Caracterización y análisis de los mecanismos de falla en el acero de las turbinas hidráulicas

Abstract

The objective of this study was to analyze and characterize the mechanisms of failure due to torsion, traction and impact in the steel of hydraulic turbines (ASTM A743 CA-6NM) in order to determine the type of fracture that the material presents, due to the CIRT wear and Failure Analysis Laboratory does not have a record of standard photographs of these mechanisms Verification of ASTM A743 CA-6NM steel was carried out by spectrometric, metallographic and hardness tests. Specimens were machined, and later the torsion, traction and impact tests were carried out according to the standards: NTE INEN 140: 2013, ASTM E8-E8M-15a and ASTM E23-07A, respectively. Based on the “ASM INTERNATIONAL FAILURE ANALYSYS AND PREVENTION” handbook, the fractographic analysis was performed using the scanning electron microscope (SEM) and a stereoscope; with which macroscopic and microscopic qualitative characteristics were established. In the torsion failure mechanism, a smooth texture with rubbing in the periphery and smooth in the central zone was found macroscopically, microscopically micro voids with an elliptical geometry were observed; in traction, macroscopically a fibrous texture was presented and cut lips with a smooth texture were formed, and microscopically there was the presence of circular micro-voids; on impact, macroscopically it has a fibrous texture, and microscopically circular and semi-elliptic micro-voids are observed. These characteristics made it possible to determine that the material of the turbines presents a ductile fracture in each failure mechanism, with this investigation a considerable contribution is made to the optimal recovery of hydraulic turbines, reducing the time of fractographic analysis of the failures. It is recommended to characterize progressive fractures such as fatigue fracture, stress corrosion fracture and abrasive wear to expand the study of failure mechanisms.