Failure Analysis of Boat Rudder Fitting Fabricated from a Type 304 Stainless Steel

Abstract

The failure of a type 304 stainless steel component subassembled by welding and used on a boat in a marine environment was investigated. The mechanism of damage initiation and the cause of final failure were investigated. Initial examination of the component indicated deep branching cracks that were thought to have developed during service. The combination of microhardness test and finite element modeling (FEM) was employed to probe micromechanical properties of the damaged area. The corrosion observed was followed with scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). FEM analysis suggests that the cracked area had been subjected to tensile stresses in service. Microhardness across the welded section did not show any mechanical degradation across the weld and heat-affected zone. The cracked area was evidently corroded, and the microanalysis in the SEM/EDS indicated the presence of corrosion products. Regions around the cracks especially at the root of the crack were found to be severely depleted of Ni. It is evident that the primary course of failure was from the cracking from SCC attack and that the pitting observed is a secondary effect in the cracked region.