Case Study: Brittle Cracking of 17-4 PH Shafts

Case Study: Brittle Failures of 17-4 PH Shafts 17-4 PH stainless steel is often used in industrial applications because of its combination of good corrosion resistance and excellent strength. However, because of its complex microstructure and thermal treatments, this alloy is also susceptible to uncommon failure mechanisms. This paper describes the brittle cracking of 17-4 PH high-torque shafts that failed in service. Visual examination of the fracture surfaces showed clear intergranular cracking. Mechanical testing indicated that the parts met the applicable ASTM standard requirements, including longitudinal Charpy values. However, transverse Charpy results were very low, indicating significant anisotropic behavior. The percentage of retained austenite was also found to be minimal. These factors are known to promote a failure mechanism known as sustained load cracking. Strategies to prevent this type of failure are discussed.