EP1281182B1 - Iron-cobalt alloy, in particular for electromagnetic actuator mobile core and method for making same - Google Patents

Abstract

An iron-cobalt alloy containing in weight percentages: 10 to 22% of Co; traces to 2.5% of Si; traces to 2% of Al; 0.1 to 1% of Mn; traces to 0.0100% of C, a total of O, N and S content ranging between traces of 0.0070%; a total of Si, Al, Cr, Mo, V, Mn content ranging between 1.1 and 3.5%; a total of Cr, Mo and V content ranging between traces of 3%; a total of Ta and Nb content ranging between traces and 1%; and the rest being iron and impurities resulting from production wherein: 1.23×(Al+Mo) %+0.84 (Si+Cr+V) %−0.15×(Co %−15)≰2.1, and 14.5×(Al+Cr) %+12×(V+Mo) %+25×Si %≧21. The inventive alloy is useful for making electromagnetic actuator mobile cores.

Description

The invention relates to the field of magnetic iron-cobalt alloys. More specifically, it relates to iron-cobalt alloys intended to constitute electromagnetic actuator cores.

An electromagnetic actuator is an electromagnetic device that converts electrical energy into mechanical energy. Some actuators of this type are so-called linear actuators, converting electrical energy into a rectilinear movement of a moving part. Such actuators are found in solenoid valves and electro-injectors. A preferred application of such electro-injectors is the direct injection of fuel into combustion engines, especially diesel engines. Another preferred application relates to a particular type of solenoid valve used for the electromagnetic control of valves of internal combustion engines (gasoline or diesel).

In these actuators, the electrical energy is supplied in a winding by a series of current pulses, creating a magnetic field that magnetizes a non-closed magnetic yoke, thus having a gap. The geometric characteristics of the cylinder head make it possible to direct most of the magnetic field lines axially vis-à-vis the gap zone. Under the effect of the electric pulse, the air gap is subjected to a magnetic potential difference. The actuator also comprises a core made mobile by the action of the electric current in the coil. Indeed, the magnetic potential difference introduced by the coil between the mobile core resting on a pole of the cylinder head and the opposite pole of the cylinder head creates an electromagnetic force on the magnetized core, via a magnetic field gradient. The magnetized core is thus set in motion. The rest position can also be located in the middle of the air gap, thanks to two symmetrical springs, favoring by their stiffness the dynamics of the moving part (case of the electromagnetically controlled valves).

The movement of the mobile core occurs with a phase shift with respect to the moment of creation of the electrical pulses. For optimal operation of the actuator, it is shown that it is necessary for the metal that composes it to have high electrical resistivity and a low coercive field. These conditions make it possible to obtain low currents induced in the cylinder head and the magnetic core, making it possible to quickly reach the minimum magnetization of the nucleus which causes it to move. It is also important that the core has a high saturation magnetization so as to allow as high a maximum pulse force as possible. It is indeed this force which guarantees the maintenance of the open or closed position of the actuator, which is particularly important when it comes, for example, to completely interrupt the flow of a fluid at a high level. pressure, and / or to compensate for the restoring force of one or more springs.

These magnetic cores have various shapes and can be made from wires or bars. In this case, they must have a high plastic aptitude for deformation, so that they can be deformed without risk of rupture. It is favorable to have an elongation at break of the material of at least 35%. Such cores can also be manufactured by cutting plates or rolled sheets. In this case, they must have a high punching ability, for which minimum hardness and strength are required. A good resistance of the magnetic properties to repeated mechanical shocks to which the core will be subjected is also necessary. These characteristics of hardness and mechanical strength are also favorable to a good efficiency of the cutting of the core. It is recommended to have a material hardness after annealing greater than 200 HV for these uses.

Three major categories of alloys are traditionally used to form electromagnetic actuator cores as just described.

A first category consists of iron-silicon alloys comprising from 2 to 3% of silicon. They have the advantage of having relatively high resistivities. On the other hand, their saturation magnetization is relatively low.

