FOCUS ON SUSTAINABILITY
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Carbon Footprint Study Compared Battery Cases
Steel Reference Stainless Steel Variants Aluminium Alternative
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Parameter Steel Reference Stainless Steel Variants Aluminium Alternative Dimensions [ mm ] 1700 x 1534 x 140 1700 x 1534 x 140 1760 x 1450 x 140 Weight [ kg ] 91.2 76.3 58.9 Energy Content [ kWh ] 56 56 58
Carbon Footprint Study Production Phase
• Production phase
different . For example , steel mills often take differing approaches to energy efficiency and procurement of low carbon energy for their processes , as well as sourcing low carbon raw materials ,” explained Outokumpu .
“ Another challenge is that carbon reporting varies between suppliers and countries . Not all reporting methods consider carbon dioxide ( CO₂ ) emissions from ‘ cradle to gate ’. That makes it important to seek the right data so that ‘ like ’ is compared with ‘ like ’,” it continued .
The challenge for automotive designers is that while a growing number of manufacturers strive to publish data on the carbon footprint of their materials , there is no standard on how it should be calculated ( especially in terms of covering Scopes 1 , 2 and 3 ). It is therefore hard to ensure that ‘ like ’ is always compared with ‘ like ’. There is also very little practical information on how the construction material impacts the overall global warming potential ( GWP ) of automotive components throughout their service life . This dilemma prompted Outokumpu and FKA , its Aachenbased research partner for the automotive industry , to collaborate on this project
• Conversion of Steel Reference into Stainless Steel Variants
• All Battery Cases :
• Perform similarly mechanically
• Contain similar amounts of energy → Assessment of Carbon Footprint as third KPI
• Aspects considered : Raw materials , manufacturing processes , joining processes and corrosion protection .
• Raw materials : Steel , Stainless Steel , Aluminum
• Manufacturing process : Deep-drawing , stamping , extrusion , bending , etc .
• Use of publicly available values , where possible
Raw Material GWP [ kg CO 2 -eq / kg ] Source Stainless Steel : Forta H800 3.25 [ Outukumpu ] Stainless Steel : 1.4301 2H ( Standard ) 1.52 [ Outukumpu ] Stainless Steel : 1.4301 2H ( Circle Green ) 0.66 [ Outukumpu ] Steel : Hot rolled coil 2.22 [ WOR18 ] Steel : Hot-dip galvanized 2.70 [ WOR18 ] Aluminium : Used in EU 8.60 [ EAA18 ]
to evaluate the carbon footprint of a real-world component during both production and use .
Carbon footprint study
Stefan Lindner .
“ The project explored the use of standard carbon steel , stainless steel and aluminium for the battery case of a typical passenger electric vehicle ( EV ). The results challenge current thinking since , by using stainless steel , the carbon footprint of this component is 112.8 % lower than aluminium and 29.9 % lower than carbon steel — under current recycling regimes and when powered by the EU ’ s electricity grid mix ,” outlined Stefan Lindner , Outokumpu Application Development Manager Mobility and Urbanisation , introducing the project during the roundtable .
The wall thickness of the tray varied between 0.8 and 1mm . The higher strength of the stainless steel allows a reduction in section with a consequent reduction in weight compared to the reference carbon steel , while offering the same
Outokumpu ’ s Tornio ferrochrome facility .
Stainless steel in focus
Stainless steel is a good lightweight material for sustainable solutions as it is 100 % recyclable , efficient and long-lasting . Stainless steel ’ s natural Cr2O3 passivation layer means that no coating is needed and corrosion resistance is built-in . It also has antibacterial properties .
The production of stainless steel is based on the use of scrap . Outokumpu ’ s use of scrap content is reportedly 94 %. The company operates its own mine for the production of ferrochrome ( FeCr ), which is a vital raw material used to manufacture stainless steel .
“ This means that ferrochrome has a low carbon footprint , 67 % smaller than the industry average , and FeCr production is considered in our Scope 1 and 2 emissions , unlike other industry players . This shows how the structure of the supply chain can influence carbon footprint calculations ,” highlighted Stefan Lindner .
energy storage capability . Using aluminium involved an even more significant weight reduction and a small increase in energy storage .
“ The performance of the materials was modelled initially in a crush test . The target was for no contact between the deforming structure and battery modules at 100kN . This was achieved by all three materials . The next stage was to carry out a bollard test simulation . The target was no contact between the structure and the battery modules at 20N . Again , this was achieved by all three materials ,” confirmed Stefan Lindner .
Having established that the competing materials satisfied the performance criteria , the investigation moved on to evaluate their carbon footprint in the production phase . This considered a comprehensive range of aspects including raw material production ; manufacturing processes ( such as deepdrawing , stamping , extrusion , bending etc .); joining processes and corrosion protection .
88 | ismr . net | ISMR October 2024