US3615367A - Low-loss magnetic core of ferritic structure containing chromium - Google Patents

Abstract

Corrosion-resistant magnetic core of low hysteresis loss and low eddy-current loss and alloy containing about 9% to 20% chromium, about 0.01% to 3% silicon and/or aluminum, manganese up to about 4%, carbon up to about 0.15%, about 0.15% to 1% sulfur and/or selenium, about 0.02% to 1% titanium and/or zirconium, and remainder substantially iron.

Description

United States Patent .Patented Assignee Inventor Harry Tanczyn Baltimore, Md.

July 31, 1968 Oct. 26, 197 l Armco Steel Corporation Middletown, Ohio Appl. No. Filed LOW-LOSS MAGNETIC CORE OF FERRITIC STRUCTURE CONTAINING CHROMIUM [56] References Cited UNITED STATES PATENTS 3,177,577 4/1965 Fujimura 75/126 D 1,835,960 12/1931 Palmer 75/126 L 1,941,202 12/1933 De Fries 75/126L 3,362,813 1/1968 Ziolkowski 75/124 3,401,035 9/1968 Moskowitz 75/124 Primary Examiner-l-Iyland Bizot Alt0rney-John Howard Joynt ABSTRACT: Corrosion-resistant magnetic core of low hysteresis loss and low eddy-current loss and alloy containing about 9% to 20% chromium, about 0.01% to 3% silicon and/or aluminum, manganese up to about 4%, carbon up to about 0.15%, about 0.15% to 1% sulfur and/or selenium, about 0.02% to 1% titanium and/or zirconium, and remainder substantially iron.

LOW-LOSS MAGNETIC CORE OF FERRITIC STRUCTURE CONTAINING CHROMIUM As a matter of introduction, my invention is concerned with a magnetic core for electrical apparatus, and alloy steels.

One of the objects of the invention is the provision of a mag netic core possessing a combination of good magnetic properties along with good corrosion resistance.

Another object is the provision of a magnetic core and corrosion-resisting steel of high magnetic permeability, low reluctance, low hysteresis loss and low eddy-current loss, all at minimum cost, that is, comparatively low cost in the ingot, in processing in the mill, and in use.

A further object of my invention is the provision of a corrosion-resisting alloy steel which is suited to the production of bars, rod, wire and like mill products possessing a good combination of magnetic properties and machinability, that is, which readily lends itself to cutting, threading, tapping, turning, milling and the like, as in the production of a variety of magnetic parts or components for electrical machinery, apparatus and equipment.

A still further object is the provision of an alloy steel and various flat-rolled products, such as sheet, strip, and the like, suited to various machining, forming and shaping, as in the production of the cores for electrical machinery and apparatus.

Other objects of my invention in part will become apparent and in part particularly pointed to in the following description.

My invention resides in a magnetic core and steel, more particularly in the combination of ingredients, making up the same, and in the relation between the ingredients, all as more particularly described herein, the scope of the application of which is set out in the claims at the end of this specification.

BACKGROUND OF THE INVENTION In order to gain a better understanding of certain features of my invention, it may be well to note at this point that the straight chromium grades of stainless steel have long been accepted in the art, many being identified by American Iron and Steel Institute type numbers. For example, 1 refer to the more popular AlSl Type 403 (11.5 to 13% chromium, carbon 0.15% max., manganese 1.00% max., silicon 0.50% max., phosphorus 0.040% max., sulfur 0.030% max., and remainder iron); Type 405 (like Type 403 except 11.5 to 14.5% chromium, carbon 0.08% max., silicon 1.00% max. and 0.10 to 0.30% aluminum); Type 414 (like Type 403 except 11.5 to 13.5% chromium, silicon 1.00% max., and 1.25 to 2.50% nickel); and Type 416 (like Type 403 except 12 to 14% chromium, manganese 1.25% max., phosphorus 0.060% max., sulfur atleast 0.15%, and silicon 1.00% max.

The steels noted, this with the exception of the Type 405 are suited to a variety of machined articles, parts and components. The steel of Type 405, as distinguished from the others, is nonhardenable. it is particularly suited for welded assemblies which are free of the air-hardening noted in the steels of Types 403 and 410.

