EP1051714B2 - Soft magnetic nickel-iron alloy with low coercive field strength, high permeability and improved resistance to corrosion - Google Patents

Abstract

The invention relates to a soft magnetic nickel-iron alloy containing 35-65 mass % nickel, one or several of the rare earths cerium, lanthanum, praseodymium or neodymium and the impurities introduced during smelting, the sum of the rare earths being between 0.003 and 0.05 mass %.

Description

The invention relates to a soft magnetic nickel-iron alloy.

From the book " Magnetic Materials and Their Technical Application "by Carl Heck, Hütig Verlag, Heidelberg 1975, p. 349ff It is known that soft magnetic materials are used for the material of armature and yoke in relays.

The main requirements of the material are a high saturation flux density to achieve large magnetic holding forces at low energy, high permeability, so that a small magnetic field strength, i. a small excitation current and a high flux density in the air gap can be generated and so acts a large attraction to the anchor. Low coercive field strengths allow easy opening of the relay when the excitation current decreases.

In addition to the magnetic requirements of a relay material still the requirement of corrosion resistance in a Wechselklimatest, since a correct function of the relay is required in all weather conditions This requirement can be achieved in insufficiently corrosion-resistant materials only by additional coating of the finished parts with a corrosion-resistant layer.

The contact surfaces of the armature and yoke must have the smallest possible gap in order to achieve a high permeability of the magnetic circuit yoke and armature. They must not be damaged by switching the relay, because then the tripping current of the relay changes.

Similar requirements also exist for other shaped and stamped parts made of soft magnetic materials.

The magnetic requirements for a relay material are described in DIN 17405 "Soft Magnetic Materials for DC Relays". The following Table 1 shows an excerpt from DIN 17405. Table 1: Relay materials according to DIN 17405 material coercivity minute magnetic induction in T Characteristic alloy components short name Material number Max. Hc in A / m at a field strength H in A / m Mass fraction in% 20 50 100 300 500 4000 RNi24 1.3911 24 0.20 0.45 0.70 0.90 1.00 1.18 36 Ni RNi 12 1.3926 12 0.50 0.90 1.10 1.25 1.35 1.45 50 Ni RNi 8 1.3927 8th 0.50 0.90 1.10 1.25 1.35 1.45 50 Ni RNi 5 2.4596 5 0.50 0.65 0.70 0.75 70 to 80 Ni, small amounts of Cu, Cr, Mo RNi 2 2.4595 2.5 0.50 0.65 0.70 0.75

DIN 17745 "Nickel and Iron Putties describes the alloy NI 48 (material numbers 1.3926 and 1.3927) as starting materials for the grades RNI 12 and RNI 8 (see Table 2) The alloy Ni 36 (material number 1.3911) is the starting material for the grades RNi 24. Table 2: Excerpt from DIN 17745 short name Material number Composition in mass% Leglerungsbestandtelle Permitted admixtures Ni 48 1.3928
1.3927 Ni min. 48, Fe 49 to 53 C 0.05, Mn 0.5, Si 0.3 Ni 36 1.3911 about 36

In the melting of nickel-iron alloys, in addition to the desired alloying elements, deoxidizing and / or desulfurizing elements such as manganese, silicon and aluminum are necessary. In addition, certain minimum admixtures of oxygen, sulfur, phosphorus, carbon, calcium, magnesia, chromium, molybdenum, copper and cobalt can not be avoided if one wants to make these alloys because of the low cost with conventional steelwork technology. Conventional steelworks technology is understood to mean melting in an open-hearth furnace with subsequent ladle metallurgy and / or VOD treatment for deoxidation, desulfurization and degassing. Thereafter, the block or the continuous casting slab is thermoformed in one or two steps to a thickness of about 4 mm and then cold-worked to final thickness if necessary with intermediate annealing. The magnetic properties deteriorate, as z. In DE 19612556 A1 by admixtures of carbon, nitrogen, oxygen, sulfur and non-metallic inclusions. Non-metallic impurities arise due to the required deoxidation and / or desulfurization treatment of the melt prior to casting. Depending on the deoxidation and / or desulphurisation, for example, oxides of calcium, magnesium or aluminum.

To avoid this difficulty, therefore soft magnetic materials are produced with the highest requirements of the prior art so far with selected clean materials using the vacuum technology, as shown in the DE-A 3910147 and in the DE-C 1259367 expressly stated. Another possibility known from the literature is the In DE-A 4105507 described very complex and expensive Elektroschlackenumschmelzverfahren under vacuum or inert gas of previously melted under vacuum or inert gas blocks.

