Role of nano-sized precipitates on LCF failure behavior for the CrMoV steel welded joint after long-term high temperature service

•Nano-sized M23C6 or M6C precipitated at the turbine part after long-term service.•Nano-sized precipitates could delay softening of weld through dislocation pinning.•Low cycle fatigue failure competition occurred between weld and over tempered zone.•Higher strain amplitude leads to more severe softening and failure in the weld metal.