One of the turbine blades made of carbon steel Cr12 used at Suralaya Power Station experienced failure after being used for 33 years. The cause of such failure was studied in this work based on post-mortem data of the chemical composition, fracture morphology, and mechanical properties of the fractured section. The composition analysis by an x-ray fluorescence spectrometer (XRF) showed a slightly higher Cr and Ni content of 16.1 wt% in the fractured material, which probably due to the accumulation of scale deposit on the surface. The XRD analysis detected only the martensite phase indicating no phase transformation occurred during the long period of exposure to elevated temperature. Many fine cavities were observed in the cross-section material. The cavities were likely formed as a result of the absorption of hydrogen gas from the environment. The material was exposed to H2S gas during operation. Infiltration of hydrogen in the material contributed to increasing the material hardness to 324 HB and lowering the tensile strength to 95 MPa. The standard material has a mechanical hardness and tensile strength value of 240 HB and 530 MPa. The cavities became the initiation site for cracks. Under the cyclic load during operation, a crack was inevitably occurred, leading to material failure. The existence of beach marks in the fractured surface confirmed that the material experienced fatigue failure.