Prakt. Met. Sonderband 38 (2006) 37 
d subgrain oe —o— Experimental Data with GBR Filtered 
; the grains 0.16 ~Polygonal Ferrite 
se without Es 
itic, have a ; —- Bainitic Ferrite 
the grains 0.12 FE a Mieraconstituents 
7ariation of 5 01 
very much 8 
uently, the = 
nt types of 0.06 . 
R= 40.t 
0.04 234% 7 N \ 
0.02 by AF 10.8% A 
0 Lor, O=C—0 Novos OK) 
0- 10 20 30 40 60 60 70 80 90 100 110 
Normalized Image Quality 
Figure 6: The IQ analysis of the HSLA hot band microstructure shown in Figure 2 
using the Multi-Peak model. 
Microstructure of a Dual-Phase Advanced High Strength Steel After CGL Processing 
In this study, two low carbon dual-phase steels were hot rolled, cold rolled and intercritically annealed 
and further processed using a CGL simulation.[18,19] The steels had a composition of 0.06wt%C, 
1.5%Mn, 0.45%(Cr+Mo), and either 0.02 or 0.04%Nb, depending on whether 590 or 780 properties 
were expected. After cold rolling, the steels were heated to the intercritical annealing temperature, 
soaked and then cooled at different cooling rates to 460°C, held for various times and then quenched to 
RT. The final microstructure consisted of five contributions: (i) recrystallized ferrite formed from the 
cold rolled ferrite in the cold band, (ii) unrecrystallized ferrite from the cold rolled ferrite in the cold 
band, (iii) new ferrite that formed during cooling from the intercritically formed austenite, (iv) 
martensite that formed from the intercritically formed austenite, and (v) some undissolved NbCN 
inherited from hot band. Examples of these microstructures taken with SEM are shown in Figure 7.[19] 
> for grain 
o 15°. 
, shown in 
e from the 
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individual Figure 7: Typical SEM micrographs observed in both steels after the CGL simulation treatment. 
h IQ peak (a) BDP-580 3°C/s; (b) BDP-790 8°C/s (c) BDP-790 15°C/s. 
ch type of : ; : : 
ve may be The 1Q-Multi-peak analysis of these structures revealed three peaks, for recrystallized ferrite, for 
unrecrystallized ferrite and for martensite. Note that the unrecrystallized peak contains both the non- 
recrystallized cold rolled ferrite plus the new ferrite formed upon cooling from the annealing to the zinc 
of lattice pot or overaging temperature. The 590 DP steel microstructure is shown in Figure 8. This work has 
shown that the 590 DP steel exhibited about 19% martensite, Figure 8, while the 780 grade had about