Effect of Heat Treatment and of Primary Austenite Grain Size on the Minimum Size of Detectable Defect on 26NiCrMoV11.5 High Strength Steel

This study is focused on the sensitivity of ultra-sonic test (UT) performed on special carbon steel as a function of their microstructure. UTs was carried out on several samples divided into two families and featured by different process-histories. The estimation of the attenuation of the ultrasonic signals as a function of the microstructural features was performed. The samples underwent different thermal treatments to modify their parent austenite grain size and the associated martensite islands by re-austenitization process and by the following grain growth. The difference of UT results mainly depends upon the wave scattering and the energy absorption due to the difference in the grain size and in the crystal lattice orientation.