The Effect of Silicon Content on Impact Toughness of T91 Grade Steels

The impact resistance of silicon (Si)-containing modified 9Cr-1Mo steels has been investigated within a temperature regime of −40 to 440 °C using the Charpy method. The results indicate that the energies absorbed in fracturing the tested specimens were substantially lower at temperatures of −40, 25, and 75 °C compared to those at elevated temperatures. Lower impact energies and higher ductile-to-brittle-transition-temperatures (DBTTs) were observed with the steels containing 1.5 and 1.9 wt.% Si. The steels containing higher Si levels exhibited both ductile and brittle failures at elevated temperatures. However, at lower temperatures, brittle failures characterized by cleavage and intergranular cracking were observed for all four tested materials.