NICKEL-IRON BASE MAGNETIC ALLOY HAVING HIGH PERMEABILITY

Abstract: Ni-Fe base magnetic alloy contains 77.5 -79.5 wt.% Ni, 3.8-4.6 wt.% Mo, 1.8-2.5 wt.% Cu, 0.1-1.10 wt.% Mn, 0.010 or less wt.% P, 0.0020 or less wt.% S, 0.0030 or less wt.% O, 0.0010 or less wt.% N, 0.020 or less wt.% C, B, and Fe (the rest). The compsn. of the alloy is such that: B-10.8/14 N = 0.005 to 0.0070 wt.%. The amount of B in Osterite or near-Osterite particulate state is 10-50 atom %.

Description: This invention relates to a nickel-iron base magnetic alloy having high permeability and more particularly to a nickel-iron base magnetic alloy having improved magnetic properties, such as permeability and shielding properties in a direct current and low frequency region. A nickel-iron base magnetic alloy equivalent to JIS PC is a magnetic material which now finds very wide applications such as magnetic head cases and various cores, transformation cores and various magnetic shielding materials. Such a PC permalloy is characterized by high permeability and low coercive force, and examples of the PC permalloy which has been put to practical use up to now include 80 % nickel - 5 % molybdenum - iron (: superalloy) and 77 % nickel - 5 % copper - 4 % molybdenum - iron (: Mo, Cu permalloy). The permeability level obtained by the above described alloys is usually 150,000 for the initial permeability (hereinafter refferred to as " µ i ") and about 300,000 for the maximum permeability (hereinafter reffered to as " µ m "). The development of electronics in recent years has brought about a reduction in the size and an improvement in the performance of the various instruments, so that a further improvement has been desired in the characteristics of the above described magnetic alloys as well. In order to answer the above-described desire, development has been made on a technique disclosed in JP-A Nos. 62-227053 and 62-227054 wherein the magnetic properties of the magnetic alloy comprising the above-described component system have been improved by decreasing impurity elements and adding chromium. In order to improve the magnetic properties, JP-A No. 63-149361 proposes to conduct deboronization during magnetic annealing of a material comprising an alloy of the above-described component system and boron added thereto for the purpose of improving the hot workability during manufacture of the magnetic material. In the meantime, the described component system is expensive because it contains about 80 wt.% of nickel. For this reason, the component system has been thoroughly reconsidered and development has been made on a technique described in JP-B2 No. 62-13420 wherein high initial permeability has been attained by decreasing the content of nickel and adding, instead of nickel, copper and manganese more inexpensive than nickel; and a technique described in JP-A Nos. 63-247336 and 63-247339 wherein a suitable amount of aluminium is added in addition to the technique described in said JP-B2 No. 62-13420 for the purpose of decreasing inclusions and enhancing the magnetic properties. In particular, the maximum µ i values of the alloys proposed in said JP-A Nos. 63-247336 and 63-247339 are on a level as high as 426,000. In recent years, in addition of the above-described demand for an improvement in the magnetic properties, it is also demanded to manufacture at lower cost a magnetic material having necessary characteristics. A proposal of a technique in this respect has been made in JP-A No. 1-100232. In specifically, this technique is characterized by adding 1 to 4 wt.% of silicon to an ordinary molybdenum superalloy to attain satisfactory permeability even at a relatively low magnetic annealing temperature, e.g., at about 1,030°C or below. Even in the technique described in JP-A Nos. 62-227053 and 62-227054 are characterized by decrease of the impurities and addition of chromium, the level of direct current magnetic properties after heat treatment (1,100°C × 3 hr) in a hydrogen atmosphere as the final step is, e.g. 100,000 at the highest in terms of µ i , which renders the alloy unsuitable for applications where a higher level of magnetic properties is required. In the proposal described in JP-A No. 62-227054, the cost becomes high because chromium is newly added to the ordinary Ni-Fe-Mo base or Ni-Fe-Mo-Cu base component. The proposal described in JP-A No. 62-227053 has, besides a problem of high cost derived from the addition of chromium, a problem on manufacture of a magnetic material that the hot workability becomes very poor due to the manganese level (must be made to 1.2∼10 wt.