Date of Award


Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Materials Science and Engineering (MS)

Administrative Home Department

Department of Materials Science and Engineering

Advisor 1

Paul Sanders

Committee Member 1

Matthew Enloe

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.