Revealing Final Destination of Special Steel Materials with Input-Output-Based Material Flow Analysis

摘要

Special steel materials, including alloy steel and stainless steel, are among the most widely utilized materials in our society. Many kinds of metals other than iron accompany the special steel materials. Therefore, to achieve sustainable metals use in the steel industry, it is important to untangle the logistics of special steel materials in society. In conventional material flow analysis (MFA) studies based on a top-down approach, primary inputs of materials into industries tend to be regarded as "end use" of material. However, materials are often traded between industries or even exported as intermediate or final products to foreign countries. In this study, discrepancies in requirements for materials between their primary and final versions are revealed by means of a waste input-output MFA (WIO-MFA) model for special steel materials made in Japan in 2005. The result shows that only 45% of the primary demand is domestically consumed as finished product because exports of products such as automobiles and machinery contain significant amounts of special steel materials. In addition, non-negligible inter-industrial transactions are observed. The results imply a need for the careful accounting and precise understanding of material usages, and their sustainable management is crucial.