%) higher than the ordinary level. Boron is added in both the described proposals. The addition of boron in this case is conducted for the purpose of improving the hot workability and punchability, and mere addition of boron intended in the above proposals brings about no significant improvement in the magnetic properties and sometimes deteriorates the magnetic properties. In JP-A No. 63-149361, the magnetic properties are improved by the deboronization treatment. In this case, the level of the magnetic properties after treatment is 75,000 at the highest in terms of µ i , i.e., the same as that obtained in the ordinary Ni-Fe-Mo-Cu base alloy. Therefore, this technique is unsuitable for applications where a higher level of magnetic properties is necessary. The technique described in JP-B2 No. 62-13420 and JP-A Nos. 63-247336 and 63-247339 can provide a permalloy having a high µ i value, but has a problem of substantial lowering in the hot workability during manufacture of the magnetic material due to an increase in the manganese and copper contents. The saturation magnetic flux density of the alloy prepared in this proposal is, e.g., 5,000 gauss in terms of B₁₀ (magnetic flux density at 10 oersted), namely, lower than that of the superalloy and Mo, Cu permalloy, namely, 7,000 to 8,000 gauss in terms of B₁₀. This means that the magnetic flux in the alloy is unfavorably saturated in a lower external magnetic field than that in the case of the superalloy and Mo, Cu permalloy, which renders the alloy unsuitable for use a shielding material in a place where the external field is relatively high. The technique of JP-A 1-100232 has a problem of deterioration of workability and lowering in the production property of the magnetic material due to addition of a large amount of silicon. Further, in this technique, the shielding performance is on a necessary level at 50Hz but disadvantageously slightly poor in a direct current. Disclosure of Invention : The inventors of the present invention have made further studies on the effect of major components, such as nickel, molybdenum, copper and iron, on the magnetic characteristics with a view to substantially improving the magnetic properties, such as permeability, and shielding performance in a direct current and a low frequency region and further enabling the magnetic annealing for attaining the properties on the same level as that in the case of the background art to be conducted at a temperature of about 100 °C lower than the conventional annealing temperature, and conducted experiments and research on the relationship between the properties obtained in the studies and the components with extension to the boron-added system, which has led the completion of this invention. Specifically, attainment of high permeability and shielding property which could not be observed in the conventional Mo, Cu permalloy and superalloy of the same system and a lowering by about 100°C in the necessary magnetic annealing temperature for attaining the required properties on the same level as that in the background art becomes possible by optimizing the amount of addition of each of nickel, molybdenum, copper, manganese, iron and boron under proper control of impurity elements and controlling the balance of the amounts of the components in a particular range through the use of nickel-iron base high permeability magnetic alloy consisting 77.5 ∼79.5 wt.% of nickel, 3.8∼4.6 wt.% of molybdenum, 1.8∼2.5 wt.% of copper, 0.1∼1.10 wt.% of manganese, not exceeding 0.010wt% of phosphorus, not exceeding 0.0020 wt% of sulphur, not eceeding 0.0030 wt.% of oxygen, not exceeding 0.0010 wt.% of nitrogen, optionally a minor amount up to 0.0017 wt.% of calcium, and not exceeding 0.020 wt.% of carbon and further boron in an amount within the range defined by the following formula: 0.0005 wt.% ≦ [B] - 10.8 14 [N] ≦ 0.0070 wt.% with the balance essentially consisting of iron, the contents of said nickel, molybdenum, copper, manganese and iron being respectively in the ranges satisfying the following formula: 3.3 ≦ 2.02 × [Ni] - 11.13× [Mo] - 1.25× [Cu] -5.03 × [Mn] 2.13 × [Fe] ≦ 3.8 Optional features of the invention are set out in the dependent claims. Brief Description of Drawings : Fig. 1 is a diagram showing the relationship between the initial permeability µ i and the parameter X and [B] - 10.8 14 [N] ; Fig. 2 is a diagram showing the relationship between the degree of shielding and the parameter X and [B] - 10.8 14 [N] ; Fig. 3 is a diagram showing the relationship between the effective permeability and the parameter X and [B] - 10.8 14 [N] ; Fig. 4 is a diagram showing the relationship between the squareness at 50 Hz and the parameter X and [B] - 10.8 14 [N] ; Fig. 5 is a diagram showing the relationship between the initial permeability µ i and the amount of boron in the austenite grain boundary and in the vicinity of the boundary. At the outset, the improvement in the magnetic properties intended in this invention can be attained under control of the level of impurities in the alloy, and the reasons for limitation of the contents (wt.