Auger electron spectroscopy evidence of grain boundary segregation in boron containing high permeability 3% Si-Fe

Conventional grain oriented 3% Si-Fe used in power and distribution transformers at 15kG has a permeability at 10 oersteds of approximately 1800 G/Oe ( ). Higher permeability ( ) alloys of 3% Si-Fe have recently been developed specifically to lower core loss at higher flux densities, e.g., 17kG. Presently, there are two different metallurgical approaches to the production of high permeability silicon steel, i.e., selective secondary grain growth by either particle or solute inhibition. Results of the application of AES to fractured surfaces of high permeability 3% Si-Fe are discussed. Materials inhibited by B, N and/or S exhibited positive grain boundary segregation. These elements were distributed at isolated intergranular interfaces. Boron and nitrogen were always positively correlated. Sulfur segregates occur with boron and nitrogen or separately. Depth profiling demonstrates grain boundary segregation is confined to a zone of <100Å. Similar investigations on conventional grain oriented silicon steel revealed intergranular regions characterized by high sulfur, but no boron or nitrogen.