A second category consists of iron-cobalt alloys with a high cobalt content, of the order of 50%. Such alloys have a significantly higher saturation magnetization higher than that of previous iron-silicon alloys. On the other hand, their resistivity is somewhat lower. In addition, because of the massive presence of cobalt, these alloys are very expensive. Finally, their mechanical properties are not optimal, which makes the manufacture of the cores difficult.

A third category consists of iron-cobalt alloys containing about 6 to 30% cobalt and various other alloying elements. The document EP-A-715,320 give an example of such alloys. It describes iron-cobalt alloys for electromagnetic actuator cores comprising 6 to 30% cobalt, 3 to 8% of one or more elements selected from chromium, molybdenum, vanadium and tungsten, the balance being iron . Preferably, the cobalt content is from 10 to 20% and the content of chromium, molybdenum, vanadium and / or tungsten is from 4 to 8%. These alloys have a good electrical resistivity, which may be greater than 50 μΩ.cm, but their saturation magnetization is relatively low, of the order of 1.9 to 2T, except for the most heavily loaded cobalt variants (which are therefore the most expensive) where this saturation magnetization can reach 2.3 T. In general, the coercive field of the alloys given as examples in this document is also high, substantially greater than 1.5 Oe. In general, the alloys given as examples in this document do not make it possible to reach an optimal compromise between a high saturation magnetization, a low coercive field and a high resistivity.

The document WO 96/19001 proposes to use iron / cobalt alloys containing between 5 and 20% of cobalt, and having an aluminum and manganese or vanadium content of up to several%: up to 7% of aluminum, and up to 8% of manganese or 4% vanadium. Alloys described in this document have a very high resistivity (greater than 60 μΩ.cm), and a fairly high saturation magnetization (from 2 to 2.2 T). But no precise information is given on the mechanical properties of these alloys, as well as on their coercive field.

A yoke and a core made of an iron-cobalt alloy also comprising Si, Mn, Al, Mo and V are known from JP 060933199 .

The object of the invention is to provide iron / cobalt alloys particularly suitable for the manufacture, economically, cores for electromagnetic actuators. These nuclei should present a more favorable compromise than the existing materials between the different electromagnetic characteristics, namely the saturation magnetization, the resistivity and the coercive field. They should also have mechanical properties making their manufacture particularly easy.

• de 10 à 22% de Co ;
• de traces à 2,5% de Si ;
• de traces à 2% d'Al ;
• de 0,1 à 1% de Mn ;
• de traces à 0,0100% de C ;
• une somme des teneurs en O,N et S comprise entre des traces et 0,0070% ;
• une somme des teneurs en Si, Al, Cr, V, Mo, Mn comprise entre 1,1 et 3,5%, de préférence entre 1,5 et 3,5% ;
• une somme des teneurs en Cr, Mo et V comprise entre des traces et 3% ;
• une somme des teneurs en Ta et Nb comprise entre des traces et 1% ;

le reste étant du fer et des impuretés résultant de l'élaboration,
en ce que : $$1,23x\left(\mathrm{Al}+\mathrm{Mo}\right)\%+0,84\left(\mathrm{Si}+\mathrm{Cr}+\mathrm{V}\right)\%-0,15x\left(\mathrm{Co}\%-15\right)\le 2,1$$

et en ce que : $$\mathrm{14}\mathrm{,}\mathrm{5}x\left(\mathrm{Al}\mathrm{+}\mathrm{Cr}\right)\mathrm{\%}\mathrm{+}\mathrm{12}x\left(\mathrm{V}\mathrm{+}\mathrm{Mo}\right)\mathrm{\%}\mathrm{+}\mathrm{25}\mathrm{x\; Si}\mathrm{\%}\mathrm{\ge }\mathrm{40.}$$

For this purpose, the subject of the invention is an iron-cobalt alloy, characterized in that it comprises, in weight percentages:

