Mitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
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Endless Hot Rolled Coil (eHRC) from Arvedi ESP– A New Standard in Rolled Materials
P r i m e t a l s Te c h n o l o g i e s A u s t r i aGmbHEndless Strip Production
Scholler J, Piemonte C
Tu r m s t r a s s e 4 4 , 4 0 3 1 L i n z , A u s t r i a
h t t p s : / / w w w. p r i m e t a l s . c o m / l a n d i n g - p
ages/esp-endless-strip-production

Since the development of rolling technology, steel flat products have traditionally been
divided into two prominent groups: hot-rolled coils (HRC) and cold-rolled coils (CRC).
After the invention of Arvedi Endless Strip Production (ESP) technology, featuring endlesscasting and rolling of hot-rolled coils, a new class of rolled coils emerged: the endless hot-rolledcoils (eHRC).
eHRC dramatically extends the domain of hot-rolled material into applications traditionallyserved only by cold-rolled products. This new set of hot-rolled coils offers significant economic
savings in transformation costs, dramatically reducing both CAPEX—thanks to the unprecedented
layout compactness of ESP plants—as well as OPEX—thanks to the lowest total energy
consumption and the highest material yield among all thin slab casting and rolling technologies on
the market.
Due to the absence of any immediate fossil fuel consumption and the direct rolling of the castslabs taking advantage of the original thermal energy of the liquid steel, Arvedi ESP also
represents the standard in reducing greenhouse gas emissions in direct and indirect emissions.
The peculiar thermal regime during casting and rolling, without long holding times at hightemperatures, makes the Arvedi ESP process much less prone to hot shortness phenomena and,hence, more tolerant concerning the presence of tramp elements in liquid steel. This feature makes
Arvedi ESP the perfect match for electric arc furnace-based meltshops using large quantities ofscrap. Arvedi ESP pairs with scrap-based production without sacrificing the final product’s
quality, thus boosting the principles of the circular economy.
With Arvedi ESP, limited space requirements, best-in-class energy utilization, and reduced
carbon footprint levels go hand in hand with superior coil quality for profitable and eco-friendly
steelmaking.

|1. The Beginning of the Journey: “The Thinner the Better”
One of the first goals that historically pushed the development of the “endless” process in thecasting and rolling of flat products was the need to produce thinner and thinner gauges as HRC.
As well known, achieving a commercially stable production of gauges below 1.2 mm with aconventional hot-rolling mill, which uses thick slabs, is challenging. The main factors limiting suchproduction are the very high reductions during rolling that affect the stability of the mill and,primarily, the difficulty of threading the very thin strip heads into the finishing mill stands and latertransporting them from the exit of the finishing mill to the downcoiler without risking a very highcobble rate.
The introduction of the “thin slab” design concept (in coil-to-coil mode) slightly reduced the
problem of mill instabilities due to lower reductions required but did not solve the “flying strip
head issue”.
In the 1980s / beginning of the 1990s, the semi-endless process was introduced as a tentative
solution, feeding the mill with very long thin slabs that corresponded to several coils each and wereas long as the tunnel furnace between caster and mill permitted. This configuration allowed the firstMitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
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coil from the slab to be rolled at a “reasonable” gauge to have the head “safely” reach thedowncoiler and then to progressively reduce the thickness on the following coils, while they arerolled in the mill before being divided in separate coils by the final shear, which was now installed
just in front of the down coiler.
This process allowed for the first time the production of coils below 1.0 mm on a commercial
scale but had the limitation that only a very small amount of thin gauge coils could be produced ina discontinuous campaign. Moreover, the length of tunnel furnaces necessary to produce the very
long “mother slabs” made the mill layout extremely long, with very high gas consumption needed
to reheat these huge tunnel furnaces on top. These limitations made semi-endless mode not morethan an exception in the scenario of hot-strip mills.
The “game changer event” has been the development of the endless process that allowed forthe linking of casting and rolling in an uninterrupted sequence for the first time. The “flying head”
problem was eliminated because only one strip head had to be threaded at the start of the casting
sequence. The production of ultra-thin gauges can then continue, not for just 2 or 3 coils as insemi-endless but for, literally, hundreds of kilometers, uninterrupted.
This paradigm shift was made possible by:- The evolution of caster design, allowing very high mass flows,- The direct rolling of the cast strand without reheating to produce the transfer bar,
- The development of reliable induction heating solutions for transfer bar temperature
control, and- the deployment of automation architectures and models that, simultaneously controllingthe casting and rolling process, can ensure a flawless production in both steady andtransitory conditions.
Figure 1 illustrates a layout with the typical ESP plant configuration.

