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Journal ArticleDOI

Effect of nitrogen addition on formation of secondary austenite in duplex stainless steel weld metals and resultant properties

TL;DR: In this article, the influence of nitrogen on the phase balance of duplex stainless steel (DSS) welds and its controlling effect on the secondary austenite formation in multiple pass welds was investigated.
Abstract: The gas tungsten arc (GTA) welding process is widely employed for fabricating duplex stainless steel (DSS) components. The microstructural phase balance is disturbed in DSS welds owing to the thermal cycles associated with welding and the desired phase balance is generally achieved either through control of heat input or by altering the composition. In GTA welding, the phase balance is obtained either via the use of nickel fortified fillers or by introduction of nitrogen. Control of ferrite in the welds is essential, since metastable ferrite may transform to secondary austenite during multiple pass welding. The present work describes the influence of nitrogen on the phase balance of DSS welds and also its controlling effect on the secondary austenite formation in multiple pass welds. It was observed that neither the nitrogen addition nor the secondary austenite formation influenced the hardness of the welds, but formation of secondary austenite led to a deterioration in corrosion resistance. The c...
Citations
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Journal ArticleDOI
TL;DR: In this article, the effect of nitrogen addition in the plasma operation gases and of the increase of nickel in the filler metal, on the microstructure and on the mechanical properties of super-duplex stainless steels welded by the plasma transferred arc (PTA) technique was investigated.
Abstract: Super-duplex stainless steels present excellent combination of mechanical and corrosion resistance, due to their strict composition control and ferrite–austenite phase balance This balance may, however, be disturbed during welding in both the fusion and HAZ due to the rapid cooling rates and may lead to loss of the good corrosion and mechanical properties of the weldments The present investigation is studying the effect of nitrogen addition in the plasma operation gases and of the increase of nickel in the filler metal, on the microstructure and on the mechanical properties of super-duplex stainless steels welded by the plasma transferred arc (PTA) technique Results have shown that nitrogen addition in the plasma operation gas affects the mechanical properties of the weldments It is shown that nitrogen addition in the plasma and protective gas and higher nickel content in the filler metal have both a positive effect on the elongation of the welded specimens and after optimization of the welding parameters very good results may be obtained in terms of tensile strength

67 citations

Journal ArticleDOI
TL;DR: The effects of nitrogen addition in shielding gas on microstructure evolution and localized corrosion behavior of duplex stainless steel (DSS) welds were studied in this paper, where 2% N 2 to pure Ar shielding gas improved the localized corrosion resistance in the DSS welds, which was due to compensation for nitrogen loss and promoting nitrogen further solution in the austenite phases.

66 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that the Widmanstatten and allotriomorphic forms of austenite may not be identically oriented even when the former appears to originate from the latter.
Abstract: Two kinds of austenite grow from δ-ferrite during the cooling of the duplex stainless steel weld deposits studied here, Widmanstatten plates and allotriomorphs which precipitate at δ–δ grain boundaries. It is found using microtexture measurements that the preferred crystallographic orientation of the Widmanstatten austenite can be estimated using established theory if it is assumed that there is an interaction between external stress and the growing plates. It is also demonstrated that the Widmanstatten and allotriomorphic forms of austenite may not be identically oriented even when the former appears to originate from the latter; this may be a consequence of differences in the transformation mechanisms of these two forms of austenite.

62 citations

Journal ArticleDOI
TL;DR: In this article, the microstructural evolution, orientation relationships, boundary characteristics, grain type, local deformation, and microhardness across the welded interface of duplex stainless steel (DSS) were investigated.

37 citations

Journal ArticleDOI
TL;DR: In this article, a duplex stainless steel composite plate was welded by shielded metal arc welding, and the appropriate joint design and welding procedure were carried out by using SEM and TEM.
Abstract: In the present study, the duplex stainless steel (DSS) composite plate (SAF2205/16MnR) was welded by shielded metal arc welding, and the appropriate joint design and welding procedure were carried out. After welding, the mechanical behaviors and microstructure of welded joint were analyzed by using SEM and TEM. Results show that the tensile strength of welded joint satisfied the requirement, and the plate-like γ-phase was uniformly distributed in α-Fe based solution matrix at interface between the DSS and weld metal, a carbon-rich layer and decarburized layer formed in carbon steel-weld metal interface due to migration of the element carbon. However, there were only α and γ phases in weld metal of the joint transition layer, which is advantageous to the properties of welded joint.

