The schematic of process heating technologies discussed in this article is illustrated in Figure 2. Process heating segment referred in this article largely corresponds to reheating of semifinished steel in reheating furnaces to enable hot rolling and further heat treatment to produce plate, cold rolled and other steel products. The energy input for process heating in the steel industry is largely provided by burning fossil fuels such as natural gas, coke oven gas and blast furnace gas.

Figure 2: Segmentation of Energy Use in Steel Production (Source: VT Advisory and Aichelin)

Figure 2: Segmentation of Energy Use in Steel Production (Source: VT Advisory and Aichelin)

These gases in various combinations form a critical fuel source along the downstream processes including but not limited to hot rolling, cold rolling, galvanising and other metal coating processes. Although process heating in the steel industry may be broadly segmented as reheating and annealing, there are other process heating technologies such as quench and tempering, normally applied to specialist plate used in energy sector. However, reheating and annealing are amongst the most widely employed process heating technologies in the steel industry.

Table 1: Schematic illustrating process heating technologies across steel product families (Source: VT Advisory)

Table 1: Schematic illustrating process heating technologies across steel product families (Source: VT Advisory)

The purpose of any heat treatment is to improve mechanical properties in steel such as enhanced tensile strength, improved fatigue resistance and others. Such interventions significantly improve the performance of the steel product in highly demanding operating environment. Table 1 aims to illustrate the process heating technologies employed across key steel product families. It may be noted that this is by no means comprehensive and there may be certain processes not listed / mapped in this table. Reheating is a vital aspect of the steel production and demand for reheating is driven by the production of hot rolled products such as hot rolled coil, plate, rebar, structural products. Annealing is an intermediary heat treatment process employed in the production of cold rolled and related downstream products such as galvanised steel, tinplate and electrical steels among others. The role of annealing is quite critical in the steel industry since it enables the production of specialist products such as advanced high strength steels (AHSS) used in the manufacture of high strength low weight automotive components. The annealing of AHSS grade steels involves heating the strip to elevated temperatures of ~900 °C compared to conventional steels at ~700 °C and thus requiring higher energy inputs.

Figure 3: Schematic Illustrating Steel Grades and Tensile Strengths (Source: WorldAutoSteel)

Figure 3: Schematic Illustrating Steel Grades and Tensile Strengths (Source: WorldAutoSteel)

AHSS steels are family of steel products with tensile strengths greater than 700 MPa relative to mild steels of the order of 300 MPa. The share of AHSS steels in automotive components including electric vehicles has been growing strongly over the last few years driven by lightweighting of automobiles.
AHSS steels offer an invaluable combination of high strength with ductility, enabling the design and manufacture of automotive components with complex geometry which ultimately strengthens crash resistance properties of automobiles. This is particularly important in case of electric vehicles, where battery accounts for ~ 25 % of the weight of the automobile and there is limited opportunity to reduce the battery weight without compromising on the driving range, e. g. of the vehicle. AHSS steel delivers some degree of flexibility to the designers in terms of being able to install a larger battery and enhance the range of the vehicle.

The other major segment demanding heat treatment being the energy sector. This includes tubular products for the oil and gas industry, wind towers, pressure vessels and reactors and others. These segments mainly use steel plate as a substrate for fabricating the required equipment. Plate used in these applications is subject severe operational stresses, fatigue and impact and require enhanced mechanical properties including but not limited to high strength. Such properties may be achieved via specialist chemistry incorporating molybdenum, vanadium etc. and/ or a specialist heat treatment at elevated temperatures such as quench and tempering. The demand for such heat treatment is driven by wind tower manufacture supporting renewable energy capacity growth and highly demanding pipeline infrastructure to access oil and gas from challenging geological landscape. The decarbonisation of the energy sector is driving the growth in wind towers and other renewable energy sources.

Similarly, decarbonisation of transport sector is driving the demand for electric vehicles with superior design architecture that ensures low overall carbon footprint although alternative materials such as aluminium is being actively incorporated in the vehicle components, the economics appear to be largely in favour of steel especially with the AHSS steels. Moreover, the manufacturing sector is well equipped to handle steel processing be it forming complex shapes, welding and joining technologies and others. Similarly large equipment fabricators are well invested to fabricate complex equipment and ambitious projects using steel plate to support energy sector.

With the continued demand growth in the decarbonisation era and rapid industrial growth in India and other emerging Asian countries, the demand for AHSS steel and specialist plate is forecast to strengthen even more. Thus, driving the demand for heat treatment facilities such as annealing, QT and others. The existing heat treatment technologies mainly use fossil fuels and heat treatment segment needs to develop low carbon alternatives and aim to replace fossil fuel based furnaces with hydrogen and / or explore using electricity as to generate the required amount of heat.

The EU’s HyInHeat programme aims to support research activities associated with the use of hydrogen in heating and melting segments of the steel sector. Under this programme, funding is being allocated towards various research and development projects to study the application of hydrogen in heating and melting applications. Pilot project examples include:

1. Reheating furnace (SWERIM, Lulea, Sweden): Retrofit light oil/ air with H₂/air/ O₂ burner technology. Potential CO₂ savings: 386 ktpa on a 3.1 mtpa reheating furnace capacity
2. Hot dip Galvanising line (ArcelorMittal, Gijon, Spain): Retrofit natural gas/ air with H₂/air burner technology. Potential CO₂ savings: 31 ktpa on a 550 ktpa throughput line.

Other related research being:

• Italy’s RINA led Project HYDRA aims to create a 100 % hydrogen fuelled pilot plant which includes the development of hydrogen fired reheating furnace.
• Demonstration project involving hydrogen based reheating furnace at Purdue University NorthWest in the USA

In conclusion, the demand for annealing and other heat treatment technologies in steel industry is forecast to grow strongly over the next decade or so, driven by carbon reduction initiatives and demand growth in emerging markets. The demand growth is likely to be stronger relative to crude steel production growth. Heat treatment segment is a vital partner in achieving steel decarbonisation goals since it enables production of steel products with higher strength to weight ratio resulting in reduction in overall material footprint. However, the heat treatment market is quite complex and characterisation of this market is fraught with challenges. It is important to understand this market in greater granularity to appreciate the key value elements embedded in this segment to attract investments to support market growth and enhanced research spend.

References:

[1] World Steel Association

[2] World Autosteel

[3] W. Zhang and J. Xu ; Advanced lightweight materials for Automobiles: A review ; Materials & Design 221 (2022) 110994

[4] HyInHeat group presentation

[5] Purdue University Northwest – CIVS

[6] https://www.aichelin.at/en/products/topics/ heat-treatment-processes

[7] Various journal and news articles

Abbreviations used in the article

BF: Blast Furnace; BOF: Basic Oxygen Furnace; EAF: Electric Arc Furnace; HRC: Hot Rolled Coil; CRC: Cold Rolled Coil; HDG: Hot Dip Galvanised Strip; Mtpa: Million tonnes (metric) per annum; AHSS: Advanced High Strength Steel; MPa: Mega pascal; ktpa: Kilotonnes (metric)per annum

Author

Vijay Thangavelu (Source: VT Advisory)

Vijay Thangavelu
Director
London
+44 7957749983
vthangavelu@vtadvisory.co.uk