Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
  • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
  • H01F1/147—Alloys characterised by their composition

Definitions

• Iron-cobalt alloy in particular for a mobile electromagnetic actuator core, and its manufacturing process.
• 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 in electro-injectors. A preferred application of such electro-injectors is the direct injection of fuel into internal combustion engines, in particular diesel engines. Another preferred application concerns a very specific type of solenoid valve, used for the electromagnetic control of the valves of internal combustion engines (petrol or diesel).
• the electrical energy is supplied in a winding by a series of current pulses, creating a magnetic field which magnetizes an unclosed magnetic yoke, therefore comprising an air gap.
• the geometrical characteristics of the cylinder head make it possible to direct most of the magnetic field lines axially with respect to the air gap area.
• the air gap is subjected to a difference in magnetic potential.
• the actuator also includes a core made mobile by the action of electric current in the coil. Indeed, the difference in magnetic potential introduced by the coil between the movable core at rest on one 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 magnetic 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, promoting by their stiffness the dynamics of the moving part (in the case of electromagnetically controlled valves).
• the setting in motion of the mobile core occurs with a phase shift compared to the moment of creation of the electrical pulses.
• the metal which composes it has high electrical resistivity and low coercive field. These conditions make it possible to obtain low currents induced in the yoke and the magnetic core, making it possible to quickly reach the minimal magnetization of the core which generates its setting in motion. It is also important that the core has a high saturation magnetization, so as to allow a maximum force at the end of the pulse as high as possible.
• These magnetic cores have various shapes and can be made from wires or bars. In this case, they must have a great plastic aptitude for deformation, so that they can be deformed without risk of breaking. It is preferable to have an elongation at break of the material of at least 35%.
• Such cores can also be manufactured by cutting sheets or laminated sheets. In this case, they must have a great ability to punch, for which minimum hardness and mechanical resistance are necessary. Good resistance of the magnetic properties to the repeated mechanical shocks to which the core will be subjected is also necessary. These hardness and mechanical resistance characteristics are also favorable to good efficiency of the cutting of the core. It is recommended to have a hardness of the material after annealing greater than 200 HV for these uses.
• 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 weak.
• a second category consists of iron-cobalt alloys with a high cobalt content, of the order of 50%. Such alloys have significantly more saturation magnetization higher than that of the previous iron-silicon alloys. However their resistivity is somewhat lower. In addition, due to the massive presence of cobalt, these alloys are very expensive. Finally, their mechanical properties are not optimal, which makes the fabrication of the cores difficult.
• a third category consists of iron-cobalt alloys containing approximately 6 to 30% of cobalt and various other alloying elements.
• EP-A-715 320 gives an example of such alloys. It describes iron-cobalt alloys for electromagnetic actuator cores comprising 6 to 30% of cobalt, 3 to 8% of one or more elements chosen from chromium, molybdenum, vanadium and tungsten, the rest being iron .
• the cobalt content is from 10 to 20% and the chromium, molybdenum, vanadium and / or tungsten content is from 4 to 8%.
• alloys have good electrical resistivity, which can be greater than 50 ⁇ .cm, but their magnetization at saturation is relatively weak, of the order of 1.9 to 2T, except for the variants most loaded with cobalt (which are therefore the most expensive) where this saturation magnetization can reach 2.3 T.
• the coercive field of the alloys given in example in this document is also high, substantially greater than 1.5 Oe.
• the alloys given as an example in this document do not allow an optimal compromise to be reached between a magnetization at high saturation, a weak coercive field and a high resistivity.
• Patent WO 96/19 001 proposes using iron / cobalt alloys containing between 5 and 20% of cobalt, and having an aluminum and manganese or vanadium content which can reach several%: up to 7% of aluminum, and up to 8% manganese or 4% vanadium. Alloys described in this document have a very high resistivity (greater than 60 ⁇ .cm), and a fairly high magnetization at saturation (from 2 to 2.2 T). But none. precise information is not given on the mechanical properties of these alloys, as well as on their coercive field.
• the object of the invention is to provide iron / cobalt alloys which are particularly suitable for the economical production of cores for electromagnetic actuators. These nuclei should present a more favorable compromise than with the materials existing 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.
• the subject of the invention is an iron-cobalt alloy, characterized in that it comprises in weight percentages:
• this iron-cobalt alloy contains 14 to 20% of Co and the sum of the contents of Ta and Nb is between
• 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%.
• the sum of the contents of Si and Al is between 1 and 2.6%, and the sum of contents of Cr, V, Mo, Ta, Nb 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 35 ⁇ .cm at 150 ° C and at least 31 ⁇
• the subject of the invention is also 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, wire, plate or sheet has a preferred fiber texture with axis ⁇ 100> for a bar or wire, or a strong texture component ⁇ 100> for a laminated plate or sheet, deflected by less than 20 ° from the rolling direction hot, for at least 30% (by volume of the material) of the grains, preferably for at least 50%.
