Fracture behavior of thick-section weldment in Fe-12Cr-12Ni-10Mn-0.24N stainless steel at liquid helium temperature

Type JJ1, a nitrogen-strengthened austenitic stainless steel (Fe-12Cr-12Ni-10Mn-0.24N), is emerging as the preferred structural material for superconducting fusion magnet casings to operate at liquid helium temperature (4 K). This article describes an examination of the cryogenic fracture behavior of thick-section (200 mm) weldment in JJ1 forged stainless-steel plate. The compact tension geometry was used for the elastic-plastic fracture toughness tests at 4 K. The through-thickness fracture toughness was investigated with particular attention to the influence of the nitrogen and inclusion contents. The magnitude of the 4-K fracture toughness decreased with increasing inclusion content. In addition to fracture toughness data, temperature rise near the crack tip during fracture was measured. Significant adiabatic heating occurred, and internal temperature rises up to 52 K were reported.