Figure 1

ESP layout

The ESP high-speed thin-slab caster plays a critical role in generating the necessary mass
flow and sustaining the endless process. Each component of the caster has been meticulously
designed and optimized to ensure stable operations, ultra-high productivity, and superior slab
quality, marking it as a key component in the Arvedi ESP process.
The high-reduction mill performs the first rolling step directly after the strand exits thethin-slab caster. It leverages the inverse temperature profile, with a hotter core than the surface
temperature, to achieve high reductions, energy savings, and tight tolerances on the transfer bar
geometries. No CO2-emitting furnaces are used in the ESP process.
A powerful and flexible inductive heater provides precise temperature control for thefinishing rolling. Transversal and longitudinal flux solutions, along with adjustable clearance
between the heating coil and transfer bar, optimize the inductive heating efficiency for varying
product thicknesses. Additionally, there is no energy consumption during idle times.
The finishing mill rolls the transfer bar to the final target product dimensions. It is equippedwith modern actuators like hydraulic AGC (Automatic Gauge Control), work roll bending/shifting,
dynamic work roll cooling, work roll lubrication, and fast hydraulic loopers. The mill produces
strips with the narrowest geometrical tolerances, even for hard steel grades at maximum width. The
stable endless operation drastically increases work roll lifetime up to double of batch operated
processes and contributes with this big lever to heavily reduced OPEX including maintenancecosts.
In the cooling section, the endless mode of ESP operation eliminates the challenges of
speedups and related cooling obstacles, resulting in uniform temperatures and a consistent strip
microstructure.

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Just before reaching the down coiler, the strip receives a first straight cut by the high-speed
shear. Head and tail crop cuts are history, resulting in the highest overall yield. The down coiler has
special features for coiling ultra-thin as well as ultra-thick gauges of the same quality.

|2. Endless Strip Production Experience Since 2009
As is well known, the dawn of the new Endless Strip Production era is marked by the startupof the Arvedi ESP plant in Cremona, Italy, in 2009 in partnership with Primetals Technologies. The
stable, industrial-scale production of massive quantities of thin and ultra-thin strips below 1.0 mm
in thickness became a real fact. The goal for the first ESP plant was to reach a thickness of 0.8 mm,
a milestone achieved in 2010. However, this was just the beginning: our Chinese ESP customers
already consolidated the production of 0.7 mm and even 0.6 mm minimum gauge, the latterachieved in 2018.
The advantage of this progress is evident: a large portion of products that in the past needed
to be first hot rolled and then also cold rolled to reach the desired final thickness can now be
produced directly as hot rolled coils. In case cold rolling cannot be completely omitted because thefinal thickness must be even less, our customers (and/or other re-rollers) can still benefit from theuse of thinner input material to decrease both CAPEX and OPEX in their cold complex.
As shown in Figure 2, the percentage of the market currently served by CRC that can betargeted by eHRC is significant. The left side shows the typical production ranges of ESP, Coldrolling and Hot rolling. On the right, the pie chart shows the typical world wide distribution of Coldrolling thickness as by average product mix of cold rollers. More than 50% is above 0.8 mm andhence accessible for eHRC and therefore marked orange/blue.

