Classifications

• • 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
  • H01F1/147—Alloys characterised by their composition
  • H01F1/14766—Fe-Si based alloys
  • H01F1/14775—Fe-Si based alloys in the form of sheets
  • H01F1/14783—Fe-Si based alloys in the form of sheets with insulating coating
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/68—Temporary coatings or embedding materials applied before or during heat treatment
  • C21D1/70—Temporary coatings or embedding materials applied before or during heat treatment while heating or quenching
• • 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
  • C21D8/1277—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties involving a particular surface treatment
  • C21D8/1288—Application of a tension-inducing coating
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23D—ENAMELLING OF, OR APPLYING A VITREOUS LAYER TO, METALS
  • C23D5/00—Coating with enamels or vitreous layers

Definitions

• ABSTRACT A process is described for producing silicon steel containing nominally 3.25 percent silicon, by a continuous annealing process.
• the magnetic characteristics exhibited by the fully processed steel approach those of commercially available silicon steel but without the necessity of extensively desulfurizing the steel from that sulfur content which is usually obtained employing a commercial process.
• the process consists of selecting a cold worked, decarburized semiprocessed silicon steel which is thereafter subjected to a continuous strand annealing at a temperature in the range between about 1,000C and about 1,l 00C in order to substantially completely recrystallize the steel by a secondary recrystallization process and the application of a tensile stress of at least 200 psi to the underlying steel for producing improved watt losses over that material having substantially the same-sulfur content but which was manufactured by regular commercial processes.
• the present invention relates to a method of producing cube-on-edge oriented silicon steels which are characterized by exhibiting magnetic characteristics similar to those steels in commercial production today but without the use of an expensive desulfurization process which the commercially produced steels in use today are subjected to during normal commercial manufacture.
• the present commercial practice for producing cube-on-edge orientation in nominally 325 percent silicon steel usually comprises a long time high temperature box anneal which develops both the orientation or texture of the material and removes sulfur to'a value below about 50 ppm for, optimum magnetic quality.
• This long time high temperature box anneal usually requires a programmed cycle for heating the'material in slow stages to a temperature of about 1,200C, maintaining the steel at this temperature for periods of time usually of about 24 hours or more and thereafter a programmed cooling of the matefial in order to obtain the desired magnetic characteristics in the final product.
• the material must be maintained at such temperature for about 20 minutes.
• the additional annealing time and the high temperature involved are quite disadvantageous both from a technical as well as economic point of view.
• the present invention alleviates some of the shortcomings of the prior art through the use of the higher sulfur containing silicon steel-material and imparting a residual tensile stress to the material. This results in the final material exhibiting magnetic characteristics comparable to those of material which is presently commercially produced through a high temperature desulfurization box anneal as part of the final heat treatment process.
• the present invention employs a steel containing nominally about 3.25 percent silicon as the starting composition.
• This steel is melted, hot rolled, cold worked in one or more operationsto the desired finished gauge and then subjected to a decarburizing anneal. Thereafter, the steel; is subjected to a continuous anneal in which a' strand 'of the material is passed through a furnace and the strand is heated to a temperature within the range. between 1,000C and about l, C fora time period sufficient to substantially completely secondarily recrystallize the structure to obtain the desired orientation.
• the secondarily recrystallized steel is then subjected to the application of a tensile stresswhich produces a stress in the steel within the range betweenabout 200 psi and about 800 psi.
• a tensile stress which produces a stress in the steel within the range betweenabout 200 psi and about 800 psi.
• the process of the present invention contemplates the use of a steel containing nominally about 3.25 percent silicon. It will be understood however that the process is applicable to steels containing anywhere between about 2 percent and about 6 percent silicon so long as the steel is capable of having developed therein an orientation which is characterized by a cube-onedge orientation or (1 10) [001] in Miller Indices.
• the steel having the requisite chemical composition is melted, preferably cast into ingots, hot worked and then cold worked in one or more operations with one or more intermediate anneals interposed therebetween until the steel has been cold reduced to finished gauge thickness.
• These operations are all well known in the art for producing, for example type M-5 grain oriented silicon steel.
• the steel of final gauge is thereafter subjected to a decarburizing heat treatment for example by a wet hydrogen anneal, in order to remove the carbon content to a sufficiently low value to prevent both magnetic as wellas mechanical aging during use.
• a decarburizing heat treatment for example by a wet hydrogen anneal
• semiprocessed grain oriented silicon steel having a potential cube-on-edge orientation.
• the semiprocessed silicon steel is usually obtained in large coils ready for additional processing.
• the prior used practices include the application of a separator insulation coating which is applied to the surfaces of the steel strip which are thereafter recoiled and the coil is thereafter set on edge in a box annealing furnace.
• a programmed heat treatment is applied to the silicon steel'coil in thepresence of a dry hydrogen atmosphere and upon heating to a temperature of l,200C the steel is substantially completely secondarily recrystallized and by holding at saidelevated temperature for a time period of about 24 hours, the residual sulfur content is'reduced so thatthe optimum magnetic characteristics may be developed in the steel.
• the present invention subjects the semiprocessed silicon steel to a continuous strand annealing by uncoiling the material and passing a single strand of the semiprocessed steel througha continuous annealing furnace.
• a plurality of noncontacting paralled strands can be processed simultaneously. While not necessary to do so the steel is hung usually in an essentially horizontal catenary form suspended from each-endof a horizontally disposed furnace and continuously moves through the furnaceat a predetermined rate.
• the steel strand issubjected to a heat treatment wherein the steel is rapidly heated to a temperature of from l,00O to about l,lOC and maintained at such temperature fora period of usually betweenabout 5 'minutes and about minutes.
