Improvement of Ductility of DO_3 Type Intermetallics

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6.5mass% silicon steel (DO_3 type intermetallics) has good soft magnetic properties. The material, however, is brittle, and the brittleness prevents its practical use. This research aims at studying the cause of the brittleness and improving its formability. The results are summarized as follows:1. Ductile-brittle transition: (1) Brittle fracture takes place at temperatures below 600K (region B), and the material is ductile above the temperature (region D). In the ductile temperature region, however, fracture surfaces contain brittle fracture facets at lower strain rates (region B/D), (2) The boundary between regions B and D moves toward lower temperature as strain rate increases, suggesting that the material can plastically be formed at higher strain rates even at lower temperatures.2. Microstructural observation: (1) Active slip system: {110}<111> and {112}<111> slip systems are operative both in regions D and B. Five independent slip systems necessary for plastic deformation are available in the material. This indicates that the material is essentially ductile. (2) In region B, a number of cracks are formed at grain boundaries as well as within grains. In region D, however, cracks are observed only in special locations. This difference causes the two regions.3. Rolling: The material was rolled at various rolling speeds. At lower rolling speeds the material is brittle, but at higher rolling speeds it becomes ductile. This confirms the expectation of 1(2). The material could be rolled at 473K at high rolling speeds.