BENEFICIAL EFFECT OF CU CONTENT AND AUSTEMPERING PARAMETERS ON THE HARDNESS AND CORROSION PROPERTIES OF AUSTEMPERED DUCTILE IRON (ADI)

The effect of copper content (0.031 wt.% Cu, 0.32 wt.% Cu, 0.51 wt.% Cu and 0.91 wt.% Cu) on the hardness and corrosion properties of ADI was investigated. Samples austenitization were carried out at 850 degrees C for 60 min followed by its austempering at temperatures from 250 degrees C to 420 degrees C for different time (30 to 60 min) in 50% (KNO3 + NaNO3) salt bath. It was concluded that hardness rises with copper content but decreases with higher austempering temperatures and times. The corrosion properties of the samples with minimum and maximum Cu content were investigated by electrochemical methods in 0.5 M NaCl solution. Samples with a higher copper content have shown higher values of polarization resistance (Rp) and lower values of corrosion current (icorr). After polarization measurements, corroded surfaces were analyzed with SEM/EDS analysis.