Microstructure, Pitting Corrosion Resistance and Impact Toughness of Duplex Stainless Steel Underwater Dry Hyperbaric Flux-Cored Arc Welds

Abstract

Duplex stainless steel multi-pass welds were made at 0.15 MPa, 0.45 MPa, and 0.75 MPa pressure, simulating underwater dry hyperbaric welding by the flux-cored arc welding (FCAW) method, with welds of normal pressure as a benchmark. The purpose of this work was to estimate the effect of ambient pressure on the microstructure, pitting corrosion resistance and impact toughness of the weld metal. The microstructure measurement revealed that the ferrite content in the weld metal made at 0.45 MPa is the lowest, followed by that of 0.75 MPa and 0.15 MPa. The analysis of potentiodynamic polarization tests at 30 °C and 50 °C demonstrated that the pitting corrosion resistance depends on the phases of the lower pitting resistance equivalent numbers (PREN), secondary austenite and ferrite. The weld metal made at 0.45 MPa had the best resistance to pitting corrosion at 30 °C and 50 °C with the highest PRENs of secondary austenite and ferrite. The weld metal made at 0.15 MPa displayed the lowest pitting corrosion resistance at 30 °C with the lowest PREN of secondary austenite, while the weld metal made at 0.75 MPa was the most seriously eroded after being tested at 50 °C for the lowest PREN of ferrite, with large cluster pits seen in ferrite at 50 °C. The impact tests displayed a typical ductile-brittle transition because of the body-centered cubic (BCC) structure of the ferrite when the test temperature was lowered. All the weld metals met the required value of 34 J at −40 °C according to the ASTM A923. The highest ferrite content corresponded to the worst impact toughness, but the highest toughness value did not correspond to the greatest austenite content. With the decreasing of the test temperature, the drop value of absorbed energy was correlated to the ferrite content. Additionally, in this work, the weld metal made at 0.45 MPa had the best combined properties of pitting resistance and impact toughness.

Dissimilar underwater wet welding of HSLA steels

“…The pressure inside the chamber could be the same as in the air (isobaric dry welding) or can be due to the depth (hyperbaric dry welding). This method also increases the cost but the quality of the joints could be similar to the joints made in the air [18,19]. The second method of underwater welding is welding with a local dry chamber.…”

Advantages of the Application of the Temper Bead Welding Technique During Wet Welding

“…There are three methods of welding in underwater conditions. The first is dry welding, in which the welder and welding area are in a specialized chamber without contact with the aqua environment [4,5]. The second method is welding with the use of a local dry chamber.…”

Cold Cracking of S460N Steel Welded in Water Environment

“…From several dozen years an issue of conducting repair of ocean-engineering and hydro-technical structures has been appeared more and more often. The developing offshore industry demands to make the repairs in water environment , without disassembling the elements and moving them into air [1,2]. The most widely used repair method is wet welding which, for economic reasons, is carried out generally with covered electrodes [3,4].…”

“…For assessment of steel weldability in water environment the self-restraint CTS tests and Tekken tests are used [1,2,6]. As underwater welding operations, especially those connected with failure repair, require making fillet joints, the CTS test was selected for the assessment of susceptibility to cold cracking of the S460N steel.…”