Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1216—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the working step(s) being of interest
  • C21D8/1222—Hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
  • C21D8/1261—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest following hot rolling
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
  • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
  • H01F1/16—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of sheets
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
  • C21D8/1255—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest with diffusion of elements, e.g. decarburising, nitriding

Definitions

• ferrous material produced for magnetic uses consists of high alloy metal, such for example as the silicon-iron of commerce, there is a substantial market for low alloy metals for use in low horsepower rotating electrical machinery and elsewhere. These low.
• alloy metals are not generally classified as electrical steels in the industry, but on the contrary correspond roughy to SAE grades 1008 and 1010.
• the basic objects of this invention include the provision of improved methods for the production of such ferrous materials, and the provision of ferrous mate rials of the low alloy class which have improved magnetic permeabilitiesand other magnetic characteristics.
• More specific objects of the invention include the provision of low alloy ferrous materials which will respond to a final anneal at low' temperatures for the development of their ultimate magnetic properties, which do not require decarburization during a customers anneal, which will have uniform and stable magnetic properties including low core loss and high permeability for materials of the class, and'which will have good punching properties.
• the initial ferrous material for conversion into the product of this invention is preferably a rimming steel which can be formed in any suitable way such as in the open hearth furnace (with-or without oxygen blowing), or by any of those processes in which the metal is blown with oxygen.
• the steel is preferably cast into ingots in bottle top molds, i.e., ingot molds having a small opening at the top, which opening is mechanically capped after teeming. The use of such molds has an effect on the amount of carbon which may be lost during the solidification of the metal.
• the metal as teemed or cast may be as follows:
• the manganese promotes good low temperature recrystallization and contributes to the volume resistivity of the product, which cuts down core loss. In general, a manganese content of over 0.3% is desirable.
• the phosphorus and silicon increase the volume resistivity of the metal and also increase hardness.
• silicon may be regarded as a residual impurity; and in the product of this invention, the silicon may lie within the last mentioned range.
• the pickled material is subjected to a low temperature decarburization in a decarburizing atmosphere.
• the decarburized product is cold rolled to final gauge or substantially to final gauge.
• the cold rolled product is subjected to a relatively low temperature anneal. This may be practiced either by the manufacturer of the ferrous material or by his customer after punching. This anneal is a non-carburizing anneal.
• the material may be temper rolled, i.e. rolled with a small elongation, say,
• the generalized series of steps outlined above may be practiced wholly by the steel manufacturer or in part by the steel manufacturer and in part by the customer. In the former of these instances, the steel manufacturer will perform all six of the steps noted, and the stock so produced will be referred to as finished stock.
• the customer will receive coils or sheets, of the stock after the step 5 anneal has been practiced thereon; and the stock will generally be temper rolled as above defined, not only to produce flatness but also to harden the stock slightly to put it into better condition. for punching.
• the stock may be sold to the customer as semi-finished stock after the completion of the cold rolling which is step 4.
• the steel manufacturer will usually take precautions to insure flatness in the coils or sheets. This may be done in various known ways, one of such ways being the giving of at least a final light cold rolling pass to the steel under conditions of tension.
• the initial material is relatively high in carbon for a reason which will be set forth later.
• the hot rolling may be carried on otherwise in any suitable way and on any suitable apparatus; but continuous hot rolling is preferably practiced, the ferrous ma terial being reduced to the desired intermediate gauge from ingots either Without reheating, or with a reheating of slabs formed from the ingots during the course of the reduction.
• the intermediate gauge to which the ferrous material is hot rolled can be considerably varied in the light of the final sheet gauge desired, taking into account the available hot rolling apparatus.
• the ferrous material has been hot rolled to a gauge of about .080 leaving a reduction of about 70 to 80% to be performed in the subsequent cold rolling.
• a cold rolling with about a 40% or 50% reduction is desirable for grain size, so that in general the gauge of'the hot I rolled stock may be as light as can be obtained with the available apparatus in a satisfactory hot rolling operation.
