Corrosion resistant Cr-coating on mild steel by powder roll bonding

• Chromium coating on mild steel is formed by roll-bonding and annealing at 1200 °C.
• It uses pure Cr powder and 170–250 μm thick diffusion layer (~ 14% CR) is obtained.
• The coated surface shows similar passivation like 304 SS steel.
• Exaggerated grain growth of surface below coating is due to decarburization.
• The coated samples are highly bendable and coating is very adherent and strong.

Chromium powder coating on mild steel was developed by roll-bonding followed by annealing at 1200 °C for different duration in hydrogen atmosphere to promote diffusion bonding and finally furnace cooling. All the coated samples were characterised using scanning electron microscopy, electron probe micro analyser, bend test and potentiodynamic polarisation test in 0.2 N H2SO4 solution. Diffusion layer thickness was in the range of 170–250 μm depending on the annealing time, and the Cr content reached up to 13 wt% in the diffusion layer. Diffusion layer exhibited high ductility and adhesion, since no crack was observed even after 180° bending. The chromium coated mild steels showed comparable stable passivity and corrosion rates in 0.2 N H2SO4 solution as observed in a 304 stainless steel. The corrosion rate decreased from 5.51 mm/y for the uncoated mild steel to 0.2–1.0 mm/y for the coated mild steel sample.