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

Raw material.

According to the invention it is provided that in a first step the surface of the workpiece is coated with a coating agent consisting of an oxide phase, an additive or an adhesive and a binding agent, at least partially covered and the coating is allowed to solidify, after which, in a subsequent step, the preliminary material is heated to the deformation temperature and this is brought to a shaping agent and processed or forged or forged with this into a molded body or rolled product is rolled.

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.

DVR 0078018

AT 508 322 B1 2012-04-15 Austrian

Patent office

description

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 raw material heated to the forming temperature.

A hot deformation of a workpiece made of metal, such as ingot or primarily deformed starting 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 discharge of the part from the forming agent.

Sufficient deformability of the material of the workpiece is often only given in a narrow temperature window because lower molding temperatures lead to brittleness and higher temperatures also lead to brittleness and / or coarse grain formation of the structure of the material.

The limit of sufficient deformability may be at high temperatures of over 1000 ° C.

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

If high forming temperatures are required, it is therefore difficult and / or expensive 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 reshaping 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 the resulting occurrence of defects such as cracks.

[0009] To solve this problem, it has already been proposed and, if necessary, the warmed-through 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.

There are also known methods (DE 40 16 340 C1) to enclose the workpiece in a capsule or a casing and to heat and deform it in this. Such a method can be very effective with regard to reshaping a part in a narrow temperature window, especially when developing an alloy, but it requires a great deal of effort.

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

The invention now aims to provide a new method of the type mentioned for reshaping a workpiece, which the disadvantages of the known method / 6

AT 508 322 B1 2012-04-15 Austrian

Patent Office overcomes.

This goal is achieved in a generic method in that, in a first step, the surface of the workpiece 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, in particular, the radiation and thus the temperature loss in the unit of time are reduced while the workpiece is being 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 during heating and when it is subsequently brought 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 primary material is coated at a temperature of the same of over 100.degree. C., preferably at about 200.degree.

If, as has been found, the surface of the workpiece or pre-material is coated by dipping in or spraying with a coating agent, a largely uniform layer thickness on the surface can be achieved 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 surface quality of the deformed workpiece on the other hand, it can be advantageous if the coating has 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 the heat radiation from a workpiece or raw material heated to the forming temperature, which means can be applied slightly thin and with the same layer thickness to the surface of a workpiece before heating, does not peel off during the heating process in the oven, has sufficient adhesion when brought to the tool up to the first forming step and improves the forging quality.

This object is achieved by an agent consisting of an oxide phase as the main component and one or more additive (s) or adhesive (s) as an additive and liquid components.

According to the invention, the oxide phase acts as a heat-resistant insulating component, with one or more additive (s) or adhesives with minor proportions connecting (connecting) the oxide grains and holding (holding) 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 essential in terms of weight Reduction of the heat radiation turned out to be particularly favorable.

If now the proportion of zirconium oxide is greater than 70 wt .-%, a means at wel2 / 6

AT 508 322 B1 2012-04-15 Austrian

Patent Office chem the additives are formed from 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, particularly advantageous for coating TiAl alloys can be used because this type of alloy and the coating material have only slightly different coefficients of expansion.

As a liquid component, sodium silicate glass is added to the agent in a percentage by weight of 15 to 65, preferably 20 to 60, this addition relating to the oxide phase with the additive (s).

As a particularly evenly applicable adhesive and good thermal insulation effect has been found to be an agent in which the oxide phase is formed with a grain diameter of 1 pm to 50 pm, preferably an average grain size of d₅₀ = 12.5 pm.

As previously mentioned with the 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 -Base alloy turned out to be particularly advantageous, This alloy can be heated to over 1280 ° C. and the defect-free coating causes a considerable reduction in the temperature drop in the zone of the workpiece near the surface 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.

It show:

[0030] FIG

Figure 2

Figure 3

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

Specimen with the position of the measuring points

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

Cooling curves over time of the coated rod and the bare rod in the rod core

Fig. 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 on the basis of the illustration that the thermal expansion of the two materials shows only minor differences, which is why the layer does not flake off from the base material.

In Fig. 2, a test body with a diameter of 40 mm 0 is shown, which has a near-surface bore and a central bore for thermocouples.

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. 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. About 30 seconds after the test specimens have been discharged, an uncoated rod has a surface temperature of approx. 1165 ° C and one with a zirconium layer has a temperature of approx. 1215 ° C.

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 show

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AT 508 322 B1 2012-04-15 Austrian

Patent Office clearly shows that a zirconium oxide-based coating on a specimen made from a gamma-titanium-aluminum-based alloy reduces heat radiation.