超微細粒鋼の塑性加工限界までの真応力－ひずみ関係におよぼす試験片サイズの影響

抄録

The effect of specimen size on tensile deformation behavior of the ultrafine-grained ferrite-cementite (FC) steel was studied from the viewpoint of true stress (σ)-true strain (ε) relationship. In this study, we took notice of the estimation of σ-ε relationship up to the plastic deformation limit in order to discuss tensile deformation behavior up to fracture, especially in the local deformation behavior which the size dependence on mechanical properties is large. From the ultrafine-grained FC steel, round tensile test specimens with various sizes of gage length (GL) and gage diameter (φ) were prepared. Static tensile tests and stepwise tensile tests were performed with an initial strain rate of 5.0 × 10^-4 s^-1 at 296 K using a gear-driven-type machine. In the nominal stress-strain curves, the lower yield strength and total elongation increased with a decrease in the gage length. The σ-ε relationship up to the plastic deformation limit was almost independent of the specimen size, whereas the true strain at the plastic deformation limit and reduction of area decreased when the value of GL/φ became less than 1. The σ-ε relationship up to the plastic deformation limit estimated by Bridgman equation is unique data independent of specimen size and is effective to discuss the effect of specimen size on deformation behavior.