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 silicon-alloyed steels is the presence of carbide-free bainite, obtained by low-temperature austempering. 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 to increase the wear resistance of AHSS. In the present work, samples were borided at 900 °C for 2 h, direct-cooled from that temperature and isothermally held in a salt bath at 360 °C for 1 and 3 h. The substrate and the layers produced were characterized by optical microscopy (OM), 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 microscopic analysis showed the effectiveness of boro-austempering treatment in the production of carbide-free bainite microstructure and the surface borided layers. As a result, there were increases in surface wear resistance up to 115% when compared to the substrate.