Influence of Welding Energy on Intergranular and Pitting Corrosion Susceptibility of UNS S32205 Duplex Stainless-steel Joints

Henrique Boschetti Pereira,Tarcisio Henrique Carvalhaes Pimentel,Carlos Alberto Da Silva,Cesar Roberto Farias De Azevedo,Zehbour Panossian

doi:10.1590/1980-5373-mr-2021-0488

Henrique Boschetti Pereira, Tarcisio Henrique Carvalhaes Pimentel + Show 3 more

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https://doi.org/10.1590/1980-5373-mr-2021-0488

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Abstract

This study analysed the integrity of welded joints of a UNS S32205 duplex stainless steel, using different welding energies: 0.5 kJ.mm-1, 1.0 kJ.mm-1, and 3.5 kJ.mm-1. Microstructural characterisation, tensile testing, intergranular attack susceptibility testing (ASTM A262 practice A) and pitting/crevice corrosion resistance tests (critical pitting temperature test, ASTM G48 practice C) were performed in these welded joints. The results showed that the tensile properties of the welded joints did not vary significantly with the welding energy. The microstructure's ferrite content in the molten zone (MZ) was proportional to the welding energy: the ferrite concentration in the 0.5 kJ.mm-1 weldings was approximately 75%. When the welding energy increased to 3.5 kJ.mm-1, the amount of ferrite dropped to 54%. The 3.5 kJ.mm-1 welded joint featured a comparatively higher proportion of coarser austenite grains. The HAZ of the 3.5 kJ.mm-1 welded joint was comparatively more susceptible to the intergranular attack along the α/γ interfaces, while in the base metal and the other two welded joints, the intergranular attack along the α/γ interfaces was not prominent. Additionally, the pitting corrosion took place preferentially in the ferrite phase of the HAZ for all welding conditions.

Highlights

Wrought and cast duplex stainless steels are commonly used in the oil extraction industry due to their high mechanical strength and corrosion resistance
Their microstructure is composed of austenite (FCC) and ferrite (BCC)[1,2], and there are different classes of duplex stainless steels which are classified by their pitting resistance equivalent numbers (PRENs) (Pitting Resistance Equivalent Number)[3] value, see Equation 1, which varies from 24.5 to 48.14
The root pass was made with purge gas (Ar), and the welding was performed with a pulsed current and a positive-polarity electrode (CC+) so that all welding passes were carried out with the droplet-metal transfer

Summary

Introduction

Wrought and cast duplex stainless steels are commonly used in the oil extraction industry due to their high mechanical strength and corrosion resistance. Their microstructure is composed of austenite (FCC) and ferrite (BCC)[1,2], and there are different classes of duplex stainless steels which are classified by their PREN (Pitting Resistance Equivalent Number)[3] value, see Equation 1, which varies from 24.5 to 48.14. The proportion of α and γ phases in duplex-stainless steels depends on the cooling rate from the ferritic field.

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