• the invention also relates to 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, a plate is produced. or a sheet rolled from a blank of an alloy according to the invention by rolling, starting in the austenitic phase and ending in the ferritic phase, the reduction in thickness undergone by the bar, the wire, the plate or the sheet in ferritic phase being at least 30%, preferably at least 50%, and in that any subsequent annealing is carried out at a temperature below the austenitic transformation temperature.
• the subject of the invention is also a movable core of an electromagnetic actuator, characterized in that it has been manufactured from a bar or a wire or a plate or a sheet laminated according to the preceding process , as well as an electromagnetic actuator comprising a movable core of iron-cobalt alloy, characterized in that said core is of the preceding type and in that it has a preferred texture of axis ⁇ 100>, this axis being substantially parallel to the main direction of the excitation field.
• the invention also relates to an injector for an internal combustion engine controlled by electronic regulation. 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 actuator of an electronically controlled internal combustion engine valve, characterized in that it is of the previous type.
• the iron / cobalt alloy according to the invention is classified in the category of Fe-Co alloys with a low or medium cobalt content, and comprises contents of other relatively moderate alloying elements.
• these alloying elements must be present in respective well-defined proportions. It is only under these conditions that optimum properties are obtained for these alloys and for the cores of electromagnetic actuators which result therefrom, both on the magnetic and on the mechanical plane, for a cost of material (linked to the presence of cobalt) very moderate compared to Fe-Co alloys with 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 ⁇ .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 ⁇ .cm. At the same time, this good reactivity of the actuator is also due to a weak 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 the pulse time.
• the alloys according to the invention have a saturation magnetization at 150 ° C greater than 2.1 T. This value is certainly greater than those usually observed with iron / silicon alloys at 3% silicon. At 20 ° C, the saturation magnetization of the alloys according to the invention is greater than 2.12 T.
• the saturation magnetization decreases when the temperature increases; therefore, to guarantee a magnetization at saturation greater than or equal to 2.1 T at 150 ° C, the magnetization at saturation at 20 ° C must be greater by 1%, or greater than or equal to 2.12 T.
• the alloys according to the invention have mechanical characteristics which are particularly favorable for the preparation of the cores of electromagnetic actuators.
• the alloys have a great ability to plastic deformation by stamping or stamping, since they have a maximum elongation at break of at least 35%.
• these alloys are suitable for good cutting and machining quality, 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 weight percentages.
• the cobalt content is between 10 and 22%, and preferably between 14 and 20%, in order to significantly increase the saturation magnetization compared to the iron / silicon alloys, while maintaining a high resistivity.
• the limitation to 22% of the cobalt content provides mechanical properties and a more favorable cost price than in the case of iron / cobalt alloys containing 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 does 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 transformation. Each of these elements (except manganese) may only be present in traces resulting from the processing.
• 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 under these conditions that a resistivity of the alloy equivalent to that of the iron / silicon alloys containing 2 to 3% of silicon is obtained.
• the contents of these elements must verify the following two equations: 1.23 X (Al + Mo)% + 0.84 (Si + Cr + V) - 0.15 x (Co% -15)% ⁇ 2.1
• the sum of the contents of chromium, molybdenum and vanadium must be at most 3%, so as not to degrade the magnetization at saturation of the material.
• tantalum and niobium contents as well as the sum of their contents, must each be less than or equal to 1%.
• the sum of these contents is between 0.05 and 0.08%.
• the function of tantalum is to increase the ductility of the alloy, and niobium to increase mechanical strength and wear resistance, as well as resistivity. The upper limit of 1% is motivated by the need not to degrade the saturation magnetization of the material. These elements may only be present in traces resulting from the processing.
• 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 carbon, oxygen, nitrogen and sulfur elements are considered as impurities and may only be present in trace amounts resulting from the production.
• the alloy When the alloy is intended to undergo a stamping or stamping operation, for which it is desirable to have a significant maximum plastic elongation (greater than or equal to 35%), the alloy must preferably 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 carried out on an alloy which is initially found in the form of bars, wires or thick plates (at least 1 mm).
• the composition of the alloy meets the following two characteristics:
• 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 complement to 100% of the compositions is consisting of iron and impurities resulting from the production.
• the results of the calculation of the first members of equations (1) and (2) have also been reported.
• Table 1 Examples of alloy compositions according to the invention and of reference alloys, with their electromagnetic and mechanical characteristics
• the reference alloy 9 is an iron / cobalt alloy with approximately 50% cobalt. Its magnetic characteristics are excellent, as well as its hardness which makes it suitable for being cut or machined. On the other hand, it has an extremely low elongation at break which makes it unsuitable for undergoing 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 significantly lower hardness after annealing which makes it less suitable for undergoing cutting or machining.
