34 Prakt. Met. Sonderband 38 (2006) 
is often immediately attributed to precipitation hardening. In most cases, the precipitation hardening In a 
increment is calculated by assuming that the difference between the measured and calculated strength, distor 
based on grain size and solutes, is caused by particle hardening. However, this claim of a given level of quan 
precipitation hardening is almost never supported with independent verification, e.g., through the dislo 
combination of the application of the Orowan-Ashby precipitation hardening relationship[9,14] using of th 
inputs from solubility relationships and especially thin foil TEM. value 
corre 
The goal of this present paper is to describe what is considered a new and better method of identifying repre 
and characterizing the individual ferrite components in complex microstructures of the kind observed in or m 
high strength hot rolled strip or plate processed steels subjected to IAC with low WET. This approach phase 
can also be used in: (a) the analysis of multi-phase microstructures as found in the advanced high dislo 
strength sheet steels (AHSS) with dual-phase, TRIP and Complex Phase microstructures; (b) annealing 
studies where the IQ value is related to the level of recovery or recrystallization of individual grains, and App! 
(c) in heat affected zones of welds. 
As-C 
New Metallographic Technique based on EBSD Image Quality 
Ina: 
Modern MA steels subjected to IAC with low WET can exhibit a final microstructure containing at least 0.03; 
five distinct components: four types of ferrite: (i) polygonal ferrite, (ii) non-polygonal ferrite, (iii) was | 
acicular ferrite, (iv) bainitic ferrite, and (v) the complex microconstituent martensite-austenite-cementite in F 
(MAC). Although the types of ferrite differ from one another in many ways, the one systematic micr 
difference is in their own particular dislocation density, which increases with falling transformation abov 
temperature. Hence, the intrinsic dislocation density would be expected to increase as we go from final 
polygonal to non-polygonal to acicular to bainitic to martensitic. An example in going from polygonal to of tt 
acicular ferrite is shown in Figure 3.[15,16] Likewise, we would expect the line broadening of the distri 
Kikuchi peaks to spread and peak heights to fall in a similar fashion; polygonal ferrite not much, non- analy 
polygonal a little more, acicular more and bainite more still. the | 
meas 
° Equiaxed grains +1250 nea 
x Plate-like grains micr 
© Mean 
. 174 
3 { 
10" 78 
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He es eres eee] 75 
650 700 750 800 
Transformation Temperature, °C 
Figure 3: Dislocation densities as a function of transformation temperature. Fe-0.21Ti-0.08C.[16]