36  Prakt. Met. Sonderband 38 (2006) 
EBSD maps of the microstructure are shown in Figure 5, in which (a) is the grain boundary and subgrain 
boundary misorientation map and (b) is the gray scale image quality map. It is observed that the grains 
with interior subgrain boundaries always have relatively lower 1Q values compared to those without 
subgrains. The ferrite types formed at low temperatures, e.g. non-polygonal, acicular and bainitic, have a 
higher degree of lattice distortion and a larger density of subgrain boundaries. Even for the grains 
without subgrain boundaries, the IQ values vary noticeably from one grain to another. This variation of 
IQ values implies a difference in lattice imperfection, e.g., dislocation density, which is very much 
determined by the mechanism and temperature of formation of the ferrite type. Consequently, the 
differentiation of 1Q values caused by the lattice imperfection serves to identify the different types of 
ferrite. 
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Figure 5: EBSD maps of the HSLA steel hot band microstructure shown in Figure 2. 
(a) The grain boundary and subgrain boundary misorientation map, where the thick curves are for grain 
boundaries with misorientations larger than 15° and the thin curves are for those from 2° to 15°, 
(b) The gray scale image quality map of the identical area of (a). 
The result of applying the multi-peak model to the microstructure presented in Figure 2 is shown in 
Figure Figure 6. A total of five normal distribution peaks is summed up and the difference from the 
experimental data curve is around 1.7 pct. Because the traditional classification of ferrite is mainly based 
on the visualized grain morphology and the IQ method relies on the lattice imperfection, the 
correspondence of the multi-peaks in Figure 6 to the particular ferrite types is based on two assumptions. 
The first assumption is that each component of the final microstructure has its own, individual 
characteristic peak in the IQ distribution curve. The second is that the mean value for each IQ peak 
decreases with falling transformation temperature or increasing lattice defect density of each type of Th 
ferrite. Thus, some correspondence of the microstructural variation and the IQ distribution curve may be S 
possible, as indicated in Figure 6. nie 
recry: 
The IQ analysis itself is a method of characterizing microstructures based on a 3-D view of lattice pot 0 
imperfection, as opposed to the traditional analysis based on 2-D surface visualization. show