Modern Tools for Understanding Steel Heat Treat Metallurgy

Historically, steels or other metals were heat treated by annealing or hardening to achieve a desired hardness level. For structural applications, tensile tests, impact tests, fatigue tests and fracture toughness tests were developed to better characterize the mechanical performance. All of these properties are achieved as a result of microstructural changes caused by changes in chemical composition and solid state processes including heat treatment. Parallel to mechanical property improvements, methods to understand the microstructural changes have increased dramatically over the past decades. Basic light optical metallography (LOM) has given way to techniques like advanced electron microscopy (SEM, EBSD, TEM, etc), advanced x-ray techniques (SAXS and WAXD), Mossbauer spectroscopy, Auger spectroscopy, secondary ion mass spectrometry (SIMS), precise ion beam sectioning (FIB), and atom probe tomography (APT). This presentation provides a simplified overview of what some of these techniques are and how they are used to reveal the microstructural changes at scales far smaller than the resolution of LOM.