Abstract: In the high-temperature service environment of 350-500 °C for low-pressure steam turbine rotors, 30Cr2Ni4MoV rotor steel usually exhibits serious aging embrittlement after long-term aging, which can induce intergranular fracture (IGF). Mn partitioning at grain boundaries (GBs) and its effect on aging embrittlement of 30Cr2Ni4MoV rotor steel during aging at 500 °C for 0-10,000 h were investigated mainly by electron backscattering diffraction (EBSD), transmission Kikuchi diffraction (TKD) and atom probe tomography (APT). Aging at 500 °C, there is limited Mn partitioning between M₂₃C₆ and matrix. And before aging, Mn is uniformly distributed at GBs. But after aging, Mn enrichment level at GBs increases, and H-GBs with larger misorientations contain higher Mn enrichment. The tensile and impact testing results reveal that Mn partitioning at H-GBs and L-GBs during aging has a relatively small effect on the tensile properties, but reduces impact toughness. During impact process, crack initiation energy remains stable due to small variation of M₂₃C₆ size. Interestingly, crack propagation energy drops obviously after Mn partitioning at H-GBs. The reason is that Mn partitioning at H-GBs decreases GB cohesion and promotes crack propagation along GBs with mainly H-GBs, leading to IGF formation.

Key words: Grain boundary, Mn partitioning, Intergranular fracture (IGF), Aging embrittlement, 30Cr2Ni4MoV rotor steel