Dissolution Behaviors of Dual Phase Steel during Pickling

Dual phase steels have been widely used in the automotive industry to produce lighter weight vehicles to meet stringent safety and fuel economy regulations. While the phenomena of steel dissolution in the acidic solution have been reported on carbon steel and stainless steel, little is known about the dissolution behavior of dual phase steel, which could compromise the coating adhesion performance in the subsequent electrogalvanzing line (EGL) or continuous galvanizing line (CGL). A fundamental study was undertaken to understand variables that could affect dissolution of dual phase steel in the acidic solution. The results show that the dissolution kinetics is strongly influenced by temperature, acid concentration and the steel microstructure. Different dissolution mechanism is observed in HCl and H 2 SO 4 . Dual phase steel displays a non-uniform dissolution behavior of which the ferrite phase dissolves faster than martensite phase. This selective dissolution phenomenon could be attributed to galvanic corrosion between ferrite and adjacent martensite phase and a higher resistance of martensite phase to dissolution than ferrite phase.