Doctoral Dissertations

Keywords and Phrases

Adaptive machine learning; Continuous-cooling-transformation; Microsturcture; Modified Gaussian approximation; Optimization; Time-temperature-transformation

Abstract

Evolution of microstructures, such as polygonal ferrite, acicular ferrite, bainite, and martensite, plays a pivotal role in determining the final microstructural and mechanical properties of steel products. Given the established inter-relationship between processing parameters, microstructure, properties, and performance, precise control of phase transformation is essential to achieve pre-determined properties. To understand transformation routes in different steel grades, time-temperature-transformation (TTT) and continuous-cooling-transformation (CCT) diagrams are necessary and can be described using the Johnson-Mehl-Avrami-Kolmogorov equation and Scheil’s additivity rule. This study presents a comprehensive computational framework for predicting and optimizing microstructure and mechanical properties in advanced high-strength steels (AHSS) using adaptive machine learning, supported by experimental validation. In Part 1, a machine learning model was developed to predict bainite formation under three cooling rates using the Linseis DIL L78 dilatometer. JMatPro-generated bainite TTT diagrams were used as precursors and refined to experimental data through a bisection optimization method. Part 2 focused on predicting polygonal and acicular ferrites formation across five cooling rates. Modified Gaussian approximation method was used to generate TTT diagrams, while neural network autoencoders enabled conversion of CCT into TTT. In Part 3, mechanical properties were evaluated using a modified rule-of-mixture approach. Hardness measurements obtained from a Struers hardness testing system under five cooling conditions were used to develop predictive models based on three key parameters, ideal hardness, apparent hardness, and phase volume fraction.

Advisor(s)

Chandrashekhara, K.

Committee Member(s)

Okafor, A. Chukwujekwu (Anthony Chukwujekwu)
Buchely, Mario F.
O'Malley, Ronald J.
Corns, Steven

Department(s)

Mechanical and Aerospace Engineering

Degree Name

Ph. D. in Mechanical Engineering

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2026

Journal article titles appearing in thesis/dissertation

Paper I, found on pages 13–33, has been published in Iron and Steel Technology Journal.

Paper II, found on pages 34–77, has been submitted to Ironmaking and Steelmaking Sage Journal.

Paper III, found on pages 78–96, is intended for submission to Journal of Materials Engineering and Performance.

Pagination

xiii, 103 pages

Note about bibliography

Includes_bibliographical_references_(pages 101-102)

Rights

© 2026 Henry Adekola Haffner , All Rights Reserved

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 12594

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