• a hot roll gauge as light as .050 can be achieved, a cold rolling reduction of will produce a sheet stock having a thickness of .025", which is suitable for many uses.
• the intermediate and final gauges of the material may be varied as desired so long as an adequate cold rolling reduction, as hereinafter set forth, is practiced.
• the hot rolled material is then pickled in the ordinary way for the purpose of removing the hot mill scale from its surfaces.
• the hot rolled intermediate gauge ferrous material After the hot rolled intermediate gauge ferrous material is pickled, it will be subjected to a low temperature decarburization. This is best accomplished by loose coiling the material and heating it in a muffle furnace. It is necessary for proper decarburization that the furnace atmosphere have ready access to all of the surfaces of the stock.
• a strand-like separator between the convolutions of the coil. In some procedures the strand is removed before annealing, while in other procedures a strand which will withstand the temperatures of the anneal, and is so configured as to permit the passage of the furnace gases between the convolutions is left in place in the coil.
• the atmosphere is (for economic reasons) preferably one. containing from 20 to 40% hydrogen and having a dew point of about 120 F.
• Hy-- drogen to which water vapor has been added may be used as such, or HNX ordissociated ammonia or mixtures of the two may be used.
• the controlling factor here is the ratio of 'H :H O. It should be such that rapid decarburization will occur without oxidation of the iron.
• the atmosphere should not contain appreciable amounts of strongly carburizing gases.
• the decarburizing time increases with the thickness of perature in the described atmosphere will be suflicient for a thirty ton charge.
• Some muffies are provided with means for producing a positive circulation of the atmosphere within the furnace so as to enforce a flow of the atmosphere between the .convolutions of the coil, and this increases the efficiency of the decarbu'ri'zing treatment, as indicated in the above example.
• furnace atmosphere between the convolutions will increase in carbon content, so that for rapidity of operation this build-up must be diluted as by the continuous addition of fresh gas, or by scrubbing out someof the carbon.
• a low temperature decarburization is meant a decarburization within a temperature range of about 1250 F. to 1600 F. It is known that efficient decar burization will also occur at a higher temperature range, say 1750 F. and above; butthe material beingtreated is diflicult to handle properly at suchhightemperatures.
• decarburization is so carried on as to reduce the carbon content of the metal to at most about 0.005%, and prefe'rably to 0.003% or lower.
• the initial carbon content also has an effect upon the decarburization time; but by way of example a treatment of material having a thick.- ness of .080" and a carbon content greater than about .05 but less than .l% for about twelve hours at temnaked eye.
• The'material will further'be bright, since it was pickled prior to the decarburization and since the furnace atmosphere is oxidizing toward carbon but substantially non-oxidizing toward iron.
• a cold rolling of the material is practiced.
• the cold rolling which can be carried on in any cold rolling mill or tandem train, preferably produces about 40% to 50% reduction in the thickness of the material; and a reduction of this order appears to be desirable for grain size.
• the cold rolled product which is the result of step 4 in the routing given above may be supplied to the customer for stamping or punching in the fullhard condition providing it has satisfactory flatness.
• it may be given a brief, relatively low temperature anneal followed by a temper rolling (as above defined) to obtain a desired hardness for punching.
• the annealing treatment which follows the cold rolling reduction in the routing given above, and constitutes step 5 thereof, should produce arecrystalli'zation of the material and therefore should be above about 1100 F.
• the normal temperature range will be between about 1100 and about 1400 F. Somewhathigh'er temperatures may be used. 'Too high a temperature should be avoided, since excessive temperatureslower the permeability, possibly because they'tend to impair the orientation hereinafter described- As a general rule, the temperature should not be allowed to rise above 1650 F.,
• a normalizing treatment i.e., a heating of the material to above its A point followed by a rapid cooling, should be avoided, if it is desired to take advantage of the high permeabilities resulting from the, favorable orientation.
• the anneal may advantageously be carried on with the material in coiled form in a muffle or box, when performed by the steel manufacturer. With care it can be carried on in a continuous furnace; but a time at temperature which is characteristic of the operation of box or mufile furnaces is advantageous to the production of the optimum magnetic properties.
• the steel producer anneals the cold rolled stock, it may prove advantageous to follow the anneal with the temper rolling hereinabove mentioned to increase the stiffness of the stock for better punching characteristics.
