Prakt. Met. Sonderband 38 (2006) 35 
hardening In a recent series of studies, a technique based on EBSD image quality (IQ), as defined by the elastic 
d strength, distortion of the diffracted intensity associated with the Kikuchi bands, has been used to identify and 
en level of quantify the different types of ferrite, found in complex microstructures, and varying in intrinsic 
hrough the dislocation density.[17] In this technique, IQ values are determined from each grain in the analyzed area 
),14] using of the sample and IQ values from the grain boundary regions are eliminated. The resulting, corrected 
values are then normalized such that all IQ values fall between zero and 100. This total histogram of 
corrected and normalized values is then de-convoluted into multiple peaks, where the number of peaks 
identifying represents the number of types of ferrite contributing to the total. This is called the Multi-peak analysis 
observed in or model. In the final analysis, the area under a given peak represents the amount of that particular 
Ss approach phase and the location of the peak on the IQ axis (abscissa) gives the peak IQ value or an index of the 
anced high dislocation density for that particular phase or microconstituent. 
) annealing 
grains, and Application of the New IQ Technique 
As-Coiled Microstructure of High Strength Low Alloy (HSLA) Steel Hot Band 
In a recent study of the origins of variability of strength in the hot strip mill processing of 0.08C-1.4Mn- 
ing at least 0.038Nb-0.050V HSLA steel with a yield strength near 490MPa, it was found the final microstructure 
errite, (iii) was strongly influenced by the finishing and coiling temperatures. An example of these results is shown 
>-cementite in Figure 4,[18] which shows the influence of finishing and coiling temperatures on the final 
systematic microstructure, as qualitatively described by optical microscopy. One such microstructure was shown 
sformation above in Figure 2 for low temperature finish rolling and low coiling temperatures, and it is clear that the 
e go from final microstructure is a mixture of several different types of ferrite. The corresponding EBSD analysis 
olygonal to of the specimen used for Figure 2 are presented in Figures 5 and 6, where Figure 5 shows the 
ing of the distribution of grain boundary misorientations and IQ in terms of gray scale, and Figure 6 shows the 1Q 
nuch. non- analysis using the multi-peak model. For a complex microstructure like this, the visual identification of 
the ferrite types based on the morphological descriptions might be possible, but any quantitative 
measurement is extremely difficult, if not impossible. It is therefore nearly impossible to get an accurate 
measure of the volume fractions of the various types of ferrite present by using any of the traditional 
microstructural analyses in complex microstructures. 
Fok Fot Fy +P Fare, F +P FP Poti 
A FF. F.7FC FFs Fu+Fa+C 
550 a = = - = = 
High Reheating, High Roughing High Reheating, Low Roughing 
' FaP F +F +P F +P F +P F+F 
. 650 m = = a = = 
EE, +P Fu+F,+(P) FutFa+C F.+P F AF, tC 
R57 = w = = = = 
Low Reheating, High Roughing Low Reheating, Low Roughing 
FY es0 1007 gor "980 1000 
Finishing Temp (°C) 
Figure 4: Mapping of the phase mixtures for different reheat and 
3C.[16] roughing temperatures in CT- FT space. Hot-rolled Nb+V steel.[18]