Abstract:

Aging treatment of a martensite stainless steel (17-4PH) was conducted at three different regimes: (1) 442 °C, 8 h air cooled, (2) 465 °C, 4 h air cooled and (3) 480 °C, 1 h air cooled, respectively. The formation of aging precipitates on 17-4PH stainless steel was investigated by Transmission Electron Microscope (TEM) and Selected Area Electron Microscope (SAEM) technique. The results show that under regime (1), ε-Cu particles and metastable phases Nb6C(N)5 and Nb2C(N) with the sizes less than 10 nm were precipitated dispersedly in the martensite. Under regime (2), ε-Cu particles and stable phase NbC(N) with about 10~15 nm in size were precipitated. Under regime (3), the sizes of precipitated particles in the martensite became larger, and the type of precipitates were still ε-Cu and NbC(N) particles with size about 20~25 nm. NbC(N) phase and martensite were coherently precipitated, and the orientation relationship between both phases was NbC\[001\]//α-Fe\[001\].

Key words: metal materials, 17-4PH stainless steel, aging, microstructure