Effects Of Nb And Cr Addition On Structure And Properties Of Fe-based Amorphous Alloys Used In Transformers

Fe-based amorphous alloys, which have excellent soft magnetic property, energy saving, environmental protection and other advantages, have gradually replaced the traditional silicon steel and are widely applied in transformer industry. However, Fe-based amorphous alloys suffer atmospheric corrosion commonly, which limits their industrial application seriously. In order to solve the above problem, we developed FeSiBNb and FeSiBCr soft magnetic amorphous alloys with better corrosion resistance by adding element Nb and Cr to the original component, Fe79.5Si9.5B11. In addition, X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to detect the amorphous structure and the thermal stability, vibrating sample magnetometer (VSM) and DC B-H loop tracer were employed to measure saturation magnetization and coercivity after stress relief annealing. Potentiodynamic poliarization experiments and immersion test uncovered the corrosion resistance of the amorphous alloys. The effects of Nb and Cr on the structure and properties of amorphous alloys were detected, the mechanism of corrosion was revealed. Main researches include:(1) Microstructure, thermal property, soft magnetic property and corrosion resistance of GC glassy ribbons (domestic Fe79.5Si9.5B11 amorphous alloys), RL glassy ribbons (Fe79.5Si9.5B11 amorphous alloys imported from HITACHI) and DN glassy ribbons (Fe79.5Si9.5B11 amorphous alloys prepared in laboratory) were compared. We found that the corrosion resistance of RL glassy ribbons is better than the corrosion resistance of GC glassy ribbons.(2) (Fe0.795Si0.095B0.11)100-xNbx(x= 0,1,2,3,4,5 at.%) glassy ribbons by adding Nb to Fe79.5Si9.5B11 glassy alloys were prepared. The microstructure, thermal property, soft magnetic property and corrosion resistance of these glassy ribbons were studied. We found that the stability of the amorphous phase was improved and the crystallization process became more complicated, saturation magnetization and coercivity after stress relief annealing reduced with Nb addition. (Fe0.795Si0.095B0.11)100-xNbx glassy alloy ribbons showed high corrosion resistance in NaOH solution and the content of Nb didn't effect the corrosion resistance. The corrosion resistance of (Fe0.795Si0.095B0.11)100-xNbx glassy alloy ribbons in NaCl solution was enhanced slightly with Nb addition.(3) (Fe0.795Si0.095B0.11)100-xCrx(x= 0,1,2,3,4,5 at.%) glassy ribbons by adding Cr to Fe79.5Si9.5B11 glassy alloys were prepared. The microstructure, thermal property, soft magnetic property and corrosion resistance of these glassy ribbons were studied. We found that the second crystallization process was inhibited, saturation magnetization and coercivity after stress relief annealing reduced with Cr addition. The corrosion resistance of (Fe0.795Si0.095B0.11)100-xCrx glassy alloy ribbons in NaOH and NaCl solution was enhanced with Cr addition. When the Cr content ?5at.%, the corrosion resistance of the ribbons in NaCl solution has been significantly improved, the corrosion rate was only 1.1× 10-4g·m-2.h-1 after immersed in 0.1 M NaCl solution for 120h.(4) Fe79.5-xSi9.5B11Crx(x= 0,1,2,3,4,5,7,9,11 at.%) glassy ribbons by substituting Fe with Cr were prepared. The microstructure, thermal property, soft magnetic property and corrosion resistance were studied. We found that the crystallization process was changed with Cr addition. The corrosion resistance of Fe79.5-xSi9.5B11Crx glassy alloy ribbons in NaOH and NaCl solution was enhanced with Cr addition. And when the Cr content ?5at.%, the corrosion resistance of the ribbons in NaCl solution has been significantly improved.(5) The corrosion mechanism of FeSiBNb and FeSiBCr in NaCl solution were similar: when corrosion reaction occurs, Nb/Cr accumulated in the amorphous surface and Nb/Cr oxide film was formed to protect the amorphous matrix. In addition, the Cr oxide film shows strong anti-pitting corrosion resistance, which enhanced the corrosion resistance of FeSiBCr glassy ribbons more significantly.(6) (Fe0.795Si0.095B0.11)98Nb2, (Fe0.795Si0.095B0.11)99Cr1 and Fe78.5Si9.5B11Cr1 glassy alloy ribbons with good corrosion resistance and excellent soft magnetic properties were obtained. The saturation magnetization and coercivity after stress relief annealing were 1.50T and 2.33 A/m,1.53T and 2.46A/m and 1.56T and 2.33 A/m, respectively.