| The aim of this experimental work is to find out the possibility of boronizing of spheroidal graphite cast iron (SGCI) in order to improve surface hardness and wear-resistivity. Samples with various silicon content were prepared in a Kryptol furnace and heat-treated to obtain the pearlitic or ferritic matrix. Liquid boronization in a molten bath containing borax, boron carbide and ammonium chloride was carried out with these samples having different silicon content and matrix. The boronized layer consisted of iron boride layer and boron-diffused layer, the former was mainly Fe₂B and the latter contained the precipitated phase of boro-carbides. The depth of the iron boride in the annealed matrix was increased to a certain extent rather than in the as-cast matrix, but its change with silicon content was not remarkable, Hardness of the boron-diffused layer was increased as the silicon content increases. In the case of high silicon content, graphite accumulated zone was formed beneath the iron boride layer, resulting in tearing off the iron boride layer. When as-cast structure containing cementite was boronized, elongated graphites appeared sporadically in the iron boride, causing the decrease of hardness. Both surface hardness and wear-resistivity of the boronized SGCI, except for high silicon contained, were improved remarkably. |
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