Failure Analysis and Hot Tearing Susceptibility of Stainless Steel CF3M

摘要

Hot tear formation has been witnessed during the solidification of the ferrous alloy by pulling the columnar dendrites in the transverse direction. The hot tearing susceptibility of an alloy is influenced by solidification rate, microstructure and the stress/strain conditions. It is valuable to predict the occurrence of tearing in a casting. In this study, hot tearing susceptibility of stainless steel CF3M grade casting was investigated using the method of constrained T-shaped solidification shrinkage and inducing strain by pulling dendrites in a transverse direction. An experimental setup equipped with the real-time measurement of temperature, displacement and contraction/applied force during solidification at elevated temperature has been developed. In this study, the sectioning technique was adopted for residual stress measurement after casting solidification, wire electric discharge machining has been identified as a suitable method of cutting along with a coordinate measuring machine sufficiently accurate for measurement, and finite element modeling and analysis were performed to calculate the stress. A metallographic study using an optical microscope and scanning electron microscope was performed to evaluate macro- and microstructure at failure zone of the casting. The study aims to investigate crack morphology and differentiate hot tear from other types of cracks in order to troubleshoot effectively. Stress, strain and temperature data provide onset of hot tearing and provide a base for mathematical model and validation. The results show that the strain or strain rate is more critical for hot tearing than stress. The studies on residual stress show that the tensile stress is not required to generate hot tears, but only the tensile strain is sufficient to form a hot tear.