Wire + Arc Additive Manufacture of 17-4 PH stainless steel: effect of different processing conditions on microstructure, hardness, and tensile strength.

Wire + Arc Additive Manufacture (WAAM) is receiving increasing attention as it offers a way to fabricate meter scale parts, with low capital cost and material waste. A wide range of metallic alloys are suitable for this process. Martensitic grade precipitation-hardening stainless steel 17-4 PH offers a good compromise between high strength and corrosion resistance. Hence, it is important to investigate the behaviour of this alloy in WAAM. In the present work, the effect of different process variables such as shielding gas, deposition path and post-fabrication heat treatment, on microstructure and mechanical properties was studied. A series of samples were manufactured by WAAM using the Fronius Cold Metal Transfer (CMT) process under different conditions and they were subsequently characterized by optical and electron microscopy and mechanical properties in terms of strength and hardness. It was found that using shielding gases that result in higher heat input reduces the amount of retained austenite in the as-deposited microstructure. Additionally, it was demonstrated that required tensile properties can be achieved by adequate post-processing heat treatment. However, it is suggested that direct aging in as deposited condition resulted in formation of harmful interdendritic phases which embrittles the deposit.