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
  • C21D8/1205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties involving a particular fabrication or treatment of ingot or slab

Definitions

• This invention relates to a method of producing grain-oriented silicon-iron sheet or strip for magnetic purposes.
• the grain orientation to which this invention refers is that wherein the body-centered cubes making up the grains or crystals are oriented in the cube-onedge position, designated (110) [001] in accordance with the Miller lndices. More specifically, this invention relates to an improved and economical method of producing grain-oriented silicon-iron, whereby the temperature range to which the silicon-iron is heated prior to hot rolling is lowered by maintaining the oxygen content of the silicon-iron below a critical lower limit.
• silicon-irons having the (1 [001] orientation are characterized by a relatively high permeability in the rolling direction and a relatively low permeability in a direction at a right angle thereto.
• a commercial product of this nature has been used successfully for many years for the manufacture of laminations or cores in transformers, generators and the like, because of its low coreloss and high permeability in the rolling direction.
• the greater part of the cube-on-edge'oriented silicon-iron sheet stock is currently made from the raw materials by a number of steps which include melting, refining, casting and hot rolling ingots or slabs of a suitable composition to hot bands usually less than 0.1 inch thick. Following annealing and pickling steps, the material is cold rolled in one or more stages with intermediate anneals, subjected to a decarburizing step, and finally annealed at a temperature high enough to cause secondary recrystallization.
• the secondary recrystallization has been of the grain boundary energy type.
• current practice begins the hot rolling step either with a slab or directly with an ingot.
• an ingot is cast.
• the ingot is soaked at a high temperature of about 2,200 F. to 2,300 F. for several hours in order to equalize the ingot temperature to obviate problems caused by differential cooling in the ingot.
• the ingot is then rolled into a slab, generally about 6 inches thick, and allowed to cool slowly.
• the slab Prior to the hot rolling step, the slab is reheated to about 2,500 to 2,550 F.
• inhibitors such as manganese selenide may be used, for purposes of an exemplary showing the process of the present application will bedescribed in terms of manganese sulfide as the inhibitor.
• the composition of the silicon-iron is critical.
• the amount of oxygen should not exceed 0.0045 percent and'preferably' should not exceed 0.0030 percent.
• the vmanganese content should be from about 0.03 percent to about. 0.08 percent, and preferably from about 0.045 percent to about 0.065 percent.
• the lower limit is determined by the amount of manganese necessary to form a sufficient quantity of manganese sulfide to act as a grain growth inhibitor;
• the upper limit is determined by the solubility of the manganese sulfide prior to hot rolling, the higher manganese causing the sulfide tobe less soluble.
• higher manganese contents render sulfur additions to the silicon-iron at later stages of the processingless effective.
• Initial sulfur should be presentin about 0.025 percent.
• Selenium may be substituted for tial carbon content should be from about 0.015 percent to about 0.035 percent, and preferably from about 0.020 percent to about 0.030 percent.
• the silicon con tent may be from about 1.8 to '4 percent or higher, the lower limit being the minimum silicon which will avoid a phase change to gamma iron upon heating, while the upper limitisdependent upon the ability of the material to be cold rolled without breakage.
• the nitrogen content should not exceed about 0.007 percent and preferaly should not exceed about 0.004 percent. No more than about 0.008 percent total aluminum should be present. It is preferred to have thatv portion of the aluminum present in the acid-soluble form constitute less than 0.002 percent.
• any low oxygen refining process may be used, including vacuum techniques.
• One process which has the advantage of being amenable to the use of existing apparatus such as the open hearth or electric furnace, is disclosed by Boni and Heck, U.S. Pat. No. 3,305,354.
• the re-ladling process of their invention is capable of removing oxygen to a level of about ten parts per million or 0.001 percent.
• the silicon-iron having the melt composition given above may be conventionally cast into ingots or it may be continuously. cast into slab-ingots.
• slabs and ingots are intended to in- I clude silicon-iron which has been continuously cast.
• the siliconiron Prior to the step of rolling to hot bands, the siliconiron will be heated whether it be in ingot form (where direct rolling to strip is usedlor slab form (where a reheating step is practiced).
• the slabs or ingots are heated to within a temperature range between the lowest temperature at which the ingots or slabs are workable and the highest temperature at which no appreciable amount of slag will be formed.
• the slabs will be held at temperature for a period of less than one hour, while ingots are generally soaked for several hours.
• the highest temperature at which no appreciable amount of slag will be formed is dependent upon a number of factors. These factors include time at temperature, atmosphere,- type of flame and the like. Nevertheless, it has been determined thatlthe above depractice of the present invention, the temperature at which the hot rolling is completed is not considered to be critical in and of itself. It is preferred that the finish-' ing temperature be above 1,650 P. Similarly, the coiling temperature has not been found to be extremely critical. A temperature of about 1,200 F. is normal.
• the steps of the process following hot rolling are conventional.
• the hot band may be annealed before it is cold rolled in order to improve the structure. If an initial anneal is used, the temperature may vary from about 1,650 F. to about 2,000 F., and preferably is about l,800 F., for a time of up to about four minutes at temperature.
• Oriented silicon-iron having a final thickness of ent invention the teachings herein are particularly ap-- plicable to the production of oriented silicon-iron having a final thickness of about 0.014 inch or less.
• the silicon-iron will be decarburized to a value of 0.003 percent or less during one or more of the anneals. This may be done in an atmosphere such as wet hydrogen.