Others of the commonly known and used straight chromium grades which are not generally hardenable are the Type 430 (14 to 18% chromium, carbon 0.12% max., manganese 1.00% max., phosphorus 0.040% max., sulfur 0.030% max., silicon 1.00% max. and remainder iron); Type 430F (generally like Type 430 but with sulfur at least 0.15%); Type 430FSe (similar to Type 430 but with at least 0.15% selenium instead of the 0.15% sulfur); and Type 442 (generally similar to Type 430 except 18 to 23% chromium and carbon 0.20% max). These various steels are suited to a variety of applications where a nonhardenable corrosion-resisting steel is required; the steels containing a high sulfur and/or selenium content are employed for a variety of machined articles and components.

While the straight chromium grades of stainless steel, as noted above, are suited to a wide variety of applications, none seems peculiarly adapted to the use in electrical machinery, i.e., magnetic cores for solenoid, relay and the like. Nor, indeed, for wider applications where a controlled magnetic field of high permeance, low reluctance, and a minimum loss is desired. And while the steel of Type 4301- is readily machinable and, as such, is suited to many applications, 1 findthat in straightening bar, rod, and wire stock, high stresses are developed which adversely affect the magnetic characteristics of the metal, as well as the mechanical properties.

It is an object of my invention, therefore, to provide asteel which enjoys a combination of corrosion resistance, good mechanical properties and good magnetic properties,narnely, high permeance, low hysteresis loss, and low eddy-current loss, all at minimum cost. 1

SUMMARY OF THE lNVENTlON hysteresis Referring now more particularly to the practice of my invention, 1 provide a magnetic core and an alloy steel essentially consisting of about 9 to about 20% chromium (particularly about 12 to about 18% chromium), about 0.01 to about 3% silicon and/or aluminum (especially about 0.50 to about 2% silicon), about 0.15 to about 1% sulfur and/or selenium (especially about 0.15to about 0.50 sulfur), about 0.02 to about 1% titanium and/or zirconium (particularly about 0.1 to about 0.6% titanium), and remainder substantially all iron. Carbon, of course, is present in my steel, this in amounts up to about 0.15%, more particularly about 0.01% or even 0.001%, to just under 0.06%, say to about 0.05%; for best results about 0.01% to about 0.04%. Manganese, too, is present in my steel, this in amounts up to about 4%, more particularly about0.0l to about 1%. The remainder of the steel, of course, is substantially all iron. The metal is not hardenable by heat-treatment; it is wholly ferritic with an absence of austenite. And, of course, there is an absence of a martensitic constituent.

1 find that with with controlled carbon content and the essential presence of sulfur and titanium in the amounts indicated, the steel not only is possessed of good mechanical properties with minimum adverse elTect resulting from straightening, bending, or the like, but that it is possessed of good magnetic properties. More particularly, the steel is of high magnetic permeance and of low loss, i.e., low hysteresis loss and low eddy-current loss. I attribute the superior magnetic characteristics to a virtual freedom of the steel from intermetallic compounds involving the iron present. In the prior corrosion-resisting steels, I feel that certain compounds of iron, chromium, and carbon, and even iron, chromium and nitrogen, are present which adversely affect the magnetic properties in that while readily magnetized, they are not readily demagnetized. And, in a way, serving as permanent magnets as they do, substantial loss is encountered with rapid reversal of the magnetic field as in alternating current electrical machinery, apparatus and equipment.

in the steel of my invention, I am inclined to the view that the carbon present in the metal appears in the form of titanium carbides, and the nitrogen as titanium nitrides, or perhaps other compounds involving titanium, carbon, nitrogen, and one or more of the alloying ingredients present, this excluding the iron, however. These compounds introduce no magnetic effects, this because of the absence of iron in the compound.

Moreover, in my steel I feel that the eddy-current loss is effectively minimized as a result of the increase in the electrical resistance of the metal by reason of the chromium content, and, to some extent, the silicon and aluminum contents. in consequence, the eddy-currents which develop in the use of the metal as magnetic core for alternating current electrical applications are minimized by reason of the increased electrical resistance of the metal. Thus, there is enjoyed more efficient operation with less heating in use.

in the steel of my invention, I feel that the desired magnetic permeability with low hysteresis loss :may be had with the use of one or more of columbium, vanadium and molybdenum instead of the titanium and/or zirconium addition. in general, however, I prefer the titanium addition for reasons of economy and for the further reason that it combines with both the carbon and nitrogen contents of the steel, effectively eliminating the adverse effects of both.

In my steel the particular composition is considered to be in every sense critical. Although a rather wide latitude of chromium content is contemplated, that is, from about 9 to about 20 percent, a steel with less than about 9 percent chromium is not acceptable because of a sharp loss in corrosion resistance and, conversely, a steel having a chromium content exceeding about 20 percent is not desired because of a sacrifice in magnetic permeability. While the electrical resistivity of the metal increases with the chromium addition, the permeability decreases. For best results a chromium content of about 12 to about 18 percent is desired.

