Control of Thickness and Microstructure of Surface Alloyed Layers on Mild Steels During Sand Casting

In this study, the ability to control the thickness and composition of surface alloyed layer on mild steel (produced by coating the surface of the mold with metal powders) has been demonstrated. The surface alloying process was conducted during lab-scale sand casting by coating the mold surfaces with slurries containing Ni, Cr, Fe-Si, and Fe-Mn as alloying powders. Two different compositions of surface alloying powders were tested for their level of enrichment and effect on the properties of Wrought Carbon Grade B (WCB) steel. The powder quantity per unit area of mold surface was varied to control the thickness of the surface alloyed (SA) layer between 1000 and 4000 microns; the thickness varied linearly with the amount of powder per unit area. The microstructure, composition, and phases of the alloyed layers were characterized for a few selected samples. The presence of austenite, ferrite, and limited chromium oxide was observed in the surface alloyed layers by x-ray diffraction (XRD). Limited testing of surface alloyed samples showed an increase in the hardness and corrosion resistance as compared to WCB steel substrate. These improved properties can lead to an increase in the life of the cast components with a minimal increase in the production cost.