%; hereinafter referred to simply as "%") of phosphorus, sulphur, oxygen, nitrogen and carbon are as follows. Phosphorus is an element which is detrimental to the hot workability of high Ni-Fe alloy intended in this invention and weakens the tendency of forming a cubic aggregate structure during final annealing with hydrogen. When the phosphorus content exceeds 0.010 %, not only the permeability deteriorates but also the hot workability as well as becomes poor. For this reason, the upper limit of phosphorus was set to 0.010 %. The lower limit is preferably 0.0010 % from the viewpoint of economy of ingot. Sulfur is detrimental to the hot workability and very deterimental also to the magnetic properties because it hinders the grain growth during final annealing with hydrogen through formation of a sulfide and brings about a reduction in the particle diameter after annealing, so that no improvement in the permeability is attained. When the sulfur content exceeds 0.0020 %, no improvement in the magnetic properties intended in the present invention can be attained even when the contents of nickel, molybdenum, copper, iron and boron are optimized as described below, and further the hot workability remarkably deteriorates, which makes it necessary for the upper limit of the sulfur content to be 0.0020 %. The sulfur content is more preferably 0. 0005 % or less from the viewpoint of a further improvement in the permeability in a direct current and an alternating current. Oxygen exists as an oxide inclusion in the alloy intended in this invention, and when the amount of oxygen is large, no improvement in the permeability is attained because it hinders the grain growth during final annealing with hydrogen and reduces the particle diameter after annealing. Therefore, oxygen is an element which is very detrimental to the magnetic properties. More particularly, the oxygen content was limited to 0.0030 % or less because, as with the above-described sulfur, the presence of oxygen in an amount exceeding 0.0030 % makes it impossible to improve the magnetic properties intended in this invention even when the contents of nickel, molybdenum, copper, iron and boron are optimized. The oxygen content is more preferably 0.0010 % or less from the viewpoint of a further improvement in the permeability in a direct current. Nitrogen easily bonds to boron in an alloy containing boron added thereto, thereby forming BN, which brings about a lowering in the amount of effective boron. Further, the presence of nitrogen in a large amount gives an adverse effect such as remarkable deterioration of the magnetic properties due to the formed BN. The upper limit of the nitrogen content was set to 0.0010 % because when the content exceeds 0.0010 % the magnetic properties remarkably deteriorates for the above-described reason. The nitrogen content is more preferably 0.0005 % or less from the viewpoint of a further improvement in the permeability in an alternating current. Carbon is an element which is detrimental to the magnetic properties because it exists as an interstitial element in an alloy intended in this invention and when the amount of carbon is large the permeability lowers. The upper limit of the carbon content was set to 0.020 % because the magnetic properties remarkably deteriorates for the above-described reason. The object of the present invention cannot be attained without optimization of amount of addition of nickel, molybdenum, copper, iron and boron under control of impurity elements and control of the balance of the amounts of the components in a particular range. More specific description thereon will now be given. Nickel provides high magnetic properties and high shielding properties intended in the present invention when the content is 77.5 to 79.5 %. The lower limit and upper limit of the content was limited to 77.5 to 79.5 %, respectively, because when the content is less than 77.5 % or exceeds 79.5 % the permeability lowers. Molybdenum provides high magnetic and high shielding properties intended in the present invention when the content is 3.8 to 4.6 %. When the molybdenum content is less than 3.8 % or exceeds 4.6 %, no improvement in the permeability can be attained, which makes it necessary for the content to be 3.8 to 4.6 %. Copper serves to markedly improve direct current magnetic properties, the effective permeability in an alternating current and the squareness (Br/Bm) in an alternating current (50 Hz) of an alloy falling within the scope of the present invention in the presence of boron which will be described later. The above-described effects can be attained when the nickel and molybdenum contents are 77.5 to 79.5 % and 3.8 to 4.6 %, respectively, and the optimal copper content is 1.8 to 2.5 %. The copper content was limited to 1.8 to 2.5 % because when the content is less than 1.8 % no improvement in the properties by copper can be attained while when the content exceeds 2.5 % the properties deteriorate. As with molybdenum and copper, manganese is an element which has an influence on the magnetic properties of an alloy intended in this invention. Although it is possible to attain high permeability intended in this invention even when the manganese content is 1.10 % or less, the hot workability unfavorably deteriorates when the content is less than 0.10 %. Therefore, the lower limit was set to 0.10 %. Boron is an element necessary for attaining high permeability intended in the present invention. The object of the present invention can be effectively attained when is 0.0005 to 0.0070. However, when the value is less than0.00005 % no