Corrosion behaviour of an alloy formed by inductive melting of a cobalt-based alloy and AISI 4140 steel

A bimetal of Co-based alloy/AISI 4140 steel was fabricated by induction melting. The microstructure of the Co-based alloy was examined and the influence of on the alloy of acid solutions, the temperature of these solutions, and the immersion time was investigated. The results show that the microstructure of Co-based alloy consisted of a Co-rich phase, a Cr-rich phase, and W3CoB3. In a solution of 20% HCl and 6% FeCl3, the Co-rich phase was attacked to form porous channels but transformed to a Si-rich passivation film to prevent further attack in the solution of 72% H2SO4. Therefore, the relative corrosion resistance of Co-based alloy to acid solution is 72% H2SO4 > 20% HCl > 6% FeCl3.