The microstructure evolution and its effect on corrosion properties of 18Cr-12Ni-2,5Mo steel annealed at 500-900°C

Abstract

The process of the secondary phases precipitation controls the mechanical and physical properties of the stainless steels. The process of precipitation and its influence on corrosion resistance was analysed in the experimental steel AISI 316. The corrosion test ASTM A 262 practice A was used for evaluation of the experimental steel to intergranular corrosion. Results showed that the solution-annealed samples (1100°C/1h - followed by water quenching) did not present susceptibility to intergranular corrosion. The heat treatment in the range from 500 to 900°C resulted in susceptibility to intergranular attack. Precipitation of carbide M23C6 accelerates sensitisation of the experimental steel. Increasing of holding time cased precipitation σ-phase and carbide M6C, which were detected at grain boundaries. Transmission electron microscopy was used for identification of particles at the grain boundaries, measurement of their size and studied of their morphology.