Mechanical properties and corrosion behaviors in 3.5% NaCl solution of grade-A and dual-phase steels welded by FCAW

Abstract

The first aim of this study is to demonstrate the transformation of Grade-A steel into dual-phase steel by heat-treatment at the chosen 730°C and 800°C intercritical temperature for 60 min followed by cold water quenching. The second aim of this study is to investigate the mechanical properties and the corrosion behaviours in 3.5% NaCl solution of Grade-A and dual-phase steels welded by flux-cored arc welding (FCAW). It was carried out the mass loss measurements and investigated the micro and macrostructures of welding zone using by optical microscope.

The present study has demonstrated that Grade-A ship steel consisting of ferrite and pearlite can be successfully transformed to the dual-phase steel at the chosen intercritical temperatures. The microstructure of transformed dual-phase steel consists of island of martensite in a ferrite matrix. The Grade-A and transformed dual-phase steels were successfully joined by FCAW. The mechanical results showed that the tensile strength of the transformed dual-phase steel were higher, but lower elongation than that of the Grade-A steel. The results from the immersion test in 3.5% NaCl solution showed that the corrosion behaviours of the dual-phase and Grade-A steels depend upon the morphology of the phase constituents. The corrosion rate of the transformed dual-phase steel with ferrite-martensite structure was lower than that of the Grade-A steel with ferrit- pearlite structure. The corrosion has preferential started at fusion line and progressed towards the heat affected zone (HAZ) of the welded dual-phase and Grade-A steels.