Metallurgical Analysis of Stainless Steel Failed Shaft Due to Excessive Precipitation

Precipitation is a strengthening mechanism. Precipitation hardening allows higher corrosion resistance and mechanical strength. Incorrect heat treatment is usually associated to cases of their failure. This study investigates the failure of 17-7 PH Stainless steel 25 mm dia pump drive shaft used in processing industry which experienced a premature failure. Design load found within material limits, and its presumed material is cause of premature failure. Furthermore, investigation reveals that the shaft failed due to material processing issues. A detailed failure analysis was carried out including, visual inspection, chemical analysis, hardness evaluation, metallography, mechanical testing and fractography were conducted. The study found that the hardness of the shaft varied from the grains to the grain boundaries. It can be concluded from various test results that excessive precipitation hardening on the grain boundaries is root cause of the failure, as temperature exposure of material and non-standard heat treatment. Various evidence pertaining to excessive precipitation hardening of failure shaft were discussed in this article.