A series of investigations were conducted to clarify the change in mechanical properties of SBHS subjected to heating and cooling assuming fire, and to examine whether the change can be estimated by hardness tests. When SBHS was heated above 600 ℃ and then cooled, the material strength decreased due to recrystallization and transformation. A clear correspondence was observed between the mechanical properties of SBHS subjected to heating and cooling and the Leeb and Vickers hardnesses. The yield stress and tensile strength could be estimated by the hardness tests with an error of approximately 5 % from the tensile test results.