• from 10 to 22% Co;
• traces of 2.5% Si;
• traces of 2% Al;
• from 0.1 to 1% Mn;
• trace amounts of 0.0100% C;
• a sum of O, N and S contents between traces and 0.0070%;
• a sum of the contents of Si, Al, Cr, V, Mo, Mn of between 1.1 and 3.5%, preferably between 1.5 and 3.5%;
• a sum of Cr, Mo and V contents between traces and 3%;
• a sum of the contents of Ta and Nb between traces and 1%;

the rest being iron and impurities resulting from the elaboration,
in that : $$1,23x\left(\mathrm{al}+\mathrm{MB}\right)\%+0,84\left(\mathrm{Yes}+\mathrm{Cr}+\mathrm{V}\right)\%-0,15x\left(\mathrm{Co}\%-15\right)\le 2,1$$

and in that : $$\mathrm{14}\mathrm{,}\mathrm{5}x\left(\mathrm{al}\mathrm{+}\mathrm{Cr}\right)\mathrm{\%}\mathrm{+}\mathrm{12}x\left(\mathrm{V}\mathrm{+}\mathrm{MB}\right)\mathrm{\%}\mathrm{+}\mathrm{25}\mathrm{x\; Si}\mathrm{\%}\mathrm{\ge }\mathrm{40.}$$

Preferably, this iron-cobalt alloy comprises 14 to 20% of Co and the sum of the contents of Ta and Nb is between 0.05 and 0.8%.

According to a variant of the invention, the sum of the contents of Cr and V is between 1.1 and 3%, preferably between 1.5 and 3%, and the sum of the contents of Si, Al and Mo is between traces and 1% to obtain an elongation at break of at least 35%.

According to another variant of the invention, the sum of the contents of Si and Al is between 1 and 2.6%, and the sum of Cr, V, Mo, Ta, Nb content is between traces and 2% to obtain a hardness of at least 200 HV after annealing.

The saturation magnetization of the alloys according to the invention is at least 2.1 T at 150 ° C and at least 2.12 T at 20 ° C, their resistivity is at least 35μΩ.cm at 150 ° C. ° C and at least 31 μΩ .cm at 20 ° C, their coercive field is less than 1.5 Oe at 20 and 150 ° C, and preferably less than or equal to 1 Oe.

The invention also relates to a bar, a wire, a plate or a rolled sheet of iron-cobalt alloy, characterized in that said alloy is of the preceding type, and in that the bar, the wire, the plate or the sheet has a preferential fiber texture of <100> axis for a bar or wire, or a strong texture component <100> for a rolled plate or sheet, deviated by less than 20 ° from the rolling direction at least 30% (by volume of the material) of the grains, preferably for at least 50%.

The subject of the invention is also a method for producing a bar, a wire, a plate or a rolled sheet of the above type, characterized in that a bar, a wire or a plate is produced. or a sheet rolled from a blank made of an alloy according to the invention by performing a rolling beginning in the austenitic phase and ending in ferritic phase, the reduction in thickness experienced by the bar, the wire, the plate or the sheet in ferritic phase being at least 30%, preferably at least 50%, and any subsequent annealing is carried out at a temperature below the austenitic transformation temperature.

The invention also relates to a mobile electromagnetic actuator core, characterized in that it has been manufactured from a bar or a wire or a plate or sheet rolled according to the preceding method , and an electromagnetic actuator comprising a mobile core of iron-cobalt alloy, characterized in that said core is of the above type and in that it has a preferential texture of axis <100>, this axis being substantially parallel to the main direction of the field of excitation.

The invention also relates to an injector for a combustion engine controlled by electronic control comprising an electromagnetic actuator with high power density, low response time and high reliability of use of the previous type.

The invention finally relates to an electromagnetic valve actuator of an electronically controlled internal combustion engine, characterized in that it is of the preceding type.

As will be understood, the iron / cobalt alloy according to the invention is in the category of Fe-Co alloys with a low or medium cobalt content, and contains contents of other relatively moderate alloying elements. However, these alloying elements must be present in respective proportions well defined. It is only in these conditions that, for these alloys and for the electromagnetic actuator cores derived therefrom, optimum properties are obtained, both magnetically and mechanically, at a cost of material (related to the presence of cobalt) very moderate compared to Fe-Co alloys at 50% cobalt.

