A Correlative Approach for Identifying Complex Phases by Electron Backscatter Diffraction and Transmission Electron Microscopy

Abstract

A new method was introduced to distinguish the ferrite, bainite and martensite in transformation induced plasticity (TRIP) steel by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). EBSD is a very powerful microstructure analysis technique at the length scales ranging from tens of nanometers to millimeters. How ever, iron BCC phases such as ferrite, bainite and martensite cannot be easily distinguished by EBSD due to their similar surface morphology and crystallographic structure. Among the various EBSD-based methodology, image quality (IQ) values, which present the perfection of a crystal lattice, was used to distinguish the iron BCC phases. IQ values are very useful tools to discern the iron BCC phases because of their different density of crystal defect and lattice distortion. However, there are still remaining problems that make the separation of bainite and martensite difficult. For instance, these phases have very similar IQ values in many cases, especially in deformed region; therefore, even though the IQ value was used, it has been difficult to distinguish the bainite and martensite. For more precise separation of bainite and martensite, IQ threshold values were determined by a correlative TEM analysis. By determining the threshold values, iron BCC phases were successfully separated.

Reproducible Quantification of the Microstructure of Complex Quenched and Quenched and Tempered Steels Using Modern Methods of Machine Learning

“…In addition, the IQ can be used to compare local dislocation densities qualitatively. Thus, this information can provide further evidence for an assignment to the ground truth [24,25]. Due to the displacive forming mechanism, martensite exhibits the highest misorientations, as well as the highest density of dislocations.…”

Microstructural Characterization of a 1200 MPa Complex-Phase Steel

“…Their microstructure may contain ferrite (intercritical and non-isothermal), bainite (including upper, lower, degenerated, granular and acicular), martensite, retained austenite and, in some cases, pearlite, making it hard to quantify without using several complementary characterization techniques. Therefore, combinations of light optical microscopy (LOM) 15 and electron backscatter diffraction (EBSD) [16][17][18][19][20][21][22][23] were used here for reliable quantification of microconstituent volume fractions.…”