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Welding in the World

, Volume 63, Issue 1, pp 3–10 | Cite as

Welding design methodology for optimization of phase balance in duplex stainless steels during autogenous arc welding under Ar–N2 atmosphere

  • A. Rokanopoulou
  • P. SkarvelisEmail author
  • G. D. Papadimitriou
Research Paper
  • 79 Downloads

Abstract

This study deals with the selection of appropriate welding parameters during autogenous arc welding of duplex stainless steels in order to achieve an optimum phase balance of austenite and ferrite in the as-welded microstructure. Specimens of duplex stainless steel 2205 with dimensions (40 × 40 × 10) mm3 were welded using autogenous arc welding under 95% Ar + 5% vol. N2 atmosphere. The weld pool temperature was measured by non-contact infrared temperature measurement, the weld bead dimensions were determined using scanning electron micrographs, and the final nitrogen concentration was evaluated by optical emission spectroscopy. The kinetics of nitrogen absorption and desorption in molten duplex stainless steel was discussed and all the relevant variables were presented. The effect of welding current and speed on the final nitrogen concentration was also discussed. Finally, based on this analysis, a method was set up which can be used to optimize the phase balance by using predictive methods of the Ferrite Number, such as the Welding Research Council (WRC)-92 diagram.

Keywords

Duplex stainless steel Arc welding Nitrogen solubility Kinetic model Phase balance 

Nomenclature

\( \frac{d{m}_N}{dt} \)

rate of mass transfer of nitrogen (kg s−1)

Κa

rate constant for the reaction of absorption of monatomic nitrogen in a stainless steel melt (kg m−2 s−1 atm−1)

A

weld pool surface area (m2)

N(g)

the monatomic nitrogen content of the arc (atm)

Neq(g)

the monatomic nitrogen content of the arc plasma required for equilibrium with the nitrogen in the steel (atm)

ρ

the density of the molten weld metal (kg m−3)

V

the weld pool volume (m3)

α

weld pool radius (m)

h

weld pool depth (m)

fN, T

the activity coefficient of nitrogen in the stainless steel melt at temperature T

eNX

first-order interaction parameter of nitrogen

rNX

second-order interaction parameter of nitrogen

Ni

the initial nitrogen concentration of the stainless steel

Xrefeq

wt% equivalent concentration of element i (the content of the reference element which provides the same nitrogen activity as the content of element i)

crefi

equivalent factor

Xi

wt% concentration of alloying element i in stainless steel

ΔΤ

difference between the weld pool temperature and the melting point of the stainless steel

v

welding speed (m/s)

L

weld pool diameter (m)

Κd

rate constant for the reaction of nitrogen desorption from the weld pool to the arc atmosphere (kg m−2 s−1 (wt%)−2)

Nsteel

the final nitrogen concentration in the solidified steel (wt%)

Neq

nitrogen concentration in the weld pool for equilibrium with the nitrogen in the gas (wt%)

fo

the activity coefficient of oxygen in the stainless steel melt

fs

the activity coefficient of sulfur in the stainless steel melt

[%Ο]

wt% concentration of oxygen in the weld pool

[%S]

wt% concentration of sulfur in the weld pool

Td

dissociation temperature of diatomic to monatomic nitrogen

T

weld pool temperature

Notes

Acknowledgements

The State Scholarships Foundation of Hellas (IKY) is gratefully acknowledged for the financial support to A. Rokanopoulou (Grant No. 4327) and P. Skarvelis (Grant No. 4246).

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Copyright information

© International Institute of Welding 2018

Authors and Affiliations

  1. 1.School of Mining and Metallurgical Engineering, Laboratory of Physical MetallurgyNational Technical University of AthensZografouGreece

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