27th IFHTSE CONGRESS & EUROPEAN CONFERENCE ON HEAT TREATMENT 2022

Precipitation hardening martensitic stainless steel 17-4 PH is a classic grade that receives renewed attention because of its suitability for metal additive manufacturing (MAM). Conventionally, 17-4 PH is subjected to austenitizing before it transforms into martensite during cooling. Subsequently, an aging treatment is performed to achieve strengthening by precipitation of copper particles. It is generally believed that no precipitation reaction is possible while the material is austenitic. This would make it robust to variations in the treatment process and thus avoid precipitation during MAM. In the present study we demonstrate that this belief is unjustified and that austenite does age. Accordingly, martensite formation is affected as well as martensite’s aging response. It is demonstrated that the aging phenomena occurring in austenite can affect the properties of the steel at the end of the thermal cycle, and hence its performance in service. The implications and the potential exploitation of the revealed phenomena are discussed.