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: FeBx(x > 1) ⇒ FeB ⇒ Fe2B ⇒ Fe3B ⇒ FeyB(y > 3) ⇒ Fe. Determination of the optimum conditions for the boriding of DIN EN 10130-99 DC04 low carbon steel are; 10% Na2CO3 + 90% Na2B4O7, 900 °C, 1 h, and 200 mA/cm2. The corrosion tests for the given material were carried out in different media; HCl, H2SO4, HNO3, H3PO4, 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 H3PO4. However, it was not resistant to HNO3 with a considerable corrosion rate of 0.3 g/cm2/day.