Producing method for microcrystal rare-earth permanent-magnet with high performance
The present invention relates to a kind of manufacture method of high-performance micro rare earth permanent magnet.
Since the rare-earth-iron-boron permanent magnetic material came out, the patent content of having published was summarized as follows:
1. chemical analysis:
Nearly all disclosed patent about RE permanent magnetic alloy, its chemical analysis all is roughly the same basically: the R that promptly presses atomic percentage conc 8~33%, 12~28% B, surplus is Fe, add metallic element M(M and represent V, Nb, Ta, Cr, Mo, W, Ge, Bi, Si, Al, Ti, Zr, Hf, Mn, Ni, Sn, Sb, Zn etc.) and with≤50% Co replacement Fe, with N replacement B etc.
2. manufacturing process:
(1) powder metallurgic method:
Adopt traditional technology and the equipment of powder metallurgy industry: i.e. technologies such as vacuum induction furnace (argon shield) smelting ingot casting, Mechanical Crushing, ball milling powder process, die mould, sintering, heat treatment, cutting, grinding, make permanent magnet.With SUMITOMO CHEMICAL particulate metal company is that the patent of representative has US4597938, US4773950, EP0274034, EP0101552, CN85101455A etc., all adopt the powder metallurgy traditional handicraft, and the aspects such as control of ingot casting shape, crystallite dimension, composition segregation and field trash are not all proposed effective measures: to ingot casting, powder process aspect, each patent application does not propose special claim yet
(2) oxide thermal reduction:
Rare earth oxide (R
2O
3), with reactive metal calcium, receive or calcium hydride, the thermal reduction diffusion is carried out in heating, produce the method for rare-earth-iron-boron basis raw meal, General Motors Overseas Corporation and SUMITOMO CHEMICAL particulate metal company, the publication number of relevant patent is US4767450, US4806155, US4898613, EP0254251, CN85100812A, CN85100813A, CN85107738A, CN86103244A, CN1042024A.The oxide thermal reduction can directly use the rare earth oxide (R of ore body form
2O
3), removed expensive rare earth metal extractive process from, thus with low cost.But impurity content height, especially oxygen content height, even oxygen content can reach tens of times to hundreds of times of the smelting method, influence performance.
(3) quick quenching technique:
This method is that the Russian at first proposes (seeing J.J.Croat and L.Kabacoff et al.J.Appl.phys.53(3), 1931.2255~2257), General Motors Overseas Corporation applies for a patent the earliest, disclosed patent has EP125725, US4533408, US4840684, US4767474, US520170, EP0725752, EP0284033, GB2100286A, J57-97606, CN1039926A etc., content is summarized as follows:
Alloy melt is injected into one by on the water-cooled high speed rotating plate with certain flow, on the water-cooled rotating disk, make the flake powder that thickness is 10~100 μ m with quick quenching technique, because rotary speed is fast, the cooling rate height, the powder of making mainly is an amorphous structure, also may produce a part of microstructure, this powder of its crystallite dimension minimum (0.02~0.5 μ m) is a magnetic isotropy.
Above-mentioned amorphous or microcrystalline powder are mixed with a certain proportion of binding agent, inject compression moulding in the mould, can make the magnet of Any shape easily, also need not carry out magnetic field orientating when pressing shape.This method major defect is the magnetic isotropy goods, and magnetic property is lower, Br=6~8kG, iHc=8~11KOe, (HB) max≤10MGOe.
(4) aerosolization method:
U.S. crucible material company applied for a patent in 1986: US4585473, and its subject matter is as follows:
Use vacuum induction furnace,, inject spray chamber,, liquid alloy is atomized into droplet, be frozen into the spheric granules powder rapidly through an annular high pressure argon gas spray gun with certain flow with alloy melting.This particles of powder is of a size of 1~5 μ m, can directly adopt common powder metallurgic method to make permanent magnet, and the major defect of this method is the cost height.
(5) hot demagnetization method:
General Motors Overseas Corporation proposes a new technology about the demagnetization of permanent magnetism body heat in nineteen ninety, and patent application proposed, patent publication No.: US4900374, main contents are as follows: under atmospheric conditions, permanent magnet is heated above 100~300 ℃ of Curie points, insulation 30min naturally cools to room temperature then.Adopt this hot demagnetization method, can reduce or eliminate magnetic loss.The shortcoming of this demagnetizing method is magnet heating and cooling under atmosphere, and heating-up temperature is higher, can cause the severe oxidation of magnet like this.
