Aircraft aerodynamic measurement equipment

Abstract

Aerodynamic Measurement Equipment for Aircraft The present invention relates to aerodynamic measurement equipment for an aircraft (A), said equipment comprising an appendage (12) adapted to protrude from the skin of said aircraft, rotatably movable and mounted on a rotating shaft (14) adapted to be mounted under the skin of the aircraft, said rotating shaft being guided via rotating interfaces (22) housed respectively in bodies (18, 20) fixed to said aircraft, and adapted to transmit its position by being coupled to an angular sensor operating magnetically or inductively, said angular sensor comprising a fixed part (36) and a movable part (38) whose relative positioning is to be maintained, over a predetermined temperature range, within a predetermined positioning range depending on the required measurement accuracy, said equipment comprising, for each rotating interface,a porous interface (50) located between said rotating interface and said fixed body. Figure for the abbreviation: Figure 4,

Description

Title of the invention: Aerodynamic measurement equipment for aircraft

[0001] The present invention relates to an aerodynamic measuring device for an aircraft, said device comprising an appendage adapted to protrude from the skin of said aircraft, movable in rotation and mounted on a rotating shaft adapted to be mounted under the skin of the aircraft.

[0002] The present invention also relates to an aircraft comprising at least one such aerodynamic measuring device.

[0003] The present invention also relates to a method of manufacturing such aerodynamic measuring equipment.

[0004] The invention is in the field of aeronautics.

[0005] To perform its mission, an aircraft includes several aerodynamic measurement devices comprising flush parts or appendages protruding from the skin of the aircraft, each being rotationally mobile and mounted on a rotating shaft suitable for mounting under the skin of the aircraft.

[0006] These appendages or protruding parts belong, for example, to probes enabling the measurement of various aerodynamic parameters of the airflow surrounding the aircraft, such as the incidence of the airflow in the vicinity of the aircraft skin.

[0007] The present invention relates more specifically to angle-of-attack probes suitable for providing a measurement of the angle of attack of the aircraft (also called angle of attack probe AoA (from the English angle of attack).

[0008] The angle of attack is the angle of incidence relative to the airflow and monitoring it makes it possible to avoid exceeding the maximum permissible angle of incidence for the aircraft before stalling.

[0009] In order to be able to measure the incidence of the airflow, the rotating assembly is designed to transmit its position by being coupled to an angular sensor whose proper functioning must be ensured over the entire life profile of the aircraft, which, during its use, is subject to temperature variations ranging from: -55°C to +120°C.

[0010] Currently, angular sensors are used in an assembled version, as illustrated by [Fig.1] schematically representing in cross-section, along the Z-axis of height, the arrangement 10, relative to the skin of the aircraft, of an angle-of-attack probe with a conventional sensor in an "assembled" version according to a specific mechanics illustrated by [Fig.1].

[0011] More specifically, according to the arrangement 10 of [Fig.1], the aircraft aerodynamic measuring equipment, corresponding to an angle-of-attack probe, includes first of all an appendage 12, in particular a wind vane, suitable for emerging from the skin A of said aircraft.

[0012] This appendage 12 (i.e. this wind vane) is mobile in rotation and mounted on a rotating shaft 14 suitable for mounting under the skin A of the aircraft.

[0013] The part of the aircraft aerodynamic measuring equipment, corresponding in particular to an angle-of-attack probe, located under the skin A of the aircraft is called the probe foot 16.

[0014] More specifically, within this probe foot 16, the rotating shaft 14 is adapted to be mounted under the aircraft skin A, via a body attached to an aeronautical plate P_A of the aircraft skin A. In the example of [Fig. 1], the body comprises an upper part 18 (also called the upper body) and a lower part 20 (also called the lower body). According to another variant, not shown, a one-piece body is used.

[0015] Conventionally, as illustrated by the cross-sectional view in [Fig. 1], the rotating shaft 14 is guided via rotating interfaces, such as bearings or plain bearings 22, housed respectively in the upper and lower bodies 18 and 20 fixed to the aircraft (or, according to the variant not shown, housed in a single-piece body designed to ensure its retention). More specifically, along the Z-axis, upper rotating interfaces provide guidance in the upper part of the rotating shaft 14, these upper rotating interfaces being housed in the upper body 18 fixed to the aircraft, while lower rotating interfaces provide guidance in the lower part of the rotating shaft 14, these lower rotating interfaces being housed in the lower body 20 integral with the upper body 18, itself fixed to the aircraft.

