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The testing of hot hardness is recently widely practised and drawing attention as a convenient way to find the mechanical properties of engineering materials, e.g. tensile strength, creep strength and creep rupture strength at an elevated temperature.There are two types of apparatuses for testing hot hardness that are now available in Japan to measure the Vickers hardness of materials, both metallic and non-metallic, and the measured values of the hot hardness are greatly variable depending on the measuring conditions and methods.In order to obtain the reliable values of hot hardness it is absolutely necessary, therefore, that the measuring conditions and method will be carefully studied. We have performed a number of experimental studies regarding the testing procedures and the conditions in connection therewith, and have been able, thanks to the cooperation of twelve research laboratories, to obtain a criterion for proper conditions and methods for the testing of hot hardness.(Received Nov. 1, 1971)

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