before describing the method steps according to the present invention , for producing a rigid magnetic circuit component , with the aid of fig2 to 15 , we shall explain in greater detail a fuel injector of the related art , with the aid of fig1 , as a possible product for the insertion of a magnetic circuit component produced according to the present invention . the valve that is operable electromagnetically , shown in exemplary fashion in fig1 in the form of an injector for fuel injection systems of mixture - compressing , externally ignited internal combustion engines , has a core 2 , surrounded by a magnetic coil 1 , used as fuel intake neck and inner pole , which has , for example , a constant outer diameter over its entire length . a coil shell 3 graded in the radial direction accommodates a winding of magnetic coil 1 and , in conjunction with core 2 , enables the fuel injector to have a compact design in the region of magnetic coil 1 . a tubular , metal , nonmagnetic intermediate part 12 is connected to a lower core end 9 of core 2 by welding , concentrically to a longitudinal valve axis 10 , and partially surrounds core end 9 in an axial manner . a tubular valve - seat support 16 , which is rigidly connected to intermediate part 12 , extends downstream from coil shell 3 and intermediate part 12 . an axially movable valve needle 18 is situated in valve seat support 16 . at downstream end 23 of valve needle 18 a spherical valve closure member 24 is provided , at whose circumference , for example , five flattened regions 25 are provided for the fuel to flow past . the fuel injector is actuated electromagnetically , in the known manner . for the axial displacement of valve needle 18 , and thus for the opening counter to the spring force of a restoring spring 26 , or for the closing of the fuel injector , the electromagnetic circuit having magnetic coil 1 , core 2 and an armature 27 is utilized . pipe - shaped armature 27 is rigidly connected to the end of valve needle 18 facing away from valve - closure member 24 , by a welded seam , and is aligned with core 2 . a cylindrical valve - seat member 29 having a fixed valve seat 30 is mounted in the downstream end of valve - seat support 16 facing away from core 2 , using welding , so as to form a seal . spherical valve - closure member 24 of valve needle 18 interacts with the valve seat 30 of valve - seat member 29 , which is frustoconically tapered in the direction of flow . at its lower end face , valve seat member 29 is connected to a pot - shaped spray orifice disk 34 , for example , rigidly and sealingly by a welded seam that is developed , for example , using a laser . in spray orifice disk 34 , at least one , but , for example , four , spray - discharge orifices 39 are provided that are formed by eroding or stamping , for example . in order to conduct the magnetic flux for the optimal activation of armature 27 , when magnetic coil 1 is supplied with current , and with that to the secure and accurate opening and closing of the valve , magnetic coil 1 is surrounded by at least one conductive element 45 , developed , for instance , as a bracket and used as a ferromagnetic element , which surrounds magnetic coil 1 at least partially in the circumferential direction , and which lies with its one end against core 2 and with its other end against valve seat support 16 , and is able to be connected to the latter , for instance , by welding , soldering or adhesion . core 2 , nonmagnetic intermediate part 12 and valve seat support 16 form an inner metallic valve pipe as skeleton and , with that also the housing of the fuel injector , and they are firmly connected to one another and altogether extend over the entire length of the fuel injector . all additional functional groups of the valve are ordered within or round about the valve pipe . this arrangement of the valve pipe involves the classical three - part design of a housing for an electromagnetically operable aggregate , such as a valve , having two ferromagnetic or magnetizable housing regions which , for the effective conduction of the magnetic circuit lines of force in the region of armature 27 , are magnetically separated from each other or at least connected to each other via a magnetic throttling point , using a nonmagnetic intermediate part 12 . the fuel injector is largely surrounded by a plastic extrusion coat 51 , which extends in the axial direction from core 2 , over magnetic coil 1 and the at least one conductive element 45 , to valve - seat support 16 , the at least one conductive element 45 being completely covered in the axial and circumferential directions . part of this plastic extrusion coating 51 is a likewise extruded electrical connection plug 52 , for instance . using the method steps of the method according to the present invention that are schematically indicated in fig2 to 7 , for producing a rigid