Steels_ Metallurgy and Applications, Third Edition

Low-carbon strip steels 59

300

E

b,,,

200

9 ~ C loo

I I II I II I I I I Illlll

0 - - I I,

800 1000 1200

Tamp (~

Figure 1.62 Austenite grain-growth characteristics in steels contain various micro-alloy
additions (After Cuddy and Roley 9a )

1050

a....,

~1ooo

~ 950

~ 850

Nb

0.250

Initial solute content (atom per cent)

Figure 1.63 The increase in recrystallization-stop temperature with increase in the level
of micro-alloy solutes in a 0.07 C, 1.40 Mn, 0.25 Si steel (After Cuddy 99)

clear that the addition of niobium has the greatest effect, but with a much smaller
effect from titanium. Jonas l~176 has studied the effect of all three alloy additions
and has expressed the results in the form of the following equation:

Tstop = 887 -k 464C + (6445Nb - 644Nb 1/2) + (732V - 230V 1/2)

+ 890Ti + 363A1 + 357Si

As mentioned previously, the recrystallization characteristics of any steel
during hot rolling depend on the amount of deformation given and the strain rate,
as well as on the composition and the deformation temperature. 1~ Thus different
recrystallization temperatures would be obtained for the different strains, strain
rates and interpass times than would be obtained in the successive stands of a
hot mill.
At temperatures above the recrystallization stop temperature, full or partial
recrystallization may take place between each stand or before cooling, but the