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EVALUATION OF THE EFFECT OF THE BASE METAL PREHEATING ON THE PHASE BALANCE IN GTAW WELDING OF SUPER DUPLEX STAINLESS STEEL UNS S32750

Grant number: 24/00616-6
Support Opportunities:Scholarships in Brazil - Scientific Initiation
Effective date (Start): April 01, 2024
Effective date (End): March 31, 2025
Field of knowledge:Engineering - Mechanical Engineering - Manufacturing Processes
Principal Investigator:Eli Jorge da Cruz Junior
Grantee:Raul Henrique Ribeiro
Host Institution: Instituto Federal de Educação, Ciência e Tecnologia de São Paulo (IFSP). Campus Itapetininga. Itapetininga , SP, Brazil

Abstract

Super duplex stainless steels (SDSS) have a biphasic microstructure, with approximately equal volumetric fractions of ferrite and austenite, giving them excellent mechanical properties and high corrosion resistance. Due to this combination of mechanical properties and corrosion resistance, these steels have a wide range of applications in oil and gas, pulp and paper, and offshore industries. The Gas-Shielded Tungsten Arc Welding (GTAW) process affects the microstructure of SDSS, resulting in unbalanced volumetric fractions or even precipitation of deleterious intermetallic phases, compromising their properties and applications. To obtain a balanced microstructure, the addition of austenite stabilizing elements or the application of heat treatments is indicated. This addition can result in a significant increase in the cost of the process, making heat treatments more economically viable. Due to the characteristic cooling rate of the GTAW process, there is not enough time for the formation of austenite, resulting in a predominantly ferritic microstructure. By heating the material before welding, the temperature will be maintained for a longer time in the ranges of transformation from ferrite to austenite, resulting in a more balanced microstructure suitable for industrial applications. Due to the importance of phase balance in the properties and applications of SDSS, this project aims to study the application of a pre-welding heat treatment as a way to correct the volumetric fractions of the microstructure resulting from the GTAW process. The welds will be evaluated through microstructural characterization, evaluation of mechanical properties, and corrosion resistance.

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