improvement in the permeability can be attained while when the value exceeds 0.0070 % the permeability lowers. Therefore, the upper and the lower limits of were specified to 0.0005 % and 0.0070 %, respectively. In this invention, it is necessary to conduct optimization of balance of nickel, molybdenum, copper, iron and boron components under optimization of amount of addition of each of the above-described components for the purpose of improving the properties intended in this invention. Figs. 1 to 4 are diagrams respectively showing the initial permeability, the degree of shielding, the effective permeability at 1 kHz and the squareness at 50 Hz obtained in each material under test, wherein the parameter specifying the balance of said components (this parameter is represented by X and 3.3 ≦ 2.02 × [Ni] - 11.13 × [Mo] - 1.25 × [Cu] - 5.03 × [Mn] 2.13 × [Fe] ≦ 3.8 is plotted as ordinate and the amount of addition of boron as abscissa. All the materials under test shown in Figs. 1 to 4 have nickel, molybdenum, copper, manganese, boron, phosphorus, sulfur, oxygen, nitrogen and carbon contents falling within the scope of this invention and were prepared by repeating cold rolling and annealing after hot working to prepare a thin sheet sample having a thickness of 0.5 mm and punching the sheet to prepare JIS-ring samples each having an outer diameter of 45 mm and an inner diameter of 33 mm, heat-treating the samples at 1,100 °C for 3 hr in a high-purity hydrogen stream atmosphere purified by passing it through a palladium film, cooling the samples from 1,100 °C to 650 °C at a rate of 100 °C/hr and then allowing the samples to cool in a furnace. The degree of shielding was determined by applying an external magnetic field (H₀) of 500 milligauss by means of a helmholtz coil to a cylinder subjected to the same production history as that of the above materials and having a wall thickness of 0.5 mm, a diameter of 50 mm and a length of 200 mm in a direction normal to the axial direction of the cylinder and then measuring the internal magnetic field H₁ at the center of the inside of the cylinder. The figures (degree of shielding) in the drawing are each a value H₀/H₁. The measurement was conducted in a box subjected to magnetic shielding to such an extent that the influence of the earth magnetism is sufficiently negligible. The effective permeability at 1 kHz was determined by measuring the inductance permeability at 5 millioersted through the use of a ring sample having a wall thickness of 0.35 mm subjected to the same magnetic annealing as that of the above materials, and the squareness at 50 Hz was determined from the Br to Bm ratio at a magnetic field of 0.1 oersted by making use of the same sample as that used for the measurement of the effective permeability. Bm is the magnetic flux density within the material when an external magnetic field of 0.1 oersted is applied, and Br is the magnetic flux density in the case where the external magnetic field is removed from the state subjected to application of an external magnetic field of 0.1 oersted. They are hereinafter referred to simply as "Br" and "Bm", respectively. When the parameter X is 3.3 to 3.8 and the value of is 0.0005 to 0.0070 %, the initial permeability µ i is as high as at least 350,000. On the other hand, when X is less than 3.3 or exceeds 3.8 , µ i is on a level as low as less than 200,000. Further, even when X is 3.3 to 3.8, µ i is less than 200,000 and no improvement is attained if is less than 0.0005. On the other hand, when exceeds 0.0070 %, µ i lowers. As is apparent from Fig. 2, also in the degree of shielding, the materials falling within the scope of this invention exhibit a high value of 300 or more which is higher than the degree of shielding of the materials outside the scope of this invention. Fig. 3 is a diagram showing the results of measurement of the effective permeability. The materials falling within the scope of this invention exhibits a value as high as at least 6,500 which is higher than the materials outside the scope of this invention. Fig. 4 shows that in the squareness at 50 Hz as well, the materials falling within the scope of this invention exhibit a value as high as at least 0.90 which is higher than that of the materials outside the scope of this invention. From these facts, in this invention, the component balance of nickel, molybdenum, copper, manganese and boron was specified within the above-described range, and further the parameter X was specified to 3.3 to 3.8. The present inventors have repeated studies with a view to further enhancing magnetic properties by making use of the above-described alloy of this invention and, as a result, have confirmed the fact that a further improvement in the initial permeability µ i and the degree of shielding can be attained when the boron content at and near the austenite grain boundary of the alloy after heat treatment for enhancing the final magnetic properties is within a particular range. Specifically, Figs. 5 (a) to (d) are graphs respectively showing the relationship between the value of µ i , degree of