Method for hot forming a workpiece and equipment for reducing the workpiece's heat emission

The invention relates to a method for hot forming by massive forming such as forging or rolling a workpiece or starting material made of metal or of an intermetallic compound at a temperature of over 1000 ° C.

The invention further relates to a means for a coating for reducing the heat radiation from a workpiece or pre-material heated to the forming temperature.

ok

According to the invention it is provided that in a first step the surface of the workpiece is at least partially covered with a coating agent consisting of an oxide phase, an additive or an adhesive and a binder and the coating is allowed to solidify, after which in a

The next step is a warming up with a thorough warming of the primary material

Deformation temperature takes place and this is brought to a shaping agent and processed or forged or rolled with this to form a molded body or rolled product.

The agent for a coating consists of an oxide phase as the main component and one or more additive (s) as an additive and liquid components.

<img file="AT508322A1_D0001.tif" />

Process for hot forming a workpiece and means for

Reduction of heat radiation

The invention relates to a method for hot forming by massive forming 5 such as forging or rolling a workpiece or starting material made of metal or of an intermetallic compound at a temperature of over 1000 ° C.

The invention further relates to a means for a coating for reducing the radiation of heat from a material heated to the forming temperature

Workpiece or raw material.

A hot deformation of a metal workpiece, such as a cast block or a primarily deformed pre-material made of metal or of intermetallic compounds to form a forged part, requires precise temperature control for materials with poor deformation properties, from heating to the removal of the part from the forming agent.

A sufficient deformability of the material of the workpiece is often only given within a narrow temperature window, because lower molding temperatures lead to a

Brittleness and higher temperatures also lead to brittleness and / or coarse grain formation in the structure of the material.

If necessary, the limit of sufficient deformability is at high temperatures of over 1000 ° C.

The radiated heat energy generally increases with the fourth power when the temperature rises, so that at high surface temperatures of the workpiece, the energy loss and the temperature drop in the edge area are high in the unit of time.

If the deformation temperatures required are high, it is therefore difficult and / or complex to ensure a temperature with sufficient deformability of the material over a required period of time even in the edge region of the workpiece.

Workpieces are heated to forming temperature in the usual way in an oven. The heated part is then discharged from the furnace by known means, brought to a shaping means, placed on a roller table or a tool part and processed with tools in a deforming manner. During this period of time, the surface of the workpiece radiates heat and / or this is dissipated into the tools.

The general problem is therefore a rapid temperature loss in the near-surface zone of the workpiece and a resulting loss

Occurrence of defects such as cracks.

To solve this problem, it has already been proposed and, if necessary, the heated workpiece can also be moved in a short time. However, it is usually not possible to position the heating unit and the forming device in the immediate vicinity.

Attempts have also been made to heat the workpiece to such an extent that, even if the temperature drops, its surface zone is still in the temperature range of the deformability of the material. However, such a coarsening and / or deterioration of the microstructure or center errors can arise.

Methods are also known for enclosing the workpiece in a capsule and for heating and deforming it therein. Such a method can be very effective in terms of reshaping a part in a narrow temperature window, but it requires a great deal of effort.

In terms of process technology, isothermal forging of the workpiece is also possible and effective, in which the tools are heated to a temperature close to the forming temperature. However, such a method is extremely complex and costly.

The aim of the invention is to provide a new method of the type mentioned at the beginning for reshaping a workpiece which overcomes the disadvantages of the known methods.

·· ·· ···· ···· · *

9 9 9 9 ·· ·· • · · · ··· · · · · • · · · · · ···· · ···· 9 9 « « ·· 99 999 · · «··

This goal is achieved in a generic method in that, in a first step, the surface of the workpiece is coated with a coating agent consisting of an oxide phase, an additive or a binding agent, at least partially covered and the coating is allowed to solidify, after which in a subsequent step the pre-material is heated to the deformation temperature, then it is brought to a shaping agent and processed, forged or rolled with this to form a molded body or rolled product .

The advantages achieved with the method according to the invention are essentially to be seen in the fact that the abstraction and thus the temperature loss are reduced in the unit of time, particularly when the workpiece is brought to the shaping means. This also applies when the workpiece is placed on a roller table or on a tool part. Surprisingly for the person skilled in the art, it has been shown that a coated workpiece does not require longer heating times when heated in the oven.

According to the invention, it is important that the workpiece is coated with a uniform layer thickness and that the layer does not flake off

Warming and is given during the subsequent bringing to the shaping agent. The coating also reduces the heat transfer from the workpiece to the tool, at least in the first deformation step.

A particularly good adhesion of the layer can be achieved according to the invention if the surface of the workpiece or pre-material is coated at a temperature of the same of over 100.degree. C., preferably around 200.degree.