More than summarized up to now from five aspects, be reflected in the major progress about permanent magnetic material of patent aspect.Take a broad view of the permanent magnetic material development so far, remain in following shortcoming and problem in its performance, production and application facet:
A. adopt the smelting process under the vaccum sensitive stove argon shield, can not produce in a large number chemical analysis evenly, stable performance, alloy cast ingot that impurity content is low.The general spindle diameter of this smelting process more is easy to generate the composition segregation and forms thick column crystal below 70m/m when the spindle diameter is big, also easily produce loose near spindle upper section and the center and be mingled with.Be subjected to above-mentioned condition restriction, the alloy pig that each stove is smelted is heavy less, and this is the reason that prior art can not be produced permanent magnetic material in a large number.In addition, smelt increased frequency, be difficult to guarantee the consistency of each stove alloy composition and performance again.
B. present, great majority still adopt traditional powder metallurgic method to make permanent magnet, promptly smelt the alloy pig that through Mechanical Crushing, ball milling powder process, and die mould, sintering, cutting, operations such as grinding are finally made the part of definite shape.Alloy pig with thick column crystal can not be made the compact grained magnetic certainly.In addition, in view of the rare earth element of one of alloy Main Ingredients and Appearance, has higher chemism, in smelting and processing of each road and processing procedure, suffer hydrogenation and contamination inevitably, and remain in the magnet as field trash, this is a kind of serious hindrance to further raising magnet performance.
C. reduce cost is to be related to the key factor that can rare earth permanent-magnetic material be widely applied.But adopt traditional process, can not reduce cost significantly.The production process of rare earth permanent-magnetic material is various, the per pass operation all will cause spillage of material, the alloy base substrate of making at last also will be through the line cutting, technologies such as grinding, just can make the part of definite shape, therefore the total recovery rate of material is lower, and this is one of high major reason of present rare earth permanent-magnetic material cost.
The object of the present invention is to provide the manufacture method (rare earth element of at least a Y of comprising of R representative wherein of a kind of stable performance, low price, large-scale production R-T-B-M type high-performance micro rare earth permanent magnet, T represents magnesium-yttrium-transition metal Fe and Co, and M represents a small amount of additional metal element).
In order to achieve the above object, the present invention has adopted following technical proposals:
(1) with plasma continuous casting furnace melting (referring to Fig. 1), the copper crystallizer continuous casting of the water-cooled of no crucible has realized continuous charging, and continuous smelting pulls straight the production method of ingot casting.The ingot casting of pulling out can be endless in principle, and this is the important key that can produce high-performance rare-earth class permanent-magnet alloy in a large number.In addition, because copper water mold can obtain very fast condensation rate, thereby not only can reduce oxidation, reduce and stain, and can eliminate segregation, and obtain the alloy of best crystal structure.This smelting process can be eliminated the loose of rising head position and spindle center simultaneously and be mingled with, and has guaranteed to obtain the alloy pig of all even consistency of performance of chemical analysis and good reproducibility.2 is air-filled pores among the figure, the 4th, and vacuum pump, the 5th, pull bar, the 6th, ingot casting, the 7th, feeder, the 8th, power supply, the 9th, electron gun, the 10th, molten bath.
(2) in vacuum furnace, adopt rapid condensation centrifugal atomizing legal system to get crystallite magnetic (referring to Fig. 2,1 is feeder among the figure, the 2nd, water jacketed copper crucible, the 3rd, vacuum pump, the 4th, centrifugal turntable, the 5th, catch tray, the 6th, scraping blade, the 7th, gatherer, the 8th, scanning electron rifle).This method is that liquid alloy is poured into one by on the rotating disk 4 of water cooling and high speed rotating, by centrifugal force liquid alloy is atomized into droplet, droplet flies to another rapidly by on the catch tray 5 of the vertical with it high speed rotating of water cooling and direction of rotation, is frozen into the sheet-like crystallite powder.The thickness of flake powder is 10~50 μ m, and the radial dimension of sheet is 1~3m/m, and flake powder is the micro crystal structure, and crystallite dimension is 0.05~5.0 μ m.
