It has recently been revealed that high-density pre-existing hydrogen micro pores, formed during production processes, exhibit premature growth and coalescence under external loading at room temperature, thereby inducing ductile fracture. This process is incidentally supplemented by the well-established ductile fracture mechanism based on particle damage. It is reasonable to assume that the pre-existing hydrogen micro pores may also contribute to damage evolution at high temperatures. In the present study, synchrotron X-ray microtomography was applied to the in-situ observation of