Free surface contribution to sensitization of an austenitic stainless steel

Austenitic stainless steels are widely used in corrosive environments. Duri ng plastic straining these steels exhibit environmental effect. The flow st ress in air at intermediate temperatures is compared with the specimens str ained in vacuum. Static annealing in air and vacuum to a different degree s trengthens the material at room temperature. The data reported here was col lected for AISI 316 and 316L austenitic stainless steels. The specimens hav e been subjected to annealing at 900 degreesC followed by water quenching annealing at 600 degreesC in either air or vacuum. The results obtained sh ow that the resistance to corrosion of the grain boundaries in austenitic s tainless steel subjected to recrystallization annealing at 900 degreesC in air is particularly low in the near-surface layer of specimens. The additio nal annealing at 600 degreesC either in vacuum or air per se does not lead to formation of a measurable Cr-depletion along grain boundaries in the nea r-surface zone, The observation of surface sensitization proves a detriment al effect, a high temperature annealing in air on corrosion resistance of a n austenitic stainless steel. The results show that the harmful consequence of a high temperature annealing in air can be reversed by a subsequent ann ealing in vacuum at intermediate temperatures. The results also rationalize mechanical cleaning of elements subjected to a heat-treatment in air. (C) 2001 Published by Elsevier Science B.V.