• the reference alloy 11 is an iron / silicon alloy with
• the reference alloy 12 is an alloy with approximately 20% of cobalt containing vanadium. Its composition checks equation (1), and it therefore has good saturation magnetization. On the other hand, it does not check equation (2) and its resistivity is therefore poor. In addition, its O + N + S content is relatively high, which gives it too strong a coercive field.
• Reference alloy 13 is an 18% cobalt alloy containing chromium. It checks equation (2) (if one takes into account the elements Al, V, Mo and Si inevitably present as impurities) and checks equation (1). Its magnetization
• the reference alloy 14 is similar to the previous one, except that tantalum has been added to it. The elongation at break is further improved, but the coercive field remains too high so that this composition is within the scope of the invention.
• the reference alloy 15 is a 15% cobalt alloy, also containing silicon and aluminum. It checks equation (2), which gives it good resistivity, but not equation (1), resulting in a saturation magnetization a little too weak compared to what is desired. It is noted that its O + S + 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) due to a too low cobalt content compared to the total silicon and aluminum contents, and their magnetization at saturation at 20 ° C is slightly too low.
• the reference alloy 18 is a 15% cobalt iron-cobalt containing no other alloying elements at significant contents. If its saturation magnetization and its coercive field are good (equation (1) is verified and its O + N + S content is low), its resistivity is poor (equation (2) is not verified) . In addition, its mechanical properties are not particularly good, either for elongation at break or for hardness after annealing.
• the reference alloy 19 is a 15% cobalt iron-cobalt containing only 1% silicon. The same comments can be made about it as for alloy 16 except that the presence of silicon improves hardness and resistivity, without however bringing the latter to a sufficient level.
• the reference alloy 20 is an iron-cobalt containing 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%).
• the alloys 1-8 have a high hardness after annealing, greater than 210 HV, which therefore makes them particularly suitable for being cut or machined. They will therefore preferably be used to form bars, plates or sheets, from which the desired parts. These are iron-cobalt alloys containing about 15 or 18% of 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 quantities. 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.
• tantalum and molybdenum in alloys 1 and 2 gives them fairly high elongations at break, which would make these alloys also able to be shaped by stamping or stamping under conditions which would be acceptable, or which would be even mentally good for alloy 1.
• a composition is chosen comprising 18% cobalt, 0.5 to 1% chromium + vanadium, 0.05 to 0.5% tantalum + silicon and 1 to 2.5% silicon + aluminum + molybdenum.
• Alloys 4-8 according to the invention have a high elongation at break (at least 35%) which makes them suitable for being shaped by stamping or stamping. They will preferably be used to form bars or wires from which the desired parts will be made. These are iron-cobalt alloys with around 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 alloys 1-3.
• a composition comprising 18% of cobalt, 2 to 3% of chromium, 0 to 1% of vanadium, 0.05 to 0.5% of tantalum + silicon and 0 to 0, 5% silicon + aluminum + molybdenum.
• the metal thermomechanical treatment which gives it the optimal texture required.
• the aim of this treatment must be to obtain, for at least 30%, and preferably at least 50% (by volume of the material), grains or crystals having a crystallographic orientation comprising an axis ⁇ 100> deviated by less than 20 ° relative to the direction of hot or cold rolling. If we bring certain axes ⁇ 100> of the crystals closer to the main directions of use of the magnetic flux by a particular texturing, we significantly improve the magnetic properties of steels and soft magnetic alloys.
• alloys of the invention in the form of sheets or rolled sheets, these must have a preferential texture of the type ⁇ 100 ⁇ or ⁇ 110 ⁇ parallel to the rolling plane, the proportion of which in the volume of the material and orientation ⁇ 100> in relation to the rolling direction must obey the criteria mentioned above.
• An austenoferritic hot rolling is carried out of the blank in the form of a bar, wire, plate or sheet, the composition of which has been previously defined.
• austenoferritic rolling is meant a rolling starting in the austenitic phase, therefore above the transformation temperature ⁇ - » ⁇ + ⁇ (TOîy which is specified for each alloy given as an example in Table 1) and ending in the ferritic phase , so below Ta.
• This hot rolling must include a reduction step with a wrought rate of at least 30% (and preferably at least 50%) when the alloy is in the ferritic phase (the wrought rate being defined by the ratio
• the reduction in mass of the products following these operations should not exceed 10%, or better still 5%.
• a preferred application of the alloys according to the invention is the manufacture of cores for electromagnetic actuators.
• Such compact, rapid and reliable actuators comprising such cores can advantageously be used in injectors of direct injection combustion engines, in particular of diesel engines, and in moving parts of electromagnetic actuators controlling the movement of the valves of combustion engines. internal.

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