(3) get on the basis of sheet-like crystallite magnetic in rapid condensation centrifugal atomizing legal system, under hydrogen atmosphere, employing continuous shaking hydrogenation pulverizing stove (referring to Fig. 3, wherein 1 is discharger, the 2nd, and vacuum pump, the 3rd, hydrogenation room, the 4th, spiral vibrating pulverizer, the 5th, heater, the 6th, hydrogen charging port, the 7th, feeder), carry out the fine pulverizing that chemistry combines with machinery.Owing to inhale process that hydrogenation pulverizes and mainly be the crushing process along crystal boundary, thereby powder particle size and crystallite dimension may be the same order of magnitude, promptly makes the fine magnetic of crystallite, and this magnetic domain that just can guarantee the realization optimum state is orientated.Under vibration condition, carry powder, can promote and quicken the suction hydrogen process of powder, guarantee all consistency of even performance of powder pulverizing with spiral way.In addition, the powder particle that makes in this way, periphery are relatively slicker and more sly, thereby can improve the flowability of powder greatly, provide possibility for obtaining finer and close die mould.With the fine magnetic of crystallite of this profile slyness, can make the more excellent permanent magnet of performance, the easier direction proper alignment of its magnetization vector along alignment magnetic field.
(4) adopt the hot working method to prepared rare earth permanent magnet sintered body, carry out the accurate dimensions typing, hot pressing temperature is 600~850 ℃.This course of processing not only can reach the purpose of accurately finalizing the design by the product size requirement, the more important thing is that this process also has the effect of thermomechanical treatment.Magnet through thermomechanical treatment has higher magnetic property.This technical process, further improved permanent magnetic material utilance and reduce cost.Adopt hot worked method, product is carried out accurate typing in the margin of tolerance, can significantly reduce the loss of material because of courses of processing such as cutting and grindings.
(5) by the method for the certain heating and cooling speed of control, permanent magnet be can't harm demagnetization.The technical process that the present invention adopts is: in inert atmosphere permanent magnet is pressed certain programming rate, be heated to the temperature of above 10~50 ℃ of Curie point, be cooled to room temperature with certain speed again, reach the purpose of catapepsis magnetic.Demagnetization repeatedly in this way also can not cause magnetic loss.
The present invention and conventional art compare, and its advantage is conspicuous, and the unique technique viewpoint that the present invention proposes is described more specifically, it is characterized in that: produce rare-earth permanent-magnet alloy ingot with the plasma continuous casting furnace.Its feature is in the short period of time, and it is big to obtain output, reduced in segregation, and component is even, and crystal grain is thin, and the high-quality ingot casting that impurity content is low can be realized stable and production continuously economically.The ingot casting speed of pulling out of this method melting RE permanent magnetic alloy is 15~150Kg/h; Be 8~10 times of traditional smelting speed.The alloy oxygen content of smelting with this method can be less than 150ppm, and traditional method of smelting oxygen content will reach more than the 500ppm.Smelting process provided by the invention, owing to adopted the copper crucible of water-cooled of copper crystallizer of water-cooled and electron gun program scanning, replaced the crucible that traditional metal ingot mould and refractory material are made, thereby eliminated the contamination of crucible material to melt, having reduced nonmetal inclusion ingot casting cross sectional shape can be by changing the random change of shape of crystallizer; For example can adopt ingot casting, the spindle sectional dimension of circle, non-circular (square, rectangle etc.) can be 10~150m/m, optimum range is 40~80m/m.Near loose, the segregation that spindle upper section and center line, produces when this ingot casting can reduce or eliminate billet and being mingled with.
The unique technique viewpoint that the present invention proposes is described more specifically, it is characterized in that: get the sheet-like crystallite magnetic with rapid condensation centrifugal atomizing legal system, referring to Fig. 2, add thermionic electron guns 8, alloy material in the water jacketed copper crucible 2 is melted to pouring temperature, it is 2000~5000rpm that the liquid alloy of certain flow is injected into a rotating speed from cast gate, linear velocity is on 5~50m/g rotating disk 4, liquid alloy is torn up and flies to by centrifugal force on the catch tray 5 of another water cooling high speed rotation, forms flakelike powder through bump.By scraping blade 6 flake powder is scraped, enter gatherer 7.The powder that makes in this way in the form of sheets, powder sheet thickness is 10~50 μ m, the radial dimension of sheets of powder is 1~3m/m, its crystallite dimension is the crystallite magnetic of 0.05~5.0 μ m.But the centrifugal turntable of high speed rotating and catch tray continuous speed adjustment.
