PROCESSING AND CORROSION BEHAVIOUR OF DUAL PHASE STEELS

Abstract

Intercritical annealing treatment is used to develop dual phase steels. Different annealing times followed by water quenching are employed to obtain different volume fractions of martensite in the microstructure of resulting dual phase steels. Corrosion behaviour of dual phase steels with varying martensite volume fractions is studied using potentiodynamic polarization technique, weight loss measurements, and salt spray testing. The corrosion behavior in 3.5% NaCl solution has been compared to that of ferrite-pearlite steel. At low volume fractions of martensite (16.4%) the corrosion rate is lower than that of normalized steel. It is observed that with increase in martensite volume fraction the corrosion rate of dual phase steels increased. Steel with nearly fully martensitic microstructure exhibited corrosion rate close to DP steel with low martensite volume fraction and better than normalized steel. Salt spray tests and weight loss measurements confirmed the results of potentiodynamic tests.