Frequency-dependent fatigue and corrosion fatigue assessment of brazed AISI 304L/BM-2 joints in air and synthetic exhaust gas condensate

摘要

Since brazed components are often cyclically loaded in corrosive environments, the corrosion fatigue behaviour of the joints has to be investigated. Fatigue tests of brazed AISI 304L/BNi-2 joints, relevant for exhaust gas heat exchangers, were performed with specimens in the as-received condition and after pre-corrosion according to VDA 230-214. Additionally, the superimposed corrosion fatigue loading in an exhaust gas condensate was realised using a corrosion cell. Corrosion-induced and deformation-induced microstructural changes were metallographically evaluated. The influence of the test frequency from 1 to 150 Hz on the cyclic deformation and damage behaviour was characterised. In a statistical analysis, the fatigue strength of 210 MPa at 2-10~7 cycles was determined for the as-received condition with a 50% failure probability. The pre-corrosion as well as the superimposed loading lead to a reduction of the fatigue strength down to 22%. A novel test strategy is suitable for precise fatigue and corrosion fatigue assessments.