Environmental impact evaluation of wear protection materials

Abstract

Wear protection materials, especially those for high-temperature service, often contain substantial amounts of chromium, cobalt and/or nickel and/or with embedded hard phases or forming harder intermetallic phases. Due to the comparatively high environmental impact of those elements, more sustainable alternatives must be found. This study presents a life cycle assessment quantifying the environmental impacts of three groups of cast alloys for wear protection: iron-, nickel-, and cobalt-based alloys. The assessment includes the production stage from raw materials extraction to casting (upstream impacts from cradle-to-gate), with the functional unit defined as 1 dm³ wear protection material. Global average process data were used to estimate the environmental impact of the respective alloy. Results indicate that iron-based alloys as studied here cause lower greenhouse gas (GHG) emissions during production (57–103 kg CO_2eq/dm³ or 8.4–13.8 t CO_2eq/t) compared to nickel-based (185–205 CO_2eq/dm³ or 20–22 t CO_2eq/t) and cobalt-based alloys (318–347 CO_2eq/dm³ or 31.2–39.5 t CO_2eq/t). The lowest emissions during production are caused by iron aluminide-based alloys at around 57 kg CO_2eq/dm³ or approx. 8.4 t CO_2eq/t, which is up to 90 % less than cobalt-based alloys, of up to 60 % less than nickel-based alloys, and around 50 % relative to Cr-rich iron-based alloys. Further, lifetime considerations based on actual wear data of the respective alloys at ambient and elevated temperatures were accounted for, and three different case studies were evaluated, namely abrasive wear at feeder plates, erosive wear on sieves (both at ambient and high temperatures) as well as wear on grate bars of a sintering plant for pig iron. Here, it was shown that the wear materials’ lifetime of wearing materials has a crucial effect on the environmental impact, since a prolonged lifetime reduces the need for spare parts and of replacement of the goods with their embedded carbon footprint. For example, an average hot sieve can achieve GHG emission savings of approx. 50 t CO_2eq/a when using an iron-aluminium alloy instead of a cobalt-based wear protection. The exchange of 10 m³ worn grate bars for a sintering plant made of an iron aluminide instead of a white cast iron saves over 500 t CO_2eq/a. Further, over 50 % emission savings in other environmental impact categories can be achieved by this measure.