The objectives of the present paper is to clarify the effect of yield ratio of material used on structural performance and to consider the possiblity of making low-yield-ratio HT80-class steel. Mechanical analyses on deformations of typical structural elements have been conducted to determine the appropriate condition of yield ratio of materials. Based on the analysis of plastic deformation of dual-phased structure steel, consideration has been carried out of the making process of low yield ratio HT80 by using the same kind of steel as the conventional QT-HT80.
The decrease of yield ratio is effective procedure for increasing deformability of structural element. In HT80 steel, controlled rolling and on line accelerated cooling process followed by quenching from α+ γ phases is a proper treatment for obtaining low-yield-ratio steel with dual-phased structure in which martensite structure includes a certain fraction of lower strength ferrite.
