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
• • 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
  • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
  • C21D3/02—Extraction of non-metals
  • C21D3/04—Decarburising
• • 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
  • C21D8/1233—Cold 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

Definitions

• This invention relates to polycrystalline magnetically so rolled sheet metal composed principally of an alloy of iron and silicon having a high percentage of the grains comprising the material oriented such that theircrystal space lattices are arranged in a substantially identical rela-' tionship to the plane of the sheet and to a single direction in the plane of the sheet, and more particularly, to a particular composition of such materials which is particularly amenable to treatment by an improved process for formingsheet material having this desired orientation.
• the sheet materials to which our invention is directed are usually referred to in the art as electrical silicon steels or, more properly, silicon irons and are conventionally composed principally of iron alloyed with about 1.5 to 4 percent and preferably about 2.5 to 3.5 percent silicon and relatively minor amounts of various impurities such as sulfur, manganese, phosphorus and having very low carbon content as finished material.
• Such alloys crystallize in the body-centered cubic crystallographic system at room temperature. As is well known this refers to the symmetrical distribution or arrangement which the atoms forniing the individualcrystals or grains assume in such materials. In these materials the smallest prism posessing the. full symmetry of the crystal is termed the unit'eell and is cubic in form.
• This unit cube is composed of nine atoms each arranged at the corners of the unit cube with the remaining atom positioned at the geometric center of the cube.
• Each unit cell in a given grain or crystal in these materials is substantially identical in shape and orientation with every other unit cell comprising the grain.
• the unit cells or body-centered unit cubes comprising these materials each have a high degree of magnetic anistropy with respect to the crystallographic planes and directions of the unit cube, and hence, each grain or crystal comprising a plurality of such unit cell-s exhibits a similar. anisotropy. More particularly, crystals of the silicon iron alloys to. which this invention is directed are known to have their direction of easiest magnetization parallel to the unit cube edges, their next easiest direction of.
• these materials are prepared by casting ingots from alloys containing from about 2.5 to 4.0% and preferably from 2.5 to 3.5 percent by weight silicon, less than 0.035 percent carbon, about 0.02 to 0.03 percent sulfur, and less than 0.15 percent man: ganese. These ingots are conventionally hot worked into a strip or sheet-like configuration, usually less than 0.150 inch in thickness referred to as hot rolled band. This material is usually in an incompletely recrystallized form and may be annealed to effect complete recrystalli zation if deemed desirable but it is usually not necessary.
• the hot rolled band is then cold rolled with appropriate annealing treatment to the finished sheet or stripthiokness usually involving at least a 50 percent reduction in thickness and given a final or texture producing annealing treatment.
• this final anneal is accomplished in two steps.
• a short time normalizing anneal is accomplished at about 800 C. for about five minutes in a wet hydrogen or wet cracked gas? atmosphere.
• This anneal serves at least two purposes. It decarburizes the material or stated otherwise, reduces the carbon content of the material to a value of lessthan 0.030 percent by weight, and additionally causes the worked metal structure to recrystallize into a fine grain microstructure. This is usually referred to as a primary recrystallization.
• the sheet or strip material After annealing, the sheet or strip material must then be flattened to remove warping which usually occurs during the final anneal. This is usually accomplished by heating the strip or sheet and applying tension thereto.
• Strip and sheet grain oriented silicon-iron alloys have been used for a number of years as transformer core materials, electric motor and generator laminations and in other electrical and electronic applications where the high electromagnetic properties in the rolling direction of the sheet or strip may be advantageously employed. For most applications the highest degree of grain orientation obtainable is desirable. Usually materials having more than about 70- percent of their crystal structure oriented in the (110) [001] texture are considered to have a strong texture.
• our invention utilizes a relatively small amount of titanium, probably present as a dispersion of titanium carbide, effectively to control the secondary recrystallization of the silicon-iron alloys without sulfur being present.
• our titanium containing alloys may be cast, hot reduced to band and the hot-rolled band then cold reduced to sheet or strip of the final thickness with appropriate intermediate heat treatment.
• This cold worked material is then subjected to a heat treatment of a short time duration during which time a strong (110) [001] texture is developed, preferably by means of a continuous anneal.
• the strip or sheet material is then heat treated at a slightly higher temperature for a short time duration, again preferably in a continuous annealing apparatus whereby the carbon is substantially removed and the finished material is permitted to cool.
• this final annealing treatment may be accomplished with thersheet orstrip material under sufficient tension to pre-- vent warping, a subsequent flattening operation may be avoided, and since the strip or sheet is not in contact with other sheets or stripsduring the annealing, no refractory coating is necessary.