The alloys according to the invention have resistivities similar to those of iron / silicon alloys containing 2 to 3% of silicon. This resistivity at 150 ° C. is greater than 35 μΩ.cm, so as to maintain good reactivity of the actuator to the stresses to which it is subjected at its operating temperature. At 20 ° C, this resistivity is greater than 31 μΩ .cm. In parallel, this good responsiveness of the actuator is also due to a low coercive field, limited to 1.5 Oe at 20 and 150 ° C. This low value of the coercive field is obtained according to the invention by imposing on the alloy a carbon content of less than 0.0100% and a total content of oxygen, nitrogen and sulfur limited to 70 ppm. This weak coercive field strengthens the reduction of pulse time. It is also advisable, for the same purpose, to give the part from which the core will be made a preferential texture of axis <100>, and to ensure that in the core in use, this texture preferential is found substantially parallel to the main direction of field excitation.

On the other hand, the alloys according to the invention exhibit a saturation magnetization at 150 ° C. of greater than 2.1 T. This value is quite superior to those usually observed with iron / silicon alloys containing 3% silicon. At 20 ° C., the saturation magnetization of the alloys according to the invention is greater than 2.12 T.

The differences in the values of the quantities just mentioned between 20 and 150 ° C are explained by the fact that the coercive field and the saturation magnetization vary by at most 4% and 1% respectively between 20 and 150 ° C, while the resistivity increases by about 16% between 20 and 150 ° C. This property therefore varies significantly and the effect of the temperature must be taken into account: a minimum resistivity of 35 μΩ.cm at 150 ° C corresponds to a minimum resistivity of 31 μ Ω.cm at 20 ° C. The coercive field at 150 ° C is always about 4% lower than it is at 20 ° C; therefore if it is sufficiently low at 20 ° C (1.5 Oe at most), it will be a fortiori at 150 ° C. On the other hand, the saturation magnetization decreases as the temperature increases; therefore, to ensure saturation magnetization greater than or equal to 2.1 T at 150 ° C, the saturation magnetization at 20 ° C must be greater than 1%, greater than or equal to 2.12 T.

Finally, the alloys according to the invention have particularly favorable mechanical characteristics for the preparation of electromagnetic actuator cores. In certain preferred examples, the alloys exhibit a high plastic deformation by stamping or stamping because they have a maximum elongation at break of at least 35%. In another variant of the alloys according to the invention, these alloys are suitable for a good quality of cutting and machining, thanks to their hardness after annealing which is at least 200 HV.

The iron / cobalt alloys according to the invention necessarily have the following characteristics. All percentages are percentages by weight.

The cobalt content is between 10 and 22%, and preferably between 14 and 20%, in order to significantly increase the saturation magnetization with respect to the iron / silicon alloys, while maintaining a high resistivity. On the other hand, the limitation to 22% of the cobalt content provides mechanical properties and a cost more favorable than in the case of iron / cobalt alloys at 50% cobalt.

The silicon content does not exceed 2.5%; the aluminum content does not exceed 2%; each of the contents of chromium, molybdenum and vanadium does not exceed 3%, as is the sum of their contents; the manganese content is between 0.1 and 1%, preferably between 0.1 and 0.5% to facilitate the hot conversion. Each of these elements (except manganese) may be present only in the form of traces resulting from the elaboration.

