Stress Relief Cracking Susceptibility in High-Temperature Alloys

The stress relief cracking (SRC) susceptibility of a range of austenitic and ferritic alloys was tested using Gleeble (R) based test procedures. The tests were developed to study the effect of postweld heat treatment (PWHT) temperature and cold working on the SRC susceptibility. Six susceptibility parameters were identified from the test results (ductility, percentage stress relaxed, hardness increase at fracture, failure time, fracture mode, and extent/type of secondary cracks below the fracture). The susceptibility parameters were integrated with concepts of Risk Priority Number (a prioritization tool in 6-Sigma) to develop an SRC susceptibility index. Sensitivity analysis of the methodology was done to ensure its robustness. The ferritic alloys generally showed the highest SRC susceptibility at a PWHT temperature of 600 degrees C, while the austenitic alloys were generally most susceptible at 800 degrees C. Using the susceptibility index, the SRC tendency of all the alloys was divided into three regions (highly susceptible, moderately susceptible, and resistant). The newly proposed test procedure and SRC susceptibility index provide a robust approach for studying and ranking the SRC susceptibility of engineering alloys. Post-test microstructurel characterization of the SRC samples provided insight into the cracking mechanisms.