Reasons for R26 high temperature alloy bolt fracture

The R26 high temperature alloy bolt used to fix the flange of the high pressure air duct of a steam turbine unit fractured. The causes of bolt fracture were analyzed using macroscopic observation, chemical composition analysis, metallographic examination, mechanical property testing, scanning electron microscopy, and energy spectrum analysis. The results show that the high content of Ti element in the raw material of the bolt resulted in the formation of point like inclusions and precipitates in the material. After hot rolling processing, the banded structure was formed, causing a decrease in the high-temperature performance and an increase in hardness of the bolt. The bolt served in a high temperature environment for a long time and eventually experienced brittle fracture.