High resolution autoradiography for revealing sulphur segregation at austenite grain boundaries

A high resolution autoradiography technique was applied to observe the evolution of sulphur (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 μ Ci) with an exposure time of about 3 wk. The alloys were annealed at 950°C or 1150°C and also deformed at 950°C (in the hot brittleness temperature region). The S segregation revealed on austenite grain boundaries is more pronounced on the deformed specimen containing AIN precipitates. A high S concentration was observed in cracked regions. At 1150°C, the segregation level is smaller. A specimen containing only S deformed at 950°C, exhibits S segregation on dynamically recrystallized boundaries.