The ingredients silicon or aluminum generally are employed in my steel in small amounts, this not exceeding about 3 percent for the two together. These ingredients assure clean metal essentially free of contaminating oxide inclusions. A best steel employs silicon, this in the amount of about 0.05 to about 2 percent, preferably about 1 to about 2 percent for maximum cleanliness and an ease of fumacing, pouring and teeming. An excessive silicon content, however, indeed an excessive aluminum content, is not desired for it works adversely to the high magnetic permeability which is sought. The same may be said with respect to the manganese content of the steel, since I view silicon, aluminum and manganese as additiveswhich are beneficial to the melting of the steel, that is, in assuring an ease of fumacing and teeming with assured cleanliness, but not beneficial to the desired magnetic properties.

The carbon content, the sulfur content, and the titanium content of my steel, too, are viewed as critical, for with a carbon content exceeding about 0.15 percent, the workability as by straightening, bending, and the like, is inclined to suffer even though the machinability is improved. A best combination of results is had where the carbon content amounts to about 0.01 to about 0.04 percent, this assuring good bending properties, and a balance between an increase in the electrical resistivity resulting from the carbon addition and a decrease in the magnetic permeability. For some applications the carbon may range from about 0.01 percent to just short of 0.06 percent. For application where the metal is to be machined, the carbon content very well may approach the 0.15 percent figure. On the other hand, where the metal is employed in the form of sheet, strip, or the like, and a deep-drawing operation is contemplated, the carbon content should be near the minimum figure, that is, about 0.02 percent or even about 0.01 percent.

Sulfur and/or seleniumin the amount of at least about 0.05 percent is found necessary to achieve good machinability in my steel, while more than 0.50 percent seems unnecessary. A sulfur and/or selenium content exceeding about 1 percent is not acceptable, for I find with such a high content the workability in the hot-mill immediately suffers, with objectionable tearing and splitting of the metal.

The importance of the titanium and/or zirconium addition, along with the sulfur and/or selenium and the chromium contents of the steel, is particularly pointed to above. The amount of titanium and zirconium must be at least about 0.02 percent in order to enjoy any beneficial effect, but an amount exceeding about 1 percent not only produces no beneficial effect, but represents an unnecessary cost. Moreover, the -excessive titanium and/or zirconium in a measure detracts from the desired magnetic qualities of the metal. For best results it is titanium that is employed, and this in the amount of about 0.1 to about 0.5 percent.

1 conveniently melt my steel in the electric arc furnace. Where desired, of course, it may be melted in the vacuum furnace. Or a combination of arc-furnace melting and vacuumfumace refining may be employed to advantage. But however melted, the steel handles well in the furnace, it teems well, and the molds strip from the ingots with ease.

The ingots in turn work well in the hot-mill at temperatures commonly employed. And so, too, the resulting blooms, billets, and the like, as in the production of plate, sheet, strip, bars, rods, wire, and special shapes. Additionally, the metal works well in the cold-mill as in the production of cold-rolled DESCRIPTION-OF THE PREFERRED EMBODIMENTS While, as noted above, in broad aspect the magnetic core and alloy steel of my invention essentially consists of about 9 to about 20% chromium, about 0.01 to about 3% silicon and/or aluminum, manganese up to about 4%, carbon up to about 0.15% (especially about 0.01% to just under 0.06%), with about 0.15 to 1% sulfur and/or selenium (preferably about 0.15 to about 0.50% sulfur), about 0.02% to about 1% remainder substantially all iron. Such a core and steel enjoys 1 an excellent combination or magnetic permeability with low hysteresis loss, good electrical resistance and consequent low eddy-current losses, ready machinability, formability, and corrosion-resistance.

A further core and steel essentially consists of about 14 to about 16% chromium, about 0.5 to about 2% silicon, about 0.01 to less than 0.06% carbon (particularly about 0.01 to about 0.04% carbon), about 0.20 to about 0.40% sulfur about 0.1% to about 0.6% titanium, and remainder substantially all iron. in this core and steel there is had a somewhat higher electrical resistance with consequently reduced eddy-current losses in use of the metal as a magnetic core component in electricalmachinery, apparatus, and the like. The mechanical properties are good, and so, too, the magnetic permeability. And, too, the corrosion resistance is somewhat improved, suiting it to some applications in which the somewhat higher corrosion resistance is deemed desirable.

