Thesis Title: USING FDM AND FEM TO SIMULATE THE DECARBURIZATION IN AISI 1074 DURING HEAT PROCESSING AND ITS IMPACT

Abstract:  The science of metallurgy has a history almost as long as human civilization itself. A great variety of metals and metallic alloys at different stages have become the very cornerstone on which our society is based, since the inception of this ancient yet vibrant discipline.

        However, computational metallurgical mechanics remains elusive largely owing to the disconnect between the modern computational approaches and the complexity of most metallurgical topics. Just tapping into one of the most discussed metallurgical phenomena, decarburization, the work presented in this thesis summarizes the research conducted on quantifying the progression of decarburization and its impact on the mechanical properties of steel samples.

        The topics researched in this work serve, but are not limited to, the production of hollow metal proppants used for underground oil and natural gas reserve extraction, including calculating the progression and the impact of decarburization that occurs during the heat processing of steel in a time-dependent fashion and modeling the deformation behavior of a maraging steel hollow sphere. Then the decarburization model is modified to relate the overall mechanical properties of the impact-resistant Mg/Al/maraging-steel-hollow-sphere composite material to its microstructure.

        As much as 95% by weight of all metal produced worldwide is steel. In order to obtain higher strength and eliminate residual stress, steel is heated to high temperatures to allow for homogenization followed by heat treating at a variety of temperatures and times to enhance the overall mechanical properties. However, decarburization, commonly known as the loss of carbon to the environment due to  its reaction with the atmosphere, will occur and result in considerable strength loss. To avoid potential dangers such as reduced static and fatigue properties, the mechanical property variations must be determined with respect to the heat treatment temperature and time. This work also outlines the procedures used to quantify the effects of processing temperature on the microstructure. These effects include average particle size, particle volume fraction, void and porosity. Once completed, the deformation behavior of the maraging steel hollow spheres is investigated in the subsequent work to visualize the stress environment in which the proppants would function. To further the effort, the hollow maraging steel spheres are cast into Mg/Al alloy matrix and the properties of the resulted impact-resistant composite material are simulated loosely based on the microstructure model established for the decarburization process.

        Modeling makes it economically practical to assess the targeted materials' overall properties, behaviors and the mechanical responses in conjunction with stress environment, material dimensions (sphere size, sphere wall thickness, etc.) among other variables, before a structure is built. Additionally, more advanced modeling can enable the quantitative descriptions of more complex metallurgical phenomena such as the effects of impurity elements, geometric changes of the second-phase particles, and deformation under complex loading situations.