afin d'assurer que l'aimantation à saturation à 150°C est supérieure ou égale à 2,1T et supérieure ou égale à 2,12 T à 20°C; $$14,5x\left(\mathrm{Al}+\mathrm{Cr}\right)\%+12x\left(\mathrm{V}\mathrm{+}\mathrm{Mo}\right)\%+25\mathrm{x\; Si}\%\ge 21,\mathrm{de\; préférence}\ge 40$$

afin d'assurer une résistivité supérieure ou égale à 35 _µΩ.cm à 150°C et supérieure ou égale à 31 µΩ.cm à 20°C.In addition, the sum of the contents of silicon, aluminum, chromium, vanadium, molybdenum, manganese is between 1.1 and 3.5%, and preferably between 1.5 and 3.5%. It is in these conditions that we obtain a resistivity of the alloy equivalent to that of iron / silicon alloys containing 2 to 3% silicon. On the other hand, the contents of these elements must verify the two following equations: $$1,23x\left(\mathrm{al}+\mathrm{MB}\right)\%+0,84\left(\mathrm{Yes}+\mathrm{Cr}+\mathrm{V}\right)-0,15x\left(\mathrm{Co}\%-15\right)\%\le 2,1$$

to ensure that the saturation magnetization at 150 ° C is greater than or equal to 2.1T and greater than or equal to 2.12 T at 20 ° C; $$14,5x\left(\mathrm{al}+\mathrm{Cr}\right)\%+12x\left(\mathrm{V}\mathrm{+}\mathrm{MB}\right)\%+25\mathrm{x\; Si}\%\ge 21,\mathrm{preferably}\ge 40$$

to ensure a resistivity greater than or equal to 35 _μ ohm-cm at 150 ° C and greater than or equal to 31 μΩ.cm at 20 ° C.

Moreover, the sum of the chromium, molybdenum and vanadium contents must be at most 3%, in order not to degrade the saturation magnetization of the material.

The contents of tantalum and niobium and the sum of their contents must each be less than or equal to 1%. Preferably, the sum of these contents is between 0.05 and 0.08%. The purpose of tantalum is to increase the ductility of the alloy, and niobium to increase the mechanical strength and wear resistance, as well as the resistivity. The upper limit of 1% is motivated by the need not to degrade the saturation magnetization of the material. These elements can be present only in the state of traces resulting from the elaboration.

The carbon content must be less than or equal to 100 ppm, and the sum of the oxygen, nitrogen and sulfur contents must be less than or equal to 70 ppm. These conditions make it possible to limit the coercive field and to increase the dynamic permeability of the alloy. These elements carbon, oxygen, nitrogen and sulfur are considered as impurities and can be present only in the state of traces resulting from the elaboration.

• la somme des teneurs en chrome et vanadium doit être comprise entre 1,1 et 3% de préférence entre 1,5 et 3%;
• la somme des teneurs en silicium, aluminium et molybdène doit être comprise entre des traces et 1%.

When the alloy is intended to undergo a stamping or stamping operation, for which it is desirable to have a large maximum plastic elongation (greater than or equal to 35%), the alloy must preferentially meet the following two conditions:

• the sum of the chromium and vanadium contents must be between 1.1 and 3%, preferably between 1.5 and 3%;
• the sum of the silicon, aluminum and molybdenum contents must be between traces and 1%.

Such cold stamping and stamping operations are performed on an alloy which is initially in the form of bars, wires or thick plates (at least 1 mm).

• la somme des teneurs en silicium et aluminium est comprise entre 1 et 2,6% ;
• et la somme des teneurs en chrome, vanadium, molybdène, tantale et niobium est comprise entre des traces et 2%.

When the core is prepared from plate bars or sheets, and these bars, plates or sheets are to be cut or machined, it is preferable that the composition of the alloy meets both of the following characteristics:

• the sum of silicon and aluminum contents is between 1 and 2.6%;
• and the sum of the contents of chromium, vanadium, molybdenum, tantalum and niobium is between traces and 2%.

In this way we obtain an alloy whose hardness is greater than 200 HV after annealing.

Table 1 gives, for examples of alloys according to the invention and alloys according to the prior art, their chemical composition, as well as the characteristics at 20 ° C. of elongation at break, of hardness after annealing, of saturation magnetization, resistivity and coercive field resulting from these compositions. The 100% complement of the compositions is consisting of iron and impurities resulting from the elaboration. The results of the calculation of the first members of equations (1) and (2) were also reported.