Figure 2

Cold rolled products market divided by thickness share

Furthermore, when cold rolling is completely omitted, the further downstream annealing
process (to reduce the internal tensions generated within the material by deformation at low
temperatures in CRM) can also be completely avoided (Figure 3).
In this case, to fully understand the advantages of “market substitute products,” the correctcomparison is between an eHRC, sold as pickled and oiled, versus an annealed CRC for a given
material and final thickness requested by the end-user. In most cases, according to the experienceof Arvedi ESP plants worldwide, even no skin-passing is required; such a process is requested only
for the cases where the final use demands smoothing the coil surface roughness provided by
pickling.
Such eHRC is, of course, ready either for final use by the end customer or to be further
galvanized / color-coated, as the case may be.

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Figure 3

Arvedi ESP OPEX cost savings compared to a conventional process.

The production of thin and ultra-thin gauges is just the first reason for the success of theendless mode. The stable process conditions enable the production within the tightest geometricaltolerances and uniform mechanical properties across an entire coil and throughout a full sequence.
This aspect is particularly important when the target is beyond just commodity applications.
ESP producers have fully recognized the advantages of eHRC and are considering it not
merely as a different (and better) way to produce coils and save money. Thanks to its uniqueproperties, eHRC is viewed as a distinguished product with its own “personality,” to be presented
to its customers, even with dedicated brand names to emphasize their added value.
A prime example is the Arvtech™ brand by Acciaieria Arvedi, which offers metallurgicalcharacteristics and geometrical precision that make it an effective alternative to cold-rolled
products for many applications. This brand will considerably shorten delivery times compared withthe cold rolling cycle (Table 1, which is an extract of the ArvtechTM product catalog).
The quality results mentioned in Table 1 are the direct consequence of the endless process.
Having a continuous, stable, and uninterrupted process ensures that the mechanical propertiesof the coils are absolutely constant along the strip; there is no longer any difference between thehead, core, and tail of a coil: the full length of the coils becomes “core.” In endless mode,
essentially, the complete sequence of, for example, 3,000 tons represents the core.
This uniformity is highly beneficial for coil end-users, reducing the head and tail crops forpotential “out of tolerance” issues concerning both geometrical tolerances and mechanicalproperties. The head and tail ends of each coil are always a straight cut, further increasing the yieldof the ESP line.
Figure 4 provides more details on these topics. This includes beside temperature uniformity
and mechanical characteristics also geometrical tolerances like thickness, flatness (I-Unit is adimensionless number that incorporates the height and peak to peak length of a repeating flatness
wave across the strip), and profile tolerance (C40 means the value along the strip width without 40
mm from both strip edges).

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Table 1

ArvtechTM Brand Steel Type Lineup
ArvtechTM
designation

Type of steel

Mild steels
UNI EN 0111

ArvtechTM DD11
ArvtechTM DD12
ArvtechTM DD13
ArvtechTM S235JR/J0/J2

Structural steels
ArvtechTM S275JR/J0/J2
UNI EN 10025-2
Delivery condition “as rolled”(+AR)
ArvtechTM S355JR/J0/J2
Weather-resistant structural steels ArvtechTM S235J2W/J0W
UNI EN 10025-5
TM
Delivery condition “as rolled”(+AR) Arvtech S355J2WP/J0WP
ArvtechTM S315MC

Micro-alloyed steels
UNI EN 10149-2

Multi-phase steels
UNI EN 10338
Thickness range (mm)0.80 < t ≤ 1.20
1.21 < t ≤ 1.60
1.61 < t ≤ 2.00
2.01 < t ≤ 2.50
2.51 < t ≤ 3.50