magnetic circuit component , it is advantageously possible to produce , especially simply and cost - effectively , thin - walled housings 66 for various utilization purposes , among other things , preferably electromagnetically operable valves which are able to replace a three - part valve pipe described above . in a first method step ( fig2 ) a base element 55 , that is cylindrical , for example , is provided from which housing 66 is to be manufactured , and which is made of a magnetic or magnetizable material and is ferromagnetic or ferritic , for example , or has a martensitic microstructure . base element 55 may be solidly developed , for the moment , and may be made from long rod material , for example , for an especially effective production of a plurality of housings 66 . the material of base element 55 is steel in each case , which forms residual austenite and martensite based on its alloy composition . the alloying elements in the material are the elements c , n , ni and mn , which stabilize austenite . in order to achieve the different desired magnetic properties of the magnetic circuit component , base element 55 is submitted completely to a heat treatment , which is able to be performed , for instance , using hardening , deep cooling in deep - cooling refrigerators and / or by one - time or multiple reheating in ovens 56 ( fig3 ). after hardening , the microstructure may still also be made up of residual austenite proportions which are transformed into martensite by the subsequent heat treatment steps . alternatively to this , the microstructure may also be made up of ferrite , having intercalated particles such as carbides , nitrides or intermetallic compounds . the heat treatment takes place in such a way that a completely magnetic martensitic material microstructure forms in base element 55 ( fig4 ). an additional heat treatment is subsequently undertaken which , however , is only carried out in a locally limited fashion . a subregion of base element 55 is exposed , for this purpose , to short - term heat treatment using laser heating or induction heating 57 ( fig5 ). in this way , the material of base element 55 is locally austenitized and homogenized in the subregion of the second heat treatment and , after cooling of base element 55 or self - quenching by the surrounding material , it is made up of martensitic regions 58 and subregion 59 having martensite and residual austenite ( fig6 ). base element 55 is now made up of zones having various microstructures and magnetic properties . base element 55 is then finally treated in such a way that there exists a rigid housing 66 as magnetic circuit component in a desired geometry . in the case of the use of a housing 66 produced according to the present invention , in a fuel injector , it may be advantageous specifically to form housing 66 into shape by measures of production technology , such as ironing , tumbling , round - kneading , flanging and / or flaring . housing 66 then represents a component that is able completely to take over the sum of the functions of the valve pipe , consisting of core 2 , intermediate part 12 and valve seat support 16 in a known fuel injector according to fig1 , and consequently it extends , for example , over the entire axial length of a fuel injector . solid base element 55 is brought , for example , to form a pipe - shaped sleeve form , by production technology measures . solid base element 55 may be provided , in this context , with an inner longitudinal opening 60 to form pipe - shaped housing 66 ( fig7 ), either before or only after the local heat treatment . fig8 shows a schematic cutout of a fuel injector having a housing 66 produced according to the present invention , which is installed in the valve as a thin - walled sleeve , and thus surrounds core 2 and armature 27 radially and in the circumferential direction , and is itself , in this context , surrounded by magnetic coil 1 . it becomes clear that subregion 59 of housing 66 , that has been changed in its magnetic properties and is martensitic and residually austenitic , lies in the axial extension region of a working air gap 70 between core 2 and armature 27 , in order to conduct the magnetic circuit lines of force optimally and effectively in the magnetic circuit . instead of bracket - shaped conducting element 45 shown in fig1 , the outer magnetic circuit component is executed , for instance , as a magnetic pot 46 , the magnetic circuit being closed between magnetic pot 46 and housing 66 via a cover element 47 . the method according to the present invention also makes it possible locally to change housing 66 in its magnetic properties , using greater wall thicknesses , so that a higher internal pressure stability is ensured in favor of the magnetic force , in spite of the minimized magnetically active region . fig9 to 13 show schematic method steps of the method