Evaluation of the effects of the addition of Al, Ti, and Zr on microstructure, carburization and creep resistance of the HPNb alloy

The process of thermally cracking hydrocarbons and steam in pyrolysis furnaces to obtain ethylene is essential in the production chain of products relevant to our daily lives, such as fertilizers, polymers, pharmaceuticals, etc. The operating temperature of these furnaces is limited by the occurrence of carburization and/or creep in the metallic alloy used. The objective of this work was to investigate the effect of adding Aluminum (Al) at approximately 3 wt%, Titanium (Ti) at around 0.2 wt%, and Zirconium (Zr) at about 0.2 wt% on the carburization and creep resistance of the HPNb alloy. This material is a high-performance nickel-chromium-iron (Ni–Cr–Fe) system alloy enriched with niobium (Nb). Carburization in the samples was investigated by exposure to 1150 °C for 480 h in a carburizing atmosphere. Creep was evaluated through creep-rupture tests with a constant load, performed under a tension of 17 MPa and a temperature of 1150 °C, in four metallic alloys produced by static pouring with different chemical compositions. The data obtained were analyzed using optical microscopy, SEM, EDS, and EBSD. This study’s main findings indicate that while Al enhances carburization resistance, its impact on creep resistance varies depending on exposure to carburizing conditions. The addition of Ti or Zr did not significantly alter carburization resistance but contributed to improved creep resistance under specific conditions. This study provides insights into optimizing alloy compositions for enhanced performance in high-temperature industrial applications.