Sigma phase precipitation on welded SAF 2205 Duplex Stainless Steels after isothermal heat treatment

ABSTRACTDuplex stainless steels are commonly used for various applications owing to their superior corrosion resistance and/or strength. They have ferromagnetic behavior together with a good thermal conductivity and a lower thermal expansion as a result of higher ferrite content than austenitic steels. Their ferrite matrix suffers a decomposition process during aging in the temperature range 650-950° C producing precipitation of austenite, σ and χ, carbides and nitrides. These intermetallic phases are known to be deleterious for corrosion resistance and mechanical properties.In this work the effect of aging time during isothermal treatment at 850°C and 900°C on the microstructure of SAF 2205 Duplex Stainless Steels welded plates has been investigated. The aim of this work is to determine the morphology of σ phase, and perform a quantitative analysis of the precipitation process.Submerged Arc Welding is used for processing. It produces a high content of δ ferrite in the heat affected zone and low content of austenite in the weld. Microstructural examination shows that the σ phase precipitates at δ ferrite/γ interphases. Longer aging treatments give rise to an increase of volume fraction together with a coarser morphology.

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Effect of ageing time on microstructure and mechanical properties of SAF 2205 duplex stainless steel

Archives of Materials Science and Engineering ◽

10.5604/01.3001.0012.1382 ◽

2018 ◽

Vol 1 (91) ◽

pp. 23-30

Author(s):

R.N. Penha ◽

L.B. Silva ◽

C.S.P. Mendonça ◽

T.C. Moreira ◽

M.L.N.M. Melo

Keyword(s):

Heat Treatment ◽

Stainless Steel ◽

Corrosion Resistance ◽

Impact Toughness ◽

Stainless Steels ◽

Sigma Phase ◽

S Phase ◽

Duplex Stainless Steels ◽

Phase Precipitation ◽

Saf 2205

Purpose: SAF 2205 duplex stainless steels (DSSs) are materials characterized by a favourable combination of the properties of ferritic and austenitic stainless steels. This type of stainless steel presents good weldability, corrosion resistance especially for stress corrosion cracking (SCC). However, this steel presents an unavoidable disadvantage that is its potential microstructural instability. Although duplex stainless steels design idea is to present two main types of microstructure, other phases and carbides or nitrides can precipitate. In the case of DSS SAF 2205, in addition to austenitic and ferritic microstructure, during heat treatment processing, welding or use may occur precipitation of undesirable intermetallic phases such as chi, Widmanstätten austenite, sigma besides carbides and nitrides. The precipitation of s-phase is associated with effects that cause both reduction of toughness and decreases the corrosion resistance on austenitic, ferritic and duplex stainless steels. Design/methodology/approach: This study evaluated the aging treatment effect on hardness, impact toughness and ferrite content of a SAF 2205 duplex stainless steel. Samples were solubilized at 1150°C, quenched in water and aged at 850°C during 1, 5, 10, 30, 60 or 180 minutes. After aging, cooling was to room temperature in air. Findings: Aging time promoted s-phase precipitation and hardness increase. Hardness and ferrite volume measurements, microscopy and the prediction of sigma phase bases the discussion. Impact toughness decreased with time aging and intermetallic phase precipitation. Research limitations/implications: As future work could be performed some corrosion test, vary the cooling rate after aging, and using other techniques to identify phases. Focus the research at lower aging times to try the describe Cr partitioning process to form sigma phase. Practical implications: High aging time should be avoided for SAF 2205 DSS. Originality/value: Usually sigma-phase precipitation on DDS is correlated to welding process. This paper correlates it to aging heat treatment.

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Effect of σ-phase precipitation on hot ductility in δ-ferrite-austenite duplex stainless steels

Metals Technology ◽

10.1179/030716983803291406 ◽

1983 ◽

Vol 10 (1) ◽

pp. 296-303 ◽

Cited By ~ 24

Author(s):

Y. Maehara ◽

Y. Ohmori ◽

T. Kunitake

Keyword(s):

Stainless Steels ◽

Duplex Stainless Steels ◽

Hot Ductility ◽

Phase Precipitation ◽

Σ Phase ◽

Δ Ferrite

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Detrimental Cr-rich Phases Precipitation on SAF 2205 Duplex Stainless Steels Welds After Heat Treatment

Soldagem & Inspeção ◽

10.1590/0104-9224/si2102.06 ◽

2016 ◽

Vol 21 (2) ◽

pp. 165-171 ◽

Cited By ~ 3

Author(s):

Argelia Fabiola Miranda Pérez ◽

Marco Breda ◽

Irene Calliari ◽

Gladys Yerania Pérez Medina ◽

Rolf Sandström

Keyword(s):

Stainless Steels ◽

Cost Savings ◽

Filler Materials ◽

Secondary Phases ◽

Atmospheric Gases ◽

Σ Phase ◽

Δ Ferrite ◽

Temperature Decomposition ◽

Isothermal Heat Treatments ◽

Saf 2205

Abstract The austeno-ferritic Stainless Steels are commonly employed in various applications requiring structural performances with enhanced corrosion resistance. Their characteristics can be worsened if the material is exposed to thermal cycles, since the high-temperature decomposition of ferrite causes the formation of detrimental secondary phases. The Submerged Arc Welding (SAW) process is currently adopted for joining DSS owing to its relatively simple execution, cost savings, and using molten slag and granular flux from protecting the seam of atmospheric gases. However, since it produces high contents of δ-ferrite in the heat affected zone and low content of γ-austenite in the weld, high-Ni filler materials must be employed, to avoid excessive ferritization of the joint. The present work is aimed to study the effect of 3 and 6 hours isothermal heat treatments at 850°C and 900°C in a SAF 2205 DSS welded joint in terms of phases precipitation. The results showed the presence of σ-phase at any time-temperature combination, precipitating at the δ/γ interphases and often accompanied by the presence of χ-phase. However, certain differences in secondary phases amounts were revealed among the different zones constituting the joint, ascribable both to peculiar elements partitioning and to the different morphology pertaining to each microstructure.

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