High temperature corrosion fatigue of duplex stainless steel shaft

This paper describes the result of a study on fatigue corrosion failure presented by a duplex stainless steel shaft from an agrochemical plant atomization system. The 25 mm diameter shaft was driven by a 30 kW electrical motor and was running at 14,000 rpm. The shaft presented a complete section fracture near a surface bearing. In order to determine the primary cause of failure, the study was divided into different techniques depending on the objectives. Visual observation and electronic scanning microscopy were performed to obtain a fractographical description of the fracture surfaces. Next, emission spectrometry was carried out for chemical analysis of the steel, followed by a Brinell hardness test in order to establish the steel static strength. Energy consumption at the moment of the failure was used to evaluate the stress level on the shaft. Finally, optical microscopy was performed to determine the steel microstructure. The study found that the most probable cause of failure was fatigue, produced by heating generated from friction between the shaft and a poorly lubricated guide bearing filled with a corrosive and abrasive mixture of CS 2, NaOH and diamine methylene, which caused adhesive wear grooves and an excessive clearance between shaft and bearing that originated an abnormal shaft movement, turn offset the rotation center, and induced the flexional cyclic loading. Failure was accelerated by the presence of the corrosive and abrasive lubricating substance within the fatigue cracks and the high temperature at the nearby surroundings.