In-situ TEM investigation of dislocation loop evolution in HR3 steel during Fe+ ion irradiation

•Irradiation behavior of HR3 steel was first studied under Fe+ irradiation at different temperatures.•Evolution of dislocation loops in HR3 steel was in-situ analyzed in detail.•Loop rafting was found in HR3 steel for the first time.•Loop number density and size vs. irradiation dose were established at different temperatures.•The pre-existing dislocation lines had a significant effect on the density and Burgers vector of dislocation loops.