REAL-TIME MEASUREMENT BY BRAGG EDGE-DIFFRACTION OF THE REVERSE (ALPHA'-]GAMMA) TRANSFORMATION IN A DEFORMED 304-STAINLESS-STEEL

Bragg edge neutron diffraction has been used to directly measure an ev olving crystal structure, averaged over several cubic centimeters of s teel, with a temporal resolution of better than 1 min. In this demonst ration experiment, coupons of 304 stainless steel were rolled at 77 K to produce a 20% austenitic and 80% martensitic microstructure. On reh eating to in excess of 550 degrees C, the martensite to austenite retr ansformation, in the deformed coupons, was recorded using Bragg edge d iffraction. Initial and final phase compositions were determined using conventional neutron diffraction. At 670 degrees C more than 80% of t he 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 applic ation of Bragg edge diffraction for tracking bulk phase transformation s and the potential for faster measurements is discussed.