25 citations


Cites background from "Effect of nitrogen addition on form..."

  • ...The second pass welding promotes the transformation of metastable ferrite into austenite in the adjoining regions, as described in article [3]....

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  • ...Because the excellent properties of DSS joint are mainly dependent on the appropriate biphase ratio in the structure of welded joint, work has been carried out on joining of duplex stainless steels, and joint structure-property correlations have been addressed [3]....

    [...]

  • ...The microstructural phase balance is disturbed in DSS welds due to the thermal cycles associated with welding, and the desired phase balance is generally achieved either through control of heat input or by altering the chemical composition of filler metal [3]....

    [...]

References
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Journal ArticleDOI
TL;DR: An overview of duplex stainless steels with particular emphasis on super DSS is given in this paper, where a large number of references to the literature are given to aid the reader who is interested in acquiring a deeper understanding of the behaviour of this family of steels.
Abstract: This paper presents an overview of duplex stainless steels (DSS) with particular emphasis on super DSS, i.e. steels containing sufficient amounts of chromium, molybdenum, and nitrogen to produce a pitting resistance equivalent greater than 40. Duplex stainless steels have an attractive combination of mechanical and corrosion properties and are thus suitable for many marine and petrochemical applications, particularly where chlorides are present. The paper covers the following aspects of DSS: physical metallurgy, mechanical properties, corrosion properties, metallurgy of welding, machinability, and applications. A large number of references to the literature are given to aid the reader who is interested in acquiring a deeper understanding of the behaviour of this family of steels.MST/1685

854 citations

Book
01 Jan 1997
TL;DR: In this paper, the authors present a non-destructive testing of welds for service experience, based on the application of service experience in metallurgy and metallurgical applications.
Abstract: Developments, grades and specifications Alloy design Microstructure Forming and machining Physical and mechanical properties Corrosion Stress corrosion cracking Welding metallurgy Welding processes Weld properties Non-destructive testing of welds Applications Service experience.

449 citations

Journal ArticleDOI
TL;DR: The SAF 2507, with a typical composition of ~25%Cr, 3·8%Mo, ~7%Ni, and 0·27%N, has been isothermally heat treated in the temperature range 700-1030°C for times... as mentioned in this paper.
Abstract: The super duplex stainless steel SAF 2507, with a typical composition of ~25%Cr, 3·8%Mo, ~7%Ni, and 0·27%N, has been isothermally heat treated in the temperature range 700–1030°C for times ...

192 citations

Journal ArticleDOI
TL;DR: In this paper, the morphology and chemical composition of secondary austenite was analyzed in duplex stainless steel welds and the results from the analytical instruments showed that the secondary Austenite had lower concentrations of chromium, molybdenum, and nitrogen.
Abstract: The present investigation was undertaken to analyse the morphology and chemical composition of secondary austenite, which may be formed in duplex stainless steel welds. The techniques used were scanning electron microscopy, analytical transmission electron microscopy, secondary ion mass spectroscopy, and thermodynamic equilibrium calculations using the computer program ThermoCalc. The combined results from the analytical instruments showed that the secondary austenite had lower concentrations of chromium, molybdenum, and nitrogen than the primary austenite. These observations were also confirmed by thermodynamic computer calculations. The results were used to explain why secondary austenite is more susceptible to pitting attack than primary austenite.MST/2070

105 citations

Journal ArticleDOI
TL;DR: In this article, the decomposition of ∆-ferrite to austenite has been studied in a 26%Cr-5%Ni stainless steel, and it was shown by STEM microanalysis that Ni partitions to the Austenite and Cr partitions to ferrit.
Abstract: The decomposition of ∆-ferrite to austenite has been studied in a 26%Cr-5%Ni stainless steel The decomposition takes place via two mechanisms: by nucleation and growth in the high temperature range (650–1200°C) and by an athermal martensitic process in the low temperature range (300–650°C) The high temperature reaction exhibits growth kinetics which are intermediate between volume diffusion control and growth by a ledge mechanism The morpho-logical variants of the austenite mirror those described in the Dube morphological classification for low-alloy steels, and the steel was used as a ‘model system‘ for the study of bcc ⇄ fcc transformations In the low temperature range (400–600°C) the formation of α′, which gives rise to 475°C embrittlement, is shown to occur by a nucleation and growth process, and the subsequent dissolution of the α′ is explained by the precipitation of austenite Finally, it is shown by STEM microanalysis that Ni partitions to the austenite and Cr partitions to the ferrit

88 citations