STEEL + TECHNOLOGY 04/2019 EXTRACT

STEEL TECHNOLOGY | 47
Figure 8
duced 2.67 million tons and exceeded the
rated capacity of 1.5 million tons per year
during 2018 (figure 7).
Many customers expect from Big River
Steel as a newcomer in the market very
high flexibility with regard to product quality,
product dimensions, lot sizes and delivery
time. On account of the best plant
dimensioning in every process step and
the digitalization of the whole plant, all
these expectations can be met at a mean
lot size of only 7 coils. Almost 50 percent
of the strips produced have a width of
more than 1500 mm.
The CSP ® plant is of decisive importance
for the flexibility of Big River Steel.
Within one sequence, considerable changes
of the strip width can be effected. Strip
thickness variations of more than 10 mm
are realized from strip to strip (figure 8).
Moreover, in the case depicted here,
four different steel grades are cast within
the sequence. This flexibility is a decisive
factor of success for Big River Steel. On
one hand it is a benefit yielded by the
CSP ® technology due to temperature
homogeneity and CVC plus ® technology
and on the other hand it is economically
feasible due to advanced functionality to
reduce the length and the number of transition
slab or strips like the flexible analysis
approach implemented in the Level 3 system
X-Pact ® MES 4.0. It reduces the number
of transfer slab by more than 50 percent
and saves BRS millions of dollars
already during the first two years.
Within an implementation period of 8
weeks, the PQA ® system was able to do
its job and is now fully utilized in the day to
day dispatching. The fundamental benefit
of the PQA ® system is that only products
without defects leave the plant, which is
very important for the development of a
long-standing customer-supplier relationship.
Product developement
Figure 9
Just few months after the first coil
attempts were made to gradually develop
OCTG grades, API line pipe grades from
X52 to X80, AHSS HSLA steels and extra
deep drawing grades for automotive sectors.
The RH degasser was commissioned
in July 2017. With the first heat run through
RH degasser on July 28, 2017 development
started for API line pipe grades sour
and non-sour applications, electrical steels
and extra deep drawing (EDD) grades.
Strip width in mm
1900
1800
1700
1600
1500
1400
1300
1200
1100
1000
900
2600 2620 2640 2660 2680 2700 2720 2740
Strips produced
1005A04
Sequence start
1022A08
Strip width
Strip thickness
New sequence
1021A04
1021V02
June 19, 2019
All rights reserved
1022A08
Sequence end
Figure 8. Hot strip production with highest flexibility- example sequence of BRS
(Picture: SMS group)
The trails of X52 and J55 for tubular
applications were conducted at the
request of key ERW/HFW pipe manufacturers
and are now commercially produced
successfully. The first trial for the production
of API X70 grade hot rolled skelp in
12.5 mm thickness was set up in August
2017 for both sour and non-sour gas applications.
Considering the high levels of internal
cleanliness witnessed at BRS and the slab
dimensions, chemistry of first API X70 trial
heat was designed. Two heats were
made one through EAF-LMF-CC route and
the other through EAF-LMF-RH-CC route
and the heats were cast in to 80mm thick
slabs and thermo-mechanically processed
to 12.5 mm thick hot rolled coils.
Figure 9 shows full size transverse
Charpy impact values of X70 samples.
Drop weight Tear Tests (DWTT) were conducted
at temperature down to -45°C and
all the samples revealed excellent shear
25
22,5
20
17,5
15
12,5
10
7,5
5
2,5
0
1005A04
Strip thickness in mm
Data of July 2017
9
© SMS group GmbH
Figure 9. Charpy impact transition curves and fractured surfaces of DWTT samples of
X70 coils (Picture: SMS group)
down to that temperature. The requested
mechanical properties of API X70 could be
successfully obtained in the 12.5 mm thick
hot rolled strips.
Samples were
11.11.2019
tested for HIC resistance
10
All rights reserved
© SMS group GmbH
as per NACE 0284-16 specification in solution
A (pH 2.6) by an external specialist
corrosion laboratory. The tests indicating
outstanding HIC resistance of the X70
grade steel produced. Figure 10 shows
macrographs of specimens before and
after HIC tests showing no hydrogen blister
formation on the surfaces.
The installed steel making plant with
RH enables BRS to make EDDS steels
with carbon content lower than 20 ppm
and excellent sulfur and gas control.
BRS has started producing Ti-stabilized
extra deep drawing steel since Nov
2017 with average grain size of 14 µm.
Mechanical properties of fully processed
0.4 mm galvanized sheets are
typically YS: 166 MPa, TS: 327 MPa,
STEEL + TECHNOLOGY 1 (2019) No. 4