2009 年 50 巻 6 号 p. 1440-1447
Corrosion behaviors of DP-type and TRIP-type cold rolled steel sheet have been investigated using cathodic Tafel extrapolation test and immersion test, measuring nano-scale hardness of various phases and the volume fraction of various phases, and analyzing inclusion and nitride. Based upon nano-scale hardness of various phases before and after potentiodynamic anodic polarization test in deaerated 5 mass% NaCl at 35°C, the phase with the most inferior corrosion resistance in DP-type steel is martensite (α′) and that in TRIP-type steel is bainite (αB). The reasons why corrosion rate of TRIP-type steel is lower than that of DP-type steel are first, the volume fraction (39.8 vol%) of bainite (αB) in TRIP-type steel is higher than that (15.9 vol%) of martensite (α′) in DP-type steel and second, the corrosion resistance of oxide and nitride formed in TRIP-type steel is more than that of sulfide formed in DP-type steel.
