Boro-tempering of ductile iron

In this study, effects of three different heat treatments on micro structuralcharacterization of unalloyed ductile iron have been investigated. Boronizing,borotempering and austempering heat treatments were carried out on impact andcorrosion samples. Heat treated samples were subjected to impact and corrosion ofacidic medium (H2SO4) tests. Microstructural characterization of the heat treatedductile iron was carried out by using optical microscopy, scanning electronmicroscopy and X-ray diffraction analysis. The thickness and hardness of boridelayers were measured by optical microscopy and Micro-Vickers hardness tester,respectively. The corrosion rates have been determined by Tafel extrapolationmethod.Examination results show that the boride layer on the boronized and boro-tempered ductile iron contain FeB -Fe2B and globular graphite and the layer has adenticular morphology. The thickness of boride layer increases with boronizingtime but not affected by the cooling rate after boronizing treatment. The corrosionresistance of ductile iron increases with increasing boronizing time and temperingtemperature. Boro-tempering brings the material higher surface hardness than thatof standard ductile iron and austempered ductile iron. In addition, it causes to thehigher impact toughness and corrosion resistance than that of standard ductileiron. Consequently, boro-tempering heat treatment gives the optimum propertiesto ductile iron.Keywords: Ductile iron, boronizing, boro-tempering, austempering, impacttoughness, corrosion.