Correlation between microstructure, hardness, wear and electrochemical behaviour in 8.0%, 16.0% and 20.0% (by wt) chromium white irons

Microstructures, hardness, wear and corrosion behaviour of high chromium white irons with 8, 16, and 20 wt% chromium have been compared. In all the alloys, the matrix microstructure contains pearlite, martensite and retained austenite in varying proportions, while the carbide content increases from 26 vol% in alloy1 to 42 vol% in alloy2 and then to 57 vol% in alloy3. Presence of all these phases has been confirmed by XRD and SEM studies. EDS analysis confirms the formation of duplex carbide made of M3C shell around M7C3. The hardness (macro and micro) increases with the increase of chromium in the alloys. The wear of the alloys at 19.6N and 49.0N load produces closely spaced wear tracks with evidences of oxidation, edge-chipping, cracking and delamination of oxide layers. The higher chromium content of alloy 2 and 3 causes more oxidation of the worn surface under frictional heat developed during wear tests. At low wear load alloy 2 and 3 show better wear resistance, while at higher load alloy3 behaves at par with Ni-hard IV. Alloy3 appears to be most corrosion resistance exhibiting a wider passive range and with lower corrosion current density (icorr) than that of alloys 1 and 2.