Abstract:
This paper presents the results of an investigation on the effects of tempering temperatures on the corrosion
susceptibility of 0.42%C (medium carbon). Heat treatments were carried out on prepared samples in stages.
The first was austenitizing the samples followed by quenching and then tempering at 250?C, 350?C, 450?C,
550?C with holding time of 30minutes and with un-heat treated one. All specimens were prepared for
electrochemical test in NaCl solution and metallographic study of the samples was also done. The open circuit
potential (OCP), corrosion test and polarization resistance measurement were carried out to determine the
rate of corrosion. The 550?C tempered sample has lower corrosion rate of 0.5 mm/yr than samples tempered
at 450?C, 350?C and 250?C, which demonstrated that, the corrosion resistance of tempered 550?C sample is
higher than other samples. The result also showed a decrease in corrosion current ICorr (-20.582 to -3.722)
?A during the potential sweep from the least tempered specimen to the highest, micrographic images also
revealed presence of cementite precipitate in the tempered martensite which became coarse as the tempering
temperature increased. |
