Dimensional and Crystallographic Tracking in Steels: A Lecture on Dilatometry, XRD, and Certified Lab Management

This lecture explores the fundamental principles of phase transformations in steels, focusing on how alterations in crystal structures dictate dimensional and volumetric changes. We will establish a foundational understanding of how atomic cells are modified by pure temperature effects, variations in chemical composition, and reconstructive or displacive phase transformations. To effectively capture and characterise these changes, the lecture will detail the complementary use of dilatometry and X-ray diffraction (XRD). First, we will examine how tracking dimensional expansion and contraction using high-resolution dilatometers allows us to calculate the Thermal Expansion Coefficient (TEC), identify critical transformation temperatures, and construct predictive Continuous Cooling Transformation (CCT) and Time-Temperature-Transformation (TTT) diagrams. Because dilatometry alone cannot provide the actual characteristics of individual phases within a microstructure, the lecture will seamlessly transition into XRD characterisation. We will cover practical XRD applications, including optimal radiation selection (such as using Co or Mo radiation to minimize fluorescence in steels), phase identification, and the rigorous analysis of peak broadening to evaluate microstrain, crystallite size, and dislocation density. Finally, the lecture will provide insights into the daily operations and management of the Phase Transformation Laboratory. We will discuss how the facility is run in strict compliance with ISO 9001:2015 quality management standards to guarantee precise, reliable, and standardized thermo-analytical measurements. This research is funded by the European Union under the RFCS project WarP – Grant Nº 101112425