shielding, effective permeability and squareness of the alloy falling within the component range of this invention (alloy 3 of this invention prepared in Example 1 which will be described later) and the boron content at and near the austenite grain boundary of the alloy. The µ i was determined by repeating cold rolling and annealing after hot working to prepare a thin sheet sample having a thickness of 0.5 mm and subjecting the sheet to punching to prepare JIS-ring samples each having an outer diameter of 45 mm, an inner diameter of 33 mm, heat-treating the samples at 1,100°C for 3 hr in a high-purity hydrogen stream atomsphere purified by passing it through a palladium film, cooling the samples from 1,100 °C to 650 °C at a constant rate of 50 to 400°C/hr, allowing the samples to cool in a furnace and then measuring the µ i value of the samples. The result are shown in the relationship with the boron content at and near the austenite grain boundary. The boron content at and near the austenite grain boundary was determined by cutting out a notched specimen mountable on a stage for the Auger observation from a sample subjected to the same hot working history as that of the thin sheet sample used for measurement of µ i , adding electrolytic hydrogen to the specimen by the cathodic electrolysis, subjecting the specimen to embrittlement to conduct fracturing of grain in vacua, conducting analysis of components on 10 points of the resultant fracture of grain by Auger electron spectroscopy and averaging the data. The unit is atm%. The degree of shielding was determined by applying an external magnetic field (H₀) of 500 milligauss by means of a helmholtz coil to a cylinder subjected to the same production history as that of the above materials and having a wall thickness of 0.5 mm, a diameter of 50 mm and length of 200 mm in a direction normal to the axial direction of the cylinder and then measuring the internal magnetic field H₁ at the center of the inside of the cylinder. The measurement of the degree of shielding (= H₀/H₁) was conducted in a box subjected to magnetic shielding to such an extent that the influence of the earth magnetism is sufficiently negligible. The effective permeability at 1 kHz was determined by measuring the inductance permeability at 5 millioersted through the use of a ring sample having a wall thickness of 0.35 mm subjected to the same magnetic annealing as that of the materials, and the squareness at 50 Hz was determined from the Br to Bm ratio at a magnetic field of 0.1 oersted by making use of the same sample as that used for the measurement of the effective permeability. In Fig. 5 (a), it is apparent that the µ i value is improved when the boron content at and near the austenite grain boundary is 10 to 50 atm%. In particular, the µ i value is 480,000 or more when the boron content is 15 to 40 atm%. Although the reason for the improvement in the µ i value has not been elucidated yet, it is believed that the presence of a suitable amount of boron at the grain boundary changes the property of the grain boundary and this change has a favorable effect on magnetic properties, particularly property value, such as initial permeability, wherein easiness of movement of magnetic domain walls or easiness of rotary magnetization are required. From these results, in the alloy falling within the scope of this invention, the boron content at and near the austenite grain boundary after magnetic annealing was specified to 10 to 50 atm% for attaining a combination of high µ i value and a high degree of shielding with a relatively high effective permeability and a relatively high squareness. The intended Ni-Fe alloy is poor in the hot workability. in order to improve the workability, addition of a minor amount of boron is often combined with addition of a minor amount of calcium. Even when calcium is added, an improvement in the initial permeability intended in this invention can be attained if the above-described characteristics features of this invention are satisfied. Further, although no detailed description is given on the silicon and aluminium inevitably contained in an iron alloy, for example, incorporation of 0.3 % or less of silicon and 0.03 % or less of aluminium besides the above-described composition is permissible in this invention. Examples : Specific Examples of the present invention will now be described. Example 1 High Ni-Fe alloy of this invention and comparative alloys having a chemical composition shown in Fig. 1 were prepared in the form of an ingot by vacuum dissolution, subjected to hot working and descaling to prepare cold rolled materials. All the materials under test had a silicon content of 0.05 to 0.15 %. These materials were then cold worked and annealed to prepare thin sheet samples having a thickness of 0.5 mm and subjected to punching to prepare as samples JIS-rings having an outer diameter of 45 mm and an inner diameter of 33 mm. Each sample was subjected to measurement of magnetic properties by heat-treating the samples in a high-purity hydrogen stream atmosphere at 1,100 °C for 3 hr, cooling