• the strip After decarburization, the strip is generally coated with an annealing separator and box annealed for at least 8 hours at a minimum temperature of 2,000 F. Higher temperatures and longer times at temperature are used when it is necessary to remove sulfur or other undesirable impurities. The sulfur content will be reduced to less than 0.002 percent during the final anneal.
• the oxygen content of the silicon-iron which may be from a trace to 0.0045 percent is in the upper portion of this range, and particularly when it is above about 0.0030 percent, it may be found desirable to heat the ingots or slabs to a temperature within the upper portion of the above given range, i.e. to a temperature from about 2,300 F. to about 2,400 F.
• the siliconiron sheet stock may be treated at final gauge, and immediately prior to or during the primary grain growth portion of the final anneal, with sulfur, selenium or their compounds from an external source.
• sulfur is preferred'for economic reasons.
• the sulfur- 6 to hot rolling, will yield a product having excellent magnetic properties.
• the addition of sulfur from an external source will insure an excellent product even at a slab or ingot heating temperature of 2,l00 F.
• silicon-iron of the above outlined composition in the form of slabs or ingots may be heated within the range of 2, 100 F. to 2,400 F. and rapidly rolled to the desired hot band thickness. If an initial anneal is used the temperature may vary from about l,650 F. to about 2,000 F. for a time of up to about four minutes at temperature. When a final product about 0.012 inch'thick is desired, the silicon-iron will be cold rolled in a first stage to an intermediate gauge of about 0.030 inch. This will be followed by an intermediate anneal at about 1,700 F., and a second stage of cold rolling to final gauge. The material may then be decarburized as described above.
• Sulfur from an external source may be added in any of the ways and in an amount as taught in .the above mentioned Kohler patents, and the material will be subjected to a final box anneal at a minimum temperature of 2,000 F. for at least 8 hours. Again, with respect to the final anneal, higher temperatures and'longer times atv temperatures will be used if it is necessary to remove sulfur or other undesirable impurities.
• sulfur addition maybe made in several ways.
• sulfur or sulfur-bearing compounds may be added to the annealing separator in the finalanneal.
• the annealing atmosphere of the final anneal may be charged with a gaseous sulfur compound providing the atmosphere is in contact with the surfaces of the silicon-iron.
• sulfur or sulfurbearing compounds may be made available at the surfaces of the sheet material during a decarburizing anneal prior to the final anneal.
• A, B and C Three slabs (hereinafter designated A, B and C) about 6 inches thick were selected from a heat of silicon-ironwhich had been melted in an open hearth using the previously mentioned method of Boni and last reduction.
• the hot rolled bands were annealed at l,800 F. j
• the samples were annealed at 1,675 F. in hydrogen for about 1 minute at their intermediate thickness of 0.026 inch. After the second coldrolling, they were decarburized at 1,500 F. for about three minutes in wet hydrogen and given a final box anneal at 2,200 F. in
• Table II shows the initial compositions and final per meability values for the materials given the two initial annealing temperatures.
• the first three values in each column refer to samples from the front, middle and back of the coil from the first slab of the respective heat.
• the next three values represent samples from the front, middle and back of the coil from the second slab of the same heat.
• the last value is an average of the values. of all six samples.
• the permeability val- 10.5 .552 .863 172 A e g ues obtained are shown below in Table V together with the analyses of thehot rolledsamples.
• Modifications may' be made in the inventionwithout EXAMPLE lV
• Two slabs about 6 inches thick representing two ingots were selected at random from each of six heats with varying amounts of oxygen. These slabs were heated to a temperature of 2,385 F. or just below the slagging temperature and hot rolled rapidly 'to hot bands 0.076 inch thick. Samples representing the center of the coils were processed in the laboratory. The hot rolled pieces were annealed at l,800 F. for about departing from the spirit of it.
• silicon-iron has an initial composition including from about 0.015 percent to about 0.035 percent carbon, from about 0.03 percent to about 0.08 percent manganese, from about 0.015 percent to about 0.030percent sulfur, 0.007 percent maximum nitrogen, 0.008 per- .cent maximum total aluminum and the balance subcon-iron has an initial composition including from 7 about 0.020 percent to about 0.030 percent carbon,
• . 12 from about 0.045 percent to about 0.065 percent manganese, from about .020% to about 0.025% sulfur, 0.004 percent maximum nitrogen, .002% maximum acid-soluble aluminum, and the balance substantially iron.
• a method for producing cube-on-edge siliconiron having a silicon content of from about l.8 percent to about 4 percent and processed by steps including hot rolling to intermediate gauge, cold rolling to final gauge, decarburizing and annealing whereby to effect secondary recrystallization favoring growth of cube-onedge nuclei by grain boundary energy comprising in combination therewith the steps of heating said silicon-iron havingan oxygen content no greater than 0.0045 percent to a temperature of from 2,100 F. to not more than 2,400 F. immediately prior to said hot rolling step, and reacting said silicon-iron with sulfur from an external source after said cold rolling and prior to said secondary recrystallization whereby to inhibit primary grain growth.

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

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Cited By (7)

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• 1966
  • 1966-09-30 US US00583459A patent/US3802937A/en not_active Expired - Lifetime
• 1967
  • 1967-08-28 BG BG8517A patent/BG17635A3/xx unknown
  • 1967-09-01 GB GB40114/67A patent/GB1197800A/en not_active Expired
  • 1967-09-05 DE DE19671583326 patent/DE1583326A1/de active Pending
  • 1967-09-13 CS CS676539A patent/CS194651B2/cs unknown
  • 1967-09-28 BE BE704464D patent/BE704464A/xx unknown
  • 1967-09-29 SE SE13420/67A patent/SE350281B/xx unknown

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