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will never exist if
T
p
2
≅
780°C. Bainite in both double-cycle HAZs is formed at shorter
∆
t
8/5
than in CGHAZ (Fig. 6–left). Smaller portion of ferrite is already present at much
higher cooling rates than in the case of CGHAZ. All this is reflected in Vickers hardness
of formed HAZs (numbers in circles). The obtained CCT diagram that corresponds to
T
p
2
≅
780°C is valid only for the retransformed part of the former CGHAZ. The rest of
microstructure is tempered former single cycle CGHAZ.
320
195
218
Figure 6. Continuous-cooling-transformation (CCT) diagrams valid for CGHAZ of two steels:
HSLA steel Nionicral 70 (left) and StE 355 Ti, fine-grained steel, microalloyed with Ti (right)
Figure 7. Continuous-cooling- transformation (CCT) diagrams valid for different double-cycle
heat-affected-subzones close to fusion line of HSLA steel Nionicral 70. Due to differences in peak
temperatures
T
p
2
the microstructures are not the same.
359