If, as has been found, a coating of the surface of the workpiece or raw material by dipping in or spraying with a

Coating agent takes place, a largely uniform layer thickness can be achieved on the surface in a favorable manner.

In order to achieve an optimum for reducing the radiation of thermal energy from the surface and good layer adhesion on the one hand and a desired high level of · · ···· · _Ä · · · · · ·· ··· · · ···

On the other hand, to achieve surface quality of the deformed workpiece, it can be advantageous if the coating is carried out with a solidified layer thickness of greater than 0.1mm, preferably with a layer thickness of 0.3mm to 3.0mm.

The further object of the invention is to provide a means for a coating to reduce heat radiation from a workpiece or pre-material heated to forming temperature, which means can be applied slightly thin and with the same layer thickness to the surface of a workpiece before heating, during the Heat process in the oven does not peel off, has sufficient adhesion when brought to the tool up to the first forming step and improves the forging quality.

This task is done by a means consisting of an oxide phase as

Main component and one or more additive (s) or adhesive (s) as an additive and liquid components, dissolved.

According to the invention, the oxide phase acts as a heat-resistant insulating component, with one or more additives or adhesives in smaller proportions

Oxide grains connect (connect) and hold (hold) on the substrate. The liquid component (s) is (are) used to homogenize the phases and to set a desired degree of liquid for homogeneous application to the surface of the workpiece or part.

An agent in which the main component or oxide phase is formed from zirconium oxide with a percentage by weight of greater than 70, preferably from 80 to 98, in particular from 90 to 97, has proven to be a significant reduction in heat radiation exposed particularly favorably.

If the proportion of zirconium oxide is greater than 70% by weight, an agent in which the additives of methyl cellulose and / or microsilica with proportions in% by weight of 0.1 to 1.0, preferably 0.2 to 0.7, or 1.0 to 10.0, preferably 2.0 to 8.0, are particularly advantageous for coating TiAl alloys, because this type of alloy and the coating material only ·· ·· ···· ···· «· ····· ·· · «• · · · ··· · · · · • · · · · ···· · · · · · · ·« ·· ·· ··· · «··· slightly different expansion coefficients to have.

As a liquid component, sodium silicate glass is added to the agent in a percentage by weight of 15 to 65, preferably from 20 to 60, this addition being based on the

Oxide phase relates to the additive (s).

An agent in which the oxide phase is formed with a grain diameter of 1 μm to 50 μm, preferably an average grain size of d 50 = 12.5 μm, has proven to be particularly uniformly applicable and has good thermal insulation properties.

As previously mentioned for thermal expansion, a use of the aforementioned method for hot forming of a workpiece and the use of an agent according to the above information to reduce the

Heat radiation from a workpiece heated to forming temperature for the hot forming of parts made of a gamma-titanium-aluminum-based alloy was shown to be particularly advantageous, with this alloy being able to be heated up to over 1280 ° C and the flawless coating significantly reducing the temperature drop near the surface Zone of the workpiece causes io in the unit of time.

The invention is to be described in more detail on the basis of results from the development work and from the comparative investigations of the temperature profile over time on test specimens.

Show it:

1 thermal expansion of a TiAl alloy and a zirconium oxide coating over temperature

Fig. 2 specimen with the position of the measuring points

3 cooling curves over time of coated rod and bare (uncoated) rod in a position close to the surface

Fig. 4 Cooling curves over time of the coated rod and the bare rod in the rod core · · ···· ·· · ·· ·· ··· · ···

1 shows the expansion of a substrate made of a gamma-titanium-aluminum base alloy and a zirconium coating as a function of the temperature up to 1000 ° C. It should be noted from the illustration that the thermal

The elongation of the two materials shows only slight differences, which is why the layer does not flake off from the base material.

In Fig. 2, a test specimen with a diameter of 40 mm 0 is shown, which has a hole near the surface and a central hole for thermocouples.

ok

The tests were carried out in such a way that uncoated and coated test specimens were equipped with thermocouples and heated to a temperature of approx. 1290 ° C. After soaking through heating, the test specimens were removed from the inert gas oven, positioned on a refractory base and the temperature profile was measured as a function of time.

3 shows the temperature drop as a function of time in the zone near the surface of uncoated and coated test specimens. Approx. 30 sec. After the test specimen has been discharged, an uncoated rod shows in the

Surface area has a temperature of approx. 1165 ° C and one with a zirconium layer has a temperature of approx. 1215 ° C.

Fig. 4 shows the temperature drop in the center of the specimen.

3 and 4 do not require any further explanation for a person skilled in the art and clearly show the effect of a zirconium oxide-based coating on a test piece made of a gamma-titanium-aluminum-based alloy to reduce the heat radiation.