Pre-qualification of additively manufactured 316L stainless steel using Small Punch and Uniaxial Creep testing

Igor Simonovski^1*Karl Fredrik Nilsson¹Stefan Holmström²Mihaela Kus¹Andrea García-Junceda¹

• ¹European Commission, Joint Research Centre, Petten, The Netherlands, Petten, Netherlands
• ²Belgian Nuclear Research Centre (SCK CEN), Mol, Belgium

Additive manufacturing represents a cutting-edge technology that offers significant reductions in both manufacturing time and cost. However, any new technology or material need to go through a qualification process, before they can be used in the nuclear industry. This paper reports on a prequalification process of 316L stainless steel, manufactured using Laser Powder Bed Fusion (LPBF) additive manufacturing process. The study compares LPBF 316L, aged and non-aged materials from two different manufacturers. A Small Punch Creep test campaign at 650oC was performed at different loads. These tests are particularly advantageous because they require only a small amount of material, making them ideal when material availability is limited. Additionally, standard Uniaxial Creep tests were performed at the same temperature for comparative reference. A good correlation for the time to rupture – equivalent stress between the two test types was observed, with the equivalent stress calculated using the Small Punch Test EN 10371:2021 standard. A significant finding is that the Small Punch Creep deflection rate curves for LPBF-manufactured 316L exhibit multiple minima, unlike single minimum observed in forged 316L. This is believed to result from micro-cracking and has important implications for determining the equivalent stress creep properties, which are based on a single minimum value in the EN 10371:2021 standard. The multiple minima feature suggests that the approach to determine equivalent stress and strain rate of Small Punch Creep tests in the EN 10371:2021 standard needs to be re-evaluated to accommodate this complexity.