Figure 4

min

max

DD11

1.0

3.5

Max
Width
[mm]
1520

DD12

1.0

3.5

1520

DD13

1.5

3.5

1300

S235JR/J0/J2

1.0

3.5

1520

Standard
designation

Thickness (mm)S275JR/J0/J2

1.25

3.5

1520

S355JR/J0/J2

1.8

3.5

1520

S235J2W/J0W

1.45

3.5

1520

S355J2WP/J0WP

2.0

3.5

1520

S315MC

1.25

3.5

1520

ArvtechTM S355MC

S355MC

1.25

3.5

1520

ArvtechTM S420MC

S420MC

1.38

3.5

1520

ArvtechTM S460MC

S460MC

1.5

3.5

1520

ArvtechTM S500MC

S500MC

1.5

3.5

1520

ArvtechTM S550MC

S550MC

1.5

3.5

1520

ArvtechTM S600MC

S600MC

2.0(**)

3.5

1520

ArvtechTM S650MC

S650MC

2.5

3.5

1300

ArvtechTM S700MC

S700MC

2.5

3.5

1300

TM DP600

Arvtech

DP600

1.5

2.5

1520

ArvtechTM FB590

FB590

1.8

3.5

1520

ArvtechTM CP800

CP800(**)

2.5

3.5

1520

Tolerance (mm)(*)± 0.04± 0.04± 0.05± 0.06± 0.06

Superior quality features of eHRC(*) The tolerance is not guaranteed from edge to 25 mm
for coils with untrimmed edges.
(**) S600MC in thickness 2 mm and the grade CP800
are in development.

Mitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
6|3. The Benefits of the Endless Process Extend Beyond Thin Gauges
The advantages of the endless process in terms of coil quality became so evident that a newmarket segment emerged as a profitable target: the production in the endless mode of relatively
thicker grades with much more advanced added value. Enhancements in ESP equipment now allow
targeting products that are qualified not only by their thin gauge but also by their mechanicalproperties.
In the first ESP plants, which were conceived to target the thin and ultra-thin gauges, themaximum coil thickness produced in endless mode was in the range of approximately 4 mm, while
thicker gauges were produced in coil-to-coil mode. The most recent developments in ESP
technology now enable the production in full endless mode of strip thicknesses up to 1 inch (25.4mm), even for hard grades (e.g., API pipe grades).
This evolution has been made possible by:- The increase of the slab thickness, allowing significant reduction rates also for thicker
strips.
- The development of optimized roughing mill configurations with 3 or even 4 roughing
mill stands.
- The introduction of multi-mode induction heaters, capable of efficiently controlling theheat transfer to both thin and thick transfer bars, making the endless operationenergetically convenient also for thicker gauges.
- Patented cooling and power cooling features, tailor-made for each thickness and steel
grade.
- The use of advanced rolling strategies to optimize the number of finishing stands
involved in rolling.
- The development of powerful shears to cut in endless mode also for thicker strips.

|4. The New Markets for eHRC
• Grades for Automotive Industry
HSLA (High Strength Low Alloy) components, which ensure lightness yet robustness forvehicle structures, have seen impressive development in recent years. With typical
thicknesses between 1.0 and 2.0 mm, eHRC with strengths up to 700 MPa is the ideal
material for such applications.
As a point of reference, these automotive applications constituted almost 30% of the market
served by the ESP at Acciaieria Arvedi, Italy, out of a total of 42% of HSLA, withthicknesses ranging from 1.0 to over 8.0 mm.
Examples of automotive applications are illustrated in Figure 5.

Figure 5

Automotive applications from Acciaieria Arvedi ESP coils

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These materials are utilized not only for structural components (such as car bodies) but
also for mechanical components (such as distribution shafts) as precision tubes.
• API pipe grades
The 2-step rolling configuration of ESP enables perfect control over the temperature profile,aiming to achieve the desired final fine-grain structure via thermomechanical rolling and“pancaking”. This production route significantly reduces the required alloying element
content (Niobium) to control the precipitation process necessary for refining the grain
structure. With the latest developments, the production of API X70 grades in endless mode
up to 25.4 mm is now possible.
• AHSS (Advanced High Strength Steels)
Thanks to exceptional temperature profile control during endless operation, AHSS grades
like DP (Dual Phase) or TRIP (TRansformation Induced Plasticity) can be produced withthe required multiphase structure, directly out of the ESP line. Such grades can be produced
up to 12.7 mm in endless mode.
• Weather-resistant steels
A prime example of direct application is the production of massive quantities of CORTEN
grades by the five ESP lines at Rizhao, PR China. The resulting eHRC, which can bedirectly used for the manufacturing of containers, typically has a thickness of 1.4 mm.

