Abstract: The pump shaft made of 17-4PH steel bent after having been placed for a period of time. Three samples were cut from the shaft for experiment testing. These samples were given solution treating at 1 020~1 060 ℃ and then aged at 540~560 ℃ with following air cooling respectively. After heat treatment, metallographic observation and Rockwell hardness test were carried out. For the pump shaft of 17-4PH precipitation hardening stainless steel, the dominant microstructure should be composed of lath martensite. However, through metallographic observation, it was found that there was a large number of retained austenite among the lath martensite, and lots of banded ferrite was observed in the axial section. The retained austenite has a tendency to transform into martensite at room temperature. When the pump shaft is placed improperly, the highly localized tensile stress would induce phase transformation which leads to shaft bending.

Key words: 17-4PH steel, pump shaft, bending failure, retained austenite, ferrite