Unraveling the Effect of Martensite Volume Fraction on the Mechanical and Corrosion Properties of Low-Carbon Dual-Phase Steel

The effect of martensite volume fraction on the mechanical and corrosion properties of low-carbon dual-phase steel is studied based on both step quenching (SQ) and intercritical annealing (IA) routes. For SQ samples, hardness and ultimate tensile strength decrease with increasing holding time at the intercritical temperature and reach a plateau, which is related to the decrease in the amount of martensite during annealing. Conversely, for the IA samples, hardness increases during holding at the intercritical temperature due to austenitization and reaches the same plateau. At a same martensite volume fraction, the work-hardening behavior of SQ samples is better than IA samples, which is related to both the finer grain size and smaller martensite islands in the former. At low martensite fractions, the corrosion properties are comparable with the as-received ferritic-pearlitic sample. It is revealed that by decreasing the volume fraction of martensite in SQ samples, the corrosion current density (i(corr)) decreases almost linearly, and at martensite content of zero, it reaches the i(corr) of the fully ferritic microstructure. The latter is found to be lower than the i(corr) of the as-received sample. Therefore, the real effect of martensite on corrosion properties is unraveled for the first time.