Papers by Keyword: Carbon Diffusivity

Abstract: Initiated by the need of industry for gas carburizing process control and optimization, this paper focuses on understanding the effect of the time, temperature and carbon potential on the mass transfer coefficient and carbon diffusivity in Austenite. A method for direct flux integration has previously been proposed to calculate these kinetic parameters from the experimental carbon concentration profiles. AISI 8620 steel discs were gas carburized at different levels of atmosphere carburizing potential for selected austenizing temperatures. Analyses of the carburized parts included experimental measurement of weight gain, surface carbon concentration and carbon concentration profiles. The time-dependent weight gain and surface carbon content measurements allowed calculation of the time average mass transfer coefficient, while carbon concentration profiles were used to calculate the concentration dependent carbon diffusivity for selected process parameters. Excellent agreement was found between the calculated mass transfer coefficient and carbon diffusivity values and those reported in the literature. The calculated values served as input in the previously developed carburizing model validating the predicted results by comparison with the experimental concentration profiles.

Abstract: Ti-V and Ti-Nb bake hardenable Ultra Low Carbon (ULC) steels are used to produce hot dip zinc coated steels for automotive applications. An important factor influencing the bake hardenability in such microalloyed ULC steels is the level of solute carbon available to diffuse for pinning dislocations during baking. The level of solute carbon must be controlled carefully during annealing of the steel in the ferritic region. Therefore, this paper summarizes highlights of research conducted to study the effects of chemical composition and annealing temperature (in the ferrite region) on the precipitation (or dissolution) of NbC and VC using a variety of Ti-Nb and Ti-V ULC steels. Carbon diffusivity is another factor that could also influence the bake hardenability through controlling the aging and baking kinetics. Therefore, the paper presents highlights of internal friction measurements performed to assess effects of microalloying elements (Nb,V) and some commonly used solid solution strengthening elements (Mn, P) on carbon diffusivity measured using the internal friction technique.