WE Colloquium: Julian Escobar, Friction Stir Welding and in situ heat treatments of a Supermartensitic Stainless Steel

State University of Campinas, Unicamp, Brazilian Nanotechnology National Laboratory, LNNano.

Abstract

Supermartensitic stainless steels (SMSS) are used by the oil and gas industry mainly in the form of seamless rolled products as drill pipe, casing and tubing. Carefully designed thermomechanical processes are used to provide low hardness (< 281 HV), adequate fracture toughness (150 J at -50 °C), moderate corrosion resistance in environments containing CO2 and Cl- , and yield strength above 500 MPa. The former characteristics are strongly influenced by an adequate distribution of finely dispersed MC carbides and reversed austenite (γr) in a tempered martensite matrix, without no presence of delta ferrite (delta ferrite). This microstructure is obtained by a carefully designed single or multi-step inter-critical tempering, involving the partitioning of γ-stabilizing elements into the reversed austenite by a diffusional process. Inadequate welding procedures for SMSS can cause detrimental microstructural modifications such as coarse fresh martensite in the fusion zone (FZ), and precipitation of delta ferrite and carbides in the high temperature heat affected
zone (HAZ), which promotes stress corrosion cracking. By using Friction Stir Welding (FSW), it is possible to suppress these detrimental effects, producing a refined microstructure composed by recrystallized martensitic grains with no presence of delta ferrite, accompanied only by low temperature austenitic and inter-critical HAZ.

Bio

Titles

• Mechanical Engineer degree at the National University of Colombia (2011).
• MSc. In Mechanical Engineering at the State University of Campinas (2013)
• Ph.D. candidate in Mechanical Engineering at the State University of Campinas (2013 - )

Research Experience

• Invited MSc and PhD student in the Brazilian Nanotechnology National Laboratory LNNano (2011 - ).
• Visiting Scholar at the University of Tennessee. Department of Mechanical, Aerospace and Biomedical Engineering. (Oct/2014 to March/2015).
• Visiting Scholar at the Oak Ridge National Laboratory. Manufacturing Demonstration Facility. (Oct/2014 to March/2015).
• Visiting Scholar at the Ohio State University. Welding Engineering Program, Department of Materials Science and engineering. (Oct 2016 – Oct 2017).