Reference alloy 9 is an iron / cobalt alloy with about 50% cobalt. Its magnetic characteristics are excellent, as well as its hardness which makes it suitable to be cut or machined. On the other hand, it has an extremely low elongation at break which renders it unfit to undergo large plastic deformations. In addition, it is an extremely expensive alloy.

Reference Example 10 is an iron / cobalt alloy with about 30% cobalt. Compared to the previous one, its resistivity is very significantly lower. In addition, if its elongation at break is better, without being excellent, this alloy has a substantially lower hardness after annealing which makes it less suitable for undergoing cutting or machining.

Reference alloy 11 is an iron / silicon alloy with 3% silicon. It presents satisfactory values for the resistivity and the coercive field; on the other hand, its saturation magnetization is relatively weak. In addition, its elongation at break remains very limited.

Reference alloy 12 is an approximately 20% cobalt alloy containing vanadium. Its composition verifies equation (1), and it therefore has good saturation magnetization. On the other hand, it does not check equation (2) and its resistivity is mediocre. In addition, its O + N + S content is relatively high, which gives it a coercive field too strong.

Reference alloy 13 is an 18% chromium-containing cobalt alloy. He checks equation (2) (if we take into account the elements Al, V, Mo and Si inevitably present as impurities) and verifies equation (1). Its saturation magnetization and resistivity are therefore satisfactory. Its high elongation at break would make it suitable for shaping by plastic deformation. On the other hand, its O + N + S content is high, which gives it a coercive field that is too strong.

Reference alloy 14 is similar to the previous one, except that tantalum has been added thereto. The elongation at break is further improved, but the coercive field remains too high for this composition is within the scope of the invention.

Reference alloy 15 is a 15% cobalt alloy, also containing silicon and aluminum. It checks equation (2), which gives it a good resistivity, but not equation (1), resulting in saturation magnetization a little too weak compared to what is desired. It is noted that its O + S + N content is low, which gives it a very low coercive field, and that silicon and aluminum give it a high hardness after annealing.

The reference alloys 16 and 17 have characteristics comparable to the previous one. They do not check equation (1) because of a cobalt content that is too low compared to the total silicon and aluminum contents, and their saturation magnetization at 20 ° C is slightly too low.

Reference alloy 18 is a cobalt iron with 15% cobalt containing no other alloying elements at significant levels. If its saturation magnetization and its coercive field are good (equation (1) is checked and its O + N + S content is low), its resistivity is mediocre (equation (2) is not verified) . In addition, its mechanical properties are not particularly good, either for elongation at break or hardness after annealing.

Reference alloy 19 is a cobalt iron with 15% cobalt containing only 1% silicon. The same comments can be made about it as for alloy 16, except that the presence of silicon improves the hardness and the resistivity, without bringing the latter to a sufficient level.

Reference alloy 20 is a cobalt iron with 18% cobalt containing 3.2% vanadium. Its electromagnetic characteristics are good, but its elongation at break is insufficient, due to the presence of vanadium in excess relative to the maximum quantity allowed (3%).

Among the alloys 1-8 according to the invention, the alloys 1-3 have a hardness after high annealing, greater than 210 HV, which makes them particularly suitable for being cut or machined. They will therefore be used preferentially to form bars, plates or sheets, from which will be manufactured the desired parts. These are iron-cobalt alloys containing about 15 or 18% cobalt, and significant amounts of silicon and possibly aluminum. Alloy 1 additionally contains tantalum and alloy 2 molybdenum; alloy 3 has no additional alloying elements in large amounts. These alloys have excellent electromagnetic characteristics, both in terms of saturation magnetization and resistivity, and therefore have a very good compromise between the various requirements of the applications envisaged. Finally, the presence of tantalum and molybdenum in alloys 1 and 2 gives them relatively high elongations at break, which would make these alloys equally suitable for forming by stamping or stamping under conditions that would be acceptable, or which would be even frankly good for the alloy 1. Typically, for this category of alloys, a composition is chosen that comprises 18% of cobalt, 0.5 to 1% of chromium + vanadium, 0.05 to 0.5% of tantalum + silicon and 1 to 2.5% silicon + aluminum + molybdenum.

