Measuring the status of stainless steel use in the Japanese socio-economic system

To reduce the amount of materials that are extracted from and emitted to the environment, reutilization and long-term use within our socio-economic system are important goals. From this perspective, the average number of times a material comes into use and the total average lifetime of a material are useful indicators for measuring the status of our material use. In general, multiple uses and long lifetime indicate effective and efficient material use. In this article, we estimate these usage and lifetime indicators for stainless steel (SS) for the Japanese socio-economic system and discuss the meanings of these indicators given its main alloying elements. The following conclusions are drawn: (1) Based on Japanese SS use in 2005, SS is estimated to be used 1.9–4.3 times in average over its entire life cycle depending on possible low and high collection rate scenarios of SS obsolete scrap. SS is estimated to be used for 19–100 years in average over its entire life cycle, under the low collection rate and short product lifetime (LCR&SPL) to high collection rate and long product lifetime (HCR&LPL) scenarios. (2) Some SS scrap is used for carbon and other alloyed steels (COAS) production. Although SS scrap that is recycled within COAS cycles no longer functions as SS, iron contained in SS does serve a function in COAS products, considering an elemental interpretation. Iron contained in SS is estimated to be used 3.2–6.8 times and for 56–170 years in average over its entire life cycle, under the LCR&SPL to HCR&LPL scenarios. (3) From the viewpoint of sustainable material use, estimated total average lifetime of SS is not considered to be satisfactory. More effective and efficient material use needs to be achieved through the improvement in collection rates of obsolete scrap and lifetimes of final products.