Abstract: Cooling method of GH4220 alloy bolts in the cooling stage of solution treatment at 1220 ℃ was changed from the air cooling of the standard heat treatment system to slow cooling (cooling to 1100 ℃ within 24 min and holding for 1 min, and then air cooling), the grain boundary morphology and mechanical properties of the alloy were observed by means of SEM and computer-controlled electronic universal testing machine. The results show that compared with the standard heat treatment system, the grain boundary after the slow cooling treatment has obvious zigzag characteristics, and the grain boundary changes from a straight grain boundary to a curved grain boundary. The room temperature (950 ℃) tensile strength is increased by 13.8% from 1004 MPa under the standard heat treatment system to 1143 MPa. Similarly, the high temperature tensile strength is increased by 11.3% from 478 MPa under the standard heat treatment system to 532 MPa. The high temperature (940 ℃) stress lasting fracture time increases significantly, from 38.2 h under the standard heat treatment system to 51.7 h, which rises by 35%.

Key words: GH4220 alloy bolts, cooling rate, morphology of grain boundary, mechanical properties