[0016] As indicated previously, according to an unrepresented variant, a one-piece body is also suitable for use in retaining the upper and lower rotating interfaces.

[0017] The rotating shaft 14 is suitable for transmitting its position by being coupled to an angular sensor 24 in an "assembled" version housed on a sensor support 26 via a coupling piece 28 generally corresponding to a bellows such that the radial and axial play taken by the rotating shaft does not impact the operation of the sensor suitable for analyzing and / or saving and / or transmitting the position of the rotating shaft via at least one electronic board, for example, two electronic boards 30 and 32 as illustrated in [Fig.1].

[0018] However, these "assembled" solutions are expensive, bulky, and require analog / digital processing of the analog information obtained which it is necessary to digitize in order to then communicate it to the flight computer, and are associated with installation constraints, an adjustment being necessary for the positioning of the sensor shaft 24 on the rotating shaft 14.

[0019] To remedy this, a new generation of sensor is proposed, based on magnetic or inductive operation, and is advantageously supplied as a kit, i.e. with a part called "stator" and a moving part called "rotor" as illustrated by arrangement 33 la [Fig.2].

[0020] The integration of these new, natively "digital" sensors in kit form makes it possible, in particular, to reduce the electronic footprint initially required for the analog / digital processing implemented by the sensors in their "assembled" form. This ultimately allows for a reduction in the overall size of the product or for the freed-up electronic space to be used to integrate the processing of the sensor's raw signal.

[0021] It should be noted, however, that whether for products with old (i.e. in assembled version) or new generation sensors (i.e. in kit version), there are systematically embedded electronic boards not shown in the figures for power supply and for heating the external appendage.

[0022] On this arrangement 33, the sensor 34 in kit form, with magnetic or inductive operation, therefore comprises a static part: the stator 36, and a moving part: the rotor 38.

[0023] These new sensors meet the current cost, integration, and performance requirements of aircraft such as small / medium-range (SMR) aircraft, new generation fighters (NGF), or regional air mobility / urban air mobility (RAM / UAM) aircraft.

[0024] However, the integration of such sensors in kit form (i.e. in two parts) must meet specific positioning requirements between the moving part 38 (i.e. the rotor) and the fixed part 36 the stator, as illustrated by [Fig.3] which focuses on box III of [Fig.2], and more specifically the relative positioning of the fixed part 36 and the moving part 38.

[0025] More specifically, as illustrated by [Fig.3], radially, the axis 40 passing through the center of the stator 36 and the axis 42 passing through the center of the rotor 38 must have a concentricity deviation 44 less than a predetermined deviation threshold depending on the required measurement accuracy, and axially, along the Z-axis of the height, the variation of the air gap 46 separating the stator 36 from the rotor 38 must also remain less than a predetermined variation threshold depending on the required measurement accuracy.

[0026] In other words, such requirements aim to maintain substantially axial and radial alignment between the rotor 38 and the stator 36 of such a kit sensor 34, with magnetic or inductive operation.

[0027] In addition, these requirements for maintaining the relative positioning of the rotor 38 and the stator 36 must be met over the entire operating temperature range of the aircraft aerodynamic measuring equipment, namely for example between -55 °C and +120 °C.

[0028] As previously stated, the rotating shaft 14 is guided via rotating interfaces 22, for example bearings, housed respectively in the lower and upper bodies 18 and 20 fixed to said aircraft, the rotating shaft 14 being conventionally made of steel and the fixed bodies of aluminium, to limit the weight of the aircraft aerodynamic measuring equipment.

[0029] During temperature variations between -55°C and +120°C, the rotating interfaces 22, usually made of steel, expand radially less than the bodies 18 and 20 made of aluminum or "light" alloys. Consequently, the outer rings of the rotating interfaces lose their guidance within the housings of the fixed bodies. This loss of guidance is likely to cause a misalignment between the rotor 38 and the stator 36 of the angular sensor 34, and therefore a measurement error.

