Microstructure and Properties of NB, V and N Modified CB₇CU-1 (17-4 PH) Steel


Microstructure and mechanical properties of CB7Cu-1 (17-4 PH) steel modified by addition of niobium, vanadium, and nitrogen were explored. ��Four heats of CB7Cu-1 steel: base, niobium modified to remove carbon from solution, vanadium modified, and vanadium plus nitrogen modified were melted in a 45 kg (100 lb) induction furnace under Ar atmosphere and cast into no-bake phenolic bonded sand molds and preheated ceramic shell molds. Computational thermodynamics, Scanning Electron Microscopy (SEM), X-ray diffraction, and optical microscopy techniques were used to characterize microstructures produced during homogenization, austenite conditioning, and quenching treatments. Age hardening kinetics were studied at 460°C (860°F) and 482°C (900°F). Tensile an Charpy impact properties were measured in peak-aged and over-aged conditions. Fracture surfaces were observed using SEM and complex niobium-vanadium carbonitrides were identified as fracture initiation sites. For a fixed elongation to failure, a higher tensile strength was obtained by over-aging the CB7Cu-1 steel modified with niobium, vanadium, and nitrogen; however, the Charpy impact energy was lower as compared to the peak aged base CB7Cu-1 alloy. Keywords: 17-4 PH, stainless steel, precipitation hardening, niobium, vanadium, nitrogen, charpy impact, tensile strength, heat treatment, X-ray diffraction


Materials Science and Engineering

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