The JP-A 07166281 relates to a magnetic alloy for magnetic heads consisting of Ni and Fe with additions of Nd, Pr or Sm. Here, the amount of Ni is over 78% by weight.

The object underlying the invention is to provide a method for melting a soft magnetic iron-nickel alloy, which satisfies the described requirements for the magnetic properties, the corrosion and the wear resistance.

This object is achieved by the features of the first claim.

Advantageous developments of the subject invention can be found in the associated dependent claims.

The alloy is preferably produced by steelworking technology, ie, open-arc melting followed by ladle metallurgy and / or vacuum-oxidation-decarburization (VOD) treatment for deoxidation, desulfurization, and degassing. After that, the. Block or the continuous cast slab in one or two steps thermoformed to a thickness of about 4 mm and then cold worked to final thickness, if necessary, with intermediate annealing to adjust the hardness required for the production of parts of this band.
Subsequent to the production of parts from this alloy and the annealing of these parts at temperatures between 800 and 1150 ° C, coercive forces of less than 8 A / m can be achieved with these parts.

Preferred applications of the alloy according to the invention are i.a. Relay parts, such as yokes and anchors.

• Ventildeckel und Ventiltöpfe von Magnetventilen
• Joche bzw. Polstücke bzw. Polschuhe bzw. Polbleche und Anker von Halteund Elektromagneten
• Spulenkerne und Statoren von Schrittschaltmotoren sowie Rotoren und Statoren von Elektromotoren
• Form- und Stanzteile von Sensoren, Positionsgebem und -aufnehmem
• Magnetköpfe und Magnetkopfabschirmungen
• Abschirmungen, wie z. B. Motorabschirmungen, Abschirmbecher für Anzeigeinstrumente und Abschirmungen für Kathodenstrahlröhren.

In addition, the iron-nickel alloy according to the invention is still useful for the following further applications:

• Valve covers and valve heads of solenoid valves
• Yokes or pole pieces or pole shoes or pole sheets and anchors of holding and electromagnets
• Coil cores and stators of stepper motors and rotors and stators of electric motors
• Shaped and stamped parts of sensors, position sensors and receivers
• Magnetic heads and magnetic head shields
• Shields, such. As motor shields, shielding cup for gauges and shields for cathode ray tubes.

From a 1.2mm thick strip made by steelmaking technology, flat samples were punched, cleaned, annealed at 1080 ° C / 4 hours under hydrogen, and then cooled in the oven to 300 ° C. The climate test described in DIN 50017 was carried out on these samples with 28 cycles of 8 hours at 55 ° C./90 to 96% atmospheric humidity and 16 hours at 25 ° C. and 95 to 99% atmospheric humidity. Alloys with nickel contents of 36% to 81% by weight and partially additives such as chromium, copper and / or molybdenum were investigated (see Table 3). The alloys with a nickel content of less than or equal to 55% by mass show, after the end of this alternating climate test, all significantly greater corrosion phenomena on the surface than the alloys with nickel contents of more than 75%. Gehrmann, H. Hattendorf, A. Kolb-Telieps, W. Kramer, W. Möttgen, in Material and Corrosion 48, 535-541 (1997). ) and thus do not meet the above-described requirements for a relay material to the corrosion resistance without additional corrosion-improving measures. On the other hand, the magnetic properties required by DIN 17405 were satisfied, as demonstrated by the coercive forces Hc given by way of example in Table 3 (prior art). Table 3 Composition in mass% Hc in A / m Max. HC according to DIN 17405 alloy Fe Ni Not a word Cr Cu Mn Si Fe-36Ni 62,90 36,50 0.01 0.03 0.03 0.27 0.18 4.2 24 Fe-40Ni 58.35 40.75 0.02 0.05 0.04 0.50 0.18 4.7 Fe-41 Ni 58.50 40.65 0.01 <0.01 0.04 0.47 0.21 3.2 Fe-45Ni 54.25 44.70 0.02 0.02 0.02 0.58 0.28 2.5 Fe-47Ni-6Cr 45.85 47.30 <0.01 6.04 0.01 0.21 0.26 3.8 Fe-48Ni 51,70 47,50 0.04 0.03 0.02 0.41 0.20 2.4 8th Fe-50Ni 48.85 50,70 0.01 0.04 0.03 0.21 0.05 3.5 8th Fe-55Ni 43.70 55.45 0.06 0.06 0.05 0.42 0.14 12.5 Fe-76Ni Cr Cu 16.05 75.95 0.10 2.00 4.96 0.60 0.22 0.87 2.5 Fe77Ni-Ti, Nb 14,80 77.30 0.01 0.10 4.50 0.49 0.24 2.4 2.5 Fe-77Ni-Mo, Cu 13.85 77.15 3.45 0.10 4.47 0.53 0.33 0.85 2.5 Fe-80Ni-Mo 13.95 80,10 4.75 0.05 0.09 0.50 0.33 0.44 2.5 Fe-Mo 8lNi 12.45 81.50 5.27 0.03 0.05 0.43 0.13 1.23 2.5

