8 - Applications of Fracture Mechanics in Stress Corrosion Cracking and Introduction to Life Prediction Approaches

Abstract

Number of loading techniques such as constant strain, constant load, slow strain rate are being used for stress corrosion testing of materials. These techniques have been useful in comparision of stress corrosion susceptibility of various alloy/environment combinations and also to evaluate the influence of metallurgical factors for a particular alloy. Fracture mechanics approach in combination with above loading techniques has been successfully utilized in getting quantitative data with respect to threshold values and crack growth rates in addition to grading the alloys with respect to cracking susceptibility. This data could be used in predictive models. In this paper, data available up to date on austenitic steels is presented and analyzed. Work carried out at authors laboratory on AISI 304LN and AISI 316LN stainless steels and their welds has been highlighted. It has been found that cold work and sensitization decrease the threshold values and adversely influence the crack growth rates. For welds of AISI 316SS, it is seen that threshold values are almost half and crack growth rates are an order of magnitude higher as compared to solution annealed condition. Based on the data generated on crack growth rates, analysis of acoustic emission records during crack growth, fractographical features and activation energy measurements attempt has been made to understand the mechanism of stress corrosion cracking of austenitic steels in chloride medium. A brief introduction to life prediction approaches such as slip dissolution model, models based on crack growth rates and statistical approach has been given.