Subsequently above-mentioned crystallite magnetic is sent into continuous shaking hydrogenation and pulverized stove, pulverize the method that combines with machinery with chemical hydrogenation, above-mentioned sheet-like crystallite magnetic further is ground into the fine magnetic of crystallite referring to Fig. 3.Concrete grammar is: in a stainless steel closed container that vacuumizes, put a spiral vibrating pulverizer 4, powder goes forward one by one along spiral groove and carries and pulverizing.The spirality vibrating pulverizer has the suction hydrogen effect that promotes and quicken powder again, from and can guarantee to obtain uniform particles and the fine powder of performance unanimity.Do not destroying under the bubble-tight condition of closed unit, powder can add continuously, continuously output.Observe with measurement and show that suction hydrogen process shows as two stages: at first by alloy phase Nd
15Fe
77B
3In active rich Nd begin mutually, follow intensification, produce intercrystalline failure, inhale the hydrogen total amount and be equivalent to Nd
15Fe
77B
3H
28Rich Nd at first begins to pulverize along crystal boundary mutually after inhaling hydrogen, along broken generation equiax crystal of crystalline flour and column crystal, and its surface smoothing, transgranular cracking may break or second boundary breaks for ruptile, cleavage surface.Should point out emphatically, spiral vibration hydrogenation is pulverized, and is the process that promotes that mutually mutual acceleration is pulverized, and this process can realize continuous charging, pulverize continuously, and the large-scale production process of continuous discharging, it can be complementary with the former roads of the present invention technology.Just can make the fine magnetic of crystallite later on through above-mentioned pulverizing, its particle size and crystallite dimension all can reach 0.05~5.0 μ m order of magnitude.The method of crystallite magnetic is produced in this machinery and chemical combined pulverizing, can normal temperature and pressure (temperature: 25~30 ℃, hydrogen pressure: an atmospheric pressure) down or HTHP (temperature :≤850 ℃, hydrogen pressure≤10
5Bar) carry out under.Above breaking method can also obtain an additional effect: the hydrogen that alloyed powder is absorbed in hydrogenation process, and in magnet heat-agglomerating process subsequently, continuous again releasing hydrogen gas, this has just reduced the consumption and the cost of inert protective gas in the sintering process.
Its magnetization vector of the fine magnetic of this crystallite is easy to implementation rule and arranges under the directional magnetic field effect.Adopt isostatic compaction and sintering process, can be made into the anisotropy permanent magnet.Under vacuum or inert atmosphere, alignment magnetic field is 5~35KOe, and briquetting pressure is 0.5~3.5T/cm
2, sintering temperature is 900~1200 ℃, and the sintered heat insulating time is 0.5~5h, and this process can be produced the permanent magnet that maximum magnetic energy product is 32~46MGOe.
The unique technique viewpoint that the present invention proposes is described more specifically, be it is characterized in that: permanent magnet is carried out more accurate size typing with the hot working method.The hardness that this method at first is based on rare earth permanent-magnetic material reduces with the rising of temperature.Referring to Fig. 4 curve.The method that proposes with the present invention is heated to 600~850 ℃ with the permanent magnet of sintering under inert atmosphere, place in the pressing mold of product specific dimensions and shape, carries out the pressurized heat typing.This road technical process has following several effect; The blank that A can make permanent magnet carries out accurate typing in the margin of tolerance by shape of product and dimensional requirement, avoids cutting the waste that causes material with grinding technics; B. make product blank carry out hot machining, this is a kind of process of thermomechanical treatment, and thermomechanical treatment can further improve magnetic property; C. making the conventional method of rare-earth permanent magnet, is that the base substrate behind the sintering if can carry out tempering heat treatment in 600~850 ℃ temperature range, can further improve magnetic property.The present invention adopts one of purpose of 600~850 ℃ of hot working typing, is exactly in the technical process of thermal finalization, finishes the process of tempering heat treatment simultaneously, the finalize the design effect of " killing three birds with one stone " that this unique technique produces of hot working that Here it is.
