Abstract
This research investigated the tribo-corrosion behavior of six experimental high chromium white cast iron (HCWCI) alloys, each cast in a 40 kg induction furnace with varying chemical compositions. The carbon content in the samples ranged from 1.95 – 3.41 wt.%, while the chromium content varied from 20.8 – 30.8 wt.%. The motivation behind this study was to examine the tribo-corrosion performance of these HCWCI alloys in synthetic mine water, with a focus on the combined effects of wear and corrosion.
The HCWCI alloys were subjected to tribo-corrosion testing using a ball-on-disc experimental setup. Electrochemical polarization was used to investigate the corrosion behavior, while microstructural characterization was carried out with optical microscopy and scanning electron microscopy (SEM). The phases present in the alloys were identified through X-ray diffraction (XRD). Micrographs revealed the presence of hypoeutectic (austenite phase), eutectic, and hypereutectic (primary M7C3 carbides) structures across the alloys. XRD confirmed the presence of austenite, M7C3 primary carbide, and M23C6 secondary carbide.
The hardness of the HCWCI alloys was found to be strongly influenced by their carbon content for fixed chromium content ranging from 306 to 539 (HBW30), with a direct correlation observed between hardness and wear resistance in the three-body dry abrasion wear tests. HCWCI –5 (2.41wt.% C and 30.10wt.% Cr) exhibited the least mass loss, attributed to its fully eutectic structure, which enhanced both hardness and abrasion resistance. The corrosion resistance of these alloys was primarily affected by the Cr/C ratio, particularly the concentration of free chromium in the matrix, which revealed the results of enhanced protective passive oxide film (Cr2O3). Corrosion rate ranged from 0.0105 mm/year for HCWCI –4 (2.01 wt.% C and 30.80 wt.% Cr) to 0.0656 mm/year for HCWCI – 1 (1.95 wt.% C and 27.70 wt.% Cr) and HCWCI –4 also showed the highest potential (most noble) and stabilized at a higher potential compared to the other alloys, also exhibiting the lowest corrosion current density of 0.553 μA, which indicated minimal corrosive attack in synthetic mine water. This behavior was linked to the higher Cr/C ratio 15.32 in HCWCI –4, which played a significant role in corrosion resistance by facilitating the formation of the passive oxide film.
Tribo-corrosion testing showed that the open circuit potential (OCP) of the HCWCI alloys remained stable initially due to the formation of a passive film but dropped significantly during sliding. HCWCI –6 (3.41 wt.% C and 30.10 wt.% Cr) exhibited the steepest decline in OCP,
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indicating greater susceptibility to localized corrosion under friction. After sliding, the OCP gradually increased, reflecting a re-passivation process that depended on the applied load. HCWCI –1 electrochemical noise was observed, indicating a higher susceptibility to localized corrosion during sliding, possibly due to de-passivation of the Cr2O3 oxide layer.
These findings highlight the critical importance of controlling the chemical composition, particularly the Cr/C ratio, to optimize the wear and corrosion performance of HCWCI alloys in tribo-corrosion environments.