[0030] The object of the invention is then to propose a solution allowing the integration of an angular sensor in kit form, namely in two parts with a fixed part the stator and a mobile part the rotor, in the foot (i.e. under the skin of the aircraft) of the aerodynamic measuring equipment, while limiting the guidance losses of the rotating shaft of said equipment in the presence of temperature variations likely to generate differential expansions in the different materials constituting the different elements of the foot of the aerodynamic measuring equipment.

[0031] To this end, the invention relates to an aerodynamic measuring device for an aircraft, said device comprising an appendage adapted to protrude from the skin of said aircraft, movable in rotation and mounted on a rotating shaft adapted to be mounted under the skin of the aircraft,

[0032] said rotating shaft being guided via rotating interfaces housed respectively in bodies fixed to said aircraft, and adapted to transmit its position by being coupled to an angular sensor with magnetic or inductive operation,

[0033] said angular sensor comprising a fixed part and a movable part whose relative positioning is to be maintained, over a predetermined temperature range, within a predetermined positioning range depending on the required measurement accuracy,

[0034] said equipment being characterized in that it comprises, for each rotating interface, a porous interface located between said rotating interface and said fixed body.

[0035] Thus, the present invention advantageously proposes to insert a porous interface between each rotating interface and the fixed body associated with said rotating interface, said porous interface, like a sponge, being suitable for damping the differences in expansion between a rotating interface, in particular made of steel, and the fixed body to which it is usually attached, generally made of aluminum.

[0036] According to other advantageous aspects of the invention, the aerodynamic measuring equipment comprises one or more of the following features, taken individually or in all technically possible combinations:

[0037] - said rotating shaft and said rotating interfaces are of the same first material or materials of equivalent nature, distinct from the material of said bodies fixed to said aircraft, said porous interface having a coefficient of expansion substantially equal to that of the material(s) of the rotating shaft and of said rotating interfaces and a Young's modulus between 40 and 50 GPa;

[0038] - said first material of the rotating shaft and of said rotating interfaces is the steel or materials of the rotating shaft and of said rotating interfaces are equivalent to steel, and said second material is aluminum;

[0039] - the porosity rate of said porous interface is approximately equal to 0.007g / cm3;

[0040] - the pore radius of said porous interface is from 1 to 100pm;

[0041] - said measuring equipment is an incidence probe suitable for providing a measurement of the angle of attack or lateral slide of the aircraft, said appendage being a weather vane;

[0042] - said predetermined temperature range is from -55°C to 120°C, and in which said positioning range, is predetermined for a measurement accuracy of the order of 0.05° of angle of attack and corresponds to a concentricity deviation of less than 0.02 mm and a variation of the air gap separating the fixed part and the moving part of the angular sensor of less than 0.1 mm.

[0043] The invention also relates to an aircraft comprising at least one aerodynamic measuring device as described above.

[0044] The invention also relates to a method for manufacturing aerodynamic measuring equipment for aircraft as described above, said method comprising:

[0045] - a sintering step of said porous interface by agglomeration at a high predetermined temperature of a powder of the material of said porous interface;

[0046] - a step of integrating porous interfaces within said measuring equipment aerodynamics, according to which, for each rotating interface, a porous interface is shrink-fitted, substantially at said predetermined high temperature, onto the fixed body associated with said rotating interface, so that said porous interface is located between said rotating interface and said associated fixed body.

[0047] According to another advantageous aspect of the invention, said powder material of said porous interface is a micrometric powder of stainless steel, and said predetermined high temperature is equal to +200°C.

[0048] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0049] [Fig-1] [Fig.2] [Fig.3] Figures 1 to 3 respectively represent views in section of an aerodynamic measuring equipment for aircraft according to two distinct embodiments, namely with an angular sensor in assembled version and in kit version of the prior art, as already described above, [Fig.3] illustrating the specific positioning requirements between the moving part and the fixed part of the angular sensor in kit version.

[0050] [Fig.4] [Fig.4] represents a cross-sectional view of an aircraft aerodynamic measuring device according to the present invention.

[0051] In the following description, the expression "approximately equal to" is understood as a relationship of equality plus or minus 10%, that is to say with a variation of at most 10%, preferably also as a relationship of equality plus or minus 5%, that is to say with a variation of at most 5%.

[0052] Fig. 4 therefore illustrates an embodiment of an aerodynamic measurement equipment for an aircraft according to the present invention.