The unique technique viewpoint that the present invention proposes is described more specifically, be it is characterized in that: the present invention proposes a novel unique harmless demagnetization new technology.Produce the technology more complicated of permanent magnet, operation is various, wants definite understanding and checks per pass technology the final performance of magnet is had what influence or the like, all require magnet could carry out smoothly under no magnetic stripe spare, so the permanent magnet demagnetization is a routine operation.Traditional demagnetization method has three kinds: (1) permanent magnet is in alternation and magnetic field that magnetic field intensity weakens gradually, certain time can reach the purpose of demagnetization, but this method is concerning the permanent magnet of high-coercive force, erasure effect is not good, still has a small amount of remanent magnetism residual after the demagnetization in the magnet.(2) magnet is heated to temperature more than the Curie point under protective atmosphere, is cooled to room temperature then,, experiment showed, that whenever carrying out a demagnetization handles, and will cause 1~2% magnetic loss though can reach the purpose of complete demagnetization.(3) permanent magnet is heated to more than the Curie point 100~300 ℃ under atmospheric conditions, insulation 30min naturally cools to room temperature then, also can reach the purpose of demagnetization.Shortcoming is that magnet will be subjected to oxidation in heating, insulation and cooling procedure, reduces magnetic property.And the harmless demagnetization technology of the high-coercive force permanent magnet that the present invention proposes promptly adopts specific mode of heating under vacuum or inert atmosphere, and specific intensification and cooling rate have drawn the complete harmless demagnetization new technology of a cover.Wherein heating-up temperature is for being higher than 10~50 ℃ of Curie points, and programming rate is 50~500 ℃/min, and cooling rate is 30~300 ℃/S.
The drawing explanation of accompanying drawing:
Fig. 1 is the structural representation of the plasma continuous casting furnace in the embodiment of the present invention.
Fig. 2 is the structural representation that the sheet-like crystallite magnetic in the embodiment of the present invention is made stove.
Fig. 3 is the structural representation of the broken stove of continuous shaking hydrogenation in the embodiment of the present invention.
Fig. 4 is the relation curve of the hardness and the temperature of rare earth permanent-magnetic material.
Embodiments of the invention 1
With the plasma electric stove of vacuum argon filling, the continuous casting process of the copper crystallizer of water-cooled, obtaining composition is Nd by atomic percent
15Fe
77B
8A kind of alloy pig, the spindle sectional dimension is 50 * 80m/m.Alloy pig to gained makes the alloy block that is of a size of 10m/m with mechanical crushing method.Then this alloy block is sent into continuously the sheet-like crystallite magnetic and made (see figure 2) in the copper crucible of water-cooled of stove.Fusing is after crystallite sheet magnetic is made in the rapid condensation atomizing of rotating disk.The average thickness of flake powder is 10 μ m, and average radial is of a size of 2m/m, and average grain size is 0.08 μ m.Subsequently above-mentioned sheet-like crystallite magnetic is sent into continuous shaking hydrogenation and pulverized the stove (see figure 3), in temperature is 150 ℃, hydrogen pressure is a little more than under 1 atmospheric pressure, carrying out continuous shaking hydrogenation pulverizes, promptly can be made into average particle size particle size and crystallite dimension is the fine magnetic of crystallite of 0.08 μ m, with the fine magnetic of this crystallite, be in the directional magnetic field of 12KOe, with 2.0T/cm in magnetic field intensity
2Pressure compression moulding.Then under vacuum condition (5 * 10
-4Torr) carry out sintering, sintering temperature is 1150 ℃, insulation 2h.Speed with 500 ℃/min is cooled to room temperature then.Object behind the sintering is heated to 800 ℃ under argon shield, determine temperature retention time according to the workpiece different-thickness, (being that 5min calculates by every millimeter section thickness temperature retention time generally).After the insulation part is sent in the pressing mold, carried out the hot working typing.Pressure direction is orientated perpendicular to directional magnetic field, makes part be quickly cooled to room temperature with the cooling rate of 300 ℃/S then.The gained magnet performance is as follows: Br=11.2KG, iHe=14.5KOe, (HB) max=35MGOe.
