Auswirkung von Druckeigenspannungen in der Oberflaeche von Dampfturbinen-Scheiben auf das SpRK-Verhalten. Final Report. (Influence of residual compression stresses on the stress corrosion cracking behaviour of turbine rotor disc material. Final report).

摘要

In this project the influence of residual compression stresses on the stress corrosion cracking behaviour of the turbine disc steel 26 NiCrMoV 14 5 (Rp(sub 0.2) = 850 N/mm(sup 2)) was investigated. The residual compression stresses were produced by shot peening and rolling. Shot peening results in residual compression stresses of -500 N/mm(sup 2) in the surface. In a depth from 600 (mu)m there still exist stresses from -100 N/mm(sup 2). CERT experiments with shot peened and unpeened specimens under hydrogen charging conditions were performed to see, whether residual compression stresses prevent the diffusion of hydrogen into the metal. This could not be established with these experimental parameters. Stress corrosion tests were carried out with shot peened tensile specimens and modified CT 2 specimens. The shot peened cylindrical specimens dependent on the stress level, have a time to failure which is ten times and more longer in 35% NaOH + 3,5% NaCl solution in comparison to untreated specimens. The CT2 specimens had a shot peened surface and a rolled bore hole of 20 mm. The residual compression stresses in the bore hole are produced by rolling in tangential direction. Compression stresses in the surface of -400 N/mm(sup 2) can be realized, with a maximum of -600 N/mm(sup 2) in a depth of 600 (mu)m. In a depth of 1500(mu)m there still exist stresses of -100 N/mm(sup 2). The CT 2 specimens were charged with hydrogen and also testet in 35% NaOH + 3,3% NaCl solution. Cracking occurred within 200 test hours at the bores of the samples which were not rolled. Crack initiation was not found in the bores of the samples which were rolled. The results show, that residual compression stresses in the critical surface regions can prevent stress corrosion cracking on turbine disks. (orig./MM) With 24 annexes. (ERA citation 16:013071)