° C. for 8 h and then quenched in water. The hydraulic press intended to carry out the operation was constructed in principle in a similar manner 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. As a tool, dies made from the well-known molybdenum alloy TZM were used, which allow working temperatures up to over 1200 ° C. The inductive heating was designed in the same way as that in example 1. 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 an average temperature of 1100 ° C in the associated induction coil and 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 pressing force began to increase, a further pressing was carried out at a pressing speed of approx. 0.1 mm / s to fill the ridge section (phase 11). After reaching the maximum force, this value was reached for about 5 minutes until the mold was finally filled. kept constant (phase 111). 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. In the present case, the mean pressing pressure reached the value of approx. 200 MPa.

The present nickel-based superalloy has a solidus temperature of approx. 1360 ° C and a solution annealing temperature of approx. 1080 ° C. In the temperature range of 1150 ° - 1200 ° C, which corresponds to a sufficiently large distance from the solidus line to prevent melting, there are still undissolved 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. Apart from the required size of such machines, the limits of the temperature-material strength (risk of surface cracks) of the die materials are also reached. With regard to mold filling capacity, there are the same disadvantages as described under Example I.

• Hochtemperaturpressen einer Turbinenschaufel aus einem oxyddispersionsgehärteten rostfreien ferritischen Stahl mit einer Solidustemperatur von ca. 1440°C.

Embodiment 111:

• High temperature presses of a turbine blade made of an oxide dispersion hardened stainless ferritic steel with a solidus temperature of approx. 1440 ° C.

• Cr = 12,5 Gew.-%
• Ti = 3,5 Gew.-%
• Mo = 1,5 Gew.-%
• C = 0,02 Gew.-% Y₂0₃ = 0,5 Gew.-%
• Ti0₂ = 1,0 Gew.-%
• Fe = Rest

A turbine blade of 200 mm in length and 50 mm in width was produced in one operation by isothermal high-temperature pressing 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 0 ₃ = 0.5% by weight
• Ti0 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 11. The workpiece temperature after preheating was approx. 1150 ° C, that of the TZM tools (upper and lower part of the die) was 1150 ° C-1200 ° C. All other parameters were adhered to in a manner similar to Example II (deformation phases I-III).

The oxidic dispersoids Y ₂ 0 ₃ and Ti0 _{2, which} are present in submicroscopic form and distribution, 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).

• Hochtemperatur-Strangpressen/Warmfliesspressen von Halbzeug und Fertigteilen aus einer Cu/AI/Ni-Gedächtnislegierung mit Oxyddispersoid mit einer Solidustemperatur von ca. 1040°C.

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 with a solidus temperature of approx. 1040 ° C.

• AI = 13 Gew.-%
• Ni = 3 Gew.-%
• A1₂0₃ = 0,4 Gew.-%
• Cu = Rest

A round rod of 5 mm in diameter was produced by isothermal high-temperature extrusion from a press bolt of 20 mm in diameter. The shape memory alloy used had the following composition:

• AI = 13% by weight
• Ni = 3% by weight
• A1 ₂ 0 ₃ = 0.4% by weight
• Cu = rest

The starting material used was a powder-metallurgically produced pre-compacted ingot produced by mechanical alloying from a Cu / Ni pre-alloy and aluminum with A1 ₂ 0 ₃ , 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 pressed at a temperature of 850 ° to 950 ° C. through 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 A1 ₂ 0 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).

• v = Werkzeuggeschwindigkeit
• h = Werkstückhöhe

The invention is not restricted to the above exemplary embodiments. Both the workpiece and the tool should be brought to a temperature for the deformation process that is between 5 Kelvin and at most 0.15 T _sol in degrees Kelvin (T _sol = solidus 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 be at most 50 ° C. and the rate of deformation from> 0 to 10 s 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. Cooling after shaping can also be done by quenching to room temperature in water or oil. Furthermore, 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. The hot forming should advantageously be carried out in a temperature range in which, in addition to a first phase, which is the main structural component, there is 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 0 ₃ , Ti0 ₂ , A1 ₂ 0 ₃ etc., or of an ordinary oxide or of a carbide. In this way, aluminum alloys, copper alloys (in particular Cu / Al / Ni), nickel-based superalloys, nickel-based dispersion alloys and nickel alloys of the Ni / Ti type (memory alloys) or Ni / Ti / Cu can be formed, for example. The process can also be applied to heat-resistant, rustproof ferritic, ferritic-austenitic and austenitic steels, especially use 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 during the molding process.

Claims (10)

1. Process for producing a semi-finished or finished component from a metallic material by hot-forming, a workpiece initially present as a cast billet, rolled billet, forging blank or blank produced by powder metallurgy and consisting of a metal alloy with the exception of Ni super-alloys brought into the superplastic state being heated to a temperature which is more than 5 degrees Kelvin up to at most 0.15 T_sol in degrees Kelvin below the solidus temperature of the material,
that the workpiece is then brought into contact with a tool, the temperature of which is kept constant and is 5 degrees Kelvin to 0.15 T_sol in degrees Kelvin lower than the solidus temperature of the material but higher than the preheating temperature of the workpiece, and that the workpiece is isothermally or quasi- isothermally deformed at a deformation rate relative to a change in cross-section of > 0 to 10 s^-1, in such a way that the temperature difference considered across the whole crosssection of the workpiece and over the total time of forming is at most 50°C, (p being defined as follows:

v = tool speed

h = workpiece height

T_sol = solidus temperature in degrees Kelvin,

that moreover the hot-forming is carried out in a temperature region of the material in which, in addition to a first phase as the main structural component, a second phase inhibiting grain growth is also present at least for the total deformation time, and that finally the workpiece is subjected to cooling.

2. Process according to Claim 1, characterised in that the phase inhibiting grain growth consists of an oxide dispersoid such as Y₂0₃, Ti0₂ or of an oxide or a carbide.

3. Process according to Claim 1, characterised in that the cooling of the workpiece consists in quenching from the deformation temperature to room temperature in water or oil or to a temperature lying above room temperature in oil, metal or salt bath and that the workpiece is then aged at room temperature or at a temperature lying above room temperature.

4. Process according to Claim 1, characterised in that the hot-forming consists of drop-forging, hotpressing, hot impact extrusion or hot die extrusion.

5. Process according to Claim 1, characterised in that, before heating for hot-forming, the workpiece is homogenised for 0.1 to 100 hours at a temperature, which corresponds to the highest, effectively arising deformation temperature of the workpiece, in order to avoid later local fusions and pore formation, and is then cooled again to room temperature.

6. Process according to Claim 1, characterised in that the material to be deformed is an aluminium alloy, in particular an AI/Cu/Mg/Ni alloy.

7. Process according to Claim 1, characterised in that the material to be deformed is a copper alloy of the Cu/AI/Ni type.

8. Process according to Claim 1, characterised in that the material to be deformed is a nickel-based superalloy or a nickel-based dispersion alloy or a nickel alloy of the Ni/Ti or Ni/Ti/Cu types.

9. Process according to Claim 1, characterised in that the material to be deformed is a high- temperature stainless ferritic steel, a ferritic oxide-dispersion hardened steel, a ferritic- austenitic steel or austenitic steel.

10. Process according to Claim 1, characterised in that the material to be deformed is a sintered material which is present in the raw state as a porous sintered body or as a green, cold- prepressed body and which, during the deformation process, is simultaneously compacted, sintered and converted to the intended shape.

Images