HIGH-RESOLUTION AUTORADIOGRAPHY FOR REVEALING SULFUR SEGREGATION AT AUSTENITE GRAIN-BOUNDARIES

A high resolution autoradiography technique was applied to observe the evolution of sulfur (S) segregation level in a high-purity iron doped with carbon (C), about 30 ppm of S and/or aluminum (Al) and nitrogen (N). The sample radioactivity was 5. 6 KBq (0. 15 mu Ci) with an exposure time of about 3 wk. The alloys were annealed at 950 degree C or 1150 degree C and also deformed at 950 degree C (in the hot brittleness temperature region). The S segregation revealed on austenite grain boundaries is more pronounced on the deformed specimen containing AlN precipitates. A high S concentration was observed in cracked regions. At 1150 degree C, the segregation level is smaller. A specimen containing only S and deformed at 950 degree C exhibits S segregation on dynamically recrystallized boundaries.