Abstract
Using miniature impact specimens of round bars, the temper-brittleness has been studied on a Si-Cr-Mn structural steel. The impact tests by this miniature round bar specimens had sufficient sensitivity in the measurements of transition temperature, but the transition temperature was found to be about 70°C lower than that of standard Charpy test pieces. Above 550°C, the higher the tempering temperature, the larger the differences in the transition temperature due to the different cooling rate after tempering. This fact was principally due to the pronounced lowering in the transition temperature when the specimens were cooled down rapidly from the higher tempering temperature. Furthermore, isothermal embrittlement of specimens as cooled rapidly after tempered at 650° has been made at various temperatures up to 600°C and the variation of transition temperatures was compared. Since Si-Cr-Mn steel showed remarkable temper-brittleness, its transition temperature has been shifted up about 240°C by reheating at 500°C for 100 hrs.
