Dissolution Behavior 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 phenomenon of steel dissolution in acidic solution has been reported on carbon steel and stainless steel, little is known about the dissolution behavior of dual phase steel. Moreover, the resulting surface morphology after pickling could compromise the adhesion performance of Zn coating at the electrogalvanizing line (EGL). A fundamental study was undertaken to understand the dissolution behavior of dual phase steel in acid. The results show that the dissolution kinetics are strongly influenced by pickling conditions and steel microstructure. The study suggests a different dissolution mechanism for dual phase steel in hydrochloric acid (HCl) and sulfuric acid (H2SO4). Non-uniform dissolution in HCl was observed for dual phase steel in which the ferrite phase dissolved faster than the martensite phase. The preferential dissolution of the ferrite phase in dual phase steel could be attributed to the higher dissolution rate of the ferrite phase than the martensite phase due to its lower activation energy for dissolution, and the galvanic couplings formed between the ferrite phases and adjacent martensite phases.