The alloys 4-8 according to the invention have a high elongation at break (at least 35%) which makes them suitable for being formed by stamping or stamping. They will be used preferentially to form bars or wires from which the desired parts will be manufactured. These are iron-cobalt alloys with about 18% cobalt, containing little or no silicon and aluminum. On the other hand, they contain chromium (2 to 2.9%). This element could be replaced at least partially by molybdenum and / or vanadium. Their electromagnetic characteristics present the same favorable compromise between the various requirements as the 1-3 alloys. Typically, for this category of alloys, a composition is chosen that comprises 18% cobalt, 2 to 3% chromium, 0 to 1% vanadium, 0.05 to 0.5% tantalum + silicon and 0 to 0, 5% silicon + aluminum + molybdenum.

Once obtained the alloy according to the invention, in the form of bars, wires, plates or sheet metal, if one wants to use this alloy to constitute electromagnetic actuators (or any other part for which similar characteristics would be required), it's important to subject the metal a thermomechanical treatment that gives it the optimal texture required. This treatment must aim at obtaining for at least 30%, and preferably at least 50% (by volume of the material), grains or crystals having a crystallographic orientation having a <100> axis deviated by less than 20 ° relative to the hot or cold rolling direction. If we approximate some axes <100> of the crystals of the main directions of use of the magnetic flux by a particular texturing, significantly improves the magnetic properties of steels and soft magnetic alloys. In the case of the alloys of the invention in the form of plates or rolled sheets, these must have a preferential texture of the {100} or {110} type parallel to the rolling plane, the proportion of which in the volume of the material and the <100> orientation with respect to the rolling direction must meet the criteria mentioned above.

On the alloys of the invention, a method for obtaining a texture corresponding to these characteristics is as follows.

The bar, wire, plate or sheet blank, whose composition has been previously defined, is subjected to a hot-rolling austenoferritic blank. By austenoferritic rolling is meant a rolling beginning in the austenitic phase, therefore above the transformation temperature α → α + γ (Tα / γ which is specified for each alloy given as an example in Table 1) and ending in phase ferritic, therefore below Tα / γ. This hot rolling must comprise a reduction step with a degree of work-up of at least 30% (and preferably at least 50%) when the alloy is in the ferritic phase (the degree of curling being defined by the ratio ( initial section - final section) / initial section). For example, if one wants to obtain a bar diameter of 20 mm, it is necessary, during hot rolling, to be in ferritic phase with an intermediate diameter of at least 24 mm, preferably at least 28 mm. Similarly, if one wants to obtain a 2.5 mm thick plate, during hot rolling, it is necessary to be in the ferritic phase at an intermediate thickness of at least 3.6 mm, preferably at least 5 mm.

Moreover, the anneals possibly carried out after the hot rolling should never bring the product to a temperature above Tα / γ, this temperature ranging from 930 to 990 ° C for the alloys according to the invention shown in Table 1.

Finally, since the most favorable texture is obtained mainly in the upper layers of the product, it is advisable to limit as much as possible the superficial removal of material during subsequent stripping or polishing operations. Preferably, the mass decrease of the products following these operations should not exceed 10%, or better 5%.

As has been said, a preferred application of the alloys according to the invention is the manufacture of cores for electromagnetic actuators. Such compact, fast and reliable actuators comprising such cores can advantageously be used in injectors of direct injection combustion engines, especially diesel engines, and in moving parts of electromagnetic actuators controlling the movement of combustion engine valves. internal.

