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

Abstract

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 2·107 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.

Fatigue and Corrosion Fatigue Behaviour of Brazed Stainless Steel Joints AISI 304L/BAu-4 in Synthetic Exhaust Gas Condensate

“…The authors investigated stainless steel joints brazed with the nickel-base filler metal BNi-2 in earlier studies [34]. The S-N curves of the brazed AISI304L/BNi-2 joints determined for fatigue and corrosion fatigue loadings are presented in a semi-logarithmic scale in Figure 9b.…”

“…A fatigue strength of 90 MPa was determined in the synthetic condensate for 2 × 10 6 cycles. Thus, a reduction of the fatigue strength down to 43% due to the superimposed corrosive loading has to be taken into consideration for the brazed AISI304L/BNi-2 joints [34].…”

“…Results of constant amplitude tests, performed in air and in synthetic condensate K2.2: ( a ) brazed AISI 304L/BAu-4 specimens of the current study; and ( b ) brazed AISI 304L/BNi-2 specimens from earlier studies [34]. …”

Interpretation of Frequency Effect for High-Strength Steels with Three Different Strength Levels via Crystal Plasticity Finite Element Method

“…For face-centered cubic materials such as stainless steel [21], aluminum alloy [22] and hexagonal-close-packed materials such as titanium alloy [23], the investigation results demonstrate no obvious or just slight differences existing in fatigue lives as low and ultrasonic loading frequencies are applied, respectively. However, as the influences of environmental factors are considered [24,25], the frequency effect is noticeable.…”