|5. Green Experience, at the Heart
What we have described here is a constant journey of progressive refinement of both
equipment technology to materialize innovative processes and operational know-how developed inclose collaboration with our partners over more than 15 years and after the production of more than
100 million tons of coils on ESP lines in endless mode.
From its inception, the ESP concept significantly evolved, now serving markets well beyond
the original commodity market, with the aim of progressively becoming a standard tool for
producing all flat steel products.
We cannot conclude this article without acknowledging the growing environmental
awareness over the past decade regarding the necessity to transform the steel industry into an
environmentally sustainable sector.
Our customers, particularly the ones serving the most demanding automotive markets, face
increasing requirements from their end customers to deliver not just high-quality steel but green
steel.
In terms of carbon footprint, the ESP eHRC represents a quantum leap compared to any otheravailable casting and rolling technology for flat products.
Given that ESP uses no fuel at all (no tunnel furnace) and is based on the full exploitation of
the thermal energy already present in the cast strand, the overall energy consumption and related
greenhouse gas emissions are reduced to an absolute minimum compared to any other process, bothconventional and thin-slab based.
This efficiency is proven by an unbeatable value of less than 1.0 kg of CO2 emitted per ton ofeHRC (Scope 1 emissions according to the greenhouse gas protocol) measured from caster to thedown coiler, and a total electrical energy consumption in the range of 120 kWh/t for 2.0 mm x
1,500 mm low carbon steel in endless mode (Scope 2 emissions according to the greenhouse gas
protocol).
The absence of long tunnel furnaces makes Arvedi ESP plants advantageously within thecircular economy. Following this trend, more plants are being designed to operate with an EAF(electric arc furnace) based meltshop, where higher charges of metal scrap can be utilized.
However, the maximum amount of scrap is limited by the tolerable amount of residual and traceelements such as Cu, as well as Sn, Sb, Pb, P, etc., since these elements are detrimental to productquality.
In particular, copper is responsible for the formation of high-temperature cracks on thesurface of the cast slab and on the final coils (hot shortness phenomena). The occurrence of such
defects happens precisely in the temperature range experienced by the slab inside the tunnel
furnace. While in a tunnel furnace-based plant, the slab is exposed to these conditions for 10 to 20

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minutes (corresponding to the travel time between the exit of the caster to the entry of the firstrolling stand), in Arvedi ESP plants, this exposure time is basically reduced to just 1 minute. This
capability allows Arvedi ESP to tolerate a Cu content approximately double that tolerated byconventional plants without compromising coil quality.

|6. Outlook
Today Arvedi ESP is the most developed thin-slab casting and rolling technology in theworld. Since 2009 the design of Arvedi ESP and the benefits of endless production have become
state of the art and improvement of the technology continues. For steel strip production Arvedi ESP
will be a key technology for the transition to green steel and a higher utilization degree of scrap.
More than 100 million tons of green steel have been produced since 2009 on the already operatingeight ESP lines.
Accepting scrap based liquid steel from EAF is essential to achieve the transition to green
steel. This includes the capability to cope with higher copper content which can be achieved mucheasier with shortest oxidation times as given by the ultra-compact design of ESP lines.
Further important aspects for accepting thin slab casting and rolling lines are economical andoperational performance. 2.5 million tons per year on a single strand have already been
demonstrated in 2017 and reaching the new mass flow record of 7.1 t/min in 2020 enables anannual capacity exceeding 3 Mtpy.