• each segment of steel strand upon entering the furnace is heated to a minimum temperature of 1,000C and up to a maximum of about 1,100C and preferably at a temperature of about l,050C. While continuously moving through the furnace at this elevated temperature, the speed of the material is regulated so that each segment of the steel is maintained at this temperature for a time period of bet-ween about 5 minutes and ab out 10 minutes.
• the sulfur content usually runs anywhere between about 200 and 250 parts per million but may be as low as 150 ppm but seldom lower than about 75 ppm.
• the steel will have a sulfur content within the range between 150 ppm and about 250 ppm, which sulfur content will not be appreciably altered during the term of the secondary recrystallization heat treatment as described hereinbefore.
• the material undergoing the continuous 4 strand annealing is subjected to a protective atmosphere, particularly good results being obtained using hydrogen having a dew point of less than about -40C. It is preferred to maintain this protective atmosphere in order to'not unduly scale the material which would adversely affect the magneticcharacteristics ultimately exhibited by the material in its finished form.
• the steel is next subjected to a process by means of which a residual tensilestress between about 200 psi and about 800 psi is applied to the steel.
• a residual tensilestress between about 200 psi and about 800 psi is applied to the steel. This is most advantageously accomplished by means of applying to the surface of the steel a slurry of a glass which has a coefficient of thermal expansion substantially less than that exhibited by the underlying steel and usually of the order of-less than about 8.5 X 10 in./in. per degree Centigrade.
• the steel upon cooling to room temperature will be placed in tension usually within the range between about 200 psi and about 800 psi.
• the glass slurry coating is preferably fused to the surface of the steel by heating the steel to a temperature within the range between about 750C and 800C, the same occurring either by means of a box anneal with the glass slurry in place thereon or by means of another continuous strand heat treatment in which an individual strand of the material is passed through the furnace and the material is heated to this temperature in order to fuse the glass .of the'slurry onto'the surface of the steel.
• the coated steel is cooled to room temperature, the difference in coefficient of thermal expansion between the glass and the steel coordinatedwith their relative thicknesses is sufficient for placing the steel in tension to effect a stress of at least 200 psi and preferably between about 400 psi and about 800 psi.
• a non-reducing atmosphere can be employed and a slightly oxidizing atmosphere is preferred.
• the glass is limited to a thickness in the range between about 0.25 mil and about 1.0 mil in total thickness, the greater thickness being used with thicker sheet steel, for example 1 mil glass on a 13 mil thick sheet, and the 0.25 mil glass coating on a 3 to 6 mil thick sheet. Such thickness is sufficient to exerting the proper degree of tensile stress without unduly reducing the stacking factor.
• the underlying steel will be substantially completely secondarily recrystallized with the requisite grain growth and at the same time, the slurry which has been applied to the surface of this steel will be fused and upon cooling the same to room temperature, the differences in the relative coefficients of thermal expansion between the glass and the metal will result in placing the underlying steel in tension sufficient to exert a tensile stress between about 200 psi and about 800 psi.
• Epstein strips of 12 mil thickness semiprocessed silicon steel containing about.3.25. percent silicon and in the cold rolled and decarburized condition were continuously annealed to obtain substantially complete secondary recrystallization and grain growth but-without any appreciable sulfur removal.
• The. final sulfur content in each instance was above 200 ppm.
• Table 1 lists the magnetic properties of this sample together with the .catalog properties for acommercial type M-5 silicon steel which is presently marketed and employed in themanufacture of power transformers.
• the process of the present invention is effective for producing commercial quality oriented cube-on-edge type silicon steel without the necessity of substantially completely desulfurizing the material.
• Such processing is effective for continuously secondarily recrystallizing the microstructure and by the application of a tensile stress thereto the steel will exhibit magnetic characteristics similar to those of commercially processed type M material.
• other magnetic characteristics are also improved, noteworthy among which is the magnetostriction exhibited by the steel. Magnetostriction is materially reduced. There characteristics are of prime importance to users of the material especially where the material is used as a core in a power transformer.
• the steps com prising continuously annealing as a single thickness the decarburized steel at a temperature within the range between about 1,000C and 1,100C for atime period sufficient to develop the cube-on-edge texture and to effect substantially complete secondary recrystallization and grain growth, the final sulfur content of the steel being in excess of 75 ppm and fusing a coating on the surface of the steel of a silicate glass having a coefficient of thermal expansion of the order of less than' about 8.5 X in./in. per degree centigrade which will effecta tensile stress in the steel of at least 200 psi while not adversely affecting the other properties of the treated steel.
• the steps comprising, continuously annealing the decarburized steel as a strand at a temperature within the range between 1,000C and 1,100C in a dry, reducing atmosphere for a time period sufficient to develop the cubeon-edge orientation and to effect substantially complete crystallization and grain growth without an appreciable change in the sulfur content applying to the surface of the recrystallized steel a slurry of a silicate glass having a coefficient of thermal expansion of the order of less than about 8.5 X 10 in./in.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Crystallography & Structural Chemistry (AREA)
• Thermal Sciences (AREA)
• Electromagnetism (AREA)
• Manufacturing & Machinery (AREA)
• Dispersion Chemistry (AREA)
• Power Engineering (AREA)
• Manufacturing Of Steel Electrode Plates (AREA)
• Soft Magnetic Materials (AREA)
• Chemical Treatment Of Metals (AREA)
• Heat Treatment Of Sheet Steel (AREA)

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Cited By (6)

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Citations (11)

• 1971
  • 1971-12-09 US US00206511A patent/US3833431A/en not_active Expired - Lifetime
• 1972
  • 1972-11-01 CA CA155,320A patent/CA963366A/en not_active Expired
  • 1972-12-07 JP JP47122088A patent/JPS5120373B2/ja not_active Expired

Patent Citations (11)

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