Cryogenic Fracture Toughness and Temperature Rise of Thick Section Weldment in Forged JJ1 Type Austenitic Stainless Steel Plate

Abstract

JJ1 type austenitic stainless steel is emerging as the preferred structural material for superconducting magnet casings to operate at liquid helium temperature (4K). In order to evaluate the cryogenic fracture toughness and the temperature rise of tangsten inertgas (TIG) weld in 200 mm thick forged JJ1 type austenitic stainless steel plate for fusion reactor magnets of the next generation, elastic-plastic fracture toughness (J_IC) tests were performed with 1T compact tension specimens at 4K. Testing was conducted in accordance with ASTM standards E813-87 for determining J_IC using the unloading compliance technique to monitor crack growth. Au/0.07% Fe -Chromel thermocouples were used to measure the temperature rise near the crack tip. The effects of specimen location and nitrogen content on J_IC are examined. Specimens were subjected to scanning electron microscopy (SEM) after fracture testing. The effect of inclusion content on the elastic-plastic fracture toughness parameters (J_Q, J_IC) is also discussed using optical microscopy and energy dispersive X-ray spectrometer (EDX).