For the production of pilot batch of hot rolling coils (6×1500 mm, steel grade
S355MC) in accordance with EN 10149-2, the heat has been melt with the following
chemical composition (see Table 2).
Table 2 Chemical composition of pilot batch (steel grade S355MC)
Nb and Ti are used as chemical composition elements, which make it possible to
monitor the grain sizes during the austenitization and rolling, and also changes in the
properties owing to carbonitride strengthening.
Based on the chemical composition (Table 2), the target thermomechanical values
of the rolling process [2, 23] are calculated, the observance of which, in the future, will
provide the necessary complex of mechanical properties in accordance with
EN 10149-2 (see Table 3).
Table 3 Thermomechanical values of the rolling process
Parameter
Unit
Parameter value
Slab reheat temperature
°C
1260 ± 20
Heat time
hours-minutes
≤ 2-00
Rolling temperature behind the stand 4а
°C
≥ 1040
Rolling temperature behind the stand 10
°C
810-860
Coiling temperature
°C
580-630
Number of sections, which are used for accelerated cooling
pcs.
8-14
Cooling rate
°C/s
45-55
In order to obtain the process parameters necessary for TMCP introduction, the
target temperature and deformation conditions were calculated preliminary
(see Table 4) [24].
The slab with a section of 250×1550 mm, previously reduced to 140×1500×5395
mm, has been used as a semi-finished product.
According to these calculations, the operating constraints for the equipment of the
roughing and finishing trains were not exceeded, which makes it possible to apply these
temperature and deformation conditions for the production of pilot batch of the rolled
products.
It should be noted that, when calculating, the required temperature level behind
the stand 10 was achieved owing to the rolling speed adjustment for the metal in the
finishing train.
The pilot batch of hot rolling coils with a section of 6×1500 mm (steel grade
S355MC, heat 255634-2) in accordance with EN 10149-2 and EN 10051 was produced
according to the calculated conditions. During production, the deformation conditions
were partially adjusted from the calculated ones, including by the process control
Heat
Mass fraction of chemical elements, %
C
Mn
Si
S
P
Cr
Ni
Cu
V
Al
Ti
Nb
255634-2
0.11
1.36
0.03 0.007 0.019 0.04 0.01
0.01 0.004 0.037 0.022 0.030
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