Real time measurement by Bragg edge diffraction of the reverse (α′ → γ) transformation in a deformed 304 stainless steel

Bragg edge neutron diffraction has been used to directly measure an evolving crystal structure, averaged over several cubic centimeters of steel, with a temporal resolution of better than 1 min. In this demonstration experiment, coupons of 304 stainless steel were rolled at 77 K to produce a 20% austenitic and 80% martensitic microstructure. On reheating to in excess of 550 °C, the martensite to austenite retransformation, in the deformed coupons, was recorded using Bragg edge diffraction. Initial and final phase compositions were determined using conventional neutron diffraction. At 670 °C more than 80% of the retransformation occurred within 15 min of the sample being placed in the furnace but during that period approximately 15 sequential edge diffraction patterns were recorded. The results illustrate the application of Bragg edge diffraction for tracking bulk phase transformations and the potential for faster measurements is discussed.