Effect of microstructures on corrosion and erosion of an alloy steel gear pump

Investigation on an alloy steel gear-pump has been carried out to understand the effect of microstructures on corrosion and erosion behavior of the material. The alloy tool steel gear pump was designed to replace an existing pump made of grey cast iron to increase the service life to 7–8 years from 4–5 years. However, the new pump, used for dispensing hot adhesive polymer at 170 C and 8 bar pressure, was damaged due to pitting corrosion within one year of service. Local galvanic cells were formed between M23C6 carbides and martensite matrix of steel plate of the pump in presence of sulfide ions sourced from liquid adhesive followed by anodic dissolution of martensitic matrix surrounding the carbides. As a consequence, hard carbide particles were dislodged and facilitated the pump to undergo wear rapidly.