Boro-austempering treatment of high strength bainitic steels

High strength bainitic steels are considered potential candidates for the 3rd generation of advanced high strength steels (AHSS). The main characteristic of these steels is the presence of carbide-free bainite, obtained by low temperature austempering. Silicon alloying is critical in that regard, suppressing cementite formation. Salt bath boriding is an effective method for increasing wear resistance and provides high corrosion resistance. The combination of these two treatments is called boro-austempering and is a promising alternative for increasing the wear resistance of AHSS. In the present work, samples were borided at 900 °C for 2 hours, direct cooled from that temperature, and isothermally hold in salt bath at 360°C for 1 and 3 hours. The substrate and the layers produced were characterized by optical (OM) and scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers microhardness (HRV) and microadhesive wear tests. The tribological characteristics of the layers were compared with those of the substrate. The microscopy analysis showed the effectiveness of boro-austempering treatment in the production of carbide-free bainite microstructure and boride layers on the surface. As a result, there was a substantial increase in surface wear resistance when compared to the substrate.