Characterization of Corrosion Within Friction Stir Weld Zones of an API X-70 Steel Using a Novel Microcell Setup

Author(s)

da Cruz, Juliane Ribeiro ^[1] ; Bertazzoli, Rodnei ^[2]

Affiliation

^[1] Aeronaut Inst Technol ITA, Grad Program Aeronaut & Mech Engn, BR-12228900 Sao Jose Dos Campos, SP - Brazil

^[2] Univ Estadual Campinas, Fac Mech Engn, BR-13083860 Campinas, SP - Brazil

• Document type: Journal article
• Source: Journal of Materials Engineering and Performance; v. 29, n. 1 JAN 2020.
• Web of Science Citations: 1

Abstract

The susceptibility of API-X70 friction stir weld zones to corrosion in a Na2SO4 acid medium is successfully investigated using an innovative microcell setup. Microstructures were characterized by optical and electron microscopy, Vickers microhardness mapping and linear potential scan voltammetry, at micro- and macroscales. Potential galvanic couples between the weld zones were identified. The most anodic zone was base metal, which, with a banded microstructure of ferrite and perlite, developed a potential difference of up to 45 mV in comparison with the adjacent heat-affected zone. Friction stir welding promoted solute redistribution and the formation of martensite/retained austenite constituent, which contributed to reduced galvanic corrosion between ferrite and cementite. The thermo-mechanically affected zone was the most cathodic region, composed of acicular ferrite, coarse bainite and martensite/retained austenite constituent. Polarization resistance progressively increased, and corrosion current density progressively decreased, from base metal toward stir zone. In addition to the reduction in galvanic corrosion, a more uniform distribution of corrosion products in the stir zone also accounted for this behavior. (AU)

• FAPESP's process: 16/10637-4 - Development of a corrosion microprobe for monitoring of the effects of laser micro welding on the properties of Ti-Nb-xSn and Ni-Ti alloys
• Grantee: Rodnei Bertazzoli
• Support Opportunities: Regular Research Grants