Investigating the morphology and corrosion behavior of electrochemically borided steel

In this study, the boriding of steels by molten salt electrolysis in borax-based electrolyte at various current densities (50-700 mA/cm²), temperatures (800-1000 °C), and time (0-2 h) was investigated. The optimum condition was determined by taking the thickness, hardness, and morphology of the boride layer into account. Different borided phases can form depending on the amount of the diffused boron from surface to matrix as follows: FeB_x(x > 1) ⇒ FeB ⇒ Fe₂B ⇒ Fe₃B ⇒ Fe_yB(y > 3) ⇒ Fe. Determination of the optimum conditions for the boriding of DIN EN 10130-99 DC04 low carbon steel are; 10% Na₂CO₃ + 90% Na₂B₄ O₇, 900 °C, 1 h, and 200 mA/cm². The corrosion tests for the given material were carried out in different media; HCl, H₂SO₄, HNO₃, H₃ PO₄, and HClO₄ (10%, vol.). Electrochemically borided low carbon steel showed a corrosion rate of 0.66 × 10^-3 g/cm²/day in HCl, 1.13 × 10^-3 g/cm²/day in H₂SO₄, 1.59 × 10^-3 g/cm²/day in HClO₄, and 3.37 × 10^-3 g/cm²/day in H₃ PO₄. However, it was not resistant to HNO₃ with a considerable corrosion rate of 0.3 g/cm²/day.