In the corroded areas of these samples sulfur was found after the end of the climatological test by means of REM / EDX.

The improvement of the corrosion behavior according to the invention is surprisingly achieved by desulfurization of the more corrosion-susceptible nickel-iron alloys having a nickel content of from 35% by weight to 65% by weight with cerium. This is preferably carried out with a mischmetal of the rare earths cerium and / or lanthanum and / or praseodymium and / or neodymium which are very similar in chemical behavior. To bind off all sulfur safely enough rare earth atoms must be present. If the formation of e.g. This is the case when more cerium atoms than sulfur atoms are present in the alloy.

Thereafter, the cerium content in mass% must be at least a factor of 4.4 greater than the sulfur content in mass% in order to achieve complete binding of the sulfur by cerium. The same applies to the other rare earths lanthanum, praseodymium and / or neodymium and to the sum of rare earths.

As previously mentioned, the addition of such a strong deoxidizing and desulphurising agent as, for example, cerium by the reaction products remaining in the material can impair the magnetic properties ( A. Hoffmann, On the Influence of Various Deoxidizing Elements on Deformation and Initial Permeability of Ni-Fe Alloys, Z. Applied Physics 32, pages 236 to 241 ). Surprisingly, the addition of rare earths can be metered so that the magnetic values of permeability and coercive field strength within the usual range of variations of the prior art melted batches.

It is known that deoxidation residues break out of the contact surfaces of the relay, remain between these areas and by their z. B. with oxidic residues greater hardness during further switching of the relay can destroy the finely ground contact surfaces. Therefore, the relay materials may only have a very low content of non-metallic inclusions according to DIN 50602 (method M). For this reason, the maximum size values of the sulfidic inclusions in line form SS smaller than 0.1 or 1.1, and the maximum size values of oxidized inclusions in dissolved form OA (aluminum oxides) must also be used for deoxidation with cerium or a mischmetal from the rare earths cerium, lanthanum, praseodymium, neodymium. kleiner2.2 bzw. 3.2 bzw. 4.2, the maximum size values of the oxide inclusions in line form OS (silicates) smaller 5.2 and / or 6.2 and / or 7.2 and the maximum size values of the oxide inclusions in globular form OG smaller 8.2 and 9.2, respectively.

As an example, steelmaking technology in the 30-t arc furnace melted a nickel-iron alloy containing about 48% nickel and minor additions of manganese and silicon (batches E5407 and E0545) and lots of a very similar composition but without the addition of rare earths ; which correspond to the state of the art (batches T4392, T5405 and T5406). The exact compositions are shown in Table 4. Table 4: Composition of the prior art (T) and the batches (E) of the invention. All figures are in mass%. element State of the art Compositions of the invention limits charge T2536 T5477 T5488 T4392 T4505 T5406 E5407 E0545 Ni 47.45 47.5 47.85 47.7 47.45 47.9 47.65 47.65 Mn 12:40 0.40 0.36 12:38 12:40 12:38 12:39 0.41 Max. 0.5 Si 12:19 0.19 0.22 0.20 0.14 12:15 0.14 12:22 Max. 0.3 al 0.005 0.005 0,007 0.009 0,007 0008 0.005 0.005 Max. 0,010 mg 0.001 0.0003 0.0008 0.0001 0.0001 0.0002 0.0006 0.0008 Max. 0,002 Ca 0.0004 0.0004 0.0003 0.0001 0.0002 0.0002 0.0003 Max. 0,002 cerium - - - - - - 0,014 0.011 La - - - - - - 0,008 0.005 pr - - - - - - 0.001 0001 Nd - - - - - - 0003 0,003 Sum of rare earths - - - - - - 0026 0,020 Max. 0,050 S 0.0020 0.0012 0.0007 0.0012 0.0008 0, OCLO 0.0010 0.0022 Max. 0, 0040 4.4 * S 0.0044 0.0088 O 0.0020 0.0010 0.0015 0.0020 0.0020 0.0020 0.0025 Max. 0.0040 N 0.0010 0.0010 0 0001 0.0010 0.0010 C 0.011 0009 0,004 0,013 0,012 0009 0,007 0.016 Max. 0.05 P 0,002 0,002 0,002 0002 0,002 0,002 0002 0,003 Cr 0.03 0.03 0.03 12:04 0.04 12:04 0.05 0.02 Not a word 0.05 0.09 0.13 0.10 0.14 0.05 12:04 0.08 Cu 12:06 0.06 0.04 12:10 0.05 0.05 0.05. 0.15 Co 0.04 12:02 0.01 12:04 0.02 0.02 12:02 12:03 B - - - 0001 0001 0.001 0001 -