the heat-treated samples from 1,100°C to 650 °C at a rate of 400 °C /hr, cooling the samples in a furnace and then measuring the magnetic properties. The results of measurement of µ i in terms of the permeability at 0.005 oersted are shown in Table 1 together with the results of measurement of the degree of shielding, effective permeability, squareness at 50 Hz, coercive force and magnetic flux density. The degree of shielding was determined by applying an external magnetic field (H₀) of 500 milligauss by means of a helmholtz coil to a cylinder subjected to the same production history as that of the above materials and having a wall thickness of 0.5 mm, a diameter of 50 mm and a length of 200 mm in a direction normal to the axial direction of the cylinder and then measuring the internal magnetic field H₁ at the center of the inside of the cylinder. The measurement of the degree of shielding (= H₀/H₁) was conducted in a box subjected to magnetic shielding to such an extent that the influence of the earth magnetism is sufficiently negligible. The effective permeability at 1 kHz was determined by measuring the inductance permeability at 5 millioersted through the use of a ring sample having a wall thickness of 0.35 mm subjected to the same magnetic annealing as that of the above materials, and the squareness at 50 Hz was determined from the Br to Bm ratio at a magnetic field of 0. 1 oersted by making use of the same sample as that used for the measurement of the effective permeability. The magnetic flux density and the coercive force were measured by making use of the same samples as those used for measurement of the initial permeability. The magnetic flux density, B₁₀₀₀, is one when an external magnetic field of 1000 A/m is applied, and the coercive force is a strength of the magnetic field necessary for making the magnetic force zero when an external magnetic field of 1000 A/m is applied and then inverted. Alloys Nos. 1 and 2 materials have carbon, phosphorus, sulfur, oxygen, nitrogen, boron, nickel, molybdenum, copper, and manganese contents all of which fall within the scope of this invention. They exhibits µ i value as high as at least 350,000 and also exhibits a degree of shielding as high as about at least 300. Further, the effective permeability, squareness at 50 Hz and coercive force as well are on a level superior to that of the control examples. Alloy Nos. 3 and 4 have carbon, phosphorus, sulfur, oxygen, nitrogen, boron, nickel, molybdenum, copper, and manganese contents falling within the scope of this invention and contain a minor amount of calcium added for improving the hot workability. In this case as well, each property value is on substantially the same level as that of the above-described alloy Nos. 1 and 2. In other words, it has been confirmed that the effect of this invention can be sufficiently exhibited in the alloy containing a minor amount of calcium added thereto. Alloy No. 5 has carbon, sulfur, oxygen and nitrogen contents reduced to a favorable level and exhibits property values higher than those of alloy Nos. 1 to 4. In these alloy Nos. 1 to 5 of this invention, the deterioration of the initial permeability during application of a face pressure of 392 kPa [4 kgf/mm²] as well is lower than that of the following control alloy Nos. 6 to 22 and 14 to 22, and it is apparent that the deterioration of characteristics against strain as well is smaller. On the other hand, alloy material Nos. 6 and 7 respectively have nickel contents exceeding the upper limit and below the lower limit, alloy material Nos. 8 and 9 respectively have molybdenum contents exceeding the upper limit and below the lower limit, and alloy material Nos. 10 and 11 respectively have copper contents exceeding the upper limit and the below the lower limit. Alloy No. 12 has a manganese contents exceeding the upper limit, alloy No. 13 has a manganese content below the lower limit, alloy Nos. 14 and 15 respectively have boron content exceeding the upper limit and below the lower limit, alloy Nos. 16 to 20 respectively have carbon, phosphorus, sulfur, oxygen and nitrogen contents exceeding the scope of composition of this invention, and alloy Nos. 21 and 22 respectively have parameter X's exceeding the upper limit and below the lower limit specified in this invention. All of these material Nos. 6 to 21 under test except for alloy No. 13 are on a lower level of property value than that of the materials of this invention. As described above, alloy No. 13 has a manganese content below the lower limit specified in this invention. This material exhibits property levels comparable to these of the material of this invention but is remarkably inferior in the hot workability during manufacture of the sample. In other words, according to this invention, excellent initial permeability, degree of shielding, effective permeability, squareness at 50 Hz and coercive force and suppression of deterioration of properties caused by strain can be attained only when nickel, molybdenum, copper, manganese, boron and iron contents are closely specified alone or in a balance