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      In the past, during the application, little mechanical shock/stress can break brittle NbCuFeSiB cores, especially for large-sized and heavy ones, leading to significant loss of coercivity Hc and permeability. Therefore, poor magnetic stability is a major problem to brittle NbCuFeSiB cores.   
      Now, we have resolved this problem by producing non-broken nanocrystalline cores with advanced surface coating technique. A new nanocrystalline core of 50g does not break even dropping from1 meter high down to the ground. Therefore the coercivity and permeability of the cores are stable during applications in different environments.
      Because of the excellent comprehensive soft magnetic properties, NbCuFeSiB nanocrystalline cores have a wide range of applications in the fields of current(voltage)transformers, voltage independent RCCBs, switched mode power supplies, common mode chokes, IGBT inverter electric welder. For example:
      *Higher initial permeability(μi=150-260k) and high permeabilits(μm =450-800k): For 30-100mA type AC voltage independent RCCBs.
      *High initial permeability and low remerance Br (μi=110-150k,Br=200-400mT): For 100mA type AC voltage independent RCCBs.
      *High initial permeability μi and lower remerance Br(μi=60-130k. Br≤150mT): For type A 10-100mA,300mA,500mA , type AC 300-500mA voltage independent RCCBs I and IGBT inverter electric welding mechine.
       *High initial permeability μi and high μimi=85k-130k, μim≥0.7). For common mode chokes.
      *High initial permeability μiand low remerance Br(μi=130-170k. Br≤300mT) For current transformers and electronic watt-hour meters.
      *Temperature magnetic stability: After aging at -25℃ for 100 hours and 120℃ for 100 hours,the irreversible loss for permeability is less than 2% and less than 3%.

Nanocrystalline soft magnetic cores
     Nanocrystaaline NbCuFeSiB is a soft magnetic material produced from amorphous NbCuFeSiB ribbon which is made through rapid solidification of molten metal at a cooling rate of about a million degrees per second. The amorphous ribbons have a thickness about 30 μm. After special heat treatment, a –Fe(si) nanocrocrystalline phase is formed at 20nm size. This nanosized structure exhibits excellent soft magnetic properties.
      Before the nanocrystalline soft magnetic material is developed, the widely used soft magnetic materials were silicon steel、permalloy、ferrite and amorphous alloys, and they play an important role in switched mode power supplies, electric power system equipment, electric meter and electric apparatus. But soft magnetic properties for the mentioned material are not perfect, the magnetic properties of all these soft magnetic materials have disadvantages. The silicon steel has high saturation flux density, but the permeability is very low particularly in high operating frequency; the ferrite exhibits good high frequency properties, but the saturation flux density and permeability is low; permalloy shows high permeability and low coercivity(Hc), but the Bs is low and can not be used in high operating frequency; the Co-based amorphous presents high permeability and low loss in wide operating frequency, but the Bs is low and the raw material is expensive;the Fe-based amorphous has a advantage of high Bs and low price raw material, but the permeability is relatively low. With high permeability(μi>100000),high saturation flux density(Bs>1.0T) and low loss(P0.2/50kHz=15w/kg),the nanocrystalline alloy exhibits excellent soft magnetic properties. The nanocrystalline cores have bright future in the fields of switched mode power supplies、common mode chokes、current transformers、 voltage independent RCCBs、IGBT inverter electric welder.
      Another factor effecting the mechanical stress magnetic stability of nanocrystalline alloy is that this kind of alloy is very fragile, slightly mechanical stress will make the material break, which leads to the significant enhancement of coercivity and the reduction of permeability. This is a magnificent difficult to hinder nanocrystalline alloy to find wide application in industry.
      By means of special heat treatment process, we can produce nanocrystalline cores with low coercivity of 0.2-0.6A/m,high initial permeability of μi equaling to 160-260k.All cores are surface treated and aged at 120℃ for 3 hour to eliminate the irreversible loss, consequently the cores show special properties as following:
      ①.With advanced surface coating technique made of epoxy resin, we can produce nanocrystalline cores with excellent mechanical stress magnetic stability. Cores weighed 50g are dropped down the ground from 1 meter high level, the cores will not break and the permeability and coercivity remain unchanged.
      ②.Impulse current withstand: when the cores are tested in voltage independent RCCBs with 3000A impulse current, their irreversible loss for permeability is less than 3%.     
      ③.Because of the excellent mechanical stress magnetic stability for the cores, the use of cores in transformers for IGBT inverter electric welder will greatly reduce the operating noise and can serve more than 20 years.   
       ④Temperature magnetic stability: after aging at -25℃ for 100 hours and 120℃ for 100 hours, the irreversible loss for permeability is less than 2% and less than 3%.