A flat plate specimen is used in the coupon tensile test in case when a round bar specimen cannot be manufactured for thin steel plates. However, effects of the specimen shapes on the mechanical properties of steels at elevated temperatures were not clarified. The coupon tensile tests at elevated temperatures were conducted with various specimen shapes, and it was clarified that the full-thickness flat plate specimens possessed the low effective strength, however that effect was very smaller than that of the variation among the steel lots.
