Crystalline characteristics of a dual-phase precipitation hardening stainless steel in quenched solid solution and aging treatments

This study investigated the development of the microstructures and aging reactions in a new dual-phase (allotriomorphic δ + γ) 17–4 precipitation-hardened (PH) stainless steel (SS) alloy. The 17–4 PH alloy, a martensitic stainless steel containing Cu (3–5 wt.%), was subjected to solid solution treatment followed by quenching using oil, H₂O, or liquid N₂. The microstructures of the steel specimens were primarily composed of lath martensite and allotriomorphic δ-ferrite. X-ray diffraction analysis indicated that the structures consisted entirely of bcc phase peaks. During aging at 560 and 600 °C, the local microstrain was released because of the tempering of the lath martensite and the formation of reverted austenite, resulting in a shift in the kernel's average misorientation distribution toward lower angles. The misorientation associated with the martensite boundaries ranged from 10° to 20° and from 47° to 57° in the packets. In the blocks, it ranged from 50° to 60°. The F1-ferrite approximately followed the Kurdjumov–Sachs orientation relationship with A1-austenite and A2-austenite.