Commercial scale production of a Fe-6.5 wt. % Si sheet has been successfully developed. Presently manufactured sheets are in coil form, whose thickness ranges from 0.1 to 0.5 mm with a maximum width of 400 mm. Magnetic properties of the manufactured sheet have been investigated. The permeability of Fe-6.5 wt. % Si sheet is about 10 times higher than the conventional nonoriented silicon steel sheet. The core losses are less than half the conventional, and even less than that of the grain-oriented silicon steel sheet at frequencies over 400 Hz. Superior soft magnetic properties are attributed to the low magnetostriction and high electric resistivity of this alloy. It is well known that the Fe-6.5 wt. % Si alloy has poor ductility in conventional mechanical work. But investigation of the forming conditions has enabled the stamping and bending of alloy sheets. Low core losses and high permeability make Fe-6.5 wt. % Si sheet adequate for motor cores, transformer cores operating at high frequencies, and magnetic shielding. Application to the micromotor core shows that Fe-6.5 wt. % Si sheet reduces the consumption of no-load electric current by 25% in comparison with the conventional silicon steel.

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Fracture mechanisms in galvannealed coatings have been studied by performing draw bead tests on galvannealed Ti stabilized interstitial free and Aluminum killed low carbon steel sheets and by investigating coating microstructures by scanning electron microscopy. Galvannealing treatments, on samples galvanized using an industrial hot-dip galvanizing process, were conducted at 450, 500 and 550°C for several time periods between 1 and 360 s in a laboratory induction furnace.In the coatings with low Fe content (up to 5 g/m 2 ), the amount of powdering during the draw bead test was minimal. Growth of cracks nucleated within the d 1 phase was arrested at the steel-coating interfaces where only a limited amount of decohesion occurred. A steep increase in the amount of powdering was observed in coatings with Fe contents between 6-9 g/m 2 . In these coatings, cracks originating from the d 1 phase reached G-G 1 -d 1 phase boundaries, which provided preferential crack growth paths and thus facilitated fracture within the coating. A fracture mechanics model was proposed to account for the powdering resistance of galvannealed coatings.

The iron-zinc alloying reactions which take place during hot dip galvanizing and galvannealing processes were investigated, with special reference to the formation and growth behavior of iron-zinc intermetallic compounds.The SEM observation and X-ray diffraction analysis of the intermetallic compounds which had formed on laboratory galvanized Ti stabilized interstitial-free steel and on low carbon aluminum killed steel sheets showed that there were two types of elementary iron-zinc alloying reactions ; one was the formation ofã nd 5, crystals and another was so-called outburst reaction.Thecrystal nucleated on the Fe-AI intermetallic compound which had been formed on the steel surface, and grew into the melt as a single phase crystal. Simultaneously, the outburst structure was generated as a result of the direct reaction between iron and molten zinc, and grew as a multiple phase structure (~, 8, and r phases). The~phase was generated at the isothermal galvannealing temperature of less than 773 K, and it was explained in terms of the iron-zinc equilibrium phase diagrem (peritectic temperature ofphase). 35 (1995), No. 11 Fig, l.

Synopsis The effects of surface microstructure and chemical compositions on characteristics of Fe-Zn compounds which formed on continuously galvanized steel sheets have been investigated by using ultra low carbon and low carbon steels. From SEM observation, morphology of Fe-Zn compounds formed at interface between steel and plating layer were classified into three types; outburst structure, fine granular structure, and pillar-like structure. The amount of outburst structure increases with decreasing solute carbon content in steels. Phosphorus inhibited the formation of outburst structure when solute carbon was combined with a carbide forming element such as Nb or Ti. A comparison between distribution of Fe-Zn compounds and corresponding steel surface indicated that the outburst structure formed preferentially at grain boundaries exposed on the steel surface, whereas fine granular structure formed mainly at the interior of surface grains.