Microstructure and intergranular corrosion of the austenitic stainless steel 1.4970

The precipitation behaviour of the DIN 1.4970 steel and its effect on the intergranular corrosion resistance were studied. Time–temperature–precipitation diagrams for the secondary phases (Ti, Mo)C, (Cr, Fe, Mo, Ni)23C6 and (Cr, Fe)2B are presented and representative samples have been selected for corrosion studies. The susceptibility to intergranular corrosion of the samples was evaluated using the double loop electrochemical potentiokinetic reactivation technique. The results showed that the solution-annealed samples and those aged at 1173 K did not present susceptibility to intergranular corrosion, whereas aging treatment from 873 to 1073 K resulted in small susceptibility to intergranular attack that decreased with aging temperature. The preferential formation of (Ti, Mo)C at higher aging temperatures comparatively to M23C6, retained the chromium in solid solution preventing steel sensitization and, consequently, intergranular corrosion.