Date of Award
Open Access Master's Thesis
Master of Science in Materials Science and Engineering (MS)
Administrative Home Department
Department of Materials Science and Engineering
Committee Member 1
Committee Member 2
Erico T. F. Freitas
Strength uniformity along the coil length of commercially produced high-strength, low-alloy (HSLA) steel hot-rolled sheet is crucial to avoid the downgrading of product that does not meet strength specifications. In addition to contributing to precipitation strengthening through the growth of niobium-titanium carbides ((Nb,Ti)-C), niobium hinders austenite recrystallization and refines ferrite grain size. The potency of these strengthening mechanisms relies heavily on the austenite to ferrite transformation kinetics of the hot-rolling process. While niobium’s effect on precipitation strengthening, Hall-Petch strengthening, dislocation strengthening, and solute strengthening have all been studied in literature independently, the interactions of these mechanisms with each other and coiling temperature in a commercial production setting is not completely understood. The strengthening behavior of niobium microalloyed HSLA steels compared to a non-niobium HSLA steel is quantified and correlated using commercially produced samples and a design of experiments with factors coil temperature and location on coil length. Hall-Petch grain size strengthening and geometrically necessary dislocation strengthening are determined from electron backscatter diffraction mapping. Orowan precipitation strength is quantified from image analysis of (Nb,Ti)-C precipitates captured on carbon extraction replica films using a scanning transmission electron microscope. Solubility of alloying elements in the ferrite matrix, and therefore solute strengthening, is calculated with Thermo-Calc. This study observed that niobium supported a trend of increased Orowan strength to balance the decrease in Hall-Petch strength that occurred as coiling temperature increased.
Jaszczak, Isabella M.W., "QUANTIFYING THE EVOLUTION OF STRENGTHENING MECHANISMS FOR COMMERCIALLY PRODUCED NIOBIUM AND TITANIUM HSLA STEEL SHEET", Open Access Master's Thesis, Michigan Technological University, 2023.