• alloys 1-4 were prepared by melting appropriate amounts of. substantially pure commercial electrolytic iron containing less than 0.01 per.- cent manganese, silicon as low aluminum 98 percent ferrosilicon substantially pure.- sponge titanium, and carbon as an iron-carbon alloy made. from electrolytic iron and graphite in an electric induction furnace in an air atmosphere.
• Alloys. 5-7 were prepared from the same basic materials but melted and castin a vacuum furnace. The air melted heats were cast into ingots measuring about. 1.” x 5 /2" x 13" and the vacuum. melted heats cast into ingots measuring about 1" x 3" x 6".
• the compositions listed in. Table I. are the results of chemical. analyses of: the alloys as cast. It should be noted that no sulfur or manganese were added to these alloys. The trace of sulfur found in. each alloy is probably due to impurities inthe raw materials. or from the refractory of the furnace crucibles.
• this anneal since the function of' this anneal is to cause recrystallization of the worked metal and not primarily to reduce the excess carbon content, or carbon which is notcombined with titanium as TiC, protective atmospheres other than hydrogen or a vacuum anneal may equally well be used. Specimens of this cold rolled strip or sheet material were then. subjected to a first annealing treatment comprising heating for between 15 to 20 minutes at about 1000 C. in dry hydrogen. After this heat treatment, it was found that these materials had. recrystallized so that about 80% of their grains had the desired [001] texture as determined by conventional torque tests, and that substantially no change had occurred in their chemical compositions.
• the carbon in these alloys is probably present as a fine disper- Since the cold worked alloys can be caused to recrystallize at temperatures between about 750 C. and l000 (3., and since the titanium carbide phase does' not substantially go into solution in the silicon-iron matrix at temperatures below about 1050 C., primary recrystallization of the cold worked material is accomplished at its temperature is raised during the initial stage of the first part of the annealing treatment. As the first part of the final anneal progresses secondary recrystallization phenomenon takes place wherein the titanium carbide particles probably inhibit the growth of grains of orientations other. than (110) [001].
• this recrystallization process is a time-temperature dependent reaction, i.e., that while recrystallization may be accomplished at temperatures below 1000 C., the rate is slower at lower temperatures. Furthermore, if the heat treatment is accomplished at temperatures above the solution temperature f 'the'titanium carbide phase, strong textures will not develop. j ,After the secondary recrystallization is substantially completed, the temperature may then be raised tojor above 1050" 0., probably causing the titanium carbide phase to go into solution in the matrix whereupon the carbon atoms may freely migrate to the surface and readily dissipate in the final decarburizing step.
• a continuous, annealing treatment may be readily substituted for the time con suming batch annealing treatment necessary with con ventional analogous material.
• compositions, melting practices, rolling schedales, and heat treatments have been particularly set forth, it will be readily apparent to those skilled in the art that variations therefrom may be employed without departing from the scope of our invention.
• other low sulfur content irons may be employed in place of electrolytic iron or the molten alloy may be sub jected to a desulfurizing treatment whereby for example, the sulfur may be removed in a slagging operation.
• the hot rolling may be accomplished with periodic reheating if deemed desirable and the final thickness of the hot rolled band may vary substantially from that disclosed. For example, it is conventional to terminate the hot working at thicknesses as great as 100 mils or greater under some circumstances.
• the cold reduction of the hot rolled material may be accomplished in one or more than the two rolling sequences specifically disclosed, however, the material at the final cold worked stage should have been exposed to at least 40% cold reduction prior to the final annealing treatments.
• the final annealing treatment may be accomplished in two separate furnaces, it will be apparent that a single furnace having two temperature zones may be employed in a continuous anneal. In this case, the cold Worked metal enters the lower temperature zone of the furnace, is recrystallized therein and progresses into the higher temperature zone where decarburization is accomplished.
• a method for producing a polycrystalline sheetlike body having a majority of the constituent grains oriented in the (110) [001] direction comprising preparing an alloy melt consisting essentially of from about 2.5 to 4.0 weight percent silicon, less than about 0.010 weight percent sulfur, and not more than about 0.035 weight percent carbon, adding up to 0.10 weight percent titanium to said alloy melt forming from 0.01 to 0.10 weight percent titanium carbide dispersion therein, casting said titanium carbide-containing alloy and hot reducing said casting to form an elongated sheet-like body less than 150 mils in thickness, cold rolling said body to elfect at least a 40 percent reduction in thickness, heat treating said cold-worked body in a protective atmosphere at a temperature from 750 to 1000 C.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Manufacturing & Machinery (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing Of Steel Electrode Plates (AREA)

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Cited By (8)

Citations (7)

• 0
  • BE BE563543D patent/BE563543A/xx unknown
• 1956
  • 1956-12-31 US US631476A patent/US2939810A/en not_active Expired - Lifetime

Patent Citations (7)

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