A comparative study on gray and nodular cast irons surface melted by plasma beam

In this study, gray cast iron (GCI) and nodular cast iron (NCI) were surface melted by plasma beam to remove the negative effect of the near-surface graphite phases. Afterward, the modified surfaces were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that the molten surface had no pores and cracks, composing of inter-dendrites and eutectics with a hypereutectic structure. The cross section micro-hardness as well as the depth of the molten surface was measured. Cementite, martensite, and retained austenite co-existed in the molten surface, improving the micro-hardness from about 315 HV0.1 of the substrate specimens to an average of 1004 HV0.1 and 933 HV0.1 of the molten surface on GCI and NCI specimens treated at the main arc current 55 +/- 0.5 A, respectively. Generally, the depth of molten surface on the treated NCI specimen was deeper than that on the treated GCI specimen under the same plasma parameters. Besides, the molten surface on the treated NCI specimen had lower mean surface roughness (Ra) under the same plasma parameters owing to the different graphite shape in cast irons. At the main arc current 55 +/- 0.5 A, the mean surface roughness of the treated GCI was 153 +/- 5 mu m, while that of the treated NCI was 83 +/- 4 mu m. (C) 2013 Elsevier Ltd. All rights reserved.