Evaluating the mechanical behavior of electrochemically borided low-carbon steel

In this study, mechanical properties of borided low carbon steels were investigated with different testing methods namely tensile, Erichsen cupping and three-point bending tests along with fracture toughness and hardness measurements. For boriding, a new electrochemical based boriding called as CRTD-Bor (Cathodic Reduction and Thermal Diffusion based boriding) was chosen. The main advantages of CRTD-Bor are its high boride growth rate and its environmentally friendly nature. Cross-sectional scanning electron microscope inspections along with thin film X-ray diffraction analyses confirmed the fast boride layer formations (i.e. about 40 μm thick Fe₂B layer in 5 min). On the other hand, some mechanical degradations were observed on the borided substrates such as decrease in yield and ultimate strength values. However, the improvement of flexural stress were detected which reached to 2.5 times higher after 30 min of boriding. The fracture toughness values were found as 0.44 MPa·m^1/2, 1.34 MPa·m^1/2 and 3.7 MPa·m^1/2 for sole FeB, the interphase of FeB/Fe₂B and Fe₂B regions, respectively. Furthermore, the surface hardness of borided steels was measured around 1400 HV which exhibited excellent adhesion to the substrate as long as the boride layer composed of single Fe₂B.