27 May 2020

Making informed choices about sustainable material

Tata Steel IJmuiden
Nick Silk
Market and Business Development Manager at Tata Steel UK

In previous blogs I have described the drivers for a focus on sustainability in the Automotive value chain and the specific challenges that these bring for steel. In this blog I want to discuss measurement and reporting of carbon performance.

A change of focus in measuring automotive carbon performance

As I have mentioned in previous blogs, legislation has been for some years and is still focused on tailpipe (use phase) emissions as a key indicator of performance improvement in the automotive sector. This has driven improvements in drive train efficiency as well as light-weighting of vehicles.

As we move into an era of electrification, where there are no longer any tail-pipe emissions and the total use phase emissions are significantly reduced (depending on a low carbon electricity grid mix), the focus has not surprisingly turned to the embodied carbon of the constituent materials used to manufacture vehicles. And this has been an industry-led shift, albeit aligned to future legislative targets for achieving carbon-neutrality.

Describing the carbon performance of materials

Using the example of steel, embodied carbon describes all of the CO2 emitted in every process from the mining of iron ore to the delivery of products to customers. In other words, the embodied carbon describes the cumulative CO2 emissions of all of the production steps - the mining of iron ore and coal, the extraction of iron from its ore, steel-making, rolling and coating up to the point it is delivered to our customers. As I will explain later however, I believe it must also include end of life if it is to be used to compare materials on a like for like basis.

The embodied carbon of a vehicle is then of course the total embodied carbon of all of the constituent materials, taking account of all the resources used in - and the associated emissions from – the production of those constituent materials. A key point to note is that if there is a poor level of material utilisation (sometimes described as yield) during parts manufacture, the carbon penalty is especially detrimental if the material from which the part is made has high embodied carbon.

Comparing the carbon performance of materials

Since a significant fraction of the weight of a vehicle is made from steel, (Fig. 1 left), it is not surprising that vehicle manufacturers focus on the contribution of steel to the overall embodied carbon of a vehicle. However, steel has relatively low embodied carbon in comparison to other materials (Fig. 1, centre) and the recycling rate at end of life is >97% for automotive steels. If the recycling rate of steel is used to calculate an end of life benefit, the sustainability of steel is directly accounted for in the embodied carbon calculation and the carbon footprint of a vehicle is truly reflected (Fig. 1, right).