Fatigue Cracking of PH Stainless Steel Parts and NDE Methods for Crack Detection

Small PH13-8Mo stainless steel parts suffered from machining‑induced fatigue cracking during manufacturing due to vibration and possible resonant frequency excitation. To simulate cyclic loading characteristic of the lathe turning process, laboratory rotating beam fatigue (RBF) testing was performed. The results showed that the presence of a sharp notch in the part geometry was the major driver for fatigue crack initiation, while the heat treatment condition (H950 vs. H1100) had a minor yet measurable effect. Scanning electron microscopy (SEM) was performed to detect cracks but was cumbersome for high part volumes and often inconclusive. To more reliably screen for damage in parts during manufacturing, a variety of established and emerging non-destructive evaluation (NDE) methods were investigated to understand fatigue crack detection limits. Among the NDE methods to be discussed include liquid dye penetrant, X-ray radiography, eddy current inspection, and ultrasonic inspection techniques. The ultrasonic-based method of Process Compensated Resonant Testing (PCRT) showed the most promise for detecting small cracks while being amenable to a production setting.

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