Date of Award
Master of Science
Pradeep K. Rohatgi
Ben C. Church, Nathan P. Salowitz
At times, the surface properties of an engineered component must be improved or enhanced when compared to the bulk of the component. Thus, various methods of surface alloying, one of the most important surface engineering processes, have been studied and developed for the decades. This study is concerned with the modification of the surface of WCB plain-carbon steel to improve corrosion and wear resistance of components used in the fresh water industry. The objective is to create a corrosion and wear resistant surface on an engineered component by enriching the surfaces with nickel or nickel and chromium, while the bulk of the component is composed of cheaper plain-carbon steel.
A unique, novel method for surface alloying has been created in this study, which involves the incorporation of metal powders of selected size into a slurry using a binder. This slurry was coated onto traditional sand cores prior to pouring the molten steel to produce the castings. The cores are placed in a sand mold, and the plain-carbon steel is cast, fills the mold, and comes in contact with the core, melting the alloying elements and rapidly solidifying them on the surface of the casting. Once solidified, the surface of the casting is expected to be enriched by with nickel or nickel and chromium on the surface.
Maynard Steel Casting Company in Milwaukee, WI assisted the project by casting the steel samples, and various UWM experiments were conducted using an induction coil capable of melting steel. Once the samples were prepared so that the cross-section of the WCB steel with the enriched layer could be analyzed, various analytical tests were conducted to demonstrate surface enrichment. Optical microscopy was used to view the quality and measure the depth of the surface layer, as well as to analyze the microstructure. The average thickness of the enriched layer for the successful trials was 339μm. An SEM was used to provide quantitative chemical analysis of the samples, which showed a chemical composition on average of 19% chromium and 7% nickel, with an iron balance. X-ray diffraction was used to investigate the phases present in the surface, which showed the presence of austenite and ferrite, similar to the diffraction pattern of CF3 stainless steel. Microhardness tests show that the surface has an average hardness of 484 HV500, while plain-carbon steel has a hardness of 155 HV500, indicating a greater wear resistance for the enriched surface. The rate of corrosion of the surfaces enriched with nickel and chromium showed a range of 0.066 – 0.087 mm/yr, while typical plain-carbon steel showed a rate of 0.609 mm/yr, indicating the enriched surface is 10.8 - 14.0 times more corrosion resistant than the base steel. This indicates that surface enrichment has occurred during this casting method, and the wear resistance increased as well as the corrosion resistance.
Beining, Michael, "Surface Alloying of Plain-carbon Steels During the Casting Manufacturing Process" (2017). Theses and Dissertations. 1584.