according to the present invention , for producing a rigid magnetic circuit component in the form of an armature bolt 66 ′. the production of armature bolt 66 ′ takes place in a comparable manner to the previously described production of housing 66 according to fig7 . in a first method step ( fig9 ), a thin cylindrical base element 55 ′ is provided , for instance , from which armature bolt 66 ′ is to be produced , and which is made of a magnetic or a magnetizable material , and is ferromagnetic or ferritic , for example , or which has a martensitic material microstructure . base element 55 ′ may , for instance , be made of long rod material for an especially effective production of many armature bolts 66 ′. the material of base element 55 ′ is a steel in each case , which forms residual austenite and martensite based on its alloy composition . the alloying elements in the material are the elements c , n , ni and mn , which stabilize austenite . in order to achieve the different desired magnetic properties of the magnetic circuit component , base element 55 ′ is submitted completely to a heat treatment , which is able to be performed , for instance , using hardening , deep cooling in deep - cooling refrigerators and / or by one - time or multiple reheating in ovens 56 ( fig1 ). after hardening , the microstructure may still also be made up of residual austenite proportions , which are transformed into martensite by the subsequent heat treatment steps . alternatively to this , the microstructure may also be made up of ferrite , having intercalated particles such as carbides , nitrides or intermetallic compounds . the heat treatment takes place in such a way that a completely magnetic martensitic material microstructure forms in base element 55 ′ ( fig1 ). thereafter , additional heat treatment is performed , which is supposed to lead to a change in the magnetic properties , exclusively at the surface in the edge regions of base element 55 ′. a surface of base element 55 ′ is exposed , for this purpose , to short - term heat treatment using laser heating or induction heating 57 ( fig1 ). in this way , the material of base element 55 ′ is locally austenitized and homogenized at the surface and , after the cooling of base element 55 ′ or self - quenching by the surrounding material , it is made up of an inner martensitic regions 58 ′ and an outer edge region 59 ′ having martensite and residual austenite ( fig1 ). base element 55 ′ or armature bolt 66 ′ is now made up of zones having various microstructures and magnetic properties . if necessary , base element 55 ′ is then finally treated in such a way that there exists a rigid armature bolt 66 ′ as magnetic circuit component , in a desired geometry . fig1 shows a schematic cutout of a magnetic circuit in plunger - type execution , having an armature bolt 66 ′ according to the present invention , which plunges through a magnetic pot 46 and is displaceable there in a movable manner . in the case of plunger - type magnetic circuits , the dynamics and the magnetic force of the magnetic valve are able to be improved , using an armature bolt 66 ′, in which outer edge region 59 ′ has residual austenite proportions . coating methods , such as carbonitriding , may be omitted . fig1 , a schematic cutout from a magnetic circuit in a flat - type armature execution is shown , having a tie plate 66 ″, produced according to the present invention . the production principle is again comparable to the previously described method steps for producing housing 66 or armature bolt 66 ′. the local second heat treatment takes place in such a way that a short - term heat treatment is performed , using laser heating or induction heating , at one side of the flat , plate - shaped base element . in this way , the material of the base element is locally austenitized and homogenized on this side and , after the cooling of the base element or the self - quenching by the surrounding material , it is made up of a martensitic region 58 ″ and an edge region 59 ″ facing magnetic coil 1 , having martensite and residual austenite . tie plate 66 ″ is now made up of zones having various microstructures and magnetic properties . using such a tie plate 66 ″, an additional air gap is able to be generated in flat - type armature magnetic circuits . this additional air gap in edge region 59 ″ may be used so as to prevent the adhesion of tie plate 66 ″ to magnet pot 46 , so as to set a specified residual air gap in the magnetic circuit or so as to have it used as an air gap having wear protection . the present invention is by no means restricted to use in fuel injectors or magnetic valves for antilock systems , but relates to all electromagnetically operable valves in different fields g 1 of application , and generally to all rigid housings in assemblies in which the zones of different magnetism are required successively .