Embodiments of the invention 2
Fill the plasma electric stove of neon with vacuum, the continuous casting process of the copper crystallizer of water-cooled, obtaining composition is Nd by atomic percent
9Pr
8Fe
70B
13A kind of alloy, spindle cross section is of a size of 70 * 70m/m.Resulting alloy pig is made the alloying pellet that particle mean size is 5m/m with mechanical crushing method, then it is sent into the sheet-like crystallite magnetic and make the stove (see figure 2), through the rotating disk rapid condensation, be atomized into the crystallite flake powder, the average thickness of powder sheet is 8 μ m, the radially average-size of sheet is 3m/m, and the average grain size of flake powder is the crystalline state of 2.0 μ m.Above-mentioned flake powder is sent into continuous shaking hydrogenation pulverize the stove (see figure 3), under normal temperature (30 ℃) normal pressure (hydrogen pressure is an atmospheric pressure), be ground into the fine magnetic of crystallite.Its average particle size particle size and crystallite dimension are 2.0 μ m.The fine magnetic of resulting crystallite in field intensity 15KOe magnetic field, is used 2.5T/cm
2Pressure compression moulding, then purity be 99.99% and the argon gas of 650Torr in carry out sintering, sintering temperature is 1140 ℃, behind the insulation 2h, is cooled to room temperature with the cooling rate of 650 ℃/min.Magnet through oversintering; in purity is 99.99%; pressure is to be heated to 750 ℃ under the argon shield of 650Torr; determine that according to section thickness the workpiece after different temperature retention time (being that 5min calculates by every millimeter section thickness temperature retention time generally) will be incubated sends in the pressing mold; carry out hot working typing, the alignment magnetic field direction of pressure direction during perpendicular to pressure forming.And making the typing workpiece be cooled to room temperature with the cooling rate of 250 ℃/S, the performance that obtains magnet is as follows: residual magnetic flux density Br=10.8KG, coercive force iHc=11.4KOe, maximum magnetic energy product (HB) max=36.4MGOe.
Embodiments of the invention 3
Fill the plasma electric stove of helium with vacuum, the continuous casting process of the copper crystallizer of water-cooled, obtaining composition is Fe by atomic percent
76Nd
13DyMoSiB
8A kind of alloy, the spindle sectional dimension is 60 * 85m/m.The gained alloy pig is made the particle that average particle size particle size is 2m/m with mechanical crushing method, then this particle is sent into the sheet-like crystallite magnetic and is made (see figure 2) in the stove, makes crystallite sheet magnetic.The average thickness of flake powder is 5 μ m, and the radially average-size of sheet is 1.0m/m, and the average grain size of crystallite flake powder is the crystalline state of 1.0 μ m.Subsequently this crystallite powder is sent into continuous shaking hydrogenation and pulverized (see figure 3) in the stove, charge into purity and be 99.99% hydrogen, hydrogen pressure 10
5Bar is warming up to 600 ℃, carries out HTHP hydrogenation.Under the synergy of HTHP hydrogenation and spiral vibrating formula pulverizer, (5min) can be ground into the sheet-like crystallite magnetic the fine magnetic of crystallite in a short period of time, and its particle size and crystallite dimension are about 1.0 μ m.In the 30KOe alignment magnetic field, use 3.0T/cm with the fine magnetic of prepared crystallite
3Pressure compression moulding.Molding blank carries out sintering in the argon gas of purity 99.99% and pressure 800Torr, sintering temperature is 1080 ℃, insulation 3h, and the speed with 830 ℃/min is cooled to room temperature subsequently.Base substrate behind the sintering is 99.99% in purity; pressure is under the argon shield of 760Torr; be heated to 800 ℃; determine temperature retention time (being that 5min calculates generally) according to different cross section thickness by every millimeter section thickness temperature retention time; workpiece after the insulation is sent in the pressing mold; carry out hot working typing, pressure direction magnetic field orientating during perpendicular to die mould, and make the workpiece after the typing be cooled to room temperature with the cooling rate of 300 ℃/S.The main performance of gained magnet is as follows: residual magnetic flux density Br=13.6KG, coercive force iHc=19.8KOe, maximum magnetic energy product (HB) max=39.5MGOe.
Above-mentioned magnet carries out thermal demagnetization and handles by unique demagnetization technology that the present invention proposes: heating is to be 99.99% in purity, and pressure is to carry out in the argon shield electric furnace of 650Torr.Heating-up temperature is higher than 20 ℃ of Curie points, and programming rate is 200 ℃/min, and cooling rate is 300 ℃/S.Check feature result is as follows: residual magnetic flux density Br=13.50KG, than reducing by 0.073% before the demagnetization; Coercive force iHe=19.90KOe is than raising 0.5% before the demagnetization; Maximum magnetic energy product (HB) max=39.4MGOe is than reducing by 0.25% before the demagnetization.Measurement result proves, magnetic free of losses in the test error scope.