[0053] For reasons of simplicity, the numerical references of the identical elements between the aircraft aerodynamic measuring equipment of Figures 1 to 3, representative of the prior art, and the aircraft aerodynamic measuring equipment according to the present invention illustrated by [Fig.4] have been retained.

[0054] In the cross-sectional view of [Fig.4], the arrangement 48 of said aircraft aerodynamic measuring equipment according to the present invention is therefore identical to the prior art of [Fig.2] in that said aircraft aerodynamic measuring equipment A still includes an appendage 12 adapted to protrude from the skin of said aircraft, movable in rotation and mounted on a rotating shaft 14 adapted to be mounted under the skin of aircraft A.

[0055] The rotating shaft 14 is also always guided via rotating interfaces 22 housed respectively in the body composed of the upper body 18 and lower body 20 fixed to said aircraft, or according to another variant, not shown, in a one-piece body, and adapted to transmit its position by being coupled to an angular sensor with magnetic or inductive operation.

[0056] According to the present invention, said angular sensor is said to be in kit form and comprises a fixed part 36 and a movable part 38 whose relative positioning is to be maintained, over a predetermined temperature range, within a predetermined positioning range according to the required measurement accuracy.

[0057] According to the present invention, said aerodynamic measuring equipment differs from that of the prior art illustrated by [Fig.2], in that it comprises for each rotating interface, in particular a bearing, a porous interface 50 located between said rotating interface 22 and the fixed body 18 or 20 to which it is associated.

[0058] In other words, to limit radial play and stresses generated at interfaces during differential expansions, as indicated in relation to the aforementioned prior art, porous interfaces 50 (i.e. porous bearings or porous rings) are integrated (i.e. inserted, shrink-fitted) at the boundary (i.e. frontier) between the rotating interfaces 22 and the fixed bodies 18 or 20.

[0059] According to a particular example, as used hereafter, said measuring equipment is an angle-of-attack probe suitable for providing a measurement of the angle of attack or lateral slip of the aircraft, said appendix 12 being a wind vane.

[0060] As an optional addition, said rotating shaft 14 and said rotating interfaces 22 are of the same first material or of materials of equivalent natures, distinct from the material of said fixed bodies 18,20 of said aircraft A, said porous interface 50 having a coefficient of expansion substantially equal to that of the material(s) of the rotating shaft and of said rotating interfaces and a Young's modulus (i.e. a modulus of elasticity) between 40 and 50 GPa.

[0061] By materials of equivalent nature, it is meant for example that the rotating shaft is made of iron-based steel while the said rotating interfaces are made of nickel alloy.

[0062] According to a variant of this optional addition, said first material of the rotating shaft and of said rotating interfaces is steel or the materials of the rotating shaft and of said rotating interfaces are equivalent to steel and said second material is aluminum. Indeed, usually, the materials used to construct, in particular, an angle of attack probe (also called an angle of attack probe, AoA), are, on the one hand, for the rotating shaft 14 and the rotating interfaces 22, stainless steel, in particular X8CRNIS18-9 steel, used for mechanical strength and wear resistance and having a coefficient of expansion substantially equal to 12 ppm (i.e.parts per million), and on the other hand, aluminium, in particular aluminium 6061, for the upper and lower bodies 18 and 20 fixed to the aircraft, aluminium having a coefficient of expansion approximately equal to 23 ppm and being used for the mass saving it provides compared to steel and its thermal conductivity.

[0063] In other words, according to this variant, each porous interface 50 has a coefficient of expansion substantially equal to that of the steel constituting the rotating interfaces, in order, like a steel sponge, to expand similarly to the rotating interface (e.g., the bearing) to which said interface is associated at one of its ends, the other end being fixed to said corresponding body.

[0064] More specifically, as indicated previously, said angular sensor comprises a fixed part 36 and a movable part 38 whose relative positioning is to be maintained, over a predetermined temperature range, within a predetermined positioning range according to the required measurement accuracy.

[0065] According to one variant, said predetermined temperature range is from -55°C to 120°C, and said positioning range is predetermined for a measurement accuracy of the order of 0.05° of angle of attack and corresponds to a concentricity deviation 44 of less than 0.02 mm and to a variation of the air gap 46 separating the fixed part and the moving part of the angular sensor of less than 0.1 mm as illustrated previously by [Fig.3].

