Evaluation of thermal aging activation energies based on multi-scale mechanical property tests for an austenitic stainless steel weld beads

Abstract

The long-term thermal aging behavior of a 316L austenitic stainless steel welds containing ∼12% of δ-ferrite was investigated using the nano-scale (nanopillar compression), micro-scale (micro-hardness and small punch), and macro-scale (tensile and J-R) mechanical property testing methods. Specimens were aged at 343, 375, and 400 °C for up to 20,000 h. The thermal aging activation energies were estimated based on the various mechanical test results using two fitting methods. The activation energies vary from 124 to 300 kJ/mol, depending on fitting and mechanical testing methods. Among the mechanical properties, the nanopillar and J-R test results showed similar activation energies lower than those from other mechanical properties. The similarities and discrepancies among the estimated activation energies were discussed in view of the contribution of embrittled δ-ferrite to the fracture and deformation of test specimens.