Effect of Crystallography On Stress Corrosion Cracking Growth in Austenitic Stainless Steels
thesisposted on 15.12.2020, 22:29 authored by Haozheng QuHaozheng Qu
This thesis aims to reveal the correlation between stress corrosion cracking propagation behavior and Schmid and Taylor factor mismatch using EBSD analysis.
Chloride induced stress corrosion cracking (CISCC) is one of the most vulnerable weaknesses for the widely used austenitic stainless steel in many industries. The complex nature of CISCC involves mechanical, electrochemical, and microstructural perspectives. The objective of this thesis is to assess CISCC phenomenon in austenitic stainless steel from the mechanical and crystallographic perspective, specifically on the effect of local strain and stress and anisotropic plastic deformation. Austenitic stainless steel 304L test coupons are bent in four-point bending fixtures to obtain tensile stress for CISCC, followed by corrosion experiment in boiling magnesium chloride solution. Stress state of the sample is evaluated by finite element analysis (FEA) and X-ray Diffraction Crystallography (XRD) prior corrosion test. Cross section of the cracked region are analyzed with Electron Backscatter Diffraction (EBSD) to analyze the relationship between CISCC behaviors and crystallographic features in the sample. Schmid factor and Taylor factor are used to quantitatively evaluate CISCC initiation and propagation behavior. It is learned that in polycrystalline FCC stainless steel, mismatch of Schmid factor and Taylor factor values in adjacent grains along crack path governs CISCC propagation susceptibility and path selection. Crack propagation factor competition model is proposed based on observations from EBSD maps, incorporating Schmid factor and Taylor factor mismatch, electrochemical condition of crack tip, and anisotropic properties.