[0066] At high temperature, particularly at +120°C, the aluminum of the upper and lower bodies 18 and 20 expands more than the steel of the rotating interfaces 22. For example, for a usual outer diameter of rotating interface of about 10 mm, the outer ring of the rotating interface (i.e. the rotating interface ring (e.g. the bearing ring)) distal to the rotating shaft 14), made of steel, expands by 0.5 mm, while the housing of the fixed body 18 or 20 made of aluminum and associated with the rotating interface (i.e. the bearing) 22 considered, expands by 0.10 mm, so that the relative clearance (i.e. the gap 44) is about 0.5 mm, which exceeds the concentricity tolerance of the sensor.

[0067] Conversely, at low temperatures, particularly at -55°C, the aluminum constituting the bodies 18 and 20 fixed to the aircraft contracts more than the steel of the rotating interfaces 22. The stresses generated in the aluminum body are greater than the limit admissible by the material.

[0068] To remedy this, a porous interface 50 is therefore proposed, located between each rotating interface 22 and the fixed body 18 or 20 associated with it, so as to dampen the aforementioned differential expansions over the entire predetermined temperature range.

[0069] According to the aforementioned optional supplement, said porous interface has both a coefficient of expansion substantially equal to that of steel and a Young's modulus between 40 and 50 GPa.

[0070] In particular, to manufacture such aerodynamic measuring equipment, the manufacturing process according to the present invention includes a sintering step of said porous interface by agglomeration at a predetermined high temperature of a powder of the material of said porous interface.

[0071] According to an optional variant, said porous interface is sintered by agglomeration of a micrometric powder of stainless steel, in order to advantageously present a coefficient of expansion substantially equal to that of the steel of the rotating interfaces 22.

[0072] Furthermore, the manufacturing process according to the present invention includes a step of integrating porous interfaces within said aerodynamic measuring equipment, according to which, for each rotating interface, a porous interface is shrink-fitted, substantially at said predetermined high temperature, onto the fixed body, (said fixed body being in particular made of aluminum), associated with said rotating interface (said rotating interface, for example a bearing, being in particular made of stainless steel), so that said porous interface, in particular obtained by agglomeration of a micrometric powder of stainless steel, is located between said rotating interface and said associated fixed body.

[0073] The gap formed, as previously indicated according to the prior art, by differential expansions at 120°C is thus eliminated according to the present invention, thanks to the porous interface.

[0074] According to an optional example, said predetermined high temperature is advantageously strictly greater than the upper bound of the predetermined temperature range, said upper bound being in particular equal to +120°C. According to this optional example, said predetermined high temperature is equal to +200°C > +120°C.

[0075] Such shrinking at a predetermined high temperature, for example +200°C, higher than the maximum operating temperature, for example +120°C, allows the porous interface to remain attached at high temperature to the fixed body considered.

[0076] Moreover, at low temperature, particularly at -55°C, where, as previously indicated according to the prior art, the aluminum of the fixed bodies 18 and 20 contracts more than the steel of the rotating interfaces 22, for, for example, a usual outside diameter of rotating interface 22 of about 10 mm, the dimensional variation between the rotating interface and an aluminum plate of the associated fixed body (lower or upper) is about 1 / 10 mm, with a maximum stress reached in the fixed bodies of about 1000 MPa, which far exceeds the elastic limit of the aluminum of the fixed bodies which would thus be deteriorated from their first cycle of use.

[0077] The porous interface proposed according to the present invention makes it possible to avoid such deterioration, by playing the role of "damper" in order to limit the over-stress generated at this low temperature of -55°C between the steel of the rotating interfaces 22 and the aluminum of the fixed bodies 18 and 20.

[0078] Indeed, according to the optional complement, the Young's modulus of porous materials (i.e., porous interfaces) is greatly reduced compared to "solid" material, whose usual value of 180 GPa is reduced to 40 GPa.

[0079] This decrease in Young's modulus allows, for the same differential displacement, in particular of about 1 / 10 mm, to proportionally reduce the stresses in the material.

[0080] By simulation, the maximum stresses in the porous interfaces proposed according to the present invention are about 150 MPa, which is less than the yield strength of aluminum, in particular aluminum 6061 whose yield strength is about 240 MPa.

[0081] As an optional addition, the porosity rate of said porous interface is approximately equal to 0.007g / cm3.

