Tohru Arai1, Masayoshi Mizutani1 and Noboru Komatsu1
1Toyota Central Research & Development Lab., Inc. Nagoya
The boronized surface of tool steels with high Si content was observed to have a complex structure comprising α -phase and granular phase zones in addition to the boronized layers of FeB and Fe2B. The formation mechanism of the structure was studied by X-ray diffraction analysis and EPMA. The results obtained were as follows.
(1) Si was concentrated beneath the boronized layer through B impregnation, resulting in the transformation of the γ -phase into an α -phase.
(2) Granular phases of M23(C, B)6 composition were observed in the α -phase and the matrix adjacent to it. B content was higher in the former, while C content was higher in the latter.
(3) An α -phase was observed even in the boronized tool steel with low Si content. But, it was granular in shape and small in size.
(4) Elements such as Ni and Co were concentrated towards the boronized layer, while Cr, Mo, V and Mn were diluted.
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