thereof while decreasing impurity elements, i.e., carbon, phosphorus, sulfur, oxygen and nitrogen. In order to obtain the required properties in this invention, a high-purity hydrogen gas described in this Example may be used as a gas for the heat treatment. Similar properties can be obtained by heat treatment in an ordinary hydrogen atmosphere specified in JIS, i.e., in a hydrogen gas stream having a dew point of -40°C or below. Example 2 Alloy Nos. 1 to 4 of this invention described in said Example 1 was cold rolled and annealed to prepare a thin sheet sample having a thickness of 0.5 mm and subjected to punching to prepare as samples JIS-rings having an outer diameter of 45 mm and an inner diameter of 33 mm. Further, a notched specimen mountable on a stage for the Auger observation was cut out from the same thin sheet sample. The samples thus prepared were heat treated at 1,100°C for 3 hr, cooled from 1,100°C to 650 °C at different colling rates, cooled in a furnace and then subjected to measurement of magnetic properties and degree of shielding. The boron content at and near the austenite grain boundary was determined by adding, after the above-described heat treatment, electrolytic hydrogen to the samples by the cathodic electrolysis for embrittlement, conducting fracturing of grain in vacua and conducting analysis of components on 10 points of the resultant fracture of grain by Auger electron spectroscopy and averaging the data. The results are summarized in Table 2. In the materials wherein alloy No. 1 of this invention is used, material Nos. 1 to 4 under test of which the boron content at and near the austenite grain boundary falls within the range specified in this invention exhibit higher µ i value and degree of shielding than those of material No. 6 under test of which the boron content at and near the austenite grain boundary is outside the range specified in this invention. In the materials wherein alloy No. 2 of this invention is used, material Nos. 8 to 11 under test of which the boron content at and near the austenite grain boundary falls within the range specified in claim 3 exhibit higher µ i value and degree of shielding than those of material Nos. 7 and 12 under test of which the boron content at and near the austenite grain boundary is outside the range specified in claim 3. In the material wherein alloy No. 3 of this invention is used, material Nos. 14 to 16 under test of which the boron content at and near the austenite grain boundary falls within the range specified in claim 3 exhibit higher µ i value and degree of shielding than those of material Nos. 13 and 18 under test of which the boron content at and near the austenite grain boundary is outside the range specified in claim 3. In the materials wherein alloy No. 4 of this invention is used, material Nos. 19, 20, 22 and 23 under test of which the boron content at and near the austenite grain boundary falls within the range specified in claim 3 exhibit higher µ i value and degree of shielding than those of material No. 24 under test of which the boron content at and near the austenite grain boundary is outside the range specified in claim 3. The material Nos. 1 to 4, 8 to 11, 14 to 16, 19, 20, 22 and 23 under test of which the boron content at and near the austenite grain boundary falls within the range specified in claim 3 exhibit higher µ i value and degree of shielding than those of material No. 24 under test of which the boron content at and near the austenite grain boundary is outside the range specified in this invention. The material Nos. 1 to 4, 8 to 11, 14 to 16, 19, 20, 22 and 23 under test of which the boron content at and near the austenite grain boundary falls within the range specified in claim 3 have a combination of excellent initial permeability and degree of shielding with relatively high effective permeability and squareness at 50 Hz. The material Nos. 2, 14, 15, 18 and 19 under test have higher initial permeability and lower coercive force. Further, in these materials under test, the deterioration of the initial permeability during application of a face pressure of 392 kPa [4 kgf/mm²] is smaller than that of the control alloys of Example 1, and it is apparent that these materials are small in the deterioration of characteristics caused by strain. The material Nos. 5, 17 and 21 under test shown in Table 2 are samples in the case where the dew point of hydrogen in an atmosphere at 1,100°C for 3 hr is above -40°C. The samples heat-treated under the above-described conditions exhibit a clearly low µ i value, i.e., about 200,000, and a degree of shielding of about 100, i.e., lower than that of other samples of this invention. In other words, the effect of this invention is properly attained by conducting heat treatment with hydrogen having a dew point of -40°C or below specified in JIS. Further, the effect of this invention can be attained also by heat treatment under high degree of vacuum. e.g., at 1 × 10 ⁻⁵ Torr. Example 3 For alloy No. 4 of this invention described in the above-described Example 1 and control alloy No. 23 shown in Table 