[0082] According to another optional complement, the pore radius of said porous interface is 1 to 100pm.

[0083] A person skilled in the art will understand that the invention is not limited to the embodiments described, nor to the particular examples of the description, the embodiments and variants mentioned above being capable of being combined with each other to generate new embodiments of the invention.

[0084] The present invention thus makes it possible to improve existing aerodynamic measurement equipment, in particular angle-of-attack probes, by allowing the integration of angular sensor(s) "in kit", supplied in two parts, thanks to the crimped porous interfaces, in particular in steel, between the rotating interfaces and the fixed bodies to respect, over the entire temperature range of use of said equipment, the positioning required by the angular sensor "in kit" (i.e. encoder in kit version).

[0085] The porous nature of said interfaces makes it possible to reduce the Young's modulus of the material, for example steel, constituting them, so as to dampen the differential expansions observed in relation to the aforementioned prior art over the temperature range of use of said equipment.

[0086] According to an optional supplement mentioned above, advantageously, the porous interfaces are further mounted in a shrink-fitted manner, particularly at approximately 200°C, in the aluminum bodies to remain attached at high temperature, particularly at approximately 120°C.

Claims

Demands

1. Aerodynamic measurement equipment for aircraft (A), said equipment comprising an appendage (12) adapted to protrude from the skin of said aircraft, movable in rotation and mounted on a rotating shaft (14) adapted to be mounted under the skin of the aircraft (A), said rotating shaft (14) being guided via rotating interfaces (22) housed respectively in bodies (18, 20) fixed to said aircraft, and adapted to transmit its position by being coupled to an angular sensor operating magnetically or inductively, said angular sensor comprising a fixed part (36) and a movable part (38) the relative positioning of which is to be maintained, over a predetermined temperature range, within a predetermined positioning range according to the required measurement accuracy, said equipment being characterized in that it comprises, for each rotating interface, a porous interface (50) located between said rotating interface (22) and said fixed body (18, 20).

2. Aerodynamic measurement equipment for aircraft according to claim 1, wherein said rotating shaft (14) and said rotating interfaces (22) are of the same first material or of equivalent materials, distinct from the material of said fixed bodies (18,20) said aircraft (A), said porous interface (50) having a coefficient of expansion substantially equal to that of the material(s) of the rotating shaft and of said rotating interfaces and a Young's modulus between 40 and 50 GPa.

3. Aerodynamic measurement equipment for aircraft according to claim 2, wherein said first material of the rotating shaft and of said rotating interfaces is steel or the materials of the rotating shaft and of said rotating interfaces are equivalent to steel, and said second material is aluminum.

4. Aerodynamic measurement equipment for aircraft according to any one of the preceding claims, wherein the porosity ratio of said porous interface is substantially equal to 0.007g / 3

5. cm. Aerodynamic measurement equipment for aircraft according to any one of the preceding claims, wherein the pore radius of said porous interface is from 1 to 100pm.

6. Aerodynamic measuring equipment for aircraft according to any one of the preceding claims, wherein said measuring equipment is an angle-of-attack probe suitable for providing a measurement of the angle of attack or sideslip of the aircraft, said appendage being a wind vane.

7. Aerodynamic measurement equipment for aircraft according to claim 6, wherein said predetermined temperature range is from -55°C to 120°C, and wherein said positioning range is predetermined for a measurement accuracy of the order of 0.05° of angle of attack and corresponds to a concentricity deviation (44) of less than 0.02 mm and a variation of the air gap (46) separating the fixed part and the moving part of the angular sensor of less than 0.1 mm.

8. Aircraft comprising at least one aircraft aerodynamic measuring device according to any one of the preceding claims.

9. A method for manufacturing an aerodynamic measuring equipment for an aircraft according to any one of the preceding claims, said method comprising: - a step of sintering said porous interface by agglomerating at a predetermined high temperature a powder of the material of said porous interface; - a step of integrating porous interfaces within said aerodynamic measuring equipment, according to which, for each rotating interface, a porous interface is shrink-fitted, substantially at said predetermined high temperature, onto the fixed body associated with said rotating interface, so that said porous interface is located between said rotating interface and said associated fixed body.

10. A manufacturing process according to claim 9 wherein said material powder of said porous interface is a micrometric stainless steel powder, and wherein said predetermined high temperature is equal to +200°C.