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.
In our socio-economic system, material is extracted from the environment, used as products that provide useful functions for human society, and eventually disposed of into the environment as waste. To reduce the amount of materials that are extracted from and emitted to the environment, reutilization and long-term use of the materials within our socio-economic system are important goals. These activities are, in general, better than one way, short-term use of materials from a resource and environmental point of view.
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. Past research has reported these indicators: for iron, 2.7 times and 63 years based on the material flows in Japan in 2000 (Daigo et al., 2005 and Matsuno et al., 2007); for copper, 1.9 times and 60 years based on the global material flows in 2000 (Eckelman and Daigo, 2008); and for wood pulp, 3.0 times based on the material flows in Japan in 2003 (Yamada et al., 2006b).
In this article, we estimate these usage and lifetime indicators for stainless steel (SS) for the Japanese socio-economic system in 2005 and discuss the meanings of these indicators given its main alloying elements. SS is “steel that contains more than 10% chromium, with or without other alloying elements” (AISI, 2008) and is roughly divided into ferritic SS that contains chromium and austenitic SS that contains chromium and nickel as major alloying elements. Characteristics of SS include corrosion resistance, strength at high temperatures, and easy maintenance. For these reasons, it is widely used in homes (e.g., tableware, kitchen sinks, and cookware), in buildings and infrastructure (e.g., building facades, lifts, and trains), and in industry (e.g., chemical plants, food processing equipment, and potable and waste water treatment plants).
This article presents results for the average number of times of use and the total average lifetime of SS which is used in the Japanese socio-economic system and discusses the meanings of these indicators given its main alloying elements. The following conclusions were drawn:
(1)
Based on Japanese SS use in 2005, SS was 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 was estimated to be used for 19–100 years in average over its entire life cycle, under the low collection rate and short product lifetime to high collection rate and long product lifetime scenarios.
(2)
Some SS scrap is used for 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 was estimated to be used 3.2–6.8 times and for 56–170 years in average over its entire life cycle, under the low collection rate and short product lifetime to high collection rate and long product lifetime 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.
This article presents a case study of SS. Similar studies for other material are encouraged in order to understand the status of our material use in the socio-economic system. As described, the collection rate of obsolete scrap and lifetimes of different product categories have significant impact on the estimation results: therefore, more accurate recycling and lifetime information are essential for more precise estimation. If time-series material flow information could be given, it enables to provide further interesting information regarding the transition of the status of our material use (see, e.g., Yamada et al., 2006b for wood pulp). Furthermore, interconnections of different materials as shown in SS flows (e.g., iron, chromium, and nickel) are also important point of view in the analysis of polices and measures for effective and efficient material use.