• step 5 anneal is performed by the customer. It will be understood that the customer may anneal the stock either before or after punching laminations from it. The annealing of punched laminations may be carried on in conventional furnaces of the continuous or batch type.
• the step 5 anneal can be carried on in conventional annealing atmospheres or in any atmosphere which is non-carburizing to the low carbon material and does not produce excessive oxidation of the steel, all as will be well understood by the worker in the art. Nitrogen, nitrogen-hydrogen mixtures, dissociated ammonia and the like can be used, as well as pure hydrogen, if desired.
• the annealing atmosphere will have a dew point low enough to preclude undesired oxidation. It is an advantage of the invention that the step 5 anneal need not be a decarburizing anneal.
• a controlled oxidation such as a steam bluing
• Such a controlled oxidation provides an insulative film on the surface of the punchings which reduces eddy current losses when the punchings are fabricated into electrical devices.
• X-ray analysis shows that the material of this invention following the cold rolling and annealing is characterized by a detectable degree of crystal orientation.
• This crystal orientation partakes in. part of the nature of cube-on-edge orientation, (110) [001] by Millers Indices.
• the degree of orientation produced is sometimes called two times random which means that if a pole figure is made in which dots in certain areas indicate crystal orientation, the density in the darkest areas produced by the clumping of the dots will be about twice the average density of the pole figure.
• This degree of orientation is not sufficient to-impart marked directional characteristics to the product; but the product of this invention has uniformly a higher permeability than products of the same chemistry otherwise produced, and in particular higher permeabilities than similar products having completely random orientation.
• the product of this invention has a uniformly low core loss.
• the core loss values for the material of this invention when measured on Epstein samples in.which half of the pieces are cut parallel to and half are cut transverse to the direction of rolling, having a thickness of .025" and having been annealed at 1300 to 1350 F. in a neutral atmosphere, will be about 1.3 to 2.0 watts per pound at 10 kga, and about 4.80 to 5.10 watts per pound at 15 kga.
• the permeability of the material will generally lie between values of 1580 to 1610 at 10 oersteds.
• the high permeability of the product at high inductions results in lower exciting currents and consequently lower copper costs in electrical machinery in which it is used.
• the steel of this invention may, if desired, be sub- .jected to a critical straining treatment for the purpose of attaining enlarged grains in the final product.
• a critical straining procedure involves subjecting the steel to a cold rolling reduction of about 10% to about 20% followed by a heat treatment at a temperature generally from about 1250 to about 1500 F. in a non-carburizing atmosphere. The critical straining treatment must follow both the cold rolling to gauge and the recrystallizing anneal.
• step 5 anneal in the routing given above. It can be performed either by the steel manufacturer or by his customer.
• the critical straining treatment can be employed as a substitute for the temper rolling which has been given as step 6 of the normal routing.
• the critical straining treatment produces a substantial grain growth in the finished product. This diminishes the degree of preferred orientation, and hence slightly lowers the permeability of the product. At the same time, the core loss characteristics are improved by the enlarged grain size, this being an advantage in some applications ofisetting a small lowering of permeability values.
• the product in either event is believed to be unique.
• a process of making a ferrous magnetic material which comprises forming a steel containing about 0.05% to 0.1% carbon, about 0.15% to 1% manganese, up to about 0.15 phosphorus, and up to about 0.1% silicon, the balance being substantially all iron with normal residual impurities, and
• the cold rolled steel is subjected to a low temperature anneal substantially in the range of 1100 to 5.
• the process claimed in claim 1 wherein the steel is decarburized in a loose coil treatment at a temperature of substantially 1250 to 1600 F., and in which the hot rolled material is coiled at a temperature not' above about 1000 F.
• step 1 the steel is cast into small top ingot molds which are then mechanically capped References Cite'alhythe Examiner UNITED'STATES PATENTS 2,512,358 6/50 Mcoear "148 122 2,672, 29 3/5 l -s 14 1 2,943,007 6/60 Wallceret al. .14s 120 DAVID L. Re'cK, Primar -Ex miner.

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Cited By (13)

Citations (3)

• 0
  • BE BE638295D patent/BE638295A/xx unknown
• 1962
  • 1962-10-08 US US229203A patent/US3180767A/en not_active Expired - Lifetime
• 1963
  • 1963-10-07 SE SE10964/63A patent/SE309255B/xx unknown
  • 1963-10-08 DE DE1433707A patent/DE1433707C3/de not_active Expired

Patent Citations (3)

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