A still further preferred core and steel enjoying a best combination of corrosion resistance, electrical resistance with minimum eddy-current loss, along with good magnetic permeability, machinability, and mechanical properties, essentially consists of about 16 to about 19% chromium, about 0.5 to about 1% silicon, about 0.01 to about 0.05% carbon (particularly about 0.02 to about 0.04%), about 0.20 to about 0.40% sulfur, about 0.1 to about 0.5% titanium, and remainder substantially all iron. Here, the lower maximum carbon content permits the lower maximum titanium content, with consequent savings and, yet, with a good combination of magnetic permeability, low eddy-current losses, and good corrosion resistance in magnetic core applications.

Another preferred core and steel essentially consists of about 12 to about 18% chromium (more particularly about 14 to about 16% chromium), about 0.50 to about 3% silicon (especially about 1 to about 3% silicon), carbon less than 0.06% and preferably not exceeding 0.04%, about 0.15 to about 0.50% selenium, about 0.1 to about 0.6% titanium, and remainder substantially all iron.

In specific illustration of the steels of my invention, 1 give TABLE I.-CHEMICAL COMPOSITION AND MAXIMUM PERMEABILIIY OF GHROMIUM-SILICON-SULPHUR- TITANIUM MAGNETIC CORE STEELS A review of the data presented above rather clearly indicates that the maximum permeability of the magnetic core steels of my invention progressively increases with an increase in the chromium content and with an increase in the titanium content. Note, for example, that for the three steels R5633-2, R5634-2 and R5635-2, having a titanium content of about 0.2%, the permeability for the steel of about 13% chromium amounts to 352, that for the 15% chromium steel comes to 546, and that for the 17% chromium steel amounts to 915. In these steel the silicon content is about 0.30% and the carbon, manganese, phosphorus, sulfur and nickel contents differ but little from one steel to the other.

For the three steels R5633-1, R5633-2 and R5633-3, with respective titanium contents of 0.01%, 0.21% and 0.37%, the maximum permeability is seen to be 237, 352 and 404, the permeability thus directly increasing with the increase in titanium content.

To like extent, the permeability increases with respect to the silicon content, for it will be seen that the steel of about 13% chromium content, 0.2% titanium content, with about 0.25% silicon, namely R5633-2, has a permeability of 352, while the steel R5636-2, with like chromium and titanium contents but with a silicon content of 0.60%, has a permeability of473. As the titanium content approaches 0.5%, however, and the chromium content is on the order of 17 little change in permeability results from an increase in the silicon content, at this chromium level the permeability actually decreasing with an increase in silicon. Compare, for example, the 17% chromium, 0.46% titanium steel R5635-3, having a silicon content of 0.30% and a permeability of 1076, with the steel R5638-2 of about 17% chromium, 0.47% titanium and 0.71% silicon, having a permeability ofonly 908.

It is in the electrical resistivity, rather than the permeability, that greatest change is had with silicon content as seen from the data present in table 11 below. In that table there are given the electrical resistivities and the permeabilities in the annealed condition of two groups of steels (and in the hot-forged condition for one group), one group of steel containing about 16% chromium and 0.2% titanium with the further ingredient selenium in the amount of about 0.15%, all of differing silicon contents, and the other containing about 14% chromium with a sulfur content of about 0.3% and titanium content of about 0.15%, also of differing silicon contents. The electrical resistivity is expressed in microohms per circular mill.

For the one group of magnetic core steels given in table II, this for a chromium content of about 16 about 2% titanium and about 0.15% selenium, it will be immediately seen that the electrical resistivity, as well as the permeability, increases with an increase in silicon content. Notably, with the increasing silicon contents of 0.48%, 0.92%, 1.89% and 2.97% for the respective steels R6050, R6051, R6052 and R6053, the electrical resistivities amount to 58.3, 72.5, 88.0 and 99.3 microohms per circular mill. And for the group of steels of about 14% chromium, 0.15% titanium, with sulfur rather than selenium, this in the amount of about 0.3%, the electrical resistivities amount to 67.5, 94.2 and 103.1 microohms per circular mill for the three respective steels R6100, R6101 and R6102, having silicon contents of 1.15%, 2.32% and 3.18%. The permeability of the steels of both groups increases with the increase in silicon content, going from 2194 in the annealed condition for the 16% chromium steel of 0.48% silicon content for the steel R6050 up to 3015 for the steel R6053, with silicon content of 2.97%. The steels of the lower chromium content of 14% are possessed of significantly lower permeability but, here again, there is an increase in permeability with an increase in silicon content, the permeability increasing from steel R6100 having a silicon content of 1.15% and permeability of 1217, up to 2628 for steel R6102 with silicon content of3.l8%.

In conclusion, it will be seen that I provide in my inventiona magnetic core and alloy steel in which the various objects hereinbefore set forth are successfully achieved. The core and steel are characterized by desired magnetic permeability, particularly in the annealed condition, together with desired electrical resistivity. The steel, moreover, is corrosion-resisting and well lends itself to a variety of machining operations, such as cutting, threading, tapping, turning, and the like, as in the production of magnetic cores for solenoid, relay and other electrical machinery, apparatus and equipment.

Inasmuch as many embodiments may be made of the core and steel of my invention, and since many variations in the embodiments herein disclosed may occur to those skilled in the art to which the invention relates, it will be understood that all matter described herein is to be considered illustrative and not by way of limitation.

I claim:

1. Magnetic core of ferritic structure and desired resistivity and permeability for solenoid, relay or other electrical machinery, apparatus and equipment, said core essentially consisting of about 9 to about 20% chromium, about 0.01 to about 3% silicon up to about about 0.15% carbon, about 0.15 to about 0.50% ingredient of the group sulfur and selenium, about 0.02 to about 1% titanium, and remainder substantially all iron.

2. Magnetic core of ferritic structure and desired resistivity and permeability for solenoid, relay or other electrical machinery apparatus and equipment, said core essentially consisting of about 12 to about 18% chromium, about 0.5 to about 2% silicon, up to about 4% manganese, carbon less than 0.06%, about 0.15 to about 0.50% sulfur about 0.1 to about 0.6% titanium, and remainder substantially all iron.

3. Magnetic core of ferritic structure and desired resistivity and permeability for solenoid, relay or other electrical TABLE II.CHEMICAL COMPOSITION, PERMEABILITY AND ELECTRICAL RESIS'IIVITY OF TWO GROUPS OF CIIROMIUM-SILICON-TITANIUM MAGNETIC CORE STEELS Maximum permeability Electrical re- Hot- 1450 F. sistance. micro- Heat No. 0 M11 P S Si Cr N 1 Ti Se forged anneal ohm/cm.

machinery, apparatus and equipment, said core essentially consisting of about 12 to about 18% chromium, about 0.5 to about 2% silicon, about 0.01 to about 0.04% carbon, about 0.15 to about 0.50% sulfur about 0.1 to about 0.6% titanium, and remainder substantially all iron.

4. Alloy steel core offerritic structure and desired resistivity and permeability for solenoid relay or other electrical machinery, apparatus and equipment, said core essentially consisting of about 12 to about 18% chromium, about 0.50 to about 3% silicon, carbon less than 0.06%, about 0.15 to about 0.50%

Claims (4)

1. 2. Magnetic core of ferritic structure and desired resistivity and permeability for solenoid, relay or other electrical machinery apparatus and equipment, said core essentially consisting of about 12 to about 18% chromium, about 0.5 to about 2% silicon, up to about 4% manganese, carbon less than 0.06%, about 0.15 to about 0.50% sulfur about 0.1 to about 0.6% titanium, and remainder substantially all iron.
2. 3. Magnetic core of ferritic structure and desired resistivity and permeability for solenoid, relay or other electrical machinery, apparatus and equipment, said core essentially consisting of about 12 to about 18% chromium, about 0.5 to about 2% silicon, about 0.01 to about 0.04% carbon, about 0.15 to about 0.50% sulfur about 0.1 to about 0.6% titanium, and remainder substantially all iron.
3. 4. Alloy steel core of ferritic structure and desired resistivity and permeability for solenoid relay or other electrical machinery, apparatus and equipment, said core essentially consisting of about 12 to about 18% chromium, about 0.50 to about 3% silicon, carbon less than 0.06%, about 0.15 to about 0.50% selenium, about 0.1 to about 0.6% titanium, and remainder substantially all iron.
4. 5. Alloy steel core of ferritic structure and desired resistivity and permeability for solenoid, relay or other electrical machinery, apparatus and equipment, said core essentially consisting of about14 to about 16% chromium, about 1 to about 3% silicon, carbon not exceeding 0.04%, about 0.15 to about 0.50% selenium, about 0.1 to about 0.6% titanium, and remainder substantially all iron.