Claims (16)

1. Iron-cobalt alloy, characterized in that it comprises, in percentages by weight:

   - from 10 to 22% of Co;

   - from traces to 2.5% of Si;

   - from traces to 2% of Al;

   - from 0.1 to 1% of Mn;

   - from traces to 0.0100% of C;

   - a sum of the O, N and S contents of between traces and 0.0070%;

   - a sum of the Si, Al, Cr, V, Mo and Mn contents of between 1.1 and 3.5%, preferably between 1.5 and 3.5%;

   - a sum of the Cr, Mo and V contents of between traces and 3%;

   - a sum of the Ta and Nb contents of between traces and 1%;

   the balance being iron and impurities resulting from the smelting,
   in that: $$1.23\left(\mathrm{Al}+\mathrm{Mo}\right)\%+0.84\left(\mathrm{Si}+\mathrm{Cr}+\mathrm{V}\right)\%-0.15\left(\mathrm{Co}\%-15\right)\le 2.1$$

   

   
   and in that: $$14,5\left(\mathrm{Al}+\mathrm{Cr}\right)\%+12\left(\mathrm{V}\mathrm{+}\mathrm{Mo}\right)\%+25\mathrm{Si}\%\ge 40.$$

   
2. Iron-cobalt alloy according to Claim 1, characterized in that it contains 14 to 20% Co.
3. Iron-cobalt alloy according to Claim 1 or 2, characterized in that the sum of the Ta and Nb contents is between 0.05 and 0.8%.
4. Iron-cobalt alloy according to one of Claims 1 to 3, characterized in that the sum of its Cr and V contents is between 1.1 and 3%, preferably between 1.5 and 3%, and in that the sum of its Si, Al and Mo contents is between traces and 1%.
5. Iron-cobalt alloy according to Claim 4, characterized in that its elongation at break is ≥ 35%.
6. Iron-cobalt alloy according to one of Claims 1 to 3, characterized in that the sum of its Si and Al contents is between 1 and 2.6% and in that the sum of its Cr, V, Mo, Ta and Nb contents is between traces and 2%.
7. Iron-cobalt alloy according to Claim 6, characterized in that its hardness HV is ≥ 200 after annealing.
8. Iron-cobalt alloy according to one of Claims 1 to 7, characterized in that its saturation magnetization is ≥ 2.1 T at 150°C and ≥ 2.12 T at 20°C and in that its resistivity is ≥ 35 µΩ.cm at 150 °C and ≥ 31 µΩ.cm at 20°C.
9. Iron-cobalt alloy according to one of Claims 1 to 8, characterized in that its coercive field at 20°C and 150°C is less than 1.5 Oe, preferably less than 1 Oe.
10. Bar, rod or plate made of iron-cobalt alloy, characterized in that said alloy is of the type according to one of Claims 1 to 9 and in that the bar, rod or plate has a preferential <100> axis fiber texture deviating by less than 20° with respect to the hot rolling direction, for at least 30% (by volume of the material), preferably for at least 50%, of the grains.
11. Rolled plate or sheet made of iron-cobalt alloy, characterized in that said alloy is of the type according to one of Claims 1 to 9 and in that it has a strong <100> axis texture component deviating by less than 20° with respect to the hot rolling direction, for at least 30% (by volume of the material), preferably for at least 50%, of the grains.
12. Process for producing a rolled bar, rod, plate or sheet according to Claim 10 or 11, characterized in that a rolled bar, rod, plate or sheet is produced from a blank made of an alloy according to one of Claims 1 to 9 by carrying out a rolling operation with a deformation ratio in the ferritic phase of at least 30%, preferably at least 50%, and in that an optional subsequent annealing treatment is carried out at a temperature below the austenitic transformation temperature.
13. Moving core for an electromagnetic actuator, characterized in that it has been manufactured from a rolled bar or rod or plate or sheet according to Claim 10 or 11.
14. Electromagnetic actuator comprising a moving core made of an iron-cobalt alloy, characterized in that said core is of the type according to Claim 13 and in that the preferential texture of said core has a <100> axis approximately parallel to the principal direction of the excitation field.
15. Injector for an internal combustion engine controlled by electronic regulation, comprising an electromagnetic actuator having a high volume power, a short response time and high reliability in use, characterized in that said actuator is of the type according to Claim 14.
16. Electromagnetic actuator for the electronically controlled valves of an internal combustion engine, characterized in that it is of the type according to Claim 14.