3, samples were prepared under the same conditions as those of Example 2, heat-treated under magnetic annealing conditions shown in Table 4 and subjected to measurement of the magnetic properties and degree of shielding in the same manner as that of Example 2. The results are shown in Table 4. In comparative alloy No. 23, the nickel and copper contents are outside the ranges specified in this invention and the contents of the other components are outside ranges specified in this invention. In alloy No. 4 of this invention, substantially the same level or slightly higher level of magnetic properties after magnetic annealing can be attained at 1000°C for 1 hr. That is, it is apparent that this invention enables the magnetic annealing temperature necessary for attaining the same properties as those of the control alloy to be lowered by about 100°C. According to this invention, the process for manufacturing a magnetic material is not limited to one described in the above Examples. Alternatively, the material may be melted to prepare an ingot, cast into a thin cast plate, descaled as cast or after hot working, cold rolled and annealed. It is possible to conduct warm working instead of the hot working or for the purpose of improving the efficiency of cold working. When excellent surface appearance, plate thickness and shape and dimensional accuracy are required, it is preferred to conduct cold working before preparation of a final annealing. Further, a series of procedures of cold working, annealing for recrystallization (e.g., at 800°C or above) and cold working may be repeated instead of single cold working. Substantially the same performance can be attained even when the above-described process is used as far as the alloy falls within the scope of the present invention. As described above, this invention enables the magnetic properties of the nickel-iron base magnetic alloy having high permeability to be properly improved, a high permeability magnetic alloy having magnetic characteristics, particularly permeability in a direct current and low frequency region much superior to those of the conventional PC permalloy to be provided, the alloy to be widely applied for various ceramic shielding materials, magnetic head cases where better shielding properties than those of the conventional material are required, cores and further materials for use in nonlinear applications such as magnetic amplifiers and pulse transformer, the magnetic annealing temperature necessary for attaining properties on the same level as that of the conventional material to be about 100°C lower than the conventional material, the deterioration of properties caused by strain to be small, necessary magnetic properties to be exhibited even when the alloy is formed into a structural part, such as shielding room, and the demand in electronic industry in recent years to be properly met.

Claims: A nickel-iron base high permeability magnetic alloy, comprising 77.5 to 79.5 wt.% of nickel, 3.8 to 4.6 wt.% of molybdenum, 1.8 to 2.5 wt.% of copper, 0.1 to 1.10 wt.% of manganese, 0.010 wt.% or less of phosphorus, 0.0020 wt.% or less of sulfur, 0.0030 wt.% or less of oxygen, 0.0010 wt.% or less of nitrogen, optionally a minor amount up to 0.0017 wt.% of calcium, and 0.020 wt.% or less of carbon and further boron in an amount within the range defined by the following formula: 0.0005 wt.% ≦ [B] - 10.8 14 [N] ≦ 0.0070 wt.% with the balance, apart from impurities, consisting of iron, the contents of said nickel, molybdenum, copper, manganese and iron being respectively in the range satisfying the following formula: 3.3 ≦ 2.02 × [Ni] - 11.13 × [Mo] - 1.25 × [Cu] - 5.03 × [Mn] 2.13 × [Fe] ≦ 3.8 A nickel-iron base high permeability magnetic alloy, according to claim 1, comprising 77.80 to 79.31 wt.% of nickel, 3.8 to 4.5 wt.% of molybdenum, 2.25 to 2.46 wt.% of copper, 0.51 to 0.65 wt.% of manganese, 0.006 wt.% or less of phosphorus, 0.0016 wt.% or less of sulfur, 0.0020 wt.% or less of oxygen, 0.0006 wt.% or less of nitrogen, 0.0016 to 0.0017 wt.% of calcium and 0.0065 wt.% or less of carbon and further boron in an amount within the range defined by the following formula: 0.0006 wt.% ≦ [B] - 10.8 14 [N] ≦ 0.0042 wt.% with the balance, apart from impurities, consisting of iron, the contents of said nickel, molybdenum, copper, manganese and iron being respectively in the range satisfying the following formula: 3.3 ≦ 2.02 × [Ni] - 11.13 × [Mo] - 1.25 × [Cu] - 5.03 × [Mn] 2.13 × [Fe] ≦ 3.7 A nickel-iron base high permeability magnetic alloy, according to claim 1 or 2, having a boron content of 10 to 50 atm% at and near the austenite grain boundary after magnetic annealing. A nickel-iron base high permeability magnetic alloy, according to claim 1 or 2, having a boron content of 11 to 35 atm% at and near the austenite grain boundary after magnetic annealing.

Inventors: INOUE TADASHI, KINOSHITA MASAYUKI, OHKITA TOMOYOSHI, INOUE, TADASHI, KINOSHITA, MASAYUKI, OHKITA, TOMOYOSHI
Applicants: NIPPON KOKAN KK, NKK CORPORATION
Application year: 1990
Main classification: C22C19
IPC codes: C22C19, H01F1