Effect of composition and microstructure on the rusting of MS Rebars and ultimately their impact on mechanical behavior

Abstract

Rebar steel is used for reinforcement to aid concrete because concrete does not sustained tension. Thermo-mechanical treatment (TMT) is an advanced manufacturing technique for rebar production but rusting problems emerged at local steel industry. Raw material sampling included ingot casting (IC) & continuous casting (CC). IC samples corroded more frequently than CC samples. Spectroscopy indicated small chromium and improper ratio of manganese to sulphur in IC samples. Improper ratio of manganese to sulphur in IC samples promoted hot cracking at grain boundaries, which results in intergranular corrosion. The microstructural results of G40 (air cooled) and G60 (water cooled) shown ferrite and martensite in different proportion. The deformed ferrite in G60 indicates inclination to corrosion and no proper stable layer of martensite was found. Percentage of martensite was not enough to retaliate intergranular corrosion. Highly pressurized water initiated pitting corrosion due formation of small pits on surface. Tensile testing revealed 10% reduction in ultimate strength, 8% reduction in yield strength and 30% reduction in percent elongation of corroded samples. The environmental study revealed that humidity level of industry was greater than the laboratory space. High values of Sox and Nox emission telltale the involvement of environment in deterioration of product surface.