A TRIAL OF RECYLING ORIENTED STEEL DESIGN

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We propsed a principal idea for future steel design to improve the recycling at the 1994 annual fall meeting of Jpn.Inst.Metals : a steel for multi-purpose use with simple chemical compositions consisting of optimistic elements from the viewpoint of natural resources is desirable. Based on this way of thinking, we have chosen an Fe-Mn-Si-C system as a typical example of "eco-steel".The rage of tensile properties which can be covered by controlling the micro-structure of one kind of Fe-Mn-Si-C steel was experimentally examined. For investigation, two steels were melted, cast and hot forget and some of them were cold rolled. Plate tension specimes were made and various kinds of heat treatment were subjected to the specimens. The resultant microstructures of single-microstructure (bainite and martensite) and multi-microstructure (ferrite-pearlite, ferrite-bainite, ferrite-martensite and ferrite-bainite-martensite) were characterized by light and scanning electron microsopes.The variations of tensile flow curves were predicted : by using data base of ISIJ (Swift equation) for single-microstructure steels and by the secant method (micromechanics) for muli-microstructure steels, respectively. The upper and lower limits in microstructure depedence of tensile properties have been discussed and the flow curve of a tri-microstructure steel were first caluclated using iterative computing technique. The predictions have been found to show good agreements with experimental results.Finally, the eco-steel design was discussed by coupling the above properties prediction method and materials life cycle analysis (MLCA).