Article ID: ISIJINT-2025-292
The strength at 600 °C in fire-resistant steel exhibits a significant dependence on strain rate, likely attributed to a shift in deformation mechanism from slip deformation to grain boundary sliding (GBS) with increasing temperature. In this study, GBS was observed using a grid method, and the strain distribution introduced by a high-temperature tensile test in a carbon steel was visualized. The characteristics of the strain distribution in the grains composing the grain boundary where GBS occurred were discussed. Although the test temperature was 500 °C, high-temperature tensile tests with strain rates of 10-3 and 10-5 s-1 orders were successfully conducted. Strain rate dependence of strength was comparably small at 500 °C. The discontinuous slide of the grid line at the grain boundary was observed after the tensile tests at 500 °C, regardless of strain rate, indicating that GBS occurred. The strain was distributed inhomogeneously during the high-temperature tensile tests. The grain boundary generating GBS lay 45 ° from the tensile direction and consisted of a pair of high- and low-strain grains. The m' value, which represents the ease of slip transfer between adjacent grains, was low at the grain boundaries generating GBS. This suggests that GBS was induced by pile-up dislocations at the grain boundary.