Minor amounts of boron can be added to improve die-cuttability, as was the case for lots T4392, T5405, T5406 and E5407. The amount of cerium content in mass% in the charge E5407 and E0545 according to the invention is greater than the factor 4.4 by mass greater than the sulfur content.

After melting, a block and then a hot strip rolling at about 4 mm and a subsequent cold forming to final thickness 1.0 mm.

From this, round samples with a diameter of 25.5 mm were punched. This applies to all batches except E0545. Here, a piece of about 15 mm x 15 mm x 5 mm was used from a casting sample whose surfaces were honed. All samples were cleaned and a portion of the samples were subjected to an annealing treatment of 970 ° C / 6 hours under hydrogen and then cooled in the oven to below 300 ° C. The second part of the samples was annealed at 1030 ° C / 2 hours under hydrogen and then cooled in the oven to below 300 ° C. All samples have been subjected to the shortened climatic test of 2 days with a temperature / humidity change at the rate of 3 hours from 25 ° C and 55% humidity to 55 ° C and 98% humidity. The samples were individually flat in glass dishes, so that prevailed on the bottom of the more severe conditions of crevice corrosion. The result is shown in Table 5. Table 5: Air test results charge After shortened climatic test: samples with corrosion rates / total number of samples tested Remarks 970 ° C / 6 hours 1030 ° C / 2 hours T5405 10/10 10/10 Both sides, several unique points per sample T5406 10/10 10/10 Both sides, several unique points per sample E5407 0/10 0/10 E0545 0/1

No corrosion was found in batch E5407 and E0545 according to the invention, whereas corrosion spots were found on both sides for the two comparative lots T5405 and T5406 on each side.

The addition of such a strong deoxidizing and desulfurizing agent as cerium, as previously described, can affect the magnetic properties due to the reaction products remaining in the material. Surprisingly, the magnetic permeability and coercivity values exhibited by the invented batches E5407 and E0545 are within the usual range of conventional melted batches, as shown in Table 6. Table 6: Magnetic values of prior art (T) and inventive batches (E) measured on samples of 1 mm thickness after 1080 ° C / 4h annealing under hydrogen and oven cooling to 450 ° C. The composition of the batches is shown in Table 4. material coercivity minute magnetic induction in T Static values short name Material number Hc in A / m at a field strength H in A / m μ4 μmax 20 50 100 300 500 4000 RNi 24 1.3911 <24 0.20 0.45 0.70 0.90 1.00 1.18 RNi 12 1.3926 <12 0.50 0.90 1.10 1.25 1.35 1.45 RNi 8 1.3927 <8 0.50 0.90 1.10 1.25 1.35 1.45 charge E5407 4.2 1.02 1.12 1.18 1.31 1.50 1.56 10200 97800 E0545 2.6 11690 133770 T2536 1.9 8000 179600 T4392 3.8 1.07 1.16 1.22 1.36 1.44 1.54 5000 154700 T5405 2.5 1.06 1.14 1.20 1.32 1.41 1.57 9200 142100 T5406 2.1 1.06 1.14 1.20 1.33 1.42 1.53 10000 158900 T5477 2.76 1.08 1.17 1.21 1.34 1.42 1.53 8200 135100 T5488 5.21 1.09 1.20 1.35 1.40 1.46 1.54 2600 99850

Second, two batches of the prior art composition shown in Table 7 were considered in their block and hot strip rolling properties.

The two batches differ essentially only by the different content of rare earths. Table 7 element limits charge T0626 T0624 Ni 36.2 36,45 Mn 0.25 0.26 max.0,5 Si 0.20 0.19 Max. 0.3 al 0.009 0.009 max.0,010 mg 0.0030 0,003 max.0,002 Ca Max. 0,002 cerium 0,029 0001 La 0,017 pr 0,002 Nd 0,006 Total rare earths 0.054 0,002 Max. 0,050 S 0,002 0,002 Max. 0.0040 O 0.0050 0.0020 Max. 0.0040 N 0.0025 0.0020 C 0,004 0.009 Max. 0.05 P 0,002 0,002 Cr 0.04 0.01 Not a word 0.06 0.06 Cu 0.05 0.09 Co 0.05 0.03 B - -

In batch T0626, with a rare earths residual content of 0.054%, cracks formed in the hot forming and the billet was scrap. Such a high content of rare earth leads to a poorer thermoforming behavior. On the other hand, batch T0624 could be rolled both on block and on hot strip with a thickness of about 4 mm. Since the rare earths behave chemically similar, according to the invention, the content of the sum of the rare earth cerium, lanthanum, praseodymium, neodymium to limit a maximum of 0.05% by mass to avoid hot forming problems.

Table 8 shows the investigation of the content of non-metallic inclusions according to DIN 50602 on different batches according to the prior art (T) and the charges (E) according to the invention. Table 8 material Purity grade according to DIN 50602: Maximum size value (method M) charge SS OA OS OG limits 0.1 or 1.1 2.2 or 3.2 or 4.2 5.2 or 6.2 or 7.2 8.2 or 9.2 E5407 k. B. 2.1 k. B. 8.0 E0545 k. B. 2.2 k. B. 8.1 T4392 k. B. 2.2 k. B. 8.0 T5405 k. B. 2.0 k. B. 8.0 T5406 k. B. 2.2 k. B. 8.0 T5477 k. B. 2.1 k. B. 8.1 T5488 k. B. 2.0 k. B. 8.0 T2536 k. B 2.7 k. B kB

The batch T2536 has a maximum size value of 2.7 for the oxide inclusions in line form (method M). This value is too high for the use of this batch as a material for relay parts. It causes wear on the contact surfaces of the relay and results in the loss of functionality of the relay. The content of non-metallic inclusions is therefore limited according to the invention as follows:

The maximum size values according to DIN 50602 of the sulfide inclusions in line form SS are less than or equal to 0.1 and 1.1, the maximum size values according to DIN 50602 of the oxide inclusions in dissolved form OA (aluminum oxides) less than or equal to 2.2, 3.2 and 4.2 respectively, the maximum size values according to DIN 50602 of oxide inclusions in line form OS (silicates) less than or equal to 5.2 or 6.2 or 7.2 and the maximum size values according to DIN 50602 of oxide inclusions In globular form OG less than or equal to 8.2 or 9.2. All other batches listed in Table 8 meet the requirements for non-metallic inclusions.

Claims (3)

1. A method of melting a soft magnetic iron-nickel alloy comprising a nickel content of 35 to 65 % by mass and one or more of the rare earths cerium, lanthanum, praseodymium, neodymium as well as melting dependent impurities by melting the alloy in the open arc furnace with subsequent ladle metallurgy and/or vacuum oxygen decarburizing treatment for deoxidation, desulphurization and degassing, wherein the sum of the rare earths is comprised between 0.003 and 0.05% by mass, the alloy contains as deoxidation and/or desulphurization additions maximum 0.5% by mass manganese, maximum 0.5% by mass silicium and admixtures of maximum 0.002% by mass magnesium, maximum 0.002% by mass calcium, maximum 0.010% by mass aluminium, maximum 0.004% by mass sulphur, maximum 0.004% by mass oxygen and small quantities of other admixtures depending on the melting, and the total portion of the rare earths cerium, lanthanum, praseodymium, neodymium in % by mass is greater by at least the factor 4.4 than the sulphur content in % by mass.
2. A method according to claim 1, characterized in that the following parameters are set in the molten alloy:

   - the maximum dimensional values of the sulphured inclusions in form of lines are beneath 0.1 or 1.1

   - the maximum dimensional values of the oxidic inclusions in dissolved form OA (aluminium oxides) are beneath 2.2 or 3.2 or 4.2

   - the maximum dimensional values of the oxidic inclusions in form of lines OS (silicates) are beneath 5.2 or 6.2 or 7.2

   - the maximum dimensional values of the oxidic inclusions in globular form OG are beneath 8.2 or 9.2.
3. A method according to claim 1 or 2, characterized in that after the production of parts made of this alloy and the annealing of these parts at temperatures